Patent Publication Number: US-2022226623-A1

Title: Adjustable shunts and associated systems and methods

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. patent application Ser. No. 17/203,284, filed on Mar. 16, 2021, entitled “ADJUSTABLE SHUNTS AND ASSOCIATED SYSTEMS AND METHODS,” which is a continuation of U.S. patent application Ser. No. 17/016,192, filed on Sep. 9, 2020, entitled “ADJUSTABLE SHUNTS AND ASSOCIATED SYSTEMS AND METHODS,” which claims the benefit of the following applications: 
     (a) U.S. Provisional Patent App. No. 62/897,943, filed Sep. 9, 2019; 
     (b) U.S. Provisional Patent App. No. 62/907,696, filed Sep. 29, 2019; 
     (c) U.S. Provisional Patent App. No. 62/907,700, filed Sep. 29, 2019; 
     (d) U.S. Provisional Patent App. No. 62/907,698, filed Sep. 29, 2019; 
     (e) U.S. Provisional Patent App. No. 62/929,608, filed Nov. 1, 2019; 
     (f) U.S. Provisional Patent App. No. 62/959,792, filed Jan. 10, 2020; 
     (g) U.S. Provisional Patent App. No. 62/976,665, filed Feb. 14, 2020; 
     (h) U.S. Provisional Patent App. No. 62/977,933, filed Feb. 18, 2020; 
     (i) U.S. Provisional Patent App. No. 62/994,010, filed Mar. 24, 2020; 
     (j) U.S. Provisional Patent App. No. 63/002,050, filed Mar. 30, 2020; 
     (k) U.S. Provisional Patent App. No. 63/003,594, filed Apr. 1, 2020; and 
     (l) U.S. Provisional Patent App. No. 63/003,632, filed Apr. 1, 2020. 
     All of the foregoing applications are incorporated herein by reference in their entireties. Further, components and features of embodiments disclosed in the applications incorporated by reference may be combined with various components and features disclosed and claimed in the present application. 
    
    
     TECHNICAL FIELD 
     The present technology generally relates to implantable medical devices and, in particular, to implantable interatrial systems and associated methods for selectively controlling blood flow between the right atrium and the left atrium of a heart. 
     BACKGROUND 
     Heart failure is a medical condition associated with the inability of the heart to effectively pump blood to the body. Heart failure affects millions of people worldwide, and may arise from multiple root causes, but is generally associated with myocardial stiffening, myocardial shape remodeling, and/or abnormal cardiovascular dynamics. Chronic heart failure is a progressive disease that worsens considerably over time. Initially, the body&#39;s autonomic nervous system adapts to heart failure by altering the sympathetic and parasympathetic balance. While these adaptations are helpful in the short-term, over a longer period of time they may serve to make the disease worse. 
     Heart failure (HF) is a medical term that includes both heart failure with reduced ejection fraction (HFrEF) and heart failure with preserved ejection fraction (HFpEF). The prognosis with both HFpEF and HFrEF is poor; one-year mortality is 26% and 22%, respectively, according to one epidemiology study. In spite of the high prevalence of HFpEF, there remain limited options for HFpEF patients. Pharmacological therapies have been shown to impact mortality in HFrEF patients, but there are no similarly-effective evidence-based pharmacotherapies for treating HFpEF patients. Current practice is to manage and support patients while their health continues to decline. 
     A common symptom among heart failure patients is elevated left atrial pressure. In the past, clinicians have treated patients with elevated left atrial pressure by creating a shunt between the left and right atria using a blade or balloon septostomy. The shunt decompresses the left atrium (LA) by relieving pressure to the right atrium (RA) and systemic veins. Over time, however, the shunt typically will close or reduce in size. More recently, percutaneous interatrial shunt devices have been developed which have been shown to effectively reduce left atrial pressure. However, these percutaneous devices often have an annular passage with a fixed diameter which fails to account for a patient&#39;s changing physiology and condition. For this reason, existing percutaneous shunt devices may have a diminishing clinical effect after a period of time. Many existing percutaneous shunt devices typically are also only available in a single size that may work well for one patient but not another. Also, sometimes the amount of shunting created during the initial procedure is later determined to be less than optimal months later. Accordingly, there is a need for improved devices, systems, and methods for treating heart failure patients, particularly those with elevated left atrial pressure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an interatrial device implanted in a heart and configured in accordance with an embodiment of the present technology. 
         FIGS. 2A-2F  are a series of schematic illustrations depicting an adjustable interatrial shunting assembly configured in accordance with select embodiments of the present technology. 
         FIGS. 3A and 3B  are a schematic illustrations of coupled actuation element members that form a part of an interatrial shunting assembly configured in accordance with select embodiments of the present technology. 
         FIGS. 4A-4C  are schematic illustrations of an interatrial shunting system having nested actuation elements and configured in accordance with select embodiment of the present technology. 
         FIGS. 5A and 5B  are schematic illustrations of coupled actuation elements for use with an adjustable interatrial shunting system and configured in accordance with select embodiments of the present technology. 
         FIG. 6  is a series of schematic illustrates depicting operation of the shunting system shown in  FIGS. 5A and 5B . 
         FIG. 7  is a schematic illustration of a coupled actuation elements for use with an adjustable interatrial shunting system and configured in accordance with select embodiments of the present technology. 
         FIGS. 8A-8F  are schematic illustrations of an adjustable interatrial shunting system having elongated actuation elements and configured in accordance with select embodiments of the present technology. 
         FIG. 9  is a schematic illustration of an adjustable interatrial shunting system having helically shaped actuation elements and configured in accordance with select embodiments of the present technology. 
         FIGS. 10A and 10B  are schematic illustrations of another adjustable interatrial shunting system having helically shaped actuation elements and configured in accordance with select embodiments of the present technology. 
         FIG. 11  is a schematic illustration of an adjustable interatrial shunting system having a plurality of discrete actuation elements and configured in accordance with select embodiments of the present technology. 
         FIGS. 12A and 12B  are schematic illustrations of serially coupled actuation elements that form a part of an interatrial shunting system configured in accordance with select embodiments of the present technology. 
         FIGS. 13A-13D  illustrate various embodiments of an actuation elements positioned within an interatrial shunting system configured in accordance with an embodiment of the present technology. 
         FIGS. 14A-14C  illustrate an adjustable interatrial shunting system in a first configuration and configured in accordance with select embodiments of the present technology. 
         FIGS. 15A-15C  illustrate the adjustable interatrial shunting system shown in  FIGS. 14A-14C  in a second configuration different than the first configuration. 
         FIGS. 16A-16D  illustrate another adjustable interatrial shunting system configured in accordance with select embodiments of the present technology. 
         FIGS. 17A-17C  illustrate another adjustable interatrial shunting system configured in accordance with select embodiments of the present technology. 
         FIGS. 18A-18C  illustrate operation of the adjustable interatrial shunting system shown in  FIGS. 17A-17C . 
         FIGS. 19A-19D  illustrates another adjustable interatrial shunting system configured in accordance with select embodiments of the present technology. 
         FIGS. 20A-20C  illustrate another adjustable interatrial shunting system configured in accordance with select embodiments of the present technology. 
         FIGS. 21A-21D  illustrate an adjustable interatrial shunting system with a mechanical adjustment mechanism and configured in accordance with select embodiments of the present technology. 
         FIGS. 22A-22C  illustrate the adjustable interatrial shunting system of  FIGS. 21A-21D  implanted across a septal wall. 
         FIGS. 23A-23C  illustrate an operation for invasively deploying the adjustable interatrial shunting system of  FIGS. 21A-21D . 
         FIG. 24  is a partially isometric view of an adjustable interatrial shunting system having radially arranged actuation elements and configured in accordance with select embodiments of the present technology. 
         FIGS. 25A-25D  illustrate additional features of the radially arranged actuation elements of the adjustable interatrial shunting system of  FIG. 24 . 
         FIG. 26  is a partially isometric view of another adjustable interatrial shunting system having radially arranged actuation elements and configured in accordance with select embodiments of the present technology. 
         FIG. 27  is a partially isometric view of another adjustable interatrial shunting system having radially arranged actuation elements and configured in accordance with select embodiments of the present technology. 
         FIGS. 28A-28D  are partially isometric views of an adjustable interatrial shunting system having stent-like actuation elements and configured in accordance with select embodiments of the present technology. 
         FIGS. 28E-28H  are partially schematic views of the stent-like actuation elements of the adjustable interatrial shunting system of  FIGS. 28A-28D . 
         FIGS. 29A-29D  illustrate an adjustable interatrial system configured in accordance with further embodiments of the present technology. 
         FIGS. 30A-30E  illustrate an adjustable interatrial shunting system having a linear actuation mechanism and configured in accordance with select embodiments of the present technology. 
         FIGS. 31A and 31B  illustrate another adjustable interatrial shunting system having a linear actuation mechanism and configured in accordance with select embodiments of the present technology. 
         FIG. 32  illustrates yet another adjustable interatrial shunting system having a linear actuation mechanism and configured in accordance with select embodiments of the present technology. 
         FIG. 33  is a graph illustrating the relationship between aperture diameter and translation of a linear actuation mechanism in an interatrial shunting system configured in accordance with an embodiment of the present technology. 
         FIGS. 34A-34D  are schematic illustrations of various anchoring scaffolds for use with adjustable interatrial shunting systems configured in accordance with select embodiments of the present technology. 
         FIGS. 35A and 35B  are schematic illustrations of an adjustable interatrial shunting system having both superelastic and shape memory properties and configured in accordance with select embodiments of the present technology. 
     
    
    
     DETAILED DESCRIPTION 
     The present technology is directed to adjustable interatrial shunting systems that selectively control blood flow between the LA and the RA of a patient. For example, in many of the embodiments disclosed herein, the adjustable interatrial devices include a shunting element having an outer surface configured to engage native tissue and an inner surface defining a lumen that enables blood to flow from the LA to the RA when the device is deployed across the septal wall. In many embodiments, the systems include an actuation assembly that can adjust a geometry of the lumen and/or a geometry of a lumen orifice to control the flow of blood through the lumen. In many of the embodiments described herein, the actuation assembly includes one or more actuation elements composed of a shape-memory material and configured to undergo a material phase transformation when heated above a transition temperature that is greater than body temperature. 
     The terminology used in the description presented below is intended to be interpreted in its broadest reasonable manner, even though it is being used in conjunction with a detailed description of certain specific embodiments of the present technology. Certain terms may even be emphasized below; however, any terminology intended to be interpreted in any restricted manner will be overtly and specifically defined as such in this Detailed Description section. Additionally, the present technology can include other embodiments that are within the scope of the claims but are not described in detail with respect to  FIGS. 1-35B . In various respects, the terminology used to describe shape memory behavior may adopt the conventions described in ASTM F2005 (Standard Terminology for Nickel-Titanium Shape Memory Alloys). 
     Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present technology. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features or characteristics may be combined in any suitable manner in one or more embodiments. 
     Reference throughout this specification to relative terms such as, for example, “about” and “approximately” are used herein to mean the stated value plus or minus 10%. 
     As used herein, in various embodiments, the terms “interatrial device,” “interatrial shunt device,” “IAD,” “IASD,” “interatrial shunt,” and “shunt” are used interchangeably and, in at least one configuration, refer to a shunting element that provides a blood flow between a first region (e.g., a LA of a heart) and a second region (e.g., a RA or coronary sinus of the heart) of a patient. Although described in terms of a shunt between the atria, namely the LA and the RA, one will appreciate that the technology may be applied equally to other medical devices. For example, the shunt may be positioned between other chambers and passages of the heart or other parts of the cardiovascular system. For example, any of the shunts described herein, including those referred to as “interatrial,” may be nevertheless used and/or modified to shunt between the LA and the coronary sinus, or between the right pulmonary vein and the superior vena cava. Moreover, while the disclosure herein primarily describes shunting blood from the LA to the RA, the present technology can be readily adapted to shunt blood from the RA to the LA to treat certain conditions, such as pulmonary hypertension. For example, mirror images of embodiments, or in some cases identical embodiments, used to shunt blood from the LA to the RA can be used to shunt blood from the RA to the LA in certain patients. In another example, the shunt may be used to facilitate flow between an organ and organ, organ and vessel, etc. The shunt may also be used for fluids other than blood. The technologies described herein may be used for an ophthalmology shunt to flow aqueous or fluids to treat gastrointestinal disorders. The technologies described herein may also be used for controlled delivery of other fluids such as saline, drugs, or pharmacological agents. 
     As used herein, the term “geometry” can include the size and/or the shape of an element. Accordingly, when the present disclosure describes a change in geometry, it can refer to a change in the size of an element (e.g., moving from a smaller circle to a larger circle), a change in the shape of an element (e.g., moving from a circle to an oval), and/or a change in the shape and size of an element (e.g., moving from a smaller circle to a larger oval). In various embodiments, “geometry” refers to the relative arrangements and/or positions of elements in the respective system. 
     As used herein, the term “manufactured geometry” can refer a preferred geometric configuration of a shape memory component. For example, the shape memory component generally assumes the manufactured geometry in the absence of mechanical stresses or other deformations. The manufactured geometry can include an “as cut” geometry, a heat set geometry, a shape set geometry, or the like. 
     The headings provided herein are for convenience only and do not interpret the scope or meaning of the claimed present technology. 
     A. Interatrial Shunts for Treatment of Heart Failure 
     Heart failure can be classified into one of at least two categories based upon the ejection fraction a patient experiences: (1) HFpEF, historically referred to as diastolic heart failure or (2) HFrEF, historically referred to as systolic heart failure. One definition of HFrEF is a left ventricular ejection fraction lower than 35%-40%. Though related, the underlying pathophysiology and the treatment regimens for each heart failure classification may vary considerably. For example, while there are established pharmaceutical therapies that can help treat the symptoms of HFrEF, and at times slow or reverse the progression of the disease, there are limited available pharmaceutical therapies for HFpEF with only questionable efficacy. 
     In heart failure patients, abnormal function in the left ventricle (LV) leads to pressure build-up in the LA. This leads directly to higher pressures in the pulmonary venous system, which feeds the LA. Elevated pulmonary venous pressures push fluid out of capillaries and into the lungs. This fluid build-up leads to pulmonary congestion and many of the symptoms of heart failure, including shortness of breath and signs of exertion with even mild physical activity. Risk factors for HF include renal dysfunction, hypertension, hyperlipidemia, diabetes, smoking, obesity, old age, and obstructive sleep apnea. HF patients can have increased stiffness of the LV which causes a decrease in left ventricular relaxation during diastole resulting in increased pressure and inadequate filling of the ventricle. HF patients may also have an increased risk for atrial fibrillation and pulmonary hypertension, and typically have other comorbidities that can complicate treatment options. 
     Interatrial shunts have recently been proposed as a way to reduce elevated left atrial pressure, and this emerging class of cardiovascular therapeutic interventions has been demonstrated to have significant clinical promise.  FIG. 1 , for example, shows the conventional placement of a shunt in the septal wall between the LA and RA. Most conventional interatrial shunts (e.g., shunt  10 ) involve creating a hole or inserting an implant with a lumen into the atrial septal wall, thereby creating a fluid communication pathway between the LA and the RA. As such, elevated left atrial pressure may be partially relieved by unloading the LA into the RA. In early clinical trials, this approach has been shown to improve symptoms of heart failure. 
     One challenge with many conventional interatrial shunts is determining the most appropriate size and shape of the shunt lumen. A lumen that is too small may not adequately unload the LA and relieve symptoms; a lumen that is too large may overload the RA and right-heart more generally, creating new problems for the patient. Moreover, the relationship between pressure reduction and clinical outcomes and the degree of pressure reduction required for optimized outcomes is still not fully understood, in part because the pathophysiology for HFpEF (and to a lesser extent, HFrEF) is not completely understood. As such, clinicians are forced to take a best guess at selecting the appropriately sized shunt (based on limited clinical evidence) and generally cannot adjust the sizing over time. Worse, clinicians must select the size of the shunt based on general factors (e.g., the size of the patient&#39;s anatomical structures, the patient&#39;s hemodynamic measurements taken at one snapshot in time, etc.) and/or the design of available devices rather than the individual patient&#39;s health and anticipated response. With traditional devices, the clinician does not have the ability to adjust or titrate the therapy once the device is implanted, for example, in response to changing patient conditions such as progression of disease. By contrast, interatrial shunting systems configured in accordance with embodiments of the present technology allow a clinician to select the size—perioperatively or post-implant—based on the patient. 
     B. Shape Memory Actuation Assemblies 
     As provided above, the present technology is generally directed to interatrial shunting systems. Such systems include a shunting element implantable into a patient at or adjacent to a septal wall. In some embodiments, the shunting element includes a frame configured to interface with the septal wall, and a membrane coupled to the frame and defining a lumen. The shunting element (e.g., the lumen) can fluidly connect the LA and the RA of the patient to facilitate blood flow therebetween. In some embodiments, the shunting element includes and/or is operably coupled to an actuation assembly that is invasively and/or non-invasively adjustable to selectively control blood flow between the LA and the RA. In some embodiments, the systems can further include energy receiving components, energy storage components, and/or one or more sensors, among other things. 
     In some embodiments, an interatrial shunting system includes an actuation assembly having one or more actuation elements. As described in detail below, the actuation elements are configured to change a geometry or other characteristic of a lumen extending through the shunting element to alter the flow of fluid through the lumen. For example, in some embodiments the actuation elements can selectively change a size and/or shape of the lumen to alter the flow of fluid through the lumen. In particular, the actuation elements can be configured to selectively increase a diameter of the lumen (or a portion of the lumen) and/or selectively decrease a diameter of the lumen (or a portion of the lumen) in response to an input. Throughout the present disclosure, reference to adjusting a diameter (e.g., increasing a diameter, decreasing a diameter, etc.) can refer to adjusting a hydraulic or equivalent diameter of the lumen, adjusting a diameter at a particular location of the lumen, and/or adjusting a diameter along a length (e.g., a full length) of the lumen. In other embodiments, the actuation elements are configured to otherwise affect a shape or geometry of the lumen. In some embodiments, the actuation elements are configured to adjust a geometry (e.g., a cross-sectional area, a diameter, a dimension) of an orifice or aperture of the lumen (e.g., an inflow orifice or an outflow orifice positioned within or adjacent the LA or the RA, respectively). For example, the actuation elements can be configured to selectively increase a cross-sectional area of the outflow orifice in the RA and/or selectively decrease a cross-sectional area of an outflow orifice in the RA in response to an input. In some embodiments, the actuation elements can selectively change a geometry of both a lumen and a lumen orifice. 
     The actuation elements can therefore be coupled to the shunting element and/or can be included within the shunting element to drive the geometry change in the lumen and/or orifice. In some embodiments the actuation elements are part of the shunting element and at least partially define the lumen. For example, the actuation elements can be disposed within or otherwise coupled to a membrane that at least partially defines a lumen of the shunting element. In other embodiments, the actuation elements are spaced apart from but are operably coupled to the shunting element. 
     In some embodiments, at least a portion of the actuation elements can comprise a shape memory element. The shape memory portion can include a shape memory metal or alloy such as nitinol, a shape memory polymer, a pH-based shape memory material, or any other suitable material configured to move or otherwise adjust in response to an input. For example, the actuation elements can include one or more nitinol elements that are configured to change shape in response to applied heat that raises the nitinol elements&#39; temperature above the material&#39;s transformation temperature. In such embodiments, the actuation elements can be selectively actuated by applying energy to heat the nitinol element(s). In some embodiments, the shape memory materials may extend around at least a portion of the lumen. In some embodiments, the shape memory materials may extend around at least a portion of a lumen orifice. In some embodiments, the shape memory materials may be separate from but operably coupled to the lumen and/or the lumen orifice. 
     Movement of an actuation element can be generated through externally-applied input and/or the use of a shape memory effect (e.g., as driven by a change in temperature). The shape memory effect enables deformations that have altered an element from its original or preferred shape-set geometric configuration (also referred to herein as “manufactured geometry” or “heat set geometry”) to be largely or entirely reversed during operation of the actuation elements. For example, sufficient heating can reverse deformations by producing a change in material state (e.g., phase change) in the actuator material, inducing a temporary elevated internal stress that promotes a shape change toward the original shape-set geometric configuration. For a shape memory alloy, the change in state can be from a martensitic phase (alternatively, R-phase) at the lower temperature to an austenitic phase (alternatively, R-phase) at the higher temperature. For a shape memory polymer, the change in state can be via a glass transition temperature or a melting temperature. The change in material state can recover deformation(s) of the material—for example, deformation with respect to its manufactured geometry—without any externally applied stress to the actuator element. That is, a deformation that is present in the material at a first temperature (e.g., body temperature) can be recovered and/or altered by raising the material to a second (e.g., higher) temperature. Upon cooling (and re-changing state, e.g., back to a martensitic phase), the actuator element may approximately retain its manufactured geometry. However, with the material in this relatively cooler-temperature condition it may require a lower force or stress to thermoelastically deform the material, and any subsequently applied external stress can cause the actuator element to once again deform away from the manufactured geometry. 
     The shape memory alloy actuation elements can be processed such that a transition temperature at which the change in state occurs (e.g., the austenite start temperature, the austenite final temperature, etc.) is above a threshold temperature (e.g., body temperature). For example, the transition temperature can be set to be about 40 deg. C., about 45 deg. C., about 50 deg. C., about 55 deg. C., about 60 deg. C., or another higher or lower temperature. In some embodiments, the actuator material is heated from body temperature to a temperature above the austenite start temperature (or alternatively above the R-phase start temperature) such that an upper plateau stress (e.g., “UPS_body temperature”) of the material in a first state (e.g., thermoelastic martensitic phase, or thermoelastic R-phase at body temperature) is lower than an upper plateau stress (e.g., “UPS_actuated temperature”) of the material in a heated state (e.g., superelastic state), which achieves partial or full free recovery. For example, the actuator material can be heated such that UPS_actuated temperature&gt;UPS_body temperature. In some embodiments, the actuator material is heated from body temperature to a temperature above the austenite start temperature (or alternatively above the R-phase start temperature) such that an upper plateau stress of the material in a first state (e.g., thermoelastic martensite or thermoelastic R-phase at body temperature”) is lower than a lower plateau stress (e.g., “LPS”) of the material in a heated state (e.g., superelastic state), which achieves partial or full free recovery. For example, the actuator material can be constructed such that LPS_activated temperature&gt;UPS_body temperature. In some embodiments, the actuator material is heated from body temperature to a temperature above the austenite start temperature (or alternatively above the R-phase start temperature) such that an upper plateau stress of the material in a first state (e.g., thermoelastic martensite or thermoelastic R-phase) is higher than a lower plateau stress of the material in a heated state, which achieves partial free recovery. For example, the actuator material can be constructed such that LPS_activated temperature&lt;UPS_body temperature. 
     In some embodiments, the actuation assembly is formed by a coupling of at least two actuation elements (e.g., that have differing manufactured geometries) to form a composite actuation element (which can also be referred to as the “actuation assembly”). In some embodiments, at least one of the elements comprising the composite actuation element is a shape memory element. In some embodiments, both the elements comprising the composite actuation element are shape memory elements. In some embodiments, the coupling is performed with at least one actuation element in a thermoelastically deformable (e.g., thermoelastic martensitic or thermoelastic R-phase) state at the implantation temperature. In some embodiments, the coupling is performed with at least one actuation element(s) in a superelastic state. In some embodiments the flow control element comprises an expandable element or a contractile element whose deformation may be achieved via the application of a force (e.g., balloon expansion) at a lower temperature (e.g., body temperature) and/or via the application of a heat (e.g., electrical resistive heating) at a higher temperature (e.g., at a temperature at or above the austenite start or R-phase start temperature). In some embodiments, a shape memory component is constructed in a manner comprising a geometry (e.g., a cross-sectional area, a diameter, a length, a radius of curvature, or a circumference). In some embodiments, at least two actuation elements have geometric configurations (e.g., diameters) D A0  and D B0 , where D A0 &gt;D B0 . In some embodiments, the actuation assembly is formed of at least two actuation elements that have been constructed in substantially the same geometric configuration (e.g., D A0 =D B0 ). The flow control element can be assembled such that, prior to or upon introduction into the patient (i.e., implantation), at least one of two or more coupled actuation elements are deformed with respect to their original geometric configuration (e.g., such that D A1 ≠D A0 , and/or D B1 ≠D B0 ). In some embodiments, at least two coupled actuation elements can be deformed prior to or upon implantation such that a geometry (e.g. a diameter) of the first actuation element is smaller (e.g., compressed) with respect to its original configuration (e.g., D A1 &lt;D A0 ), and that a geometry (e.g., a diameter) of the second actuation element is larger (e.g., expanded) with respect to its original configuration (e.g., D B1 &gt;D B0 ). Thermoelastic deformation of the actuation elements to a desired configuration can occur with the shape memory components in a first (e.g., martensitic) material state. At a given temperature, the coupled and deformed actuation elements can (e.g., at equilibrium) form a composite geometry (e.g., cross-sectional area) that has a dimension that differs from either of the shape set configurations of the first and second actuation elements. For example, the composite geometry (e.g., diameter, D C0 ) of the flow control element can be between the shape set configurations of the first and second actuation elements (e.g., D A0 &gt;D C0 &gt;D B0 ). 
     The actuation assembly can be formed such that, in operation (e.g., during actuation of an actuation element), its composite geometry and/or dimension is altered (e.g., such that D C1 ≠D C0 ). The flow control element can cause a change in an overall dimension of a fluid path (e.g., lumen). For example, the overall dimension can comprise an overall cross-sectional area, a diameter, a length, a circumference, or another attribute. In an embodiment, the first and second actuation elements that are coupled to form a composite element are arranged such that a movement of the first actuation element (e.g., via thermoelastic martensitic transformation to achieve free recovery) is accompanied by (e.g., causes) a complementary full or partial movement of the second actuation element—e.g., by inducing thermoelastic recoverable deformation of a relatively malleable second actuation element while it is at least partially in a thermoelastic martensitic (or thermoelastic R-phase) material state. (For brevity herein, in various embodiments the term “relatively malleable” is used to describe a material state where a component requires a lower force or stress to deform it when compared to another component, or when compared to the same component in a different material state). The movement(s) can comprise a compression (e.g., contraction) or an expansion (e.g., opening) of the composite element. The movement can comprise a deflection or a deformation, which may be fully- or partially-recoverable. The complementary movement of the second actuation element can comprise movement that is (a) along a same axis, (b) about a same axis, or (c) along a same dimension (e.g., radially) as the primary movement of the first actuation element, or another movement. In some embodiments, actuation of the first actuation element from a compressed geometry toward a larger shape set configuration geometry expands the composite geometry via the coupling of the first actuation element with the second actuation element. In some embodiments, this expansion places the composite geometry at a size that is larger than its equilibrium, but smaller than that of the original configuration of the first actuation element (e.g., D A0 &gt;D C1 &gt;D C0 ). In some embodiments, actuation of the second actuation element from an expanded geometry toward a smaller original configuration geometry contracts (e.g., compresses) the composite geometry, via the coupling of the second actuation element with the first actuation element. In some embodiments, this compression places the composite geometry at a size that is smaller than its equilibrium, but larger than that of the original configuration of the second actuation element (e.g., D C0 &gt;D C1 &gt;D B0 ). 
     In a method of operation of an embodiment of the present technology, selective heating of the first actuation element of the flow control element causes it to actuate toward its original geometric configuration (e.g., from D A1  toward D A0 ). Actuation can be caused by raising a temperature of the first actuation element at least to a threshold transition temperature. The transition temperature can be a phase transition temperature (e.g., R-phase start temperature, austenite start temperature, R-phase finish temperature, or austenite finish temperature). Raising temperatures to or beyond the transition temperature can induce a change of the material from a first phase (e.g., martensite or R-phase) to a second phase (e.g., R-phase or austenitic). During actuation of the first actuation element, the second actuation element is generally not heated (e.g., remains at or near body temperature), and therefore remains in a first (e.g., martensitic or R-phase) material state. As such, the second actuation element may be relatively malleable in this material state, thereby allowing the elevated forces from partial or complete free recovery of the first actuation element to drive a change in shape and/or geometry of the coupled second element (e.g., a compressive or contracting movement). Due to the relatively malleable nature of the second actuation element in this material state, it may largely retain this induced shape and/or geometry change without substantial recovery (e.g., generally only linear elastic recovery). 
     Following the completion of a heating period of the first actuation element, the first actuation element cools and transforms to the lower-temperature phase (e.g., martensite or R-phase), in which it is relatively malleable. To reverse the induced change in the configuration of the composite flow control element (e.g., its geometry), the second actuation element can be heated to or beyond its transition temperature to induce a phase change (e.g., to R-phase or austenite) and, consequently, partial or full free recovery in geometry towards its original geometric configuration (e.g., from D B1  toward D B0 ). As the first actuation element is not selectively heated and relatively malleable during this time, the return of the second actuation element to its original geometric configuration causes the composite geometry of the flow control element to change (e.g., to reduce in size). In some embodiments, the geometry of flow control element can be repeatably toggled (e.g., between expanded and contracted) by repeating the foregoing operations. The heating of an actuation element can be accomplished via application of incident energy (e.g., via a laser, resistive heating, or inductive coupling). The source of the incident energy may be either internal (e.g., delivered via a catheter) or external to the patient (e.g., non-invasively delivered RF energy). 
     In some embodiments, the first actuation element can be thermally insulated and/or electrically isolated from the second actuation element. Further, in some embodiments, the first and second actuation elements can be thermally insulated and/or electrically isolated from tissue and blood adjacent the implant site. 
     Accordingly, the present technology provides actuation assemblies having two or more shape memory material actuation elements that are manufactured into different geometric configurations and coupled together. In additional embodiments, the geometric configurations may be similar, with two or more actuation elements working in an antagonistic or complementary fashion to manipulate a geometric feature of an actuation assembly. In some embodiments, the actuation elements may be manufactured with similar chemical composition and/or thermo-mechanical post-treatments, i.e., they may have similar phase transition temperature profiles. In further embodiments, an actuation assembly may contain two or more actuation elements that have been manufactured with differing chemical composition and/or thermo-mechanical post-treatments such that they do not share identical phase transition temperature profiles. In operation of such an embodiment, energy may be applied to an entire composite actuation assembly (e.g., comprised of two or more individual actuation elements) and not all individual actuation elements may similarly deform toward their original geometric configurations. For example, a first actuation element may have a first transformation temperature profile, and a second actuation element may have a second, higher transformation temperature profile. Heating the composite actuation assembly to a temperature above the first, but below the second, transformation temperature (e.g. R-phase start, austenite start, R-phase finish, or austenite finish temperature) will induce a more substantial thermoelastic recovery in the first actuation element than the second actuation element. This will create a first geometric alteration of an actuation assembly. Heating the composite actuation assembly to a temperature above both the first and second transformation temperatures (e.g., R-phase start, austenite start, R-phase finish, or austenite finish temperature) may induce a meaningful thermoelastic recovery and actuation in both actuation elements. This will create a second geometric alteration of an actuation assembly which may differ from the first geometric alteration. 
     In embodiments, the geometric changes of an actuation assembly may be toggled between a number of states in response to the actuation of one or more actuation elements. In embodiments, reversal of a geometry change (e.g., making a lumen larger after it had previously been made smaller) is accomplished by utilizing multiple shape memory actuation elements that are coupled to work in an antagonistic manner. In embodiments, other mechanisms (e.g., springs, ratchets, elastic materials such as silicone, etc.) may be additionally or alternatively be utilized in conjunction with actuation elements to provide complementary or counter forces to those actuation elements, thereby affecting a geometry change of an actuation assembly. 
     In embodiments, the actuation assembly may be thermoelastically expanded to a cross-sectional geometry that is larger than the largest actuation element in the composite structure. For example, one actuation element may have an initial diameter, D A0 , and another actuation element may have an initial diameter, D B0 , such that D A0 &gt;D B0 . In such a composite system, the actuation of either actuation element drives the composite actuation assembly to a diameter within the range D B0 -D A0  (inclusive). If, for example, a physician expands (e.g., via the use of a balloon) the actuation assembly to a diameter greater than D A0  to enable the crossing of a tool (e.g., during deployment of a transcatheter mitral valve), the lumen of the actuation assembly may later be thermoelastically recovered by actuating either actuation element (e.g., by the application of heat) to drive the recovery of the diameter of the actuation assembly to the original range D B0 -D A0 . In various embodiments, the actuation assembly is expanded to a diameter greater than D A0  to enable the crossing of a catheter, for example a diagnostic catheter or for a therapeutic. In embodiments, plastic deformation of either (or both) actuation elements may result from the expansion to a lumen greater than D A0 . Consequently, the achievable actuatable lumen range may shift to D B1 -D A1  where D B1 &gt;D B0  and D A1 &gt;D A0  accounting for the permanent plastic deformation. 
     C. Shunting Assemblies with Adjustable Flow Lumens 
     The present technology provides interatrial shunting assemblies with adjustable flow lumens. For example,  FIGS. 2A-2F  illustrate an adjustable interatrial shunting system  200  (“system  200 ”) configured in accordance with select embodiments of the present technology. As one skilled in the art will appreciate,  FIGS. 2A-2F  are provided merely to demonstrate the adjustable nature of the shunting systems described herein. Additional details of the various components of the present technology are described in greater detail with reference to specific embodiments in  FIGS. 3A-35B . 
     Referring first to  FIG. 2A , the system  200  includes a frame  210  and anchors  230  extending from the frame  210 . The system  200  further includes a shunting element  215  composed of a membrane  220  defining a lumen  225  extending therethrough. As discussed below, the lumen  225  is configured to fluidly connect the LA and the RA to shunt blood therebetween when the shunt system  200  is implanted across a septal wall S within a heart of a patient. The lumen  225  is shown in  FIG. 2A  in a first configuration in which it has a first diameter D L1 . As illustrated, the lumen  225  can have a generally constant diameter along its entire length or substantially its entire length in the first configuration. 
     The geometry of the lumen  225  can be adjusted to change the flow of blood therethrough. In some embodiments, the diameter at a particular location of the lumen  225  is adjusted. For example, referring to  FIG. 2B , the diameter of the lumen  225  is decreased in a central portion of the lumen  225  relative to the first configuration shown in  FIG. 2A  to assume an hourglass-shaped configuration. The diameter of the lumen at the narrowest portion of the hourglass is D L2 , which is generally less than the first diameter D L1 . 
     In other embodiments, the diameter of the lumen  225  is adjusted along its entire length. For example, referring to  FIG. 2C , the diameter of the lumen  225  is decreased along its entire axial length relative to the first configuration shown in  FIG. 2A , thereby maintaining a generally cylindrical shape but having a second configuration with a smaller diameter than the first configuration. The diameter of the lumen  225 , which is generally constant along its length, is D L3 , which is generally less than the first diameter D L1  and can be the same as or different than the diameter D L2 . The geometry of the lumen  225  can be adjusted in other manners as well. For example, in other embodiments, the diameter of the lumen  225  remains generally the same, but the diameter of one or more lumen orifices is decreased. 
     In some embodiments, the geometry of the lumen  225  can be adjusted to increase the flow of blood therethrough. For example, the diameter of the lumen  225  can be increased. As shown in  FIG. 2D , the diameter of the lumen  225  has been increased to a diameter D L4 , which is greater than the first diameter D L1 . Although  FIG. 2D  illustrates the lumen  225  has having a generally constant diameter along its entire axial length, the lumen  225  may alternatively have an inverted hourglass shape (e.g., the diameter of the lumen  225  at a central portion is greater than a diameter of the lumen orifices). 
     As shown in  FIG. 2E , when the system  200  is implanted across a septal wall S in the first configuration (e.g., the configuration shown in  FIG. 2A ), the lumen  225  enables a first amount (e.g., rate, volume, etc.) of blood to flow between the LA and the RA.  FIG. 2F  illustrates the system  200  implanted across the septal wall S in the second configuration (i.e., the configuration shown in  FIG. 2C ). Relative to the first configuration (i.e., the configuration shown in  FIG. 2A ), the second configuration provides reduced blood flow between the LA and the RA. As one skilled in the art can appreciate, in some embodiments the system  200  can assume the hour-glass configuration (i.e., the configuration shown in  FIG. 2B ) to reduce blood flow. Likewise, the system  200  can assume the configuration shown in  FIG. 2D  to increase the flow of blood between the LA and the RA. 
     The present technology thus provides adjustable interatrial shunting systems that can adjust a geometry of a flow lumen and/or lumen orifice to change the flow of blood therethrough. In particular,  FIGS. 3A-23C  illustrate adjustments to the lumen geometry, and  FIGS. 24-32  illustrate adjustments to orifice geometry. The systems can be adjusted using a variety of actuation mechanisms, which will be described in greater detail below. 
     i. Stent-Like Actuation Assemblies 
       FIG. 3A  is a schematic illustration of coupled actuation elements (a first actuation element  305  and a second actuation element  310 ) that form part of an interatrial shunting device configured in accordance with an embodiment of the present technology. The first actuation element  305  can have a different original geometric configuration (e.g., D 1 ) than that of the second actuation element  310  (D 2 ). As provided above, D 1  can refer to a hydraulic or equivalent diameter of the first actuation element  305 , a diameter of the first actuation element  305  at a specific location (e.g., an orifice of the lumen, a centerpoint of the lumen, etc.), a diameter of the first actuation element  305  along a portion of its length, and/or another dimension. Likewise, D 2  can refer to a hydraulic or equivalent diameter of the second actuation element  310 , a diameter of the second actuation element  310  at a specific location, a diameter of the second actuation element  310  along a portion of its length, and/or another dimension. The first and second actuation elements  305 ,  310  may be coupled together to form an actuation assembly  300 . Direct coupling of the at least two actuation elements can be accomplished via sutures, adhesives/glue, crimps/rivets, an interference fit, welds/solder, or other techniques known to those skilled in the art. Indirect coupling of at least two actuation elements can be accomplish via direct coupling of each actuation element to a common intermediate element. Following assembly, the actuation assembly  300  can, at a first temperature (e.g., room temperature, body temperature, etc.) have a geometry that is at an equilibrium state between the original geometric configurations of the individual actuation elements (e.g., D 1 &gt;D C &gt;D 2 ). Actuation of the first actuation element  305  causes the flow control element to assume a geometry (D L ) that approaches the original geometric configuration of the first actuation element. For example, actuation of the first actuation element causes the geometry of the flow control element to increase (e.g., D L &gt;D C ). Actuation of the second actuation element  310  causes the flow control element to assume a second geometry (D S ) that approaches the original geometric configuration of the second actuation element (D 2 ). For example, actuation of the second actuation element causes the geometry of the flow control element to decrease (e.g., D S &lt;D C ). 
     In some embodiments, at least one actuation element comprises an insulative element. For example, an actuation element can be coated with electrically- and/or thermally-insulative material. In some embodiments, the insulative element is flexible. The insulative element can comprise a polyimide (e.g., Kapton®), a synthetic polymer (e.g., polytetrafluoroethylene (PTFE) or expanded polytetrafluoroethylene (ePTFE)), thin ceramic coating (e.g., TiO x ), or a urethane (e.g., ChronoFlex®), or another suitable material known to those skilled in the art. Polymeric insulative elements can have a dimension (e.g., coating thickness) that is, for example, about 50 microns, about 75 microns, about 100 microns, about 150 microns, about 300 microns, or about 1 millimeter. Ceramic insulative elements can have dimensions (e.g., layer thickness) that is, for example, about 5 nm, about 10 nm, about 100 nm, about 200 nm, about 300 nm, about 400 nm, or about 500 nm. The insulative element can have a dimension that is greater than, less than, or between any of the aforementioned dimensions. 
       FIG. 3B  is a schematic illustration of coupled actuation (elements that form a part of an interatrial shunting device configured in accordance with an embodiment of the present technology. In the example of  FIG. 3B , the actuation elements are coupled by nesting one inside of the other (e.g., nesting the element with the larger original geometric configuration within the element with the smaller original geometric configuration). In some embodiments, first and second actuators comprise elongate members (e.g., stents, scaffolds, etc.). A geometry (e.g., cross-sectional area) of the elongate members can be constructed to have different sized configurations. For example, a first member can be manufactured to have a larger cross-sectional diameter (D A ) than the cross-sectional diameter of a second member (D B ). To form an adjustable composite element (e.g., a flow control element or a portion thereof), a larger member  305   a  can be deformed and positioned (e.g., compressed) within a smaller member  310   a . The coupling of the first and second members can form a nested arrangement  300   a . In some embodiments, a nested arrangement comprises a coaxial or concentric arrangement of a plurality of stents. The geometry of the flow control element can have an equilibrium geometry (e.g., D nested , such that D A &gt;D nested &gt;D B ). When the larger member  305   a  is actuated (e.g., heated) to induce a thermoelastic recovery intended to return it toward its original geometric configuration (D A ), the composite actuation assembly  300   a  increases in size, for example to a diameter larger than D nested  and less than or equal to D A . Likewise, when the smaller member  310   a  is actuated (e.g., heated) to induce thermoelastic recovery to return it toward its original geometric configuration (D B ), the composite flow control element  300   a  decreases in size, for example to a diameter smaller than D nested  and greater than or equal to D B . In some embodiments, improvement in a granularity of geometry modification is achieved by a coupling more than two actuation elements into a composite structure (e.g., a plurality of stents nested within one another). Actuating any one (or any combination) of the elements (e.g., stents) will drive the composite structure to a different pre-determined geometric configuration. In an embodiment, the actuation elements can be assembled in progression (e.g., largest original geometric configuration to smallest) from the inside to the outside of the composite structure. For example, the assembly can be such that the smallest original geometric configuration is the outermost actuation member in the composite structure. When the outermost element (e.g., the element with the smallest shape set geometry) is actuated, it applies a force to the composite structure that decreases it to its minimum geometric configuration. This may be accomplished since the non-actuated (e.g., unheated) elements may be in a relatively malleable state and as such experience a complementary movement as a result of the elevated forces applied by the actuated element. When an intermediate element is actuated, the composite structure achieves an intermediate geometric configuration, with the non-actuated (i.e., slave) elements being driven by the actuated element to move in a complementary matter to the actuated element. When an innermost element is actuated, the composite structure may achieve a maximum geometric configuration, with the non-actuated (i.e., slave) elements being driven by the actuated element to move in a complementary matter to the actuated element. In some embodiments, at least two actuation elements are actuated substantially simultaneously. In some embodiments, simultaneous actuation of at least two actuation elements produces further granularity and/or precision in flow control element movement with respect to actuation of a single actuation element. 
       FIGS. 4A-4C  are schematic illustrations of coupled actuation element portions that form a part of an interatrial shunting device configured in accordance with an embodiment of the present technology. The individual actuation elements can be comprised of a shape memory material and be manufactured to have similar overall shapes, patterns, and/or dimensions. Referring  FIGS. 4A-4C  together, the actuation elements (e.g., stents) can be formed by wire forming, laser cutting, or another suitable process. A first actuation element  405  can be manufactured to a first (original) geometric configuration, and may comprise a series of repeating cells  406  having a first cell size C A  and a total (e.g., cumulative) unwrapped length LA (e.g., circumference when constructed in a cylindrical shape). When wrapped about a central axis, first actuation element  405  can have a geometric configuration with a first cross-sectional diameter D A . A second actuation element  407  can be manufactured to a second geometric configuration, and may comprise a series of repeating cells  408  having a second cell size C B  and a total (e.g., cumulative) unwrapped length L B  (e.g., circumference when constructed in a cylindrical shape). When wrapped about a central axis, second actuation element  407  has a geometric configuration with a second cross-sectional diameter D B . In some embodiments, the first and second actuation elements may be constructed to different geometric configurations, for example C A &gt;C B , L A &gt;L B , D A &gt;D B , etc. In embodiments, the first and second actuation elements  405 ,  407  have similar patterns to facilitate direct coupling, or features to promote indirect coupling through one or more intermediate members. 
     The first and second actuation elements  405 ,  407  can comprise segments ( 404  and  409 ) that are configured to enable coupling to another actuation element or to another component of a device. In some embodiments, the portions for coupling comprise longitudinal struts. In embodiments, the segments for coupling can be maintained at a substantially fixed dimension (e.g., length) prior to and following construction of the actuation elements. In embodiments, two or more actuation elements may be coupled together by suture, adhesives/glue, rivets/crimps, welds, an enclosing sleeve, or via other methods. In some embodiments, at least one of the coupling portions (e.g.,  404  or  409 ) comprises an insulative element. In some embodiments, the insulative element provides electrical isolation and/or thermal isolation between coupled actuation elements. As best seen in  FIG. 4C , coupling two or more actuation elements can create a composite element  415  that, at a given temperature (e.g., room temperature), has an equilibrium geometric configuration that features at least one series of repeating cells  412  having a composite cell size C C  and has a total (e.g. cumulative) unwrapped length L C . When wrapped about a central axis, the composite actuation element  415  has a geometric configuration with a composite cross-sectional diameter D C . In embodiments, this wrapped composite actuation element may serve as a flow control element that forms part of an interatrial shunting device configured in accordance with an embodiment of the present technology. In embodiments that feature one relatively larger actuation element and one relatively smaller actuation element, the geometry of the composite element may be characterized by sizes that fall between the values of the individual elements (i.e., C A &gt;C C &gt;C B ; D A &gt;D C &gt;D B ; L A &gt;L C &gt;L B ). 
     One or more elements of the composite flow control element may be actuated to impart a geometry change of the composite structure. For example, actuation of the larger element may cause an increase and/or expansion of a geometric characteristic of the composite element such that it attains a new cross-sectional diameter D N1 , where D N1 &gt;D C . Conversely, actuation of the smaller element may cause a decrease/contraction of a geometric characteristic of the composite element such that it attains a new cross-sectional diameter D N2 , where D N2 &lt;D C . 
       FIG. 5A  is a flat pattern illustration of interlocking actuation elements that may be coupled to form a part of an interatrial shunting device configured in accordance with embodiments of the present technology. In particular,  FIG. 5A  illustrates a first actuation element  505  and a second actuation element  510 . In some embodiments, the first actuation element  505  and/or the second actuation element  510  are stents or stent-like structures that are coupled to form an actuation assembly. In embodiments, the first actuation element  505  and/or the second actuation element  510  are comprised of a shape memory material. The actuation assembly can be actuated to move through two or more geometric configurations in order to alter the characteristics of fluid flow through the shunting device. The first actuation element  505  contains both arm elements  502  and zig elements  503 , with arm elements  502  terminating in eyelet openings  518  and the zig elements  503  terminating in eyelet openings  515 . Similarly, the second actuation element  510  contains both arm elements  507  and zig elements  508 , with arm elements  507  terminating in eyelet openings  519  and the zig elements  508  terminating in eyelet openings  516 . The patterns and/or shape of the first and second actuation elements  505 ,  510  may be similar. The shape and/or geometries of the first and second actuation elements  505 ,  510  may be constructed to different configurations during a pre-processing step, as elaborated upon below. Prior to coupling of the first and second actuation elements  505 ,  510 , the first and second actuation elements  505 ,  510  may be manipulated into shapes and/or geometries that differ from their original geometric configurations (e.g., by flattening shape-memory alloy structures while the structures are at a temperature where the material is at least partially in a martensitic or R-phase, and therefore relatively malleable). In embodiments, the first and second actuation elements  505 ,  510  may be coupled along the backbone corresponding to the peaks of the zig elements  503  and  508  (e.g., by using sutures or another connection means to secure the series of eyelets  515  and  516  together). Accordingly, unlike the first and second actuation elements  405 ,  407  described above with respect to  FIGS. 4A-4C , the first and second actuation elements  505 ,  510  are coupled in series or “end-to-end”, in which a first end portion of the first actuation element  505  is coupled to a second end portion of the second actuation element  510 , and in which the first actuation element  505  is not nested within (e.g., does not generally overlap with) the second actuation element  510 . This operation represents an initial coupling operation that is a step in the process of using the first and second actuation elements  505 ,  510  to create an actuation assembly that is part of an interatrial shunting device. 
     To create an actuation assembly from the first and second actuation elements  505 ,  510 , additional coupling steps may be implemented. For example, during a secondary coupling step, the flattened configuration of the stent structure (i.e., as shown in  FIG. 5A ) may be wrapped around a central axis and attached to itself, creating a structure defining a lumen or passageway. For example, the region defined by eyelet openings  504  and  509  (which are already coupled/joined) will be subsequently coupled to the region defined by eyelet openings  520  and  521  (which are also already coupled/joined). Following this operation, the composite element may take on a rounded profile (e.g., a cylindrical profile). 
       FIG. 5B  provides additional schematic illustrations of the first and second actuation elements  505 ,  510  before they are coupled together to form an actuation assembly, thus illustrating their manufactured geometry (e.g., their preferred geometry). In particular,  FIG. 5B  illustrates an isometric single element-pair view, a 2D dual element-pair view, a front view, a side view, and an isometric view of the first and second actuation elements  505 ,  510 . As mentioned above, the first and second actuation elements  505 ,  510  may be constructed (e.g., shape or manufactured) into different configurations prior to coupling. The illustrated geometric configuration involves arm elements  502  and  507  bending off-axis from zig elements  503  and  508  (i.e., in the direction “out of the page” when viewing  FIG. 5A ). In some embodiments, the angle of off-axis bend may differ for the arm elements  502  relative to the angle of off-axis bend for the arm elements  507  of the second actuation element  510 . For example, referring to the 2D dual element-pair view, the arm elements  502  and  507  are bent off-axis, with arm  502  of the first actuation element  505  bent at a relatively larger (e.g., more open) angle and the arm  507  of the second actuation element  610  bent at a relatively smaller/tighter (e.g., more closed) angle. As a result, the eyelet opening  518  of the first actuation element  505  are relatively close together (defining a smaller diameter), while the eyelet openings  519  of the second actuation element  510  are relatively further apart (defining a larger dimeter). 
     In some embodiments, a third coupling operation may be undertaken to form the composite actuation assembly that includes both the first and second actuation elements  505 ,  510 . In some embodiments, this operation involves using a flexible connection (e.g., an elastic polymer, a stretchable/flexible material, etc.) to couple the bent arms  502  and  507  of the first and second actuation elements  505 ,  510 . For example, a flexible suture material can be utilized to connect the eyelet opening  518  on the first actuation element  505  with its assembled partner eyelet opening  519  on the second actuation element  510 . Upon completion of this third coupling operation, the bend angle of arms  502  and  507  may each change and reach an equilibrium angular position. As with other coupling operations described herein, in embodiments the coupling may be performed in a way that maintains and/or establishes electrical and/or thermal isolation between the first and second actuation elements  505 ,  510 . Following or prior to this third coupling operation, a membrane material (not shown) may be interfaced with the composite structure so as to provide an enclosed channel (e.g., an enclosed lumen) through which fluid may pass through the flow control element. 
     In an example method of use, following the third coupling operation described above, the composite actuation assembly comprised of the first and second actuation elements  505 ,  510  (e.g., which can also be referred to as “a flow control element”) can be (with or without integration into an interatrial shunting system) compressed into a delivery system (e.g., a catheter delivery system) and delivered to a body of a patient. In embodiments, once the composite actuation assembly is positioned in the desired location, it may be deployed and manually expanded to a neutral position (e.g., expanded using a catheter balloon expansion). In embodiments, the composite actuation assembly is in a material state (e.g., at least partially in a martensitic phase) where it is relatively malleable such that it is deformable from a delivery configuration to a neutral configuration. In embodiments, the composite actuation assembly is manufactured such that both at a first temperature (e.g., a room temperature) and at a second temperature higher than the first temperature (e.g., a body temperature), at least a portion of the composite actuation assembly remains in a material phase where it is relatively malleable and deformable (e.g., a nitinol alloy remains at least partially in a martensitic or R-phase). 
       FIG. 6  provides schematic illustrations of various configurations of the composite actuation assembly formed by coupling the first and second actuation elements  505 ,  510  shown in  FIGS. 5A and 5B .  FIG. 6  also schematically illustrates an example mode of operation that may be used to actuate the actuation assembly. Shown in  FIG. 6  are isometric single element-pair views, 2D dual element-pair views, complete structure front views, complete structure side views, and complete structure isometric views. In  FIG. 6 , the first row in the table shows the actuation assembly in a neutral configuration (e.g., after a balloon expansion or other manipulation), the second row shows the actuation assembly in an expanded configuration that creates a relatively smaller lumen for fluid flow, and the third row in the table shows the actuation assembly in a retracted configuration that creates a relatively larger lumen for fluid flow. For clarity, the first and second actuation elements  505 ,  510  are not shown as being physically coupled (e.g., there are no sutures, welds, flexible connections, etc. in the illustrations, and actuation elements are shown slightly-spaced apart), but the configuration of the first and second actuation elements  505 ,  510  in each illustration is representative of the mechanical behavior of the coupled actuation assembly. 
     As illustrated in  FIG. 6 , the lumen of the actuation assembly may vary in shape along its elongated axis (i.e., the axis of blood flow direction, horizontal in  FIG. 6  in the “dual element 2D view” and the “complete front view”). In the configuration in which the cross-sectional short-axis diameter of the lumen is relatively the largest ( FIG. 6 , third row), the lumen is substantially-cylindrical along its elongated axis (best visualized in the “dual element 2D view” and the “complete side view”). In configurations where portions of the cross-sectional short-axis diameter of the lumen is relatively smaller, the lumen may take on different shapes (e.g., hourglass shape, funnel shape) along the long-axis (as shown in  FIG. 6 , first and second rows). 
     The functionality of the example embodiment shown in  FIGS. 5A-6  may be similar to other embodiments of actuation assemblies described herein. In a first state, for example, the actuation assembly may be configured as shown in  FIG. 6 , first row, such that its smallest short-axis cross-sectional diameter is D 1 . In order to alter the configuration of the actuation assembly into a geometric configuration that allows for a relatively lower volume of flow through a lumen, the first actuation element  505  may be actuated by applying energy to the element (e.g., by heating it beyond a phase transition temperature) in a manner that forces the arms  502  to move towards their relatively more open geometric shape-set configuration. As these arms are coupled via a flexible connection to arms  507  of the second actuation element  510 , and because the second actuation element  510  is not substantially heated and remains in a relatively malleable material state, the arms  507  are manipulated into a position corresponding to the position of the arms  502 , as shown in  FIG. 6 , second row. This actuation will change the geometry of the lumen of the actuation assembly and move the smallest short-axis cross-sectional diameter to a value of D 2 , where D 2 &lt;D 1  (as shown in  FIG. 6 , second row). Similarly, in order to alter the configuration of the actuation assembly into a geometric configuration that allows for a relatively higher volume of flow through a lumen, the second actuation element  510  may be actuated by applying energy to the element (e.g., by heating it beyond a phase transition temperature) in a manner that forces the arms  507  to move towards their relatively more closed geometric shape-set configuration. As these arms  507  are coupled via a flexible connection to the arms  502  of the first actuation element  505 , and because the first actuation element  505  is not substantially heated and will be in a relatively malleable material state, the arms  502  are manipulated into a position corresponding to the position of the arms  507 , as shown in  FIG. 6 , third row. This actuation will change the geometry of the lumen of the actuation assembly, and move the smallest short-axis cross-sectional diameter to a value of D 3 , where D 3 &gt;D 1  (as shown in  FIG. 6 , third row). 
     In additional embodiments similar to those shown in  FIGS. 5A-6 , the coupling geometry/configuration between individual actuation element structures  505  and  510  may vary. For example, actuation elements may couple in a manner such that one element substantially sits atop another element (e.g., rather than being connected in series). Alternatively or additionally, one element may be nested within the bends of another element (e.g., within the nook created by the bend of arm  502  relative to zig elements  503 ). Any number of actuation element structures may be coupled together for use. In some embodiments, the utilization of a higher number of actuation elements is useful because it enables a greater degree of precision and/or granularity in altering the geometry of a actuation assembly. 
       FIG. 7  is a schematic illustration of coupled actuation elements configured in accordance with another embodiment of the present technology. The structure of  FIG. 7  includes a first actuation element  750  and a second actuation element  760  (e.g., stent-like structures). The first and second actuation elements  750 ,  760  each have arm elements  751  and  757 , respectively, and zig elements  752  and  758 , respectively. The arm elements  751  and  757  terminate in eyelet openings  759  and  769 . The zig elements are comprised of both “peaks”  755  and “valleys”  756 . As in the example embodiment depicted in  FIG. 5A , the individual stent structures may be, during manufacturing and assembly, constructed into different geometric configurations and then manipulated away from those original geometries prior to coupling. The first and second actuation elements  750 ,  760  can be coupled together to form a composite actuation assembly structure by nesting the peaks  755  of the first actuation element  750  near to the valleys  756  of the second actuation element  760 . The composite structure can be affixed using sutures, adhesives/glue, crimps/rivets, welds, material covering sleeves, or other connection techniques known to those skilled in the art. This operation represents an initial coupling operation that is a step in the process of using the first and second actuation elements  750 ,  760  to create an actuation assembly that is part of an interatrial shunting device. The composite structure can be formed into a generally cylindrical actuation assembly that has a neutral configuration at body temperature, then manipulated through a variety of configurations by selectively heating the first actuation element  750  or the second actuation element  760  above their respective transition temperatures, as described in detail above with respect to  FIG. 6 . 
     ii. Actuation Assemblies Having Elongated Actuation Elements 
     In addition to the stent-like actuation elements described with respect to  FIGS. 3A-7 , the present technology also includes actuation assemblies having other types of actuation elements. For example, the present technology includes adjustable shunts having elongated actuation elements (e.g., wires, cables, spindles, struts, etc.). In some embodiments, the elongated actuation elements are composed of a shape memory material that can be thermally manipulated to adjust a geometry of the adjustable shunt to change the flow of fluid therethrough. 
     For example,  FIGS. 8A-8F  illustrate aspects of an adjustable interatrial system  800  (“system  800 ”) having a plurality of spindle-like shape memory actuation elements and configured in accordance with select embodiments of the present technology. Referring first to  FIG. 8A , which is a cross-sectional view of the system  800  implanted across a septal wall S in a first configuration, the system  800  includes a frame  820  deployable across the septal wall S. The frame  820  can include a first end portion positionable in the RA and a second end portion positionable in the LA. The frame  820  can include RA anchor elements  824  and/or LA anchor elements  826  that secure the frame  820  to the septal wall S. The frame  820  can comprise a superelastic material such as nitinol or another suitable material (e.g., an alloy derivative of nitinol, cobalt chromium, stainless steel, etc.). In embodiments in which the frame  820  is composed of nitinol, the nitinol has a transition temperature less than body temperature such that the nitinol is in an austenitic material state when implanted, and thus the frame  820  is resistant to geometric changes, even if heated. Certain aspects of the frame  820  are omitted from  FIG. 8A  for clarity. For example, in some embodiments, the frame  820  can have an outer layer for engaging the septal wall S and an inner layer or membrane defining a lumen  802  (e.g., similar to the outer layer and inner layers described below with respect to  FIGS. 14-16D ). In some embodiments, the frame  820  has a stent-like scaffolding structure. When secured to the septal wall S, the system  800  fluidly connects the LA and the RA to enable blood flow therebetween via a lumen  802 . 
     The system  800  includes a plurality of first actuation elements  806  (only one is shown in  FIG. 8A ) and a plurality of second actuation elements  808  (only one is shown in  FIG. 8A ) extending between the RA side and the LA side of the system  800 . The first actuation elements  806  and the second actuation elements  808  can be disposed within a membrane (not shown) defining the lumen  802 . The first and second actuation elements  806 ,  808  can be wire-like spindles that extend generally linearly and parallel to a central longitudinal axis of the lumen  802 . In some embodiments, the system  800  includes the same number of first actuation elements  806  (e.g., three first actuation elements  806 ) and second actuation elements  808  (e.g., three second actuation elements  808 ). In other embodiments, however, the number of first actuation elements  806  may differ from the number of second actuation elements  808 . The first actuation elements  806  and the second actuation elements  808  can each have opposing end portions that are secured to the frame  820  via welding, soldering, riveting, gluing, suturing, or the like. For example, the first actuation elements  806  and the second actuation elements  808  can be secured to and extending between the first end portion and the second end portion of the frame. 
     Referring now to  FIG. 8B , which is a cross-sectional view of the lumen  802  taken transverse to its axial length, the first and second actuation elements  806 ,  808  can be arranged around the lumen  802  such that they alternate between first actuation elements  806  and second actuation elements  808 . In some embodiments, the first and second actuation elements  806 ,  808  can be encased in a biocompatible material and/or membrane  810  (e.g., ePTFE), which can at least partially define the outer perimeter of the lumen  802 . The membrane  810  can be at least partially flexible to accommodate movement of the first and second actuation elements  806 ,  808  as they transition between deformed shapes and manufactured shapes, as described below. 
     The first actuation elements  806  and the second actuation elements  808  can be composed of a shape memory material, such as a shape memory alloy (e.g., nitinol). Accordingly, the first and second actuation elements  806 ,  808  can be transitionable between a first material state (e.g., a martensitic state, a R-phase, etc.) and a second state (e.g., a shape memory state, an austenitic state, etc.). In the first state, the first actuation elements  806  and the second actuation elements  808  may be deformable (e.g., plastic, malleable, compressible, expandable, etc.). In the second state, the first and second actuation elements  806 ,  808  may have a preference toward a specific manufactured geometry (e.g., shape, length, and/or or dimension). The first and second actuation elements  806 ,  808  can be transitioned between the first state and the second state by applying energy to the spindles to heat the spindles above a transition temperature. In some embodiments, the transition temperature for both the first actuation elements  806  and the second actuation elements  808  is above an average body temperature. Accordingly, both the first actuation elements  806  and the second actuation elements  808  are manufactured such that they are in the deformable first material state when the system  800  is implanted in the body. 
     If the actuation elements (e.g., the first actuation elements  806 ) are deformed while in the first material state, heating the actuation elements (e.g., the first actuation elements  806 ) above their transition temperature causes the actuation element to transition to the second material state and therefore transition from the deformed shape toward its manufactured geometry. Heat can be applied to the actuation elements via RF heating, resistive heating, or the like. In some embodiments, the first actuation elements  806  can be selectively heated independently of the second actuation elements  808 , and the second actuation elements  808  can be selectively heated independently of the first actuation elements  806  (e.g., the first and second actuation elements are thermally and/or electrically isolated). For example, in some embodiments, the first actuation elements  806  are on a first electrical circuit for selectively and resistively heating the first actuation elements  806  and the second actuation elements  808  are on a second electrical circuit for selectively and resistively heating the second actuation elements  808 . As described in detail below, selectively heating the first actuation elements  806  reduces a diameter of the lumen  802  and selectively heating the second actuation elements  808  increases a diameter of the lumen  802 . 
     To drive actuation of the system  800 , the first actuation elements  806  and the second actuation elements  808  generally are manufactured to have different manufactured geometries. Referring now to  FIG. 8E , in some embodiments the first actuation elements  806  can have a generally linear manufactured geometry having a length X. Accordingly, when heated above their transition temperature, the first actuation elements  806  will move toward or assume the shape shown in solid line in  FIG. 8E  with the length X, regardless of their shape prior to heating. However, while in the deformable first (e.g., martensitic) state and/or during attachment to the frame  820 , the first actuation elements  806  can be stretched by a distance D (shown in dashed line) to have a second length greater than X (e.g., a length equal to X+D). As noted above, subsequent heating of the first actuation elements  806  above their transition temperature will cause the first actuation elements to contract to move toward or assume the manufactured geometry having the length X. The second actuation elements  808  can also have a manufactured geometry, which in some embodiments can have a length that is generally equal to or greater than the distance X+D. When in the first (e.g., martensitic) state, the second actuation elements  808  can be deformable. However, as described below, the second actuation elements  808  can be manufactured to move toward or assume the manufactured geometry shown in  FIG. 8E  when heated above their transition temperature. When attached to the frame  820 , the second actuation elements  808  can be in their manufactured geometry or another partially deformed shape. 
     Referring again to  FIGS. 8A and 8B , the system  800  is shown in first configuration in which the lumen  802  has a first diameter D 1  at its pinch portion (e.g., the narrowest portion of the generally hourglass shaped lumen). In this configuration, at least the first actuation elements  806  are in the first (e.g., martensitic) state and deformed (e.g., stretched) relative to their manufactured shape. In the illustrated configuration, the lumen  802  has a generally circular cross-sectional area, although other configurations are possible without deviating from the scope of the present technology. 
       FIGS. 8C and 8D  illustrate the system  800  in a second configuration different than the first configuration.  FIG. 8C , for example, is a cross-sectional view of the system  800  implanted across a septal wall S in the second configuration, and  FIG. 8D  is a cross-sectional view of the lumen  802  taken transverse to its axial length. In particular, in the second configuration the system  800  has been actuated relative to the first configuration shown in  FIG. 8A  to transition the first actuation elements  806  from the first (e.g., martensitic) material state to the second (e.g., austenitic) material state. Because the first actuation elements  806  were stretched (e.g., lengthened) relative to their manufactured geometry while in the first state, heating the first actuation elements  806  above the transition temperature causes the first actuation elements  806  to reduce in length and move toward their manufactured geometry (e.g., having length X, as shown in  FIG. 8E ). As the first actuation elements  806  reduce in length toward their manufactured geometry, they pull a portion of the frame  820  (shown in dashed line) inward from a first position A to a second position B. This causes the second actuation elements  808 , which are not heated above their transition temperature and therefore still in the deformable first (e.g., martensitic) state, to hinge or otherwise bend inwards toward a center longitudinal axis of the lumen  802 . This causes a decrease in the diameter of the lumen  802  at the pinch point to a second diameter D 2  that is less than the first diameter D 1 . When implanted in a human heart, decreasing the diameter of the lumen  802  (e.g., by transitioning from the first configuration to the second configuration) is expected to reduce the flow of blood from the LA to the RA. 
     The system  800  can be returned to the first configuration shown in  FIGS. 8A and 8B  by heating the second actuation elements  808  above their transition temperature once the first actuation elements  806  have returned to the deformable first state (e.g., by allowing the first actuation elements  806  to cool below the transition temperature). Heating the second actuation elements  808  above their transition temperature causes the second actuation elements  808  to move toward their manufactured geometry ( FIG. 8A ) which in turn pushes the frame  804  from the second position B to the first position A, deforms (e.g., stretches) the first actuation elements  806 , and increases the diameter of the lumen  802 . Accordingly, the system  800  can be selectively transitioned between a variety of configurations/geometries by selectively actuating either the first actuation elements  806  or the second actuation elements  808 . After actuation, the system  800  can be configured to substantially retain the given configuration until further actuation of the opposing actuation elements. In some embodiments, additional sizes and/or geometries of the lumen  802  can be achieved by selectively heating a subset of the first actuation elements  806  and/or the second actuation elements  808 . In some embodiments, the system  800  can include additional actuation elements (e.g., third actuation elements) that have different manufactured geometries than either of the first or second actuation elements, and thus can drive the lumen to additional configurations when actuated. 
       FIG. 8F  illustrates a delivery configuration of the system  800 . In the delivery configuration, the frame  820 , including the RA anchor element  824  and the LA anchor element  826 , can be folded, flattened, or otherwise crimped to reduce the overall profile of the system  800 . In the delivery configuration, the first actuation elements  806  and the second actuation elements  808  can retain their respective lengths that they will assume when the device is deployed in the first configuration. For example, the first actuation elements  806  can have their deformed (e.g., stretched) geometry having a length equal to X+D ( FIG. 8E ), and the second actuation elements  808  can have their manufactured geometry with a length also equal to X+D ( FIG. 8E ). In other embodiments, the first actuation elements  806  and/or the second actuation elements  808  may occupy other shapes or configurations while in the delivery configuration. The crimped system  800  can be inserted into a catheter (not shown) for transvascular delivery to the heart and deployment across the septal wall. Upon deployment of the system  800  from the catheter, the superelastic properties of the frame  820  can cause the system  800  to expand. For example, upon deployment of the system  800 , the system  800  may assume the first configuration illustrated with reference to  FIGS. 8A and 8B . 
       FIG. 9  is a cross-sectional, partially schematic illustration of an adjustable interatrial shunting system  900  (“system  900 ”) having helically wrapped elongated actuation elements and configured in accordance with select embodiments of the present technology. The system  900  includes a shunting element  910 , anchoring elements  920 , an adjustable inner lumen  930 , and an actuation assembly  940 . The shunting element  910  is configured to extend between an LA and an RA of the heart when implanted across the septal wall S. The shunting element  910  can have a generally toroidal shape such that it includes an outer surface  912 , an inner surface  914 , a proximal surface  916   a , and a distal surface  916   b . The outer surface  912  (which can also be referred to as a “frame”) can engage native heart tissue when implanted in a heart. For example, in the illustrated embodiment, the system  900  is shown implanted in a human heart with the outer surface  912  engaging a septal wall S. The inner surface  914  can include a membrane that at least partially defines the adjustable lumen  930 . As illustrated, the lumen  930  fluidly connects the LA and the RA when system  900  is implanted in a heart. The proximal surface  916   a  is configured to reside within the RA and the distal surface  916   b  is configured to reside within the LA. One or more portions of the shunting element  910  can be composed of or coated with a biocompatible and/or anti-thrombogenic material (e.g., ePTFE). In some embodiments, one or more portions of the shunting element  910  (e.g., the membrane forming the inner surface  914 ) is composed of an at least partially flexible or malleable material. 
     In some embodiments, the outer surface  912 , the inner surface  914 , the proximal surface  916   a , and the distal surface  916   b  of the shunting element  910  define a generally toroidal shaped chamber  950 . The chamber  950  can be fluidly isolated from the interior of the lumen  930 . The chamber  950  can also be fluidly isolated from the environment surrounding the system  900  via the material encasing the shunting element  910 . Accordingly, in some embodiments, the system  900  is configured to prevent blood from flowing into the chamber  950 . In some embodiments, the chamber  950  can contain a compressible and/or displaceable liquid, gas, and/or gel. Accordingly, as the diameter of the lumen  930  is adjusted (as described below), the liquid or gas can be compressed, expanded, and/or displaced. In other embodiments, the shunting element  910  is substantially solid throughout its cross-section such that there is no chamber  950 . In such embodiments, the shunting element  910  comprises an at least partially compressible and expandable material to conform to changes in the diameter of the lumen  930 . The anchoring elements  920  are configured to secure the system  900  in a desired position within the heart. For example, as illustrated, the anchoring elements  920  can secure the system  900  to native heart tissue such as a septal wall S. In some embodiments, the anchoring elements  920  can include right atrium anchors and/or left atrium anchors. The anchoring elements  920  can extend from and/or be integral with one or more aspects of the shunting element  910 . 
     The actuation assembly  940  is configured to selectively adjust a diameter of the lumen  930  to control the flow of blood therethrough. In the illustrated embodiment, the actuation assembly  940  comprises a first actuation element  942  and a second actuation element  944 . The first actuation element  942  and the second actuation element  944  wrap around the lumen  930  defined by the inner surface  914 . For example, the first actuation element  942  and the second actuation element  944  have a generally helical configuration, with the lumen  930  disposed within the center of the helix. The first actuation element  942  and the second actuation element  944  can be embedded within a membrane defining the lumen and/or otherwise coupled to the inner surface  914  to drive radially movement of the inner surface  914 . For example, in some embodiments, the inner surface  914  has a thickness, and the first actuation element  942  and the second actuation element  944  are embedded within the thickness of the inner surface  914 . In some embodiments, the system  900  includes one or more fluidly, thermally, and/or electrically isolated channels  946  extending around the inner lumen  930  in a generally helical orientation. The first actuation element  942  and the second actuation element  944  can be housed within the channels  946 . The channels  946  can be positioned within the chamber  950 , can be embedded within a thickness of the of inner surface  914 , and/or can be positioned within the lumen  930  itself. In some embodiments, the system  900  can include a first channel for housing the first actuation element  942  and a second channel for housing the second actuation element  944 . In other embodiments, a single channel houses both the first actuation element  942  and the second actuation element  944 . The one or more channels  946  are sized and shaped to protect the actuation elements from the environment external to the system  900 , and may also electrically and/or thermally isolate the first actuation element  942  from the second actuation element  944 . 
     The first actuation element  942  includes a proximal end region  942   a  secured to the system  900  and a distal end region  942   b  secured to the system  900 . Likewise, the second actuation element  944  includes a proximal end region  944   a  secured to the system  900  and a distal end region  944   b  secured to the system  900 . The illustrated embodiment depicts the proximal end regions  942   a ,  944   a  secured to a portion of the anchoring element  920  and the distal end regions  942   b ,  944   b , secured to the shunting element  910 . However, one skilled in the art will appreciate that the first actuation element  942  and the second actuation element  944  can be secured to any number of structures of system  900  without deviating from the scope of the present technology. 
     The first actuation element  942  and the second actuation element  944  can be composed of any material suitable to dynamically adjust a diameter of the lumen  330 . For example, in some embodiments, the first actuation element  942  and the second actuation element  944  can be composed of a shape-memory material, such as a shape memory alloy (e.g., nitinol). Accordingly, the first and second actuation elements  806 ,  808  can be transitionable between a first material state (e.g., a martensitic state, a R-phase, etc.) and a second material state (e.g., a shape memory state, an austenitic state, etc.). In the first state, the first actuation elements  806  and the second actuation elements  808  may be deformable (e.g., plastic, malleable, compressible, expandable, etc.). In the second state, the first and second actuation elements  806 ,  808  may have a preference toward a specific manufactured geometry (e.g., shape, length, and/or or dimension). The first and second actuation elements  942 ,  944  can be transitioned between the first state and the second state by applying energy to the first and/or second actuation elements  942 ,  944  to heat (e.g., resistively heat) the first and/or second actuation elements  942 ,  944  above a transition temperature. In some embodiments, the transition temperature for both the first actuation element  942  and the second actuation element  944  is above an average body temperature. Accordingly, both the first actuation element  942  and the second actuation element  944  are manufactured such that they are in the deformable first state when the system  900  is implanted in the body until they are heated (e.g., actuated). 
     At least one of the first actuation element  942  and the second actuation element  944  can be at least partially deformed relative to its manufactured geometry when implanted. For example, if the first actuation element  942  is deformed relative to its manufactured geometry, actuating the first actuation element  942  (e.g., by heating it above its transition temperature) causes the first actuation element  942  to move toward its manufactured geometry, which can tighten the first actuation element  942  and cause the lumen  930  to decrease in diameter. If the second actuation element  944  is deformed relative to its manufactured geometry, actuating the second actuation element  944  (e.g., by heating it above its transition temperature) can loosen the second actuation element  944  and cause the lumen  930  to increase in diameter. 
       FIGS. 10A and 10B  illustrate aspects of an adjustable interatrial system  1000  (“system  1000 ”) configured in accordance with select embodiments of the present technology. The system  1000  is generally similar to the system  900  described in detail above with reference to  FIG. 9 . For example, the system  1000  can include a shunting element  1010  having an outer surface (not shown) and an inner surface  1014 , anchoring elements (not shown), an adjustable lumen  1030 , and an actuation assembly  1040 . The inner surface  1014  can include a flared proximal end portion  1014   a  configured to reside within the RA of a heart, and a flared distal end portion  1014   b  configured to reside within a LA of the heart. 
     Referring to  FIG. 10A , the actuation assembly  1040  includes a first actuation element  1042  and a second actuation element  1044 . As with the system  900 , the first actuation element  1042  and the second actuation element  1044  can be generally helical coils that wrap around the lumen  1030  defined by the inner surface  1014  (e.g., embedded within a membrane defining the inner surface  1014 ). For example, the first actuation element  1042  and the second actuation element  1044  have generally spiral-shaped configurations, with the lumen  1030  disposed within the center of the spiral. In the illustrated embodiment, the first actuation element  1042  and the second actuation element  1044  are disposed around the inner surface  1014 , although other embodiments, such as those described above with respect to system  900 , are suitable. The first actuation element  1042  has a proximal end segment  1042   a  and a distal end segment  1042   b  extending from the portion of the first actuation element  1042  wrapped around the lumen  1030 . The second actuation element  1044  has a proximal end  1044   a  and a distal end  1044   b  extending from the portion of the second actuation element  1044  wrapped around the lumen  1030 . The proximal end segments  1042   a ,  1044   a  and the distal end segments  1042   b ,  1044   b  can be secured to various structures of the system  1000  (not shown). 
     In some embodiments, the first and second actuation elements  1042 ,  1044  can be composed of a shape memory material and operate in a manner substantially similar to that described above with respect to the system  900 . In other embodiments, the system  1000  can include an additional actuator (e.g., a motor, such as an electromagnetic motor, a mechanical motor, a MEMS motors, a piezoelectric based motor, or the like; not shown) configured to selectively adjust the first actuation element  1042  and the second actuation element  1044 . For example, the actuator can adjust the first actuation element  1042  by pulling the proximal end segment  1042   a  and/or the distal end segment  1042   b  of the first actuation element  1042 , thereby tightening the first actuation element  1042  around the inner surface  1014 . Tightening the first actuation element  1042  around the inner surface causes the diameter of the lumen  1030  to decrease. For example, referring to  FIG. 10A , the first actuation element  1042  has a first configuration in which the adjustable lumen  1030  has a first diameter D 1 . To reduce the diameter of the lumen  1030 , the actuator selectively tightens the first actuation element  1042 , narrowing the diameter of the spiral formed by the first actuation element  1042  and squeezing the inner surface  1014 . As a result, the lumen  1030  is transitioned to a second configuration having a second diameter D 1  that is less than the first diameter D 2 , as illustrated in  FIG. 10B . Because the first actuation element  1042  extends from the proximal end portion  1014   a  to the distal end portion  1014   b  of the inner surface  1014 , the lumen  1030  is narrowed along a substantial length of the system  1000 . The first actuation element  1042  can be configured to retain its shape following actuation, thereby retaining the second diameter D 2  until the actuator drives the system  1000  into a third configuration (not shown). 
     Actuating the second actuation element  1044  can have the opposite effect of actuation of the first actuation element  1042 . For example, actuating the second actuation element  1044  via the actuator and/or via its shape memory properties can increase the diameter of the lumen  1030 . More specifically, actuating the second actuation element  1044  causes the second actuation element  1044  to loosen around the inner surface, allowing the inner surface  1014  to expand radially outward. This increases the diameter of the lumen  1030 . The second actuation element  1044  can be configured to retain its shape following actuation, thereby retaining the desired diameter until the actuator is further activated. Accordingly, the first actuation element  1042  can be actuated to decrease the diameter of the lumen  1030  and the second actuation element  1044  can be actuated to increase the diameter of the lumen  1030 . By having opposite effects, a user can selectively adjust either the first actuation element  1042  or the second actuation element  1044  to achieve a desired lumen diameter. 
     In some embodiments, the first actuation element  1042  can be individually tightened and/or loosened via the actuator and/or the shape memory effect, and the second actuation element  1044  can be individually tightened and/or loosened via the actuator and/or the shape memory effect. In such embodiments, a single actuation element (e.g., the first actuation element  1042 ) can be sufficient to both increase and decrease the diameter of the lumen  1030 . Additional actuation elements can still be included, however, to further increase the control and operability of the system  1000 . Accordingly, some embodiments of the system  1000  include one, two, three, four, five, six, seven, and/or eight or more actuation elements. 
       FIG. 11  is a cross-sectional, partially schematic illustration of an additional embodiment of an adjustable interatrial system  1100  (“system  1100 ”) configured in accordance with select embodiments of the present technology. The system  1100  can include certain features generally similar to the systems  900  and  1000  described with respect to  FIGS. 9-10B . For example, the system  1100  can include a shunting element  1110  having an outer surface  1112 , and inner surface  1114 , a proximal (e.g., RA) surface  1116   a , and a distal (e.g., LA) surface  1116   b . The outer surface  1112  (which can also be referred to as a “frame”) can engage native heart tissue (e.g., a septal wall S) when the system  1100  is implanted in a patient. The inner surface  1114  can include a membrane that at least partially defines a lumen  1130  configured to fluidly connect a LA and a RA of a heart. The shunting element  1110  can have a generally toroidal shape. The shunting element  1110  can be hollow to define a chamber  1150 . The system  1100  can also have anchoring elements  1120  configured to secure the system  1100  in position by engaging with native heart tissue (e.g., septal wall S). 
     The system  1100  can include a plurality of actuation elements  1142 . For example, the system can include a first actuation element  1142   a , a second actuation element  1142   b , a third actuation element  1142   c , a fourth actuation element  1142   d , a fifth actuation element  1142   e , a sixth actuation element  1142   f , and a seventh actuation element  1142   g . Other embodiments can include additional or fewer actuation elements  1142 . The actuation elements  1142  wrap around the lumen  1130  (e.g., within the membrane defining the inner surface  1114 ) and are secured to the shunting element  1110 . In some embodiments, individual actuation elements (e.g., the first actuation element  1142   a ) wrap around the lumen a single time. In other embodiments, individual actuation elements (e.g., first actuation element  1142   a ) wrap around the lumen more than once. For example, each individual actuation element could be wrapped around both the LA side and the RA side of lumen  1130  such that the diameter of the lumen  1130  is adjusted along a substantial length of the lumen  1130 . As described above with respect to  FIG. 9 , the actuation elements  1142  can be housed within one or more channels  1146 . 
     Each of the actuation elements  1142   a - g  can be individually actuated. More specifically, each of the actuation elements  1142   a - g  can be individually actuated to transition from a passive configuration to an active configuration. When an individual actuation element (e.g., actuation element  1142   a ) is in the passive configuration, it does not dictate the diameter of the lumen  1130 . When the individual actuation element (e.g., actuation element  1142   a ) is actuated and transitions to the active configuration, it adjusts the diameter of the lumen  1130  to a corresponding predetermined diameter. Accordingly, each of the actuation elements  1142   a - g  can be configured to selectively adjust the diameter of the lumen  1130  to a specific predetermined diameter. For example, actuating actuation element  1142   a  can adjust the diameter of lumen  1130  to about 12 mm, actuating actuation element  1142   b  can adjust the diameter of lumen  1130  to about 5 mm, actuating actuation element  1142   c  can adjust the diameter of lumen  1130  to about 6 mm, actuating actuation element  1142   d  can adjust the diameter of lumen  1130  to about 7 mm, actuating actuation element  1145   e  can adjust the diameter of lumen  1130  to about 8 mm, actuating actuation element  1145   f  can adjust the diameter of lumen  1130  to about 9 mm, and actuating actuation element  1145   g  can adjust the diameter of lumen  1130  to about 10 mm. Accordingly, specific actuation elements can be targeted to adjust the lumen  1130  to a desired diameter. Following actuation, individual actuation elements can be configured to remain in their active configuration, thereby retaining the corresponding lumen diameter until another individual actuation element is actuated. 
     In some embodiments, the actuation elements  1142  can be composed of shape-memory material, such as a shape memory alloy (e.g., nitinol). Accordingly, the actuation elements  1142  can be transitionable between a first material state (e.g., a martensitic state, a R-phase, etc.) and a second material state (e.g., a shape memory state, an austenitic state, etc.). In the first state, the actuation elements  1142  may be deformable (e.g., plastic, malleable, compressible, expandable, etc.). In the second state, the actuation elements  1142  may have a preference toward a specific manufactured geometry (e.g., shape, length, and/or or dimension). The actuation elements  1142  can be transitioned between the first state and the second state by applying energy to the actuation elements  1142  to heat (e.g., resistively heat) the actuation elements  1142  above a transition temperature. In some embodiments, the first material state corresponds to the passive configuration described previously and the second material state corresponds to the active configuration described previously. Therefore, in some embodiments the diameter of the lumen  1130  can be adjusted by heating an individual actuation element corresponding to a desired lumen diameter above its transition temperature, thereby transitioning the actuation element from the passive configuration to the active configuration. 
       FIGS. 12A and 12B  illustrate an actuation assembly  1220  that includes generally circular actuation elements and is configured in accordance with select embodiments of the present technology. More specifically,  FIG. 12A  is an isometric view of the actuation assembly  1220 , and  FIG. 12B  is cross-sectional front view (with the blood flow axis being horizontal in this view) of the actuation assembly  1220 . In some embodiments, the actuation assembly  1220  includes plurality of actuation elements  1202 - 1204  disposed within a sleeve or membrane  1201 . In some embodiments, the membrane  1201  can be insulative, for example thermally- and/or electrically insulative. In embodiments at least a portion of the membrane  1201  is composed of a compliant material (e.g. PTFE, ePTFE, silicone, urethane, nylon, etc.) and/or a non-compliant material (e.g., annealed stainless steel, cobalt chromium). The actuation elements  1202 - 1204  can be composed of a shape memory material (e.g., nitinol wires or tubes). Each shape memory actuation element may be shape set to have a different geometric configuration. For example, a first actuation element  1202  can be constructed to have a generally sinusoidal flattened pattern and, when wrapped about a central axis, undertake a generally circular geometric configuration with a first diameter D 1 . A second actuation element  1203  may be constructed to have a similar sinusoidal flattened pattern and, when wrapped about a central axis, undertake a second circular geometric configuration with a second diameter D 2 . A third actuation element  1204  may be constructed to have a similar sinusoidal flattened pattern and, when wrapped about a central axis, undertake a third circular geometric configuration with a third diameter D 3 . Any number of additional actuation elements may be included in a similar manner. In further embodiments, the individual actuation elements may have dissimilar shapes, sizes, and/or geometric configurations. 
     In some embodiments, the actuation elements  1202 - 1204  are coupled mechanically. In some embodiments, the actuation elements  1202 - 1204  are thermoelastically manipulated (e.g., deformed) at least partially away from their original geometric configurations (e.g., manufactured geometries) prior to being coupled mechanically. In some embodiments, the actuation elements  1202 - 1204  are coupled in a manner such that they are nested serially (e.g., with the peaks and valleys of the sinusoid patterns aligning). The actuation elements  1202 - 1204  may be coupled using sutures, adhesives/glue, rivets/crimps, welds, etc., and/or may be coupled in part using the mechanical constraints/forces applied by the membrane  1201 . In some embodiments, the actuation assembly  1220  may include insulative elements  1205  which may have a similar shape, pattern, and/or geometric configuration as one or more of the actuation elements  1202 - 1204 . In some embodiments, the insulative elements  1205  are serially nested between the actuation elements  1202 - 1204 . Additionally or alternatively, the insulative elements  1205  can be located at the ends of the composite element stack (i.e., at the front and back ends of the stack of serially nested elements, as shown in  FIGS. 12A and 12B ). The insulative elements  1205  may provide electrical and/or thermal insulation, or other types of insulation. The insulative elements  1205  may be comprised of materials such as low-density polymers, PTFE, ePTFE, polyurethanes, silicones, silica, graphene, cellulose, ceramic, or other materials. In some embodiments, the insulative elements  1205  are configured as coatings over one or more actuation elements  1202 - 1204  and not as discrete components. Once the elements  1202 - 1205  are coupled, the composite nested structure  1210  may take on an equilibrium composite geometry, for example a cylinder with a composite diameter D C . 
     To adjust a geometric property (e.g., the shape, diameter, etc.) of the actuation assembly  1220 , energy is applied to one or more of the actuation elements  1202 - 1204  to raise the temperature of the element(s) above the phase transition temperature of the material (e.g., above the R-phase start, austenitic start, R-phase finish, or austenitic finish temperature). The actuated element(s) will undergo a thermoelastic recovery resulting in a shape and/or size change towards its original geometric configuration (e.g., its manufactured geometry). The remaining elements in the composite structure (to which no direct energy and, therefore, no substantial heat, is applied) will remain relatively malleable, and therefore deform in a manner complementary to the movement to the actuated element(s) (e.g., in response to force applied by the coupled actuated elements). By selectively applying energy to various actuation elements  1202 - 1204  or to various combinations of actuation elements, the actuation assembly  1220  may change geometric configuration (e.g., change shape, expand in cross-sectional area, decrease in cross-sectional area) in a manner that would impact the flow of a fluid therethrough. In embodiments, the actuation assembly  1220  may serve as the lumen for an interatrial shunting system. In other embodiments, the actuation assembly  1220  may integrate with or interface with a lumen of an interatrial shunting system (e.g., the membrane  1201  can be placed around a membrane of the shunting system that defines the shunt lumen. 
     In some embodiments, the plurality of actuator elements can comprise 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or more discrete actuation elements. In some embodiments, the possible granularity of a geometry change of the actuation assembly  1220  can be increased by having an increased number of actuation elements. In some embodiments, geometry changes of the actuation assembly  1220  may be achieved via a partial transition of a selected actuation element from an initial state to a second state that is between the initial state and the original geometric configuration of the element. For example, pulses of energy may be delivered to heat the selected actuation element to a temperature that is between the austenite start temperature and the austenite finish temperature of the material (or alternatively between the R-phase start temperature and R-phase finish temperature). Alternatively or additionally, pulses of energy may be delivered to heat only a portion of the actuation element, leaving the rest of the actuation element at a temperature that does not induce a thermoelastic recovery. This may be accomplished, for example, by heating one or more attachments to an element (e.g., heating an element locally) instead of heating the element directly (e.g., global heating of an element). 
       FIGS. 13A-13D  illustrate various actuation assemblies integrated into an interatrial shunting system configured in accordance with select embodiments of the present technology.  FIG. 13A , for example, illustrates a cross-sectional side view of an interatrial shunt assembly  1300 . The shunt assembly  1300  includes a lumen  1301  through which a fluid (e.g., blood) may flow. Some embodiments of the shunt assembly  1300  also include anchoring elements  1302  and  1304 . Embodiments may also include a flow control element or actuation assembly  1303  that operates to control the flow of fluid through the lumen  1301 . In some embodiments, the anchoring elements  1302  and  1304  are comprised of a superelastic material, such as nitinol manufactured to have an austenitic start and/or austenitic finish temperature that is similar to or lower than body temperature. Additional components, for example sensors, energy storage components, electrical components, and data transmission components, may also be included in the shunt assembly  1300 , but are not shown in  FIGS. 13A-13D  for clarity. 
       FIGS. 13B-13D  are enlarged, cross-sectional views of various example embodiments of actuation assemblies  1303  integrated into the shunt assembly  1300 . In embodiments, the actuation assembly can comprise at least two coupled actuation elements (e.g., two shape memory actuation elements). For example, in the example illustrated in  FIG. 13B , the actuation assembly comprises concentrically nested actuation elements  1320  and  1321  (e.g., nested stents) in a manner similar to the embodiment shown in  FIG. 4A-4C . In a second example illustrated in  FIG. 13C , the actuation assembly comprises interlocking actuation elements  1330  and  1331  in a manner similar to the embodiments shown in  FIGS. 5A-7 . In a third example illustrated in  FIG. 13D , the actuation assembly comprises elongated wire-like actuation elements (e.g., rings)  1351 - 1354  in a manner similar to the embodiment shown in  FIGS. 12A-12B . In some embodiments, the actuation assembly  1303  is integrated with (e.g., covered with, encased inside, surrounding, otherwise attached-to, etc.) a material or membrane layer so as to create a lumen through which blood may flow. In embodiments, the membrane layer material is comprised of ePTFE, nylon, urethane, or another suitable material known to those skilled in the art. In some embodiments, the actuation assembly  1303 , with or without an integrated material layer, serves as the lumen for the shunting assembly  1300 . In other embodiments, the actuation assembly  1303  does not itself constitute the lumen, but directly or indirectly interfaces with and influences the geometry of the lumen of the shunting assembly  1300 . 
     The present technology also provides interatrial shunting systems having actuation elements that do not directly interface with the shunt lumen. For example, unlike the embodiments described with respect to  FIGS. 3-13D  in which the actuation assemblies define the shunt lumen, are integrated into the lumen, and/or otherwise act directly upon the lumen, the present technology further provides embodiments in which the actuation element is spaced apart from the lumen and therefore does not directly manipulate the lumen. 
       FIGS. 14A-15C , for example, illustrate an adjustable interatrial shunting system  1400  (“system  1400 ”) configured in accordance with select embodiments of the present technology. The system  1400  includes a shunting element  1401  (e.g., a generally tubular element) having a first end flow aperture  1402  and a second end flow aperture  1404 . The shunting element includes a lumen  1405  extending between the first end flow aperture  1402  and the second end flow aperture  1404 . When positioned across the septal wall (e.g., as shown in  FIG. 14B ), the first end flow aperture  1402  can be in fluid communication with a RA and the second end flow aperture  1404  can be in fluid communication with a LA. Accordingly, the lumen  1405  can fluidly connect the LA and the RA. 
     The shunting element  1401  can include a frame  1410  having an outer surface configured to engage native tissue, such as the septal wall S. In some embodiments, the frame  1410  can define a chamber  1414  that can encase a gel, fluid, foam, gas, or other substance that is compressible and/or displaceable. For example, in some embodiments, the substance can compress and/or expand in response to shape changes of the lumen  1405 , described in greater detail below. In other embodiments, the substance can be displaced and/or return to its original location in response to shape changes of the lumen  1405 . The shunting element  1401  further includes RA anchors  1424  and LA anchors  1426  configured to secure the device to the septal wall when implanted in a patient. 
     The shunting element  1401  can further include a membrane  1406  at least partially defining the lumen  1405 . The membrane  1406  can define a portion of the chamber  1414 , or can be coupled to a portion of the frame  1410  defining the chamber  1414 . The membrane  1406  can be composed of any semi-flexible and biocompatible material, such as PTFE, ePTFE, silicone, nylon, polyethylene terephthalate (PET), polyether block amide (pebax), polyurethane, blends or combinations of these materials, or other suitable materials. In some embodiments, a plurality of spindles  1408  are disposed within or otherwise coupled to the membrane  1406 . The spindles  1408  can extend at least partially between the first end flow aperture  1402  and the second end flow aperture  1404  and define a shape of the lumen  1405 . In some embodiments, and as described in more detail below, the spindles  1408  can be bendable and configured to adjust a diameter of the lumen  1405 , thereby controlling the amount of blood flowing through the lumen  1405 . In some embodiments, the spindles  1408  are nitinol spindles and can be encased in a thin polymer, such as ePTFE. In some embodiments, the spindles  1408  are hollow and thin to facilitate bending. 
     The system  1400  can further include a first end element  1416  adjacent the first end flow aperture  1402  and a second end element  1418  adjacent the second end flow aperture  1404 . The first end element  1416  can be generally circular or oval-shaped to avoid blocking blood flow through the lumen  1405 . The spindles  1408  can extend between and be connected to the first end element  1416  and the second end element  1418 . The system  1400  can further include an anchoring element  1420  positioned adjacent the first end element  1416 . As one skilled in the art will appreciate from the disclosure herein, the anchoring element  1420  can be positioned adjacent the second end element  1418  and operate in a substantially similar manner. Accordingly, while the below description describes the system  1400  with the anchoring element  1420  positioned adjacent the first end element  1416 , the present technology also includes “mirror image” embodiments in which the anchoring element  1420  is positioned adjacent the second end element  1418 . 
     In the illustrated embodiment, the anchoring element  1420  and the second end element  1418  can be secured to a portion of the system  1400  fixedly secured to the septal wall (e.g., the outer surface  1412 ) and/or can be directly secured to the septal wall. Securing the anchoring element  1420  and the second end element  1418  to the system  1400  or the septal wall prevents the anchoring element  1420  and the second end element  1418  from moving during adjustment of the lumen diameter, as described below. The anchoring element  1420  can be coupled to the first end element  1416  via one or more actuation elements  1422 . The actuation elements  1422  can be springs, coils, or other elements configured to adjust a distance between the anchoring element  1420  and the first end element  1416 . 
     The first end element  1416  is moveable with respect to the anchor element  1420 . For example, the first end element  1416  can move toward the anchoring element  1420 , thereby bending the spindles  1408  inward (e.g., toward a central longitudinal axis of the lumen  1405 ) and decreasing an inner diameter of the lumen (e.g., moving from the configuration depicted in  FIGS. 14A-14C  to the configuration depicted in  FIGS. 15A-15C ). In some embodiments, for example, the spindles  1408  can bend inward until they contact each other, thereby closing the lumen  1405  and generally blocking any flow through the lumen  1405 . In other embodiments, however, the spindles  1408  do not bend inward enough to fully close the lumen  1405 , and thus the lumen remains partially open at all times. The first end element  1416  can also move away from the anchoring element  1420 , thereby straightening and/or bending the spindles  1408  outward (e.g., away from a central longitudinal axis of the lumen  1405 ), which increases an inner diameter of the lumen  1405  (e.g., moving from the configuration depicted in  FIGS. 15A-15C  to the configuration depicted in  FIGS. 14A-14C ). As one skilled in the art will appreciate from the disclosure herein, the spindles  1408  can bend to any number of positions to define any number of central inner diameters, and not just those explicitly illustrated in  FIGS. 14A-15C . In some embodiments, a length of the lumen  1405  and or the shunting element  1401  can also change as the inner diameter of the lumen  1405  changes. For example, as the central inner diameter of the lumen  1405  decreases, the length of the lumen  1405  can also decrease. Likewise, as the central inner diameter of the lumen  1405  increases, the length of the lumen  1405  can also increase. However, even in embodiments where a length of the shunting element  1401  changes, the outer diameter of the shunting element  1401  remains generally constant. 
     Various embodiments of the system  1400  provide different mechanisms to adjust the distance between the anchoring element  1420  and the first end element  1416 . For example, in some embodiments, the actuation elements  1422  can be composed of shape-memory material, such as a shape memory alloy (e.g., nitinol). Accordingly, the actuation elements  1422  can be transitionable between a first material state (e.g., a martensitic state, a R-phase, etc.) and a second material state (e.g., a shape memory state, an austenitic state, etc.). In the first state, the actuation elements  1422  may be deformable (e.g., plastic, malleable, compressible, expandable, etc.). In the second state, the actuation elements  1422  may have a preference toward a specific manufactured geometry (e.g., shape, length, and/or or dimension). The actuation elements  1422  can be transitioned between the first state and the second state by applying energy to the actuation elements  1422  to heat (e.g., resistively heat) the actuation elements  1422  above a transition temperature. 
     The actuation elements  1422  can be used to drive movement of the first end element  1416  toward or away from the anchor element  1420 , thereby adjusting a diameter of the lumen  1405 . For example, as shown in  FIGS. 14A-14C , the actuation elements can have a first neutral configuration in which they are lengthened relative to their manufactured geometry. Heating the actuation elements  1422  above their transition temperature therefore causes the actuation element to compress toward its manufactured geometry. This pulls the first end element  1416  toward the anchor element  1420 , which, as previously described, bends the spindles  1408  toward a central longitudinal axis of the lumen  1405  and decreases a diameter of the lumen (e.g., at the “pinch point” of the hourglass shape). For example,  FIGS. 15A-15C  illustrates the system  1400  in a second configuration after the actuation elements  1422  have been actuated to decrease the flow through the lumen  1405 . 
     In some embodiments, the actuation elements  1422  may operate without relying on shape memory characteristics. For example, in other embodiments, the actuation elements  1422  are springs having a first tension (e.g., spring constant). The first tension can be adjusted to a second tension to dictate how tightly the first end element  1416  is pulled toward the anchoring element  1420 . For example, as the tension in the spring decreases, the distance between the anchoring element  1420  and the first end element  1416  increases, thereby increasing the inner diameter of the lumen  1405 . As the tension in the spring increases, the distance between the anchoring element  1420  and the first end element  1416  decreases, thereby decreasing the inner diameter of the lumen  1405 . In some embodiments, the spring tension can be adjusted via a magnet external to the patient. In other embodiments, the spring tension can be mechanically adjusted using an adjustment tool delivered via a catheter. 
     In another embodiment, the actuation elements  1422  are coils. Applying energy to the coils can adjust a length of the coils. For example, applying radiofrequency (“RF”) energy can selectively adjust the length of the coil, thereby (a) adjusting a distance between the anchoring element  1420  and the first end element  1416  and (b) adjusting the inner dimeter of the lumen  1405 . In some embodiments, the RF energy can be applied externally from the patient to minimize the invasiveness of the adjustment procedure. In some embodiments, the RF energy is delivered at a low frequency to reduce signal attenuation and/or to reduce tissue heating. Low frequency signals include signals having frequencies between about 20 kHz and 300 kHz. However, one skilled in the art will appreciate that other frequencies, such as those less than 20 kHz or greater than 300 kHz, may be used in certain embodiments of the present technology. In some embodiments, the received RF energy may comprise about 10-30 watts. Due to scattering attenuation, however, the device may receive less power than transmitted. Accordingly, the device can be configured to operate with less power than transmitted, such as one watt. 
     In another embodiment, the system  1400  can include a mechanical adjustment element (e.g., a screw located on the first end element  1416  or the anchoring element  1420 ). In such embodiments, the system  1400  can be adjusted using an adjustment tool delivered to the system  1400  via a catheter. In another embodiment, the system  1400  can be adjusted using a balloon or other expandable element. For example, a balloon can be delivered into the lumen via a catheter. Inflating the balloon can apply a force that causes the spindles  1408  to bend outward away from the central longitudinal axis of the lumen  1405 , thereby increasing the inner diameter of the lumen  1405 . The spindles  1408  can comprise a relatively malleable material such that, following deflation and removal of the balloon, the lumen  1405  maintains the set inner diameter. 
       FIGS. 16A-16D  illustrate an embodiment of an adjustable interatrial system  1600  configured in accordance with select embodiments of the present technology. The system  1600  includes a frame  1610  and a membrane  1606  positioned within the frame  1610 . The frame  1610  can be composed of a superelastic material (e.g., nitinol having a phase transformation temperature lower than body temperature). The membrane  1606  can be any semi-flexible and biocompatible material that forms a lumen  1605 . A plurality of spindles  1608  can be embedded within or otherwise coupled to the membrane  1606  to provide structural integrity to the lumen  1605 . The lumen  1605  extends between a first end flow aperture  1602  and a second end flow aperture  1604 . Accordingly, when positioned across a septal wall of a heart, the first end flow aperture  1602  can be in fluid communication with a RA and the second end flow aperture  1604  can be in fluid communication with a LA such that the lumen  1605  fluidly connects the LA and the RA. The system  1600  can also include RA anchors  1624  and LA anchors  1625  (e.g., extending form the frame  1610 ) that secure system  1600  in place when implanted. 
     The system includes an actuation assembly  1620  extending from the frame  1610 . The actuation assembly can include one or more rails  1628  and one or more actuation elements  1622 . The membrane  1606  can be slidably coupled to the one or more rails  1628   1724  such that the first end flow aperture  1602  can move along the rails in a direction parallel to the longitudinal axis of the lumen  1605 . The one or more actuation elements  1622  can be composed of shape-memory material, such as a shape memory alloy (e.g., nitinol). Accordingly, the actuation elements  1622  can be transitionable between a first material state (e.g., a martensitic state, a R-phase, etc.) and a second material state (e.g., a shape memory state, an austenitic state, etc.). In the first state, the actuation elements  1622  may be deformable (e.g., plastic, malleable, compressible, expandable, etc.). In the second state, the actuation elements  1622  may have a preference toward a specific manufactured geometry (e.g., shape, length, and/or or dimension). The actuation elements  1622  can be transitioned between the first state and the second state by applying energy to the actuation elements  1622  to heat (e.g., resistively heat) the actuation elements  1622  above a transition temperature. 
     In the illustrated embodiment, the actuation assembly  1620  includes a first actuation element  1622   a  and a second actuation element  1622   b . The first actuation element  1622   a  extends from a proximal end  1620   a  of the actuation assembly  1620  and is coupled to a portion of the lumen  1605  at or adjacent the first end flow aperture  1602 . The second actuation element  1622   b  extends from a distal end  1620   b  of the actuation assembly  1620  and is coupled to a portion of the lumen  1605  at or adjacent the first end flow aperture  1602 . At least one of the first actuation element  1622   a  and the second actuation element  1622   b  is deformed relative to its manufactured geometry. For example,  FIG. 16B  illustrates both the first actuation element  1622   a  and the second actuation element  1622   b  deformed (e.g., lengthened) relative to their manufactured geometries. Heating the first actuation element  1622   a  above its transition temperature causes the first actuation element  1622   a  to transition from the first material state to the second material state and move toward its more compressed manufactured geometry, shown in  FIG. 16C . This pulls the first inflow aperture  1602  toward the proximal end  1620   a  of the actuation assembly  1620 , which decreases a length of the lumen  1605  and causes the spindles  1608  (and thus the membrane  1606 ) to bend inwardly toward a central longitudinal axis of the lumen  1605 , thereby decreasing a dimeter of the lumen  1605 . Conversely, heating the second actuation element  1622   b  above its transition temperature causes the second actuation element  1622   b  to transition from the first material state to the second material state and move toward its more compressed manufactured geometry, shown in  FIG. 16D . This pulls the first inflow aperture  1602  toward the distal end  1620   b  of the actuation assembly  1620 , which increases a length of the lumen  1605  and causes the spindles  1608  (and thus the membrane  1606 ) to bend outwardly away from the central longitudinal axis of the lumen  1605 , thereby increasing a diameter of the lumen  1605 . Therefore, the first and second actuation elements  1622   a ,  1622   b  can be selectively heated to increase or decrease the diameter of the lumen  1605  and adjust the flow of fluid therethrough. 
       FIG. 17A  is an isometric partial cut away view of an adjustable interatrial shunting system  1700  (“system  1700 ”) configured in accordance with embodiments of the present technology. The system  1700  includes a plate  1702 , a shunting element  1710 , and an actuation assembly  1720 . The shunting element  1710  and the actuation assembly  1720  can be coupled to the plate  1702 . When the system  1700  is implanted in a patient, the plate  1702  can be secured to a septal wall or other anatomical structure to secure the system  1700  in a desired position. The plate  1702  can have any number of shapes and sizes that permit the system  1700  to be delivered across and secured to the septal wall. For example, the plate  1702  may be smaller than illustrated such that it matches the general size profile of the shunting element  1710  and/or the actuation assembly  1720 . In some embodiments, some and/or all of the actuation assembly  1720  can be spaced apart from the plate  1702  by a spacing element (not shown). For example, the actuation assembly  1720  can be spaced apart from the plate  1702  by about 1 mm or more. In such embodiments, the plate  1702  may be secured to the septal wall such that the actuation assembly  1720  extends at least partially into a heart chamber (e.g., the RA). In other embodiments, the plate  1702  can be omitted and the shunting element  1710  and/or the actuation assembly  1720  can be secured to the septal wall either directly or with other suitable anchoring mechanisms. 
     The plate  1702  is configured to reside on a first side (e.g., a RA side) of the septal wall. In some embodiments, the system  1700  may have (e.g., additional) anchors configured to secure the system  1700  to the septal wall. For example,  FIGS. 17B and 17C  illustrate an embodiment of the system  1700  having an optional anchoring mechanism.  FIG. 17B  is a view of the system  1700  from the RA and  FIG. 17C  is a view of the system  1700  from the LA. As illustrated in  FIG. 17B , the plate  1702  can optionally include anchor ports  1751 . The anchor ports  1751  can be configured to receive and secure (e.g., flared) anchors  1752  ( FIG. 17C ). As illustrated in  FIG. 17C , the flared anchors  1752  can engage the septal wall such that the system  1700  is anchored in place by the plate  1702  on the RA side of the septal wall and the flared anchors  1752  on the LA side of the septal wall. When implanted across a septal wall, the actuation assembly  1720  can be positioned on a RA side or a LA side of the septal wall. In some embodiments, the system  1700  can be collapsed into a delivery catheter having an outer diameter of about 30 Fr or less, or about 20 Fr or less, to facilitate delivery of the system  1700  to the heart. 
     Returning to  FIG. 17A , the shunting element  1710  has a lumen  1712  extending therethrough. In the illustrated embodiment, the shunting element  1710  has a generally tubular or cylindrical shape that defines the lumen  1712 . In other embodiments, however, the shunting element  1710  can have other suitable shapes. The shunting element  1710  can comprise an at least partially deformable and/or flexible material. As described in greater detail below, this enables the shunting element  1710  to change shape and/or size. When the system  1700  is implanted adjacent a septal wall, the shunting element  1710  fluidly connects the LA of the patient and the RA of the patient via the lumen  1712 . 
     The actuation assembly  1720  includes a rim  1725  having a spine portion  1725   a  with a first anchor element  1721   a  and a second anchor element  1721   b  extending from and generally perpendicular to opposing end portions of the spine portion  1725   a . The second anchor element  1721   b  can extend generally towards the shunting element  1710  to define a shunting element anchor  1726 . In some embodiments, a portion of the shunting element anchor  1726  may engage an exterior surface portion of the shunting element  1710 . Some or all of the rim  1725  can be secured to the plate  1702  and/or the septal wall. Accordingly, the rim  1725  is configured to remain static as the actuation assembly  1720  is actuated to adjust the size and/or shape of the lumen  1712 , as described in greater detail below. 
     The actuation assembly  1720  further includes a moveable element  1723 , a first actuation element  1722   a  extending between the first anchor element  1721   a  and the moveable element  1723 , and a second actuation element  1722   b  extending between the second anchor element  1721   b  and the moveable element  1723 . In the illustrated embodiment, the first actuation element  1722   a  is in a compressed state and the second actuation element  1722   b  is in a partially expanded state. However, as will be described in greater detail below with respect to  FIGS. 18A-18C , the first actuation element  1722   a  and second actuation element  1722   b  can be expanded and compressed to change the configuration of the actuation assembly  1720 . The moveable element  1723  is generally between the first actuation element  1722   a  and the second actuation element  1722   b . A moveable arm  1724  extends from the moveable element  1723  and can be generally parallel to the shunting element anchor  1726 . The moveable arm  1724  extends generally adjacent to the shunting element  1710  but on a side generally opposite the shunting element anchor  1726 . Accordingly, the shunting element  1710  is positioned generally between the moveable arm  1724  and the shunting element anchor  1726 . The moveable arm  1724  can engage the shunting element  1710  to change a size and/or shape of the lumen  1712 , as described in detail below. 
     In the illustrated embodiment, the actuation assembly  1720  has a relatively flat profile. For example, the actuation assembly  1720  may extend less than about 10 mm (e.g., less than about 5 mm or less than about 2 mm) outwardly from the plate  1702  and/or the septal wall (when implanted). Accordingly, the actuation assembly  1720  may extend less than about 10 mm (e.g., less than about 5 mm or less than about 2 mm) into a heart chamber (e.g., a RA) when implanted in a patient. Without wishing to be bound by theory, the relatively flat profile of the actuation assembly  1720  is expected to reduce a risk of thromboembolic events. Further, in some embodiments the actuation assembly  1720  can also be positioned within a bladder or other membrane (not shown) to fluidly isolate the actuation assembly  1720  from the surrounding environment. 
     Various aspects of the actuation assembly  1720  can comprise shape-memory material(s) and/or superelastic material(s) configured to at least partially transition from a martensitic phase to an austenitic phase upon application of energy. For example, at least the first actuation element  1722   a  and the second actuation element  1722   b  can be composed of a shape memory alloy such as nitinol. The first actuation element  1722   a  and the second actuation element  1722   b  can therefore change shape (e.g., expand and/or compress in length, width, etc.) in response to exposure to energy, such as light and/or electrical current, that creates a temperature increase in the material above the transition temperature. In such embodiments, the actuation assembly  1720  can be selectively actuated by applying energy directly or indirectly to the first actuation element  1722   a  and/or the second actuation element  1722   b . In some embodiments, energy can be applied to individual bend regions (e.g., bend regions  1832   a - d — FIG. 18B ) of the spring elements. Targeting individual bend regions  1832   a - d  is expected to provide more control over the adjustment of the system  1700  by enabling a user to selectively titrate the therapy, as described in further detail below. In some embodiments, other aspects of the actuation assembly  1720  can also comprise nitinol or other suitable shape memory material(s) and/or superelastic material(s). For example, the rim  1725  can be composed of nitinol but configured to exhibit superelastic properties at body temperature. Accordingly, in some embodiments, the actuation assembly  1720  can be laser cut from a single sheet of nitinol or other suitable material. 
       FIG. 18A  is a top plan view of the system  1700  in the configuration (i.e., a first configuration) depicted in  FIG. 17A . In the illustrated state, the first actuation element  1722   a  is generally compressed and the second actuation element  1722   b  is at least partially expanded. Accordingly, the first actuation element  1722   a  has a length L 1  and the second actuation element  1722   b  has a length L 2  greater than the length L 1 . As will be described in greater detail below with respect to  FIGS. 18B and 18C , the lengths L 1  and L 2  can be changed by selectively expanding or compressing the first actuation element  1722   a  and/or the second actuation element  1722   b . When the second actuation element  1722   b  is at least partially expanded, as in the illustrated configuration of  FIG. 18A , the moveable arm  1724  does not compress the lumen  1712 , and the lumen  1712  has a generally circular cross-sectional shape. For example, the lumen  1712  has a first diameter D 1  (e.g., a generally horizontal diameter) that is approximately equal to a second diameter D 2  (e.g., a generally vertical diameter). 
       FIG. 18B  is a top plan view of the system  1700  in a second configuration following at least partial actuation of the actuation assembly  1720 . In particular, the first actuation element  1722   a  is expanding from a compressed state to a partially expanded state in response to application of energy E. In the illustrated embodiment, the energy E is being applied to a second bend region  232   b  of the first actuation element  1722   a . If heated above its transition temperature, this causes the first actuation element  1722   a  to transition from a first material state (e.g., martensitic) to a second material state (e.g., austenitic) at least at the second bend region  232   b . Accordingly, in some embodiments the individual bend regions can be individually actuated. In other embodiments, more than one individual bend region is actuated and/or expands in response to the application of energy E. 
     Because the first anchor element  1721   a  and the second anchor element  1721   b  are fixedly secured to one another via the spine portion  1725   a  (e.g., they do not move as the actuation elements move), the first actuation element  1722   a  pushes the moveable element  1723  towards the second anchor element  1721   b  as the first actuation element  1722   a  expands. As a result, the second actuation element  1722   b , which remains in a relatively malleable material state, is forced from the partially expanded state towards a compressed state. Therefore, in the illustrated configuration of  FIG. 18B , the length L 1  of the first actuation element  1722   a  is approximately equal to the length L 2  of the second actuation element  1722   b . As the moveable element  1723  is pushed towards the second anchor element  1721   b , the moveable arm  1724  also moves towards the shunting element anchor  1726  and engages the shunting element  1710 . Because the shunting element anchor  1726  is also fixedly secured (e.g., it does not move as the spring elements move), the lumen  1712  is at least partially deformed (e.g., compressed, squeezed, pinched, etc.) between the moveable arm  1724  and the shunting element anchor  1726 . Accordingly, at least one of a size or shape profile of the lumen  1712  changes. In the illustrated embodiment, the lumen  1712  is compressed into a generally oval shape, such that the first diameter D 1  is less than the second diameter D 2 . Without wishing to be bound by theory, changing the shape and/or size of the lumen provides a titratable therapy/amount of shunting that can be specifically adjusted to a patient&#39;s needs. In some embodiments, the interaction of moveable arm  1724  and the shunting element  1710  deforms the lumen  1712  along the entirety of or a large portion of the element&#39;s working length (e.g., its length in the direction perpendicular to anchor  1726 ). In some variations, the interaction of moveable arm  1724  and the shunting element  1710  deforms the lumen  1712  locally in a region confined to the vicinity of where the arm and element interface. 
       FIG. 18C  is a top plan view of the system  1700  in a third configuration following further actuation of the actuation assembly  1720 . As the energy E is continually delivered to the first actuation element  1722   a  (either for longer periods of time, or in additional locations), the first actuation element  1722   a  continues to expand until the second actuation element  1722   b  is in a generally compressed state (e.g., the length L 1  is greater than the length L 2 ). This causes the moveable element  1723  and the moveable arm  1724  to move further toward the second anchor element  1721   b  and the shunting element anchor  1726 , respectively, further changing the shape and/or size of the lumen  1712 . For example, the shunting element  1710  is further pinched such that the first diameter D 1  continues to decrease and the second diameter D 2  continues to increase, relative to the configurations shown in  FIGS. 18A and 18B . When the desired shape and/or size of the lumen  1712  is achieved, the energy source can be turned off. Because the system  1700  can be at least partially composed of shape memory materials, the first actuation element  1722   a  and/or the second actuation element  1722   b  can be configured to retain their shape upon cessation of energy input. For example, the system  1700  can retain the configuration illustrated in  FIG. 18C  until further energy is applied to the first actuation element  1722   a  and/or the second actuation element  1722   b . Accordingly, once a desired lumen shape and/or size is achieved, the lumen  1712  is configured to retain the selected shape and/or size until further application of energy. 
     In some embodiments, the system  1700  may have a locking mechanism (not shown) to further anchor the actuation assembly  1720  and/or the system  1700  in the desired lumen shape and/or size. In some embodiments, the locking mechanism can be engaged and/or disengaged using (i) the same energy source that is used to adjust the actuation assembly  1720 , (ii) the same energy source operating at a different parameter value (e.g., frequency, temperature, etc.), and/or (iii) a different energy source. In some embodiments, the locking mechanism can automatically engage and lock the shunting element  1710  in a given configuration when the actuation assembly  1720  is not being adjusted. In such embodiments, actuation of the actuation assembly  1720  can generate sufficient forces to overcome the locking mechanism. 
     Altering the shape of the lumen  1712  of the shunting element  1710  may have several benefits, including titrating the rate, velocity, and/or other features of blood flow to more optimally suit a patient&#39;s needs. For example, as the shape of a lumen moves from a largely circular cross-section (e.g. as in  FIG. 18A ) to a largely ovular cross-section (e.g. as in  FIG. 18C ), the circumference of the lumen  1712  can remain constant while the cross-sectional area is reduced, thereby reducing the flow through the lumen  1712 . Although described above with reference to three specific configurations, the system  1700  can be transitioned between any number of configurations using the actuation assembly  1720 . In addition, the titratability of system  1700  is reversible: to return the system  1700  to the configuration shown in  FIG. 18A , energy can be applied to the second actuation element  1722   b , which heats the second actuation element  1722   b  above its transition temperature, causing it to expand and push the moveable element  1723  and moveable arm  1724  towards the first anchor element  1721   a  and away from the shunting element  1710 . Accordingly, the size and shape of the lumen  312  can be selectively and reversibly manipulated using the actuation assembly  1720 . 
     The lengths L 1  and L 2  of the first actuation element  1722   a  and the second actuation element  1722   b , respectively, can be the same or different when the first actuation element  1722   a  and the second actuation element  1722   b  are in comparable states. For example, the length L 1  of the first actuation element  1722   a  when it is in the compressed state ( FIG. 18A ) can be generally equal to the length L 2  of the second actuation element  1722   b  when it is in a compressed state ( FIG. 18C ). In other embodiments, the length L 1  of the first actuation element  1722   a  when it is in the compressed state is not equal to the length L 2  of the second actuation element  1722   b  when it is in a compressed state. Accordingly, as one skilled in the art will appreciate from the disclosure herein, the system  1700  can be manufactured with a variety of dimensions and configurations without deviating from the scope of the present disclosure. 
     In some embodiments, the actuation assembly  1720  can be biased before implanting the system  1700  into the patient. For example, the actuation assembly  1720  can be biased toward the configuration shown in  FIG. 18A  or the configuration shown in  FIG. 18C , depending on the anticipated needs of the patient. However, if the biased position of the system  1700  is undesirable, the actuation assembly  1720  can be actuated (e.g., either before or after implantation) to achieve the desired shape and/or size of the lumen  1712 . In some embodiments when adjusting the system  1700  after implantation, the energy E can be applied from an energy source (e.g., an ultrasound or electromagnetic energy source) positioned external to the body of the patient. Accordingly, the energy can be “non-invasive.” In some embodiments, the energy E can be applied from an energy source positioned adjacent the shunt, such as an energy source (e.g., a laser) delivered via a catheter. In some embodiments, the shunts can include one or more energy storage components storing energy at or adjacent the system  1700  and configured to selectively release the energy and apply it to the actuation assembly  1720 . 
       FIG. 19A  is a top plan view of an adjustable interatrial shunting system  1900  (“system  1900 ) configured in accordance with embodiments of the present technology. Certain aspects of the system  1900  can be generally similar to the system  1700 . For example, the system  1900  includes an actuation assembly  1920 . Similar to the actuation assembly  1720  described previously, the actuation assembly  1920  includes a first actuation element  1922   a  and a second actuation element  1922   b . The actuation assembly  1920  differs from the actuation assembly  1720 , however, in that the actuation assembly  1920  includes a first resistor or control wire  1930   a  extending along at least a portion of the first actuation element  1922   a  and a second resistor or control wire  1930   b  extending along at least a portion of the second actuation element  1922   b . The first control wire  1930   a  and the second control wire  1930   b  can be embedded within the first actuation element  1922   a  and the second actuation element  1922   b , respectively, or can be positioned on a surface of the first actuation element  1922   a  and the second actuation element  1922   b , respectively. The control wires  1930   a - b  can be configured to deliver energy to the actuation elements  1922 , thereby heating the actuation elements  1922  above their transition temperatures and inducing a phase change (e.g., transitioning from a martensitic material phase to an austenitic material phase). In some instances, using the control wires  1930   a - b  to deliver energy to the actuation elements  1922  may provide more evenly distributed heating along the corresponding actuation elements  1922 . 
     The first control wire  1930   a  and the second control wire  1930   b  can be selectively actuated to provide energy (e.g., heat) to the first actuation element  1922   a  or the second actuation element  1922   b . For example, the system  1900  can include a first actuator  1940   a  configured to energize the first control wire  1920   a  and a second actuator  1940   b  configured to energize the second control wire  1920   b . The first actuator  1940   a  and the second actuator  1940   b  can be electronic circuitry or other suitable mechanism(s) that can selectively produce current or other energy. In some embodiments, the first actuator  1940   a  and the second actuator  1940   b  can include coils that produce a current in response to magnetic energy. To adjust the shape or size of the lumen  1912 , the first actuator  1940   a  can deliver energy to the first actuation element  1922   a  via the first control wire  1930   a , causing the first actuation element  1922   a  to expand, as described in detail above with respect to  FIGS. 17A-18C . Likewise, the second actuator  1940   b  can deliver energy to the second actuation element  1922   b  via the second control wire  1930   b , causing the second actuation element  1922   b  to expand. 
     In some embodiments, each actuation element may include a plurality of independently activatable control wires  1930 . Each of the plurality of independently activatable control wires  1930  can be configured to deliver energy to a specific bend region in a corresponding spring element. For example, a first control wire may deliver energy to a first bend region  1932   a  in the second actuation element  1922   b , a second control wire may deliver energy to a second bend region  1932   b  in the second actuation element  1922   b , a third control wire may deliver energy to a third bend region  1932   c  in the second actuation element  1922   b , and a fourth control wire may deliver energy to a fourth bend region  1932   d  in the second actuation element  1922   b . Similarly, a plurality of independently activatable control wires can be configured to deliver energy to individual bend regions in the first actuation element  1922   a . Having individual control wires for the individual bend regions enables a user to selectively actuate discrete portions of the actuation elements, which is expected to provide greater precision in control over actuation of the system  1900 . 
       FIGS. 19B-19D  show schematic illustrations of an implementation of the actuation element  1922  (which can be either the first actuation element  1922   a  or the second actuation element  1922   b ). As previously described, the actuation element  1922  may be composed of a shape memory material that is constructed in a geometric configuration represented in  FIG. 19D , a triangular-wave shape member with a projected total element length D 3 . At a given temperature (e.g., room temperature), actuation element  1922  may be relatively malleable (e.g., at least partially in a martensitic material state) and can be compressed along an axis such that the triangular-wave pattern is characterized by sharper (more acute) angles and the projected total element length changes to D 1 , where D 1 &lt;D 3 , as illustrated in  FIG. 19B . In embodiments, actuation element  1922  includes a plurality of energy exchange points (e.g., electrical connection interface points)  1951 - 1955  that allow for selective actuation of the element  1922 . In an example operation, an electrical energy source, such as the first or second actuator  1940   a,b  in  FIG. 19A , is configured to deliver current through a circuit pathway defined by connection points  1951  and  1953 . Accordingly, resistive heating may preferentially occur over the portion of the actuation element  1922  bounded by connection points  1951  and  1953 . If heating is sufficient to drive the material to a phase transition temperature (e.g., to or above the R-phase start temperature, austenite start temperature, R-phase finish temperature, or austenitic finish temperature), this portion of the actuation element may expand towards its shape set geometric configuration. The resulting element geometry is shown in  FIG. 19B , where the total element length has grown to D 2 , where D 1 &lt;D 2 &lt;D 3 . To return the actuation element  1922  to (or approximately to) its original geometric configuration (projected length of D 3 ), electrical energy may be applied across a circuit between connection points  1951  and  1955 . Alternatively, energy may be applied to the entirety of the element  1922  (either simultaneously across the entire element, or incrementally across portions of the element sequentially) to return it to an approximate length D 3 . Alternatively, energy may be applied across only those elements which had not yet released their thermoeleastic energy (e.g., electrically connecting a circuit between connection points  1953  and  1955 ). As shown, adding localized energy deposition zones may increase the granularity with which a geometry change may be induced in an actuation element. In variation embodiments, a second actuation element (e.g., the opposing actuation element) that has a relatively compressed shape-set geometric configuration may be coupled to actuation element  1922 , which allows for the composite element to be toggled back and forth between relatively elongated and relatively compressed geometric configurations, as previously described. Although described with reference to system  1900 , one skilled in the art will appreciate that the description related to restively heating the shape memory actuation element can apply to any of the embodiments described herein. 
       FIG. 20A-20C  illustrate another adjustable interatrial shunting system  2000  (“system  2000 ”) configured in accordance with select embodiments of the present technology. Referring to  FIG. 20A , the system  2000  includes a first shunting element  2004  with a lumen  2003  on a first (e.g., RA) side of the septal wall S and a second shunting element  2005  on a second (e.g., LA) side of the septal wall S. In some embodiments, the first shunting element  2004  and the second shunting element  2005  may be a continuous structure that traverses the septal wall S. In other embodiments, the first shunting element  2004  and the second shunting element  2005  may be separate components of the system  2000  that are nevertheless fluidly connected. The system  2000  also includes an actuation assembly  2020  that is oriented generally parallel to the first shunting element  2004 . In some embodiments, the actuation assembly  2020  can be at least partially spaced apart from the septal wall (e.g., by spacing plate  2012 ). 
     The actuation assembly  2020  can include a first shape memory component  2006 , a second shape memory component  2007 , a shuttle component  2008  residing between the shape memory components  2006 ,  2007 , and a restriction band  2009  connected to the shuttle component  2008 . As best seen in  FIGS. 20B and 20C , the restriction band  2009  may at least partially wrap around the first shunting element  2004 . The shape memory components  2006 ,  2007  and shuttle component  2008  may interface with (either via a direct connection or via additional intermediate connectors) a stabilization component  2013  that is generally parallel to a vertical diameter axis of the lumen  2003 . The top and bottom ends of the stabilization component  2013  can include connecting arms  2010  that interface with the proximal side of the spacing plate  2012 . In some embodiments, a distal side of the spacing plate  2012  is configured to interface with the septal wall S. The spacing plate  2012  can include an access notch  2011  that allows the restriction band  2009  to rotate approximately 90 degrees from the plane containing the shuttle component  2008  and shape memory components  2006 ,  2007  and encircle the first shunting element  2004 . 
     The first shape memory component  2006  and second shape memory component  2007  can function generally similarly to the actuation elements described above with respect to  FIGS. 16A-19 . Accordingly, the first shape memory component  2006  may be activated with energy to transition the first shape memory component from a relatively contracted martensitic state to a relatively expanded austenitic state. Likewise, the second shape memory component  2007  may be activated with energy to transition the second shape memory component from a relatively contracted martensitic state to a relatively expanded austenitic state. Heating the first shape memory component  2006  pushes the shuttle component  2008  generally toward the spacing plate  2012 , and heating the second shape memory component  2007  pushes the shuttle component  2008  generally away from the spacing plate  2012 . Moving the shuttle component  2008  adjusts a force on the restriction band  2009 , which can affect the size of the shunt.  FIG. 20B , for example, is a front view of the system  2000  in a first relatively high flow state.  FIG. 20C  is a front view of the system  2000  in a second relatively low flow state. The system  2000  can transition between the configurations shown in  FIGS. 20B and 20C , among other configurations, following actuation of the actuation assembly  2020  to increase the force on the restriction band  2009 . 
       FIG. 21A  illustrates an adjustable interatrial shunting system  2100  (“system  2100 ”) configured in accordance with select embodiments of the present technology. The system  2100  includes an outer frame  2110  and an adjustable inner lumen  2130 . The frame  2110  includes a plurality of arms  2112  defining a scaffolding for the system  2100 . The frame can further include a plurality of right atrium anchors  2122  and a plurality of left atrium anchors  2124 , which in some embodiments can extend from the plurality of arms  2112 . The right atrium anchors  2122  and left atrium anchors  2124  are configured to engage native heart tissue when the system  2100  is implanted in a heart to secures the system  2100  in place. The frame  2110  can be encased in an outer membrane  2114  suitable to engage native heart tissue. For example, the outer membrane  2114  can be a biocompatible and/or anti-thrombogenic material, such as ePTFE. In some embodiments, the outer membrane  2114  is an elastomeric material that is at least partially stretchable and/or flexible. 
     The adjustable inner lumen  2130  includes a proximal end portion  2132  positionable within the RA of a human heart. The adjustable inner lumen  2130  extends the longitudinal length of the system  2100  to a distal end portion (not shown). The distal end portion of the lumen  2130  is configured to reside within the LA of the heart when the system  2100  is implanted. Accordingly, the lumen  2130  fluidly connects the LA and the RA of the heart when implanted. The lumen  2130  is defined by a plurality of struts  2134  extending along the axial length of the lumen  2130 . The plurality of struts  2134  are generally parallel to a center axis of the lumen  2130 . The struts  2134  can comprise a shape-memory material and/or a superelastic material such as nitinol, malleable materials such as annealed or non-annealed stainless steel, cobalt chromium, or other suitable materials. The struts  2134  can be connected to the frame  2110  (e.g., the arms  2112 ) via one or more connecting struts  2140 . The connecting struts  2140  can also comprise a shape-memory material and/or a superelastic material such as nitinol, malleable materials such as annealed or non-annealed stainless steel, cobalt chromium, or other suitable materials. As described below with reference to  FIGS. 21B-21D , the one or more connecting struts  2140  can be actuated to alter a position of the struts  2134  and change a diameter of the lumen  2130 . 
     The lumen  2130  is further defined by an inner membrane  2133 . In some embodiments, the inner membrane  2133  forms a sheath around the struts  2134  (e.g., the struts  2134  can be embedded within the inner membrane  2133 ). In other embodiments, the struts  2134  can be positioned adjacent to but not encased within the inner membrane  2133 . For example, the struts  2134  can be internal to the inner membrane  2133  (e.g., within the lumen  2130 ) or external to the inner membrane  2133  (e.g., outside the lumen  2130 ). When the struts  2134  are not encased within the inner membrane  2133 , the struts  2134  can be otherwise connected to the inner membrane  2133 , although in other embodiments the struts  2134  are not connected to the inner membrane  2133 . Regardless of the relative positioning of the struts  2134  and the inner membrane  2133 , the inner membrane  2133  can form a single and/or continuous membrane with the outer membrane  2114  of the frame  2110  (in such embodiments, the outer membrane  2114  and the inner membrane  2133  can be collectively referred to as a single or unitary membrane). The volume of space between the outer membrane  2114  and the inner membrane  2133  can form a generally toroidal shaped chamber  2150 , as described in greater detail below. The inner membrane  2133  can comprise the same material as the outer membrane  2114  of the frame  2110 . For example, the inner membrane  2133  can be a biocompatible and/or anti-thrombogenic material such as ePTFE and/or an elastomeric material that is at least partially stretchable and/or flexible. For example, in one embodiment, the inner membrane  2133  is ePTFE and forms a sheath around the struts  2134 . In some embodiments, the inner membrane  2133  and the outer membrane  2114  can comprise different materials. In some embodiments, the system  2100  has two, three, four, five, six, seven, eight, nine, ten, eleven, and/or twelve struts  2134 . As described in greater detail with respect to  FIGS. 21B-21D , the struts  2134  can be malleable and/or contain one or more hinges, enabling the struts to dynamically change shape (e.g., expand, fold, or otherwise bend) to change the diameter of the inner lumen  2130 . 
     As described above, the volume between the outer membrane  2114  of the frame  2110  and the inner membrane  2133  of the adjustable inner lumen  2130  defines a generally toroidal shaped chamber  2150 . The chamber  2150  can be fluidly isolated from the interior of the lumen  2130  via the inner membrane  2133 . The chamber  2150  can also be fluidly isolated from the environment surrounding the system  2100  via the outer membrane  2114 . Accordingly, in some embodiments, the system  2100  is configured to prevent blood from flowing into the chamber  2150 . In some embodiments, the chamber  2150  can contain a compressible and/or displaceable liquid, gas, and/or gel. Accordingly, as the diameter of the lumen  2130  is adjusted, the liquid or gas can either be compressed, expanded, and/or displaced. The chamber  2150  can also house one or more electronic components (e.g., battery, supercapacitor, etc.). In such embodiments, the electronic components can be electrically isolated from other system components. 
       FIGS. 21B-21D  schematically illustrate the adjustable inner lumen  2130  of the system  2100 .  FIGS. 22A-22C  are schematic illustrations of the stages of operation shown in  FIGS. 21B-21D , but further show the system  2100  implanted across a septal wall S. Referring to  FIG. 21B , the struts  2134  are connected to the frame  2110  (e.g., the arms  2112 , shown in  FIG. 21A ) via a first connecting strut  2140   a  at a proximal end (e.g., right atrium) portion and via a second connecting strut  2140   b  at a distal end (e.g., LA) portion (collectively referred to as “connecting struts  2140 ”). As described above, the struts  2134  at least partially define the shape of the lumen  2130 . The first connecting strut  2140   a  can connect the struts  2134  to the frame  2110  at a proximal connection  2136  on the RA side of the system  2100 . The second connecting strut  2140   b  can connect the struts  2134  to the frame  2110  at a distal connection  2138  on the LA side of the system  2100 . The transition between the first connecting strut  2140   a  and the strut  2134  can include a hinge or other bendable aspect  2135   a  (referred to hereinafter as “hinge  2135   a ”). Likewise, the transition between the strut  2134  and the second connecting strut  2140   b  can also include a hinge or bendable aspect  2135   b  (referred to hereinafter as “hinge  2135   b ”). As will be described below, the hinges  2135  enable the strut  2134  to bend and/or fold relative to the first and second connecting struts  2140 , thereby dynamically adjusting the diameter of the lumen  2130 . 
     Referring to  FIG. 21B , the system  2100  is shown in a first configuration in which the lumen  2130  has a first inner diameter X 1 . The frame  2110  has a diameter D, and the proximal connection  2136  and the hinge  2135   a  are separated by a distance Y 1 . To reduce the inner diameter of the lumen  2130 , the proximal end portion  2132  of the inner lumen  2130  moves distally (e.g., towards the LA), causing the struts  2134  to bend at hinges  2135   a ,  2135   b . More specifically, in the illustrated embodiment, the angle defined by the first connecting strut  2140   a  and the strut  2134  at hinge  2135   a  is increased, while the angle defined by the second connecting strut  2140   b  and the strut  2134  at hinge  2135   b  is decreased. Accordingly, in various embodiments, the struts  2134  have a fixed length but are moveable through a range of positions by the connecting struts  2140  to change the diameter of lumen  2130 . In such embodiments, the lumen  2130  defined by the struts  2134  remains a constant length (e.g., length L 1  remains substantially the same), even when the diameter of the lumen  2130  is changing. 
       FIG. 21C  illustrates a second configuration of system  2100  in which the inner lumen  2130  has a second inner diameter X 2  that is less than the first inner diameter X 1 . The proximal end portion  2132  and the hinge  2135   a  are separated by a distance Y 2  that is less than the distance Y 1 . The diameter D of the frame  2110  does not substantially change.  FIG. 21C  illustrates a third configuration of system  2100  in which the inner lumen  2130  has a third inner diameter X 3  that is less than the second inner diameter X 2 . The proximal end portion  2132  and the hinge  2135   a  are separated by a distance Y 3  that is less than the distance Y 2 . The diameter D of the frame  2110  does not change. As discussed above, the struts  2134  and/or the connecting struts  2140  can comprise a shape memory material. Accordingly, once the struts  2134  and connecting struts  2140  have been transitioned to a desired position, the struts can retain their configuration and the lumen retains a constant diameter until an active input is received (e.g. via an actuation mechanism, as discussed below). 
     In various embodiments, system  2100  is configured to adjust from a first configuration to a second configuration. In the first configuration, the lumen  2130  has a first substantially constant diameter. In the second configuration, the lumen  2130  has a second substantially constant diameter different than the first substantially constant diameter. The lumen may have a substantially constant diameter along all or substantially all of its entire length. In other embodiments, however, the lumen may have a substantially constant diameter along only a major portion of its length. For example, the lumen diameter may be substantially constant along the portion which extends through the septal wall. In another example, the lumen has a substantially constant diameter along its entire length, and has additional features adjacent to the lumen on one or both ends, such as a flare, funnel, taper, or the like. For example, as will be described in greater detail below, system  2100  shows the lumen  2130  having a funnel shaped inflow component  2137  configured for fluid communication with a left atrium of a heart (not shown) and a cylindrical shaped outflow portion  2139  configured for fluid communication with the right atrium of a heart (not shown). 
     Although  FIGS. 21B-21D  (and  FIGS. 22A-22C ) only illustrate three lumen diameters, one skilled in the art will appreciate that the struts  2134  can be actuated through a plurality of configurations (not shown), resulting in a plurality of discrete lumen diameters. For example, the lumen can take any diameter between a fully open configuration and a fully closed configuration. Moreover, in addition to decreasing the diameter of the lumen  2130  as illustrated, the struts  2134  can be selectively actuated via the connecting struts  2140  to increase the diameter of the lumen  2130 . To increase the diameter of the inner lumen  2130 , the proximal end portion  2132  of the inner lumen  2130  moves proximally (e.g., further into the RA), such that the angle defined by the first connecting strut  2140   a  and the strut  2134  at hinge  2135   a  is decreased, and the angle defined by the strut  2134  and the second connecting strut  2140   b  at hinge  2135   b  is increased. Accordingly, system  2100  enables the diameter of the lumen  2130  to by selectively adjusted to control the flow of blood through the lumen  2130 . The specific diameter for the lumen  2130  can be selected based off the patient&#39;s needs. 
     The system  2100  can be adjusted between the configurations shown in  FIGS. 21B-21D  once implanted in a heart.  FIG. 22A , for example, illustrates the system  2100  implanted across a septal wall S and in a first configuration (e.g., the configuration shown in  FIG. 21A  above). To decrease the blood flow through the lumen  2130 , the struts  2134  can be directed radially inward by bending at the hinges  2135   a ,  2135   b , as described in detail above, to assume a second configuration shown in  FIG. 22B  (e.g., which corresponds to the configuration shown in FIG.  21 C), and/or a third configuration shown in  FIG. 22C  (e.g., which corresponds to the configuration shown in  FIG. 21D ). 
     In some embodiments, the system  2100  can be adjusted using an inflatable balloon intravascularly delivered proximate the system  2100 . For example, a balloon (not shown) can be delivered via a catheter and positioned within the lumen  2130 . Inflating the balloon can push the struts  2134  radially outward, enlarging the lumen (e.g., transitioning from the configuration shown in  FIG. 22C  to the configuration shown in  FIG. 22A ). The balloon can also be used to reduce the diameter of the lumen  2130  by pushing the proximal end portion  2132 , such as at hinge  2135   a , distally. For example,  FIGS. 23A-23C  illustrate deployment of the system  2100 . The system  2100  can have a low-profile delivery configuration, shown in  FIG. 23A . The low-profile delivery configuration facilitates transcatheter delivery of the system  2100 . Following delivery of the system  2100  to the desired positioning (e.g., across a septal wall), an expandable element such as balloon  2360  can be inserted into the inner lumen  2330  of the system  2100  while the system  2100  is still in the low-profile delivery configuration. The balloon can then be inflated. As shown in  FIG. 23B , inflating the balloon expands the system  2100  into a deployed configuration. The balloon can then be deflated and removed. As shown in  FIG. 23C , the system  2100  remains in the deployed position. Once deployed, the system  2100  can be selectively actuated to adjust the diameter of the inner lumen. In other embodiments, the system  2100  can be biased toward its deployed configuration such that, upon deployment from a delivery catheter or sheath, the system  2100  automatically expands radially outward into the deployed configuration and does not require mechanical expansion via a balloon  2360 . 
     In some embodiments, the system  2100  can be adjusted using an actuation assembly implanted with the device (not shown). In some embodiments, the actuation assembly is included on the system  2100  and can actively adjust the inner lumen diameter by actuating one or more of the connecting struts  2140 , which in turn cause the struts  2134  to change position. In some embodiments, for example, the actuation assembly, when actuated, pulls the proximal end portion  2132  distally, causing the struts  2134  to bend as described above with respect to  FIGS. 21B-21D . The actuation assembly can also be configured to directly bend the struts  2134  to alter the diameter of the lumen  2130 . In some embodiments, the actuation assembly can be a motor. In addition, other materials that can convert energy to linear motion can be used (e.g., nitinol). In some embodiments, a nitinol element is coupled to a pall or other mechanical element moveable via actuation of the nitinol element. 
     In addition to the diameter of the lumen, the shape of the lumen can also promote flow through system  2100 . For example, referring back to  FIGS. 21B-21D , the second connecting struts  2140   c  can define a funnel shaped inflow component  2137  configured for fluid communication with a LA of a heart (not shown), and the lumen  2130  can include a cylindrical shaped outflow portion  2139  configured for fluid communication with the RA of a heart (not shown). As illustrated in  FIG. 21C , the cylindrical shaped outflow portion  2139  can have a length L 1  and the adjacent funnel shaped inflow component  2137  can have a length L 2 . The diameter of the lumen  2130  in the cylindrical shaped outflow portion  2139  along the length L 1  is substantially constant. The substantially constant diameter of the lumen  2130  along the length L 1  is less than the variable diameter of the funnel shaped inflow component  2137  along the length L 2 . Although length L 1  is shown as greater than length L 2  in the illustrated embodiment, other embodiments have a length L 2  greater than length L 1 . In some embodiments, length L 1  extends along a major portion of the length of the lumen  2130 , and length L 2  extends along a minor portion of the length of the lumen  2130 . In other embodiments, the struts  2134  defining the cylindrical shaped outflow portion  2139  extend between a distal inflow aperture and a proximal outflow aperture and there is no funnel shaped inflow component  2137 . The cylindrical shaped outflow portion  2139  can also have other non-circular cross-sectional shapes that have substantially constant inner dimensions along length L 1 . For example, the cross-sectional shape of the outflow portion having length L 1  can be oval, triangular, rectangular, pentagonal, etc. 
     When the system  2100  is implanted in a heart, blood flows into the lumen  2130  at the funnel shaped inflow component  2137  (e.g., through the distal inflow aperture), through the cylindrical shaped outflow portion  2139 , and into the RA. In the exemplary embodiment, the combination of the funnel shaped inflow component  2137  and the cylindrical shaped outflow portion  2139  are expected to provide the system  2100  with a number of beneficial flow characteristics. For example, the funnel shaped inflow component  2137  can increase blood flow into the lumen  2130  from the LA. The relatively larger distal inflow aperture allows for the gathering of a larger blood volume. Blood then flows from the relatively larger diameter funnel shaped inflow component  2137  to the relatively smaller diameter cylindrical shaped outflow portion  2139 . Based on the Venturi effect (Bernoulli&#39;s principle in mathematical terms), pressure decreases downstream and the flow velocity increases as the blood flows from the funnel shaped inflow component  2137  into the relatively smaller diameter cylindrical shaped outflow portion  2139 . In the exemplary embodiment, the outflow portion  2139  has a cylindrical shape with a substantially constant diameter along length L 1 . The cylindrical shaped outflow portion  2139  maintains flow therethrough. By contrast, a funnel-shaped outflow would act as a diffuser. Based on Bernoulli&#39;s Principle, an increasing diameter on the outflow would decrease flow velocity. The exemplary cylindrical-shaped outflow reduces swirl effects and turbulence from the inflow while also minimizing pressure increases. Combined, these effects are expected to enhance blood flow between the LA and the RA. Additionally, as illustrated in  FIGS. 21B-21D , the device retains the funnel shaped inflow component  2137  and the cylindrical shaped outflow portion  2139  as it transitions between configurations. 
     One will appreciate from the description herein that other lumen shapes are possible and within the scope of the present technology. In some embodiments, for example, the lumen does not have the funnel shaped inlet component but rather retains a substantially constant diameter along substantially the entire length of the lumen. For example, the lumen can be substantially cylindrical with a substantially constant diameter extending between the distal end portion and the proximal end portion. In other embodiments, the lumen is tapered and has a variable diameter extending between the distal end portion and the proximal end portion. For example, the lumen can have a relatively larger inflow aperture at the distal end portion and relatively smaller outflow aperture at the proximal end portion, with the lumen constantly tapering inward between the inflow aperture and the outflow aperture to form a funnel shape. In yet other embodiments, the lumen can have a generally hourglass shape having a central pinch point. As discussed above, altering the shape of the lumen can affect the rate of the blood flow through the lumen. Accordingly, the shape of the lumen provides an additional mechanism for facilitating increased control over the flow of blood between the LA and the RA through shunts configured in accordance with the present technology. 
     One will further appreciate from the disclosure herein that other flow control mechanisms can be used with the shunting systems described herein. For example, in some embodiments, the shunting systems can include a gate-like valve that can move between a first position blocking or at least partially blocking a flow lumen and a second position unblocking or at least partially unblocking the flow lumen. In such embodiments, the gate-like valve can be coupled to one or more shape memory elements that can be manipulated using energy, such as energy stored in an energy storage component or energy applied directly to the shape memory element via an energy source positioned external to the patient. As another example, the shunting systems can include one or more shape memory coils wrapped around a portion of the shunting element defining the flow lumen. The shape memory coils can be selectively wound or unwound to restrict (e.g., cinch) or relax (e.g., uncinch) a portion of the flow lumen. In yet other embodiments, the shunting element can include a flexible bladder filled with a fluid or gas. The flexible bladder can be generally toroidal shaped such that it defines a flow lumen therethrough. The fluid or gas can be directed into or out of the bladder to decrease or increase the size of the lumen. In yet other embodiments, the shunting element may incorporate at least partially passive concepts that can adjust a size or shape of the flow lumen based on the pressure differential between two heart chambers. Accordingly, the systems described herein are not limited to the flow control mechanisms and/or shunting devices expressly described herein. Other suitable shunting devices can be utilized and are within the scope of the present technology. 
     D. Shunting Assemblies with Adjustable Inflow and/or Outflow Orifices 
       FIG. 24  illustrates an interatrial shunting system/device  2400  (“device  2400 ”) configured in accordance with select embodiments of the present technology. The device  2400  includes a shunting element  2410  having a lumen  2401  extending therethrough. When the device  2400  is implanted across a septal wall (not shown), the lumen  2401  is configured to fluidly connect a LA and a RA to facilitate the flow of blood therebetween. The shunting element  2410  can include a frame  2412  or other outer scaffolding (e.g., stent-like structure). The frame  2412  can extend circumferentially around a diameter of the shunting element  2410 . In some embodiments, the frame  2412  is composed of a material configured to be relatively flexible (e.g., nitinol in a material state where it exhibits superelastic properties) at and above body temperature. The frame  2412  can include a central portion comprising a plurality of first struts  2411  arranged in a diamond shape, although other suitable strut shapes and configurations can be used. The frame  2412  can further include a plurality of second struts  2413  extending from the first struts  2411  and angled radially inward towards an orifice  2405  (e.g., an RA or outflow orifice) of the lumen  2401 , described in detail below. In the illustrated embodiment, the orifice  2405  is generally circular, although other embodiments can have other shapes, such as elliptical, square, rectangular, polygonal, curvilinear, and the like. 
     The frame  2412  can further include a plurality of first anchor elements  2414  extending from a first end portion of the frame  2412  and a plurality of second anchor elements  2416  extending from a second end portion of the frame  2412  that is generally opposite the first end portion. In the illustrated embodiment, the plurality of first anchor elements  2414  and the plurality of second anchor elements  2416  extend around the full circumference of the frame  2412 , although other embodiments can have different suitable configurations. For example, in other embodiments, the anchor elements  2414  and/or  2416  may be a single element (e.g., a coil-shaped element). The first anchor elements  2414  and the second anchor elements  2416  can engage native tissue to secure the device  2400  in a desired position. For example, the first anchor elements  2414  and the second anchor elements  2416  can secure the device  2400  to a septal wall such that the lumen  2401  fluidly connects the LA and the RA. In such embodiments, the first anchor elements  2414  can be positionable within the RA and configured to engage the RA side of the septal wall, and the second anchor elements  2416  can be positionable in the LA and configured to engage the LA side of the septal wall. A portion of the septal wall can be received between the first anchor elements  2414  and the second anchor elements  2416 . In other embodiments, the orientation of the device can be reversed such that the first anchor elements  2414  are positionable in the LA and the second anchor elements  2416  are positionable in the RA. In some embodiments, the first anchor elements  2414  and/or the second anchor elements  2416  are integral with the frame  2412 . In other embodiments, the first anchor elements  2414  and/or the second anchor elements  2416  are secured to the frame  2412  using techniques known in the art (e.g., welding, gluing, suturing, etc.). 
     The shunting element  2410  can include a membrane  2430  coupled to (e.g., affixed, attached, or otherwise connected) to the frame  2412 . In some embodiments, the membrane  2430  is flexible and can be made of a material that is impermeable to or otherwise resists blood flow therethrough. In some embodiments, for example, the membrane  2430  can be made of a thin, elastic material such as a polymer. For example, the membrane  2430  can be made of polytetrafluoroethylene (PTFE), ePTFE (ePTFE), silicone, nylon, polyethylene terephthalate (PET), polyether block amide (pebax), polyurethane, blends or combinations of these materials, or other suitable materials. The membrane  2430  can cover and/or enclose at least a portion of the shunting element  2410 , such as the interior or exterior surface of the shunting element  2410  between a first end portion positionable in the LA and a second end portion positionable in the RA. The membrane  2430  can extend circumferentially around the frame  2412  to at least partially surround and enclose the lumen  2401 , thereby defining (at least in part) a flow path for blood when implanted across the septal wall. 
     In some embodiments, the membrane  2430  includes a first membrane portion  2432  coupled to a second membrane portion  2434 . The first membrane portion  2432  can be operably coupled to and/or extend around a central portion of the frame  2412  (e.g., the portion having the first struts  2411 ). In some embodiments, the first membrane portion  2432  can also include a flange portion  2433  that is operably coupled to and/or extending around the second anchor elements  2416 . The second membrane portion  2434  can be operably coupled to and/or extend around the plurality of second struts  2413  angled radially inward towards the orifice  2405 . The second membrane portion  2434  can be at least partially conical or funnel shaped and extend past the second struts  2413  so that at least a portion of the second membrane portion  2434  is positioned over and partially covers the lumen  2401 , thereby defining an orifice  2405 . The first membrane portion  2432  can be secured to the second membrane portion  2434  via suturing or other suitable techniques. In other embodiments, the membrane  2430  is a unitary membrane comprising both the first membrane portion  2432  and the second membrane portion  2434 . 
     The device  2400  can further include an actuation assembly  2418  configured to change a geometry (e.g., a size and/or shape) of the orifice  2405 . The actuation assembly  2418  can include a flow control element  2420 , a plurality of first actuation elements  2422   a , and a plurality of second actuation elements  2422   b . As will be described in greater detail below, the first actuation elements  2422   a  and/or the second actuation elements  2422   b  can be selectively actuated to change a geometry of the flow control element  2420 . In turn, this adjusts (e.g., stretches and/or compresses) the second membrane portion  2434  surrounding and defining the orifice  2405 . As previously described, blood can flow between the LA and the RA via the lumen  2401  when the device  2400  is implanted across a septal wall. Accordingly, changing a geometry of the orifice  2405  is expected to change the relative flow resistance and/or the amount of blood flowing between the LA and the RA. 
     The flow control element  2420  of device  2400  generally extends around an outer circumference of the orifice  2405  and at least partially defines the geometry of the orifice  2405 . For example, the flow control element  2420  can be an annular (e.g., ring-like) structure coupled to the second membrane portion  2434 . In embodiments in which the orifice  2405  has other shapes (e.g., square), the flow control element  2420  can have a generally similar shape (e.g., square) such that the flow control element  2420  extends around an outer perimeter of the orifice  2405 . The flow control element  2420  can be flexible such that it can expand and contract to change a geometry (e.g., a diameter) of the orifice  2405 . For example, when the flow control element  2420  moves in a first manner (e.g., expands), the diameter of the orifice  2405  increases, thereby decreasing the flow resistance through the lumen  2401 . When the flow control element  2420  moves in a second manner opposing the first manner (e.g., contracts), the diameter of the orifice  2405  decreases, thereby increasing the flow resistance through the lumen. 
     The shape of the flow control element  2420  can be at least partially controlled via a plurality of first actuation elements  2422   a  and a plurality of second actuation elements  2422   b . As described in detail with respect to  FIGS. 25A-25D , the plurality of first actuation elements  2422   a  and the plurality of second actuation elements  2422   b  can be coupled to the flow control element  2420  at a first end portion and anchored to the frame  2412  or another suitable and generally static structure at a second end portion. The plurality of first actuation elements  2422   a  and the plurality of second actuation elements  2422   b  can be positioned radially around the flow control element  2420  (e.g., in a “spoke-like” configuration, with the orifice forming the central hub and the actuation elements extending outward therefrom as spokes). 
     The first actuation elements  2422   a  and the second actuation elements  2422   b  can be composed of a shape memory material, such as a shape memory alloy (e.g., nitinol). Accordingly, the first actuation elements  2422   a  and the second actuation elements  2422   b  can be transitionable between a first material state (e.g., a martensitic state, a R-phase, etc.) and a second material state (e.g., a R-phase, an austenitic state, etc.). In the first state, the first actuation elements  2422   a  and the second actuation elements  2422   b  may be relatively deformable (e.g., plastic, malleable, compressible, expandable, etc.). In the second state, the first actuation elements  2422   a  and the second actuation elements  2422   b  may have a preference toward a specific manufactured geometry (e.g., shape, length, and/or or dimension). The first actuation elements  2422   a  and the second actuation elements  2422   b  can be transitioned between the first state and the second state by applying energy (e.g., heat) to the actuation elements to heat the actuation elements above a transition temperature. In some embodiments, the transition temperature for both the first actuation elements  2422   a  and the second actuation elements  2422   b  is above an average body temperature. Accordingly, both the first actuation elements  2422   a  and the second actuation elements  2422   b  are typically in the deformable first state when the device  2400  is implanted in the body until they are heated (e.g., actuated). 
     If the actuation elements (e.g., the first actuation elements  2422   a ) are deformed relative to their manufactured geometry while in the first state, heating the actuation elements (e.g., the first actuation elements  2422   a ) above their transition temperature causes the actuation elements to transition to the second state and therefore transition from the deformed shape towards a manufactured shape. As described in detail below, heat can be applied to the actuation elements via RF heating, resistive heating, or the like. In some embodiments, the first actuation elements  2422   a  can be selectively heated independently of the second actuation elements  2422   b , and the second actuation elements  2422   b  can be selectively heated independently of the first actuation elements  2422   a . In some embodiments, portions of the actuation elements (e.g., the first nitinol portion  2422   ai  or the second nitinol portion  2422   a   2  ( FIG. 3A )) can be heated independently of the other portion of the same actuation element. As described in detail below, selectively heating first actuation elements  2422   a  (or a portion of the first actuation elements  2422   a ) reduces the diameter of the lumen  2401  and selectively heating the second actuation elements  2422   b  (or a portion of the second actuation elements  2422   b ) increases the diameter of the lumen  2401 . 
       FIGS. 25A-25D  illustrate, among other things, how the first actuation elements  2422   a  and the second actuation elements  2422   b  can change a diameter of the orifice  2405 . A number of features of the device  2400  are not illustrated in  FIGS. 25A-25D  for purposes of clarity. Referring first to  FIG. 25A , for example, the first actuation elements  2422   a  and the second actuation elements  2422   b  are shown in a state before being secured to the shunting element  2410  and/or frame  2412  ( FIG. 24 ). In particular, the first actuation elements  2422   a  and the second actuation elements  2422   b  are in their manufactured shapes. As will be apparent to one skilled in the art from the disclosure herein, the first actuation elements  2422   a  and the second actuation elements  2422   b  generally have different manufactured shapes such that the flow control element  2420  can be driven through a plurality of configurations by actuating the actuation elements  2422   a / 2422   b . For example, in the illustrated configuration, the first actuation elements  2422   a  generally have a greater length than the second actuation elements  2422   b  when in their manufactured shape. 
     Each first actuation element  2422   a  can further comprise (or be coupled to) a first clip element  2524   a  having a first fixation element  2526   a . The first fixation element  2526   a  can secure the corresponding first actuation element  2422   a  to the frame  2412  or another suitable component of the device  2400  ( FIG. 25B ). For example, the first fixation element  2526   a  can comprise an aperture to facilitate suturing of the first clip element  2524   a  to the frame  2412 . The first clip element  2524   a  can further include a first hole  2525   a . Together, the first clip element  2524   a  and the first hole  2525   a  can form an electrical connection point for receiving electricity and directing it through the corresponding first actuation element  2422   a , thereby resistively heating the first actuation element  2422   a . In the illustrated embodiment, each of the first actuation elements  2422   a  can from a general “U” or “V” shape such that the valley of the “U” or “V” is coupled to the flow control element  2420 . For example, each of the first actuation elements  2422   a  can have a first nitinol portion  2522   ai  coupled to a second nitinol portion  2522   a   2 . The first nitinol portion  2522   ai  and the second nitinol portion  2522   a   2  can be electrically coupled such that a current delivered to the first nitinol portion  2522   ai  also flows through the second nitinol portion  2522   a   2 , and vice versa. Accordingly, the first nitinol portion  2522   ai  and the second nitinol portion  2522   a   2  can form an electrical circuit for resistively heating the first actuation elements  2422   a . The first nitinol portion  2522   ai  and the second nitinol portion  2522   a   2  can be composed of a unitary (e.g., single) structure, or can comprise distinct elements coupled together. 
     Likewise, each second actuation element  2422   b  can further comprise (or be coupled to) a second clip element  2524   b  having a second fixation element  2526   b . The second fixation element  2526   b  can secure the corresponding second actuation element  2422   b  to the frame  2412  or another suitable component of the device  2400  ( FIG. 24 ). For example, the second fixation element  2526   b  can comprise an aperture to facilitate suturing of the second clip element  2524   b  to the frame  2412 . The second clip element  2524   b  can further include a second hole  2525   b . Together, the second clip element  2524   b  and the second hole  2525   b  can form an electrical connection point for receiving electrical energy and directing it through the corresponding second actuation element  2422   b , thereby resistively heating the second actuation element  2422   b . In the illustrated embodiment, each of the second actuation elements  2422   b  can form a general “U” or “V” shape such that the valley of the “U” or “V” is coupled to the flow control element  2420 . For example, each of the second actuation elements  2422   b  can have a first nitinol portion  2522   b   1  coupled to a second nitinol portion  2522   b   2 . The first nitinol portion  2522   b   1  and the second nitinol portion  2522   b   2  can be electrically coupled such that a current delivered to the first nitinol portion  2522   b   1  also flows through the second nitinol portion  2522   b   2 , and vice versa. Accordingly, the first nitinol portion  2522   b   1  and the second nitinol portion  2522   b   2  can form an electrical circuit for resistively heating the second actuation elements  2422   b . The first nitinol portion  2522   b   1  and the second nitinol portion  2522   b   2  can be composed of a unitary (e.g., single) structure, or can comprise distinct elements coupled together. 
       FIG. 25B  is a schematic illustration of aspects of the device  2400  after the first actuation elements  2422   a  and the second actuation elements  2422   b  have been fixed to the shunting element  2410  ( FIG. 2 ) via the corresponding first fixation elements  2526   a  and the second fixation elements  2526   b . In particular,  FIG. 25B  illustrates the device  2400  in a first configuration (e.g., a composite configuration) in which both the first actuation elements  2422   a  and the second actuation elements  2422   b  are at least partially deformed relative to their manufactured geometric configurations. To fix the first actuation elements  2422   a  to the shunting element  2410  ( FIG. 2 ), the first actuation elements  2422   a  are compressed (e.g., shortened) relative to their manufactured geometry ( FIG. 25A ). To fix the second actuation elements  2422   b  to the shunting element  2410  ( FIG. 2 ), the second actuation elements  2422   b  are stretched (e.g., lengthened) relative to their manufactured geometry ( FIG. 25B ). Both the first actuation elements  2422   a  and the second actuation elements  2422   b  retain the deformed positions shown in  FIG. 25B  because they are unheated (e.g., at room temperature or body temperature) and therefore in the relatively malleable material state (e.g., martensitic state). In the first configuration shown in  FIG. 25B , the orifice  2405  defined by the second membrane portion  2434  and/or the flow control element  2420  has a first diameter D 1 . 
       FIG. 25C  illustrates the device  2400  in a second configuration different than the first (e.g., composite) configuration. In particular, in the second configuration the device  2400  has been actuated relative to the first configuration shown in  FIG. 25B  to transition the first actuation elements  2422   a  from a first (e.g., martensitic) material state to a second (e.g., austenitic) material state. Because the first actuation elements  2422   a  were deformed (e.g., compressed) relative to their manufactured geometry while in the first (e.g., composite) configuration, heating the first actuation elements  2422   a  above the transition temperature causes the first actuation elements  2422   a  to expand in length as they move toward their manufactured geometry ( FIG. 25A ). As described above, the first actuation elements  2422   a  are secured to the frame  2412  or another generally static structure on the shunting element  2410  via the first fixation elements  2526   a . Accordingly, as the first actuation elements  2422   a  increase in length toward their manufactured geometry, they compress the flow control element  2420  radially inward. This deforms (e.g. stretches, relaxes, etc.) the second membrane such that it moves radially inward and the orifice  2405  assumes a second diameter D 2  that is less than the first diameter D 1 . Because the flow control element  2420  is also coupled to the second actuation elements  2422   b , the expansion of the first actuation elements  2422   a  (and corresponding contraction of the flow control element  2420 ) also causes the second actuation elements  2422   b , which are not heated above their transition temperature and therefore still in a deformable (e.g., martensitic) state, to also expand (e.g., increase in length). For example, the second actuation elements  2422   b  are expanded even further from their manufactured geometry ( FIG. 25A ) than they were in the first (e.g., composite) configuration ( FIG. 25B ). When implanted in a human heart, decreasing the diameter of the orifice  2405  is expected to reduce the flow volume of blood from the LA to the RA. 
       FIG. 25D  illustrates the device  2400  in a third configuration different than the first or second configuration. In particular, in the third configuration, the device  2400  has been actuated relative to the first configuration shown in  FIG. 25B  to transition the second actuation elements  2422   b  from a first (e.g., martensitic) material state to a second (e.g., austenitic) material state. Because the second actuation elements  2422   b  were expanded relative to their manufactured geometry (e.g., when placed into either of the first configuration or the second configuration), heating the second actuation elements  2422   b  above the transition temperature causes the second actuation elements  2422   b  to contract in length as they move toward their manufactured geometry ( FIG. 25A ). As described above, the second actuation elements  2422   b  are secured to the frame  2412  or another generally static structure on the shunting element  2410  via the second fixation elements  2526   b . Accordingly, as the second actuation elements  2422   b  decrease in length toward their manufactured geometry, they expand the flow control element  2420  radially outward. Because the flow control element  2420  is coupled to the second membrane portion  2434 , the second membrane portion  2434  is deformed (e.g. compressed, relaxed, etc.) such that it moves radially outward and the orifice  2405  assumes a third diameter D 3  that is greater than the first diameter D 1  and the second diameter D 2 . Because the flow control element  2420  is also coupled to the first actuation elements  2422   a , contraction of the second actuation elements  2422   b  (and the corresponding expansion of the flow control element  2420 ) causes the first actuation elements  2422   a , which are not heated above their transition temperature and therefore still in a deformable (e.g., martensitic) state, to also contract (e.g., decrease in length). For example, the first actuation elements  2422   a  are compressed even further from their manufactured geometry ( FIG. 25A ) than they were in the first (e.g., composite) configuration ( FIG. 25B ). When implanted in a human heart, increasing the diameter of the orifice  2405  is expected to increase the flow volume of blood from the LA to the RA. 
     The device  2400  can be repeatedly transitioned between the second configuration and the third configuration. For example, the device  2400  can be returned to the second configuration from the third configuration by heating the first actuation elements  2422   a  above their transition temperature once the second actuation elements  2422   b  have returned to a deformable first state (e.g., by allowing the second actuation elements  2422   b  to cool below the transition temperature after being heated, etc.). Heating the first actuation elements  2422   a  above their transition temperature causes the first actuation elements to move towards their manufactured geometry, which in turn pushes the flow control element  2420  radially inward and transitions the device  2400  to the second configuration ( FIG. 25C ). 
     In some embodiments, device  2400  can also be transitioned to or from intermediate configurations between the second and third configurations. In some embodiments, for example, the device  2400  can initially transition from a first composite configuration into the second configuration, the third configuration, or another configuration (e.g., the device may be transitioned to the third configuration or another configuration before being actuated to the second configuration). In some embodiments, the configuration of device  2400  can also be altered without inducing a change in material state of either the first actuation elements  2422   a  or the second actuation elements  2422   b . This may be accomplished, for example, via direct mechanical methods that apply external forces to a component or portion of the device (e.g., via a balloon expansion of flow control element  2420 , similar to previously described with respect to  FIGS. 23A-23C ). 
     Accordingly, the device  2400  can be selectively transitioned between a variety of configurations by selectively actuating some or all of either the first actuation elements  2422   a  or the second actuation elements  2422   b . After actuation, the device  2400  can be configured to substantially retain the given configuration until further actuation of the opposing actuation elements. In some embodiments, the device  2400  can be transitioned to intermediate configurations between the second configuration and the third configuration (e.g., the first configuration) by heating some, but not all, of either the first actuation elements  2422   a  or the second actuation elements  2422   b.    
     As provided above, heat can be applied to the actuation elements via RF heating, resistive heating, or the like. In some embodiments, the first actuation elements  2422   a  can be selectively heated independently of the second actuation elements  2422   b , and the second actuation elements  2422   b  can be selectively heated independently of the first actuation elements  2422   a . For example, in some embodiments, the first actuation elements  2422   a  are on a first electrical circuit for selectively and resistively heating the first actuation elements  2422   a  and the second actuation elements  2422   b  are on a second electrical circuit for selectively and resistively heating the second actuation elements  2422   b . As described in detail above, selectively heating the first actuation elements  2422   a  reduces the diameter of the orifice  2405  and selectively heating the second actuation elements  2422   b  increases the diameter of the orifice  2405 . In some embodiments, each individual first actuation element  2422   a  is on its own selectively and independently activatable electric circuit, and each individual second actuation element  2422   b  is on its own selectively and independently activatable electric circuit. Without being bound by theory, this permits individual actuation elements to be selectively actuated, thereby increasing the granularity of potential adjustments to the diameter of the orifice  2405 . 
     In some embodiments, actuation elements may be configured differently than as described above. For example, in some embodiments both the first actuation elements  2422   a  and second actuation elements  2422   b  are compressed (or alternatively, expanded) from their manufactured geometry when placed into an initial composite configuration. For example, each set of actuation elements may be compressed (or alternatively, expanded) a different amount. Variation embodiments may include more than two sets of actuation elements that are manufactured to have two or more manufactured geometries. 
       FIG. 26  illustrates an adjustable interatrial device  2600  (“device  2600 ”) configured in accordance with select embodiments of the present technology. The device  2600  can include certain features generally similar to the features described above with respect to device  2400 . For example, the device  2600  includes a shunting element  2610  comprising a frame  2612  and a membrane  2630  disposed around and/or coupled to the frame  2612 . The shunting element  2610  defines a lumen  2601  extending therethrough for fluidly connecting the LA and the RA. The membrane  2630  extends radially inward at a first (e.g., RA) end portion of the shunting element  2610  to define an orifice  2605 . As described below, a shape and/or size (e.g., diameter) of the orifice  2605  can be selectively adjusted via an actuation assembly  2618  to control the flow of blood through the lumen  2601 . The actuation assembly  2618  can include actuation elements  2622  and a flow control element  2620 . 
     However, in contrast with the device  2400  described previously, the device  2600  incorporates an actuatable flow control element  2620  disposed around the orifice  2605  (e.g., the flow control element  2620  is an annular actuation element). For example, the flow control element  2620  can be composed of a shape memory material, such as a shape memory alloy (e.g., nitinol). Accordingly, the flow control element  2620  can be transitionable between a first material state (e.g., a martensitic state, a R-phase, etc.) and a second material state (e.g., a R-phase, an austenitic state, etc.). In the first state, the flow control element  2620  may be deformable (e.g., plastic, malleable, compressible, expandable, etc.). In the second state, the flow control element  2620  may have a preference toward a specific manufactured geometry (e.g., shape, diameter, and/or dimension). The flow control element  2620  can be transitioned between the first state and the second state by applying energy to heat the flow control element  2620  above a transition temperature. Heating the flow control element  2620  above its transition temperature to transform the material to the second state causes the flow control element  2620  to move towards its manufactured geometry. If the flow control element  2620  is deformed relative to its manufactured geometry while in the first state, these deformations may be partially or completely recovered when material transitions into the second state. In some embodiments, the transition temperature for the flow control element  2620  is above an average body temperature. In some embodiments, the flow control element  2620  can be heated via RF energy, resistive heating, and the like. The flow control element  2620  can be coupled to the membrane  2630  such that dimensional adjustments to the flow control element  2620  impart a corresponding dimensional change to the orifice  2605 . 
     The device  2600  further includes a plurality of actuation elements  2622  disposed radially around the flow control element  2620 . The plurality of actuation elements  2622  can be generally similar to the plurality of first actuation elements  2422   a  described above with respect to  FIGS. 24-25D . However, because the flow control element  2620  is actuatable, the device  2600  does not necessarily need a plurality of second actuation elements positioned radially around the flow control element  2620  (e.g., in contrast with the second actuation elements  2422   b  in device  2400 ). Instead, as described below, the flow control element  2620  replaces the function of the second actuation elements. The actuation elements  2622  can be heated independently of the flow control element  2620 . For example, in some embodiments, the actuation elements  2622  can be on a different electrical circuit than the flow control element  2620 . 
     The device  2600  can be transitioned between a variety of configurations by selectively heating either the flow control element  2620  or the actuation elements  2622  (or, alternatively, by directly applying mechanical forces to flow control element  2620  while it is a relatively deformable (e.g., martensitic) material state). The illustrated configuration, for example, may be a composite configuration in which both the flow control element  2620  and the actuation elements  2622  are deformed relative to their manufactured geometries. For example, the actuation elements  2622  may be compressed (e.g., shortened) relative to their manufactured geometry, and the flow control element  2620  may be compressed (e.g., having a smaller diameter) relative to its manufactured geometry. Accordingly, to increase the diameter of the orifice, the flow control element  2620  can be heated above its transition temperature (while the actuation elements remain below the transition temperature) to transition from a first state (e.g., a martensitic state) to a second state (e.g., austenitic state), inducing a change in configuration towards its manufactured geometry due to the shape memory effect. To decrease the diameter of the orifice, the actuation elements  2622  can be heated above the transition temperature (while the flow control element  2620  remains below its transition temperature) to transition from a first state (e.g., martensitic state) to a second state (e.g., austenitic state), inducing a change in configuration towards their manufactured geometry due to the shape memory effect. In other embodiments, the actuation elements  2622  may be expanded (e.g., lengthened) relative to their manufactured geometry, and the flow control element  2620  may be expanded (e.g., having a larger diameter) relative to its manufactured geometry when the device  2600  is in the composite configuration. In such embodiments, the actuation elements  2622  are selectively heated to increase the diameter of the orifice  2605 , and the flow control element  2620  is selectively heated to decrease the diameter of the orifice  2605 . In some embodiments, stabilization features (not shown) may be included proximate to actuation elements  2622  to restrict the movement of the actuation elements in a desired way (e.g., restrict the movement to be solely or primarily the plane of elements&#39; long axis). Such features may facilitate the transfer of forces and/or movements between various aspects of device  2600 , for example between actuation elements  2622 , flow control element  2620 , and membrane  2630 . In embodiments, any number of flow control elements and sets of actuation elements may be used in combination with one another. 
       FIG. 27  illustrates an adjustable interatrial device  2700  (“device  2700 ”) configured in accordance with select embodiments of the present technology. The device  2700  can include certain features generally similar to the features described above with respect to devices  2400  and  2600 . For example, the device  2700  includes a shunting element  2710  comprising a frame  2712  and a membrane  2730  disposed around and/or coupled to the frame  2712 . The shunting element  2710  defines a lumen  2701  extending therethrough for fluidly connecting the LA and the RA. The membrane  2730  extends radially inward at a first (e.g., RA) end portion of the shunting element  2710  to define an orifice  2705 . As described below, a shape and/or size (e.g., diameter) of the orifice  2705  can be selectively adjusted via an actuation assembly  2718  to control the flow of blood through the lumen  2701 . 
     The actuation assembly  2718  includes two independently actuatable flow control elements. In particular, the actuation assembly  2718  includes a first actuatable flow control element  2720   a  and a second actuatable flow control element  2720   b . Accordingly, in some embodiments, the device  2700  does not include other actuation elements that are distinct from the flow control elements  2720   a ,  2720   b  (e.g., such as actuation elements  2422   a ,  2422   b , described with respect to  FIGS. 24-25D ). Rather, the flow control elements  2720   a ,  2720   b  are themselves actuation elements (flow control elements  2720   a,b  can therefore also be referred to as first and second actuation elements. The first flow control element  2720   a  is disposed around an outer circumference of the second flow control element  2720   b . Both the first flow control element  2720   a  and the second flow control element  2720   b  are coupled to the membrane  2730  such that adjustments to the first flow control element  2720   a  or the second flow control element  2720   b  imparts a corresponding dimensional change to the orifice  2705 . 
     The first flow control element  2720   a  and the second flow control element  2720   b  can be composed of a shape memory material, such as a shape memory alloy (e.g., nitinol). Accordingly, the first flow control element  2720   a  and the second flow control element  2720   b  can be transitionable between a first state (e.g., a martensitic state, a R-phase, etc.) and a second state (e.g., a R-phase, an austenitic state, etc.). In a first state, the first flow control element  2720   a  and the second flow control element  2720   b  may be deformable (e.g., malleable, compressible, expandable, etc.). In a second state, the first flow control element  2720   a  and the second flow control element  2720   b  may have a preference toward a specific manufactured geometry (e.g., shape, length, and/or or dimension). The first flow control element  2720   a  and the second flow control element  2720   b  can be transitioned between a first state and a second state by applying energy to the actuation elements to heat the flow control elements above a transition temperature. In some embodiments, the transition temperature for both the first flow control element  2720   a  and the second flow control element  2720   b  is above an average body temperature. Accordingly, both the first flow control element  2720   a  and the second flow control element  2720   b  are typically in the deformable first state when the device  2700  is implanted in the body except for when they are heated (e.g., actuated). 
     Heating the flow control elements (e.g., the first flow control element  2720   a ) above their transition temperature causes the flow control elements to transform to the second state and therefore transition towards their manufactured geometries. If the flow control elements (e.g., the first flow control element  2720   a ) are deformed while in the first state, these deformations may be partially or completely recovered when material transitions into the second state. Heat can be applied to the flow control elements via RF heating, resistive heating, or the like. In some embodiments, the first flow control element  2720   a  can be selectively heated independently of the second flow control element  2720   b , and the second flow control element  2720   b  can be selectively heated independently of the first flow control element  2720   a . As described in detail below, selectively heating the first flow control element  2720   a  reduces the diameter of the orifice  2705  and selectively heating the second flow control element  2720   b  increases the diameter of the orifice  2705 . Although two flow control elements are shown in  FIG. 27 , in embodiments any number of flow control elements may be integrated into device  2700 . One advantage to using a greater number of elements may be a greater degree of precision and/or granularity regarding size and/or shape changes that can be induced in orifice  2705 . 
     The device  2700  can be transitioned between a variety of configurations by selectively heating either the first flow control element  2720   a  or the second flow control element  2720   b . The illustrated configuration may be a composite configuration in which both the first flow control element  2720   a  and the second flow control element  2720   b  are deformed relative to their manufactured geometries. For example, the first flow control element  2720   a  may be expanded (e.g., having a greater diameter) relative to its manufactured geometry, and the second flow control element  2720   b  may be compressed (e.g., having a smaller diameter) relative to its manufactured geometry. Accordingly, to increase the size (e.g., diameter) of the orifice  2705 , the second flow control element  2720   b  can be heated above its transition temperature (while the first flow control element remains below the transition temperature) to transition from a first relatively malleable state (e.g., martensitic state) to a second state (e.g., austenitic state) and move towards its manufactured geometry. To decrease the size (e.g., diameter) of the orifice  2705 , the first flow control element  2720   a  can be heated above the transition temperature (while the second flow control element  2720   b  remains below its transition temperature) to transition from a first relatively malleable state (e.g., martensitic state) to a second state (e.g., austenitic state) and move towards its manufactured geometry. 
       FIGS. 28A-28D  illustrate an adjustable interatrial system  2800  (“system  2800 ”) configured in accordance with select embodiments of the present technology. More specifically,  FIG. 28A  is a partially isometric view of the system  2800  in a first configuration from an RA side of a septal wall S,  FIG. 28B  is a partially isometric view of the system  2800  in the first configuration and from a LA side of the septal wall S,  FIG. 28C  is a partially isometric view of the system  2800  in a second configuration from the RA side of the septal wall S, and  FIG. 28D  is a partially isometric view of the system  2800  in the second configuration and from the LA side of the septal wall S. The system  2800  can include certain features generally similar to the features described above with respect to devices  2400 ,  2600 , and  2700 . For example, the system  2800  includes a shunting element  2810  comprising a frame  2812  and a membrane  2830  disposed around and/or coupled to the frame  2812 . The shunting element  2810  can further comprise one or more anchors  2814  for securing the shunting element  2810  in place. The shunting element  2810  defines a lumen  2801  extending therethrough for fluidly connecting the LA and the RA. The membrane  2830  extends radially inward at a first (e.g., RA) end portion of the shunting element  2810  to define an orifice  2805 . As described below, a shape and/or size (e.g., diameter) of the orifice  2805  can be selectively adjusted via an actuation assembly  2818  to control the flow of blood through the lumen  2801 . 
       FIGS. 28E-28H  illustrate addition details of the actuation assembly  2818 . The actuation assembly  2818  can include a first stent-like actuation element  2820  and a second stent-like actuation element  2822 . The first and second actuation elements  2820 ,  2822  can be tapered or otherwise angled radially inwards, extending from the frame  2812  towards the orifice  2805 . Some aspects of the first and second actuation elements  2820 ,  2822  can be generally similar to the nested stent-like actuation elements previously described with respect to  FIGS. 3A-4C . For example,  FIG. 29E  illustrates the first and second actuation elements  2820 ,  2822  in their manufactured shapes (e.g., before deformation and coupling).  FIG. 29F  illustrates a composite configuration in which the first actuation element  2820  is nested within the second actuation element  2822 , and both the first and second actuation elements  2820 ,  2822  are deformed relative to their manufactured geometries.  FIG. 29G  illustrates a second configuration after the first actuation element  2822  has been heated above its transition temperature, thereby transitioning toward its manufactured geometry and increasing a composite diameter of the nested actuation elements (and thus increasing a diameter of the orifice  2805 , as shown in  FIG. 28C ).  FIG. 29H  illustrates a third configuration after the second actuation element  2822  has been heated above its transition temperature, thereby transitioning toward its manufactured geometry and decreasing a composite diameter of the nested actuation elements (and thus decreasing a diameter of the orifice  2805 , as shown in  FIG. 28A ). 
     Returning to  FIGS. 28A-28D , and unlike the nested actuation elements described with respect to  FIGS. 3A-4C , the first and second actuation elements  2820 ,  2822  are positioned within or coupled to a distal portion of the membrane  2830  residing within the RA, rather than a central portion of the membrane  2830  situated across the septal wall. Positioning the nested actuation in the distal portion of the membrane  2830  enables the geometry of the orifice  2805  to be adjusted while maintaining a geometry of a central portion of the lumen  2801  (e.g., as defined by the central portion of the membrane  2830 ). Accordingly, rather than adjusting the geometry of a substantial portion of the lumen  2801 , the actuation assembly  2818  enables a user to selectively adjust a diameter of a portion of lumen  2801  (e.g., at and adjacent the orifice  2805 ). The system  2800  can also include one or more energy storage components  2850  (e.g., battery, supercapacitor, etc.) for storing energy that can be used to resistively heat the first and/or second actuation elements  2820 ,  2822 . 
       FIGS. 29A-29D  illustrate an adjustable interatrial system  2900  (“system  2900 ”) configured in accordance with further embodiments of the present technology. More specifically,  FIG. 29A  is a partially isometric view of the system  2900  in a first configuration from an RA side of a septal wall S,  FIG. 29B  is a partially isometric view of the system  2900  in the first configuration and from a LA side of the septal wall S,  FIG. 29C  is a partially isometric view of the system  2900  in a second configuration from the RA side of the septal wall S, and  FIG. 29D  is a partially isometric view of the system  2900  in the second configuration and from the LA side of the septal wall S. The system  2900  can include certain features generally similar to the features described above with respect to the system  2800 . For example, the system  2900  includes a shunting element  2910  comprising a frame  2912  and a first membrane  2930  disposed around and/or coupled to the frame  2912 . The shunting element  2910  defines a lumen  2901  extending therethrough for fluidly connecting the LA and the RA. The first membrane  2930  extends radially inward at a first (e.g., RA) end portion of the shunting element  2910  to at least partially define an orifice  2905 . As described previously, a shape and/or size (e.g., diameter) of the orifice  2905  can be selectively adjusted via an actuation assembly to control the flow of blood through the lumen  2901 . 
     In this embodiment, the system  2900  can further comprise a second membrane  2932  engaged with the frame  2912  and first membrane  2930  and extending at least partially over components of the system  2900  that are spaced apart from the shunting element  2910  (e.g., anchor(s), energy storage component(s), etc.). The second membrane  2932  may be composed of, for example, a braided mesh or other suitable material. During operation of the system  2900 , the second membrane  2932  is configured to at least partially isolate the energy storage component(s) from blood within the RA and LA. This arrangement is expected to further inhibit thrombus formation after implantation of the system  2900  within the patient. The second membrane  2932  is an optional component that may have a different configuration/arrangement than the embodiment shown in  FIGS. 29A-29D . Further, in some embodiments the second membrane  2932  may be omitted. 
       FIGS. 30A-30E  illustrate an interatrial shunting system  3000  (“system  3000 ”) configured in accordance with select embodiments of the present technology. More specifically,  FIG. 30A  is a perspective view of the system  3000 ,  FIG. 30B  is a side view of the system  3000 , and  FIGS. 30C-30E  are schematic illustrations of an actuation assembly  3015  of the system  3000  during various stages of operation. Referring first to  FIGS. 30A and 30B  together, the system  3000  includes a shunting element  3002  defining a lumen  3004  therethrough. The shunting element  3002  can include a first end portion  3003   a  configured to be positioned in or near the RA (not shown) and a second end portion  3003   b  configured to be positioned in or near the LA (not shown). Accordingly, when implanted in the septal wall (not shown) of a patient, the system  3000  fluidly connects the LA and the RA via the lumen  3004 . In some embodiments, the system  3000  serves as a sub-system that interfaces with additional structures (not shown), for example, anchoring and/or frame components, to form an interatrial shunting system configured in accordance with an embodiment of the present technology. 
     The shunting element  3002  can be a frame including a first annular element  3006   a  at the first end portion  3003   a  and a second annular element  3006   b  at the second end portion  3003   b . The first and second annular elements  3006   a - b  can each extend circumferentially around the lumen  3004  to form a stent-like frame structure. In the illustrated embodiment, the first and second annular elements  3006   a - b  each have a serpentine shape with a plurality of respective apices  3008   a - b . The apices  3008   a - b  can be curved or rounded. In other embodiments, the apices  3008   a - b  can be pointed or sharp such that the first and second annular elements  3006   a - b  have a zig-zag shape. Optionally, the first and second annular elements  3006   a - b  can have different and/or irregular patterns of apices  3008   a - b , or can be entirely devoid of apices  3008   a - b . The first and second annular elements  3006   a - b  can be coupled to each other by a plurality of struts  3010  extending longitudinally along the shunting element  3002 . The struts  3010  can be positioned between the respective apices  3008   a - b  of the first and second annular elements  3006   a - b.    
     The system  3000  further includes a membrane  3012  operably coupled (e.g., affixed, attached, or otherwise connected) to the shunting element  3002 . In some embodiments, the membrane  3012  is flexible and can be made of a material that is impermeable to or otherwise resists blood flow therethrough. In some embodiments, for example, membrane  3012  can be made of a thin, elastic material such as a polymer. For example, the membrane  3012  can be made of PTFE, ePTFE, silicone, nylon, PET, polyether block amide (pebax), polyurethane, blends or combinations of these materials, or other suitable materials. 
     The membrane  3012  can cover at least a portion of the shunting element  3002 , such as the exterior surface of the shunting element  3002  between the first end portion  3003   a  and the second end portion  3003   b . The membrane  3012  can extend circumferentially around the shunting element  3002  to at least partially surround and enclose the lumen  3004 . For example, in the illustrated embodiment, the membrane  3012  extends between the first and second annular elements  3006   a - b  and over the struts  3010 . The membrane  3012  can couple the first and second annular elements  3006   a - b  to each other, in combination with or as an alternative to the struts  3010 . The membrane  3012  can extend past the first end portion  3003   a  and/or the first annular element  3006   a  (e.g., as best seen in  FIG. 30B ) so that a portion of the membrane  3012  is positioned over and partially covers the lumen  3004 . In some embodiments, the membrane  3012  does not extend past the second end portion  3003   b  and/or the second annular element  3006   b.    
     The membrane  3012  includes an aperture  3014  formed therein. When the membrane  3012  is coupled to the shunting element  3002 , the aperture  3014  can be at least generally aligned with or otherwise overlap the lumen  3004  to permit blood flow therethrough. In some embodiments, the aperture  3014  is positioned at or near the first end portion  3003   a  of the shunting element  3002 . In other embodiments, the aperture  3014  can be positioned at or near the second end portion  3003   b . Additionally, although  FIG. 30A  illustrates the aperture  3014  as having an elliptical shape, in other embodiments the aperture  3014  can have a different shape, such as a circular, square, rectangular, polygonal, or curvilinear shape. 
     The geometry (e.g., size and/or shape) of the aperture  3014  can be varied by deforming (e.g., stretching and/or compressing) or otherwise moving the portions of the membrane  3012  surrounding the aperture  3014 . The change in geometry of the aperture  3014  can affect the amount of blood flow through the lumen  3004 . In some embodiments, depending on the size of the aperture  3014  relative to the size of the lumen  3004 , blood flow through the lumen  3004  can be partially or completely obstructed by the membrane  3012 . Accordingly, an increase in the size (e.g., a diameter, an area) of the aperture  3014  can increase the amount of blood flow through the lumen  3004 , while a decrease in the size of the aperture  3014  can decrease the amount of blood flow. 
     The system  3000  can include an actuation assembly  3015  operably coupled to the aperture  3014  to selectively adjust the size thereof. The actuation assembly  3015  can include an actuation mechanism  2016  and a string element  3018  (e.g., a cord, thread, fiber, wire, tether, ligature, or other flexible elongated element). The actuation mechanism  3016  is coupled to the string element  3018  around the aperture  3014  for controlling the size thereof. For example, the string element  3018  can include a loop portion  3020  surrounding the aperture  3014  and a connecting portion  3022  coupling the loop portion  3020  to the actuation mechanism  3016 . In some embodiments, the loop portion  3020  and the connecting portion  3022  are different portions of one contiguous elongated element (e.g., arranged similarly to a lasso or snare) that attain their relative shapes (e.g., an elliptical, loop-like shape) as a consequence of how they are connected to the system  3000 . In other embodiment, the loop portion  3020  and the connecting portion  3022  can be separate elements that are directly or indirectly coupled to each other. 
     One or more portions of the string element  3018  (e.g., the loop portion  3020 ) can be coupled to the portion of the membrane  3012  near the aperture  3014 . In the illustrated embodiment, the string element  3018  (e.g., loop portion  3020 ) passes through a plurality of openings or holes  3024  (e.g., eyelets) located near the peripheral portion of the aperture  3014 . The openings  3024  can be coupled to the shunting element  3002  (e.g., to the first end portion  3003   a  and/or first annular element  3006   a ) via a plurality of flexible ribs  3026  (e.g., sutures, strings, threads, metallic structures, polymeric structures, etc.). In other embodiments, the openings  3024  are formed in or coupled directly to the membrane  3012  such that the ribs  3026  are omitted. 
     In some embodiments, the string element  3018  has a lasso- or noose-like configuration in which the loop portion  3020  can be tightened to a smaller size or loosened to a larger size by making an adjustment to (e.g., translating, rotating, applying or releasing tension, etc.) on the connecting portion  3022 . In some embodiments, a motion caused by the adjustment of connecting portion  3022  creates an induced motion in loop portion  3020  (e.g., a motion that results in the loop portion  3020  shifting to a larger or a smaller size). Due to the coupling between the string element  3018  and the membrane  3012 , the size of the aperture  3014  (e.g., a diameter, an area) can change along with the size of the loop portion  3020  such that the size of the aperture  3014  increases as the size of the loop portion  3020  increases, and decreases as the size of the loop portion  3020  decreases. For example, as the size of the loop portion  3020  decreases, the portions of the membrane  3012  surrounding the aperture  3014  can be cinched, stretched, or otherwise drawn together by the loop portion  3020  so that the size of the aperture  3014  decreases. Conversely, as the size of the loop portion  3020  increases, the portions of the membrane  3012  surrounding the aperture can be released, loosened, stretched, or otherwise allowed to move apart so that the size of the aperture  3014  increases. Accordingly, the actuation mechanism  3016  can adjust the size of the loop portion  3020 , and thus the size of the aperture  3014 , by controlling the amount of force (e.g., tension) applied to the loop portion  3020  via the connecting portion  3022 . For example, in some embodiments, the actuation mechanism  3016  increases the size of the loop portion  3020  and aperture  3014  by increasing the amount of force applied to the connecting portion  3022 , and decreases the size of the loop portion  3020  and aperture  3014  by decreasing the amount of applied force. 
     In other embodiments, the system  3000  can implement different mechanisms for mechanically and/or operably coupling the actuation mechanism  3016 , the loop portion  3020 , and the connecting portion  3022 . For example, there can be an inverse relationship between these components, e.g., the actuation mechanism  3016  can increase the size of the loop portion  3020  and aperture  3014  by increasing the amount of force applied to the connecting portion  3022 , and can decrease the size of the loop portion  3020  and aperture  3014  by decreasing the amount of applied force. In some embodiments, changes in the size of the loop portion  3020  and aperture  3014  are created via the actuation mechanism  3016  translating, rotating, or otherwise manipulating the connecting portion  3022  in a way that does not substantially increase or decrease the amount of force applied to the connecting portion  3022 . In other embodiments, the adjustment to the connecting portion  3022  made by the actuation mechanism  3016  can result in an alteration of the shape of (rather than the size of) loop portion  3020  and aperture  3014 . 
     In some embodiments, the connecting portion  3022  can be surrounded by a relatively stiff conduit  3034  (e.g., a plastic or metallic hypotube, shown in  FIGS. 30C-30E ) that can facilitate the transfer of forces from the actuation mechanism  3016 , as further described below. The conduit  3034  can be flexible or hinged to such that it can move with one or more degrees of freedom with respect to the actuation mechanism  3016  and/or the aperture  3014 . 
     The actuation mechanism  3016  can be configured in a number of different ways. In some embodiments, for example, the actuation mechanism  3016  includes one or more motors, such as electromagnetic motors, implanted battery and mechanical motors, MEMS motors, micro brushless DC motors, piezoelectric based motors, solenoids, and other motors. In other embodiments, the actuation mechanism  3016  includes one or more shape memory elements. For example, referring to  FIGS. 30C-30E  together, in some embodiments, the actuation mechanism  3016  includes a first shape memory actuation element  3028   a , a second shape memory actuation element  3028   b , and a shuttle element  3030 . The shuttle element  3030  can be positioned between and coupled to the first and second shape memory actuation elements  3028   a - b . The shuttle element  3030  can be also coupled to the string element  3018  (e.g., coupled to connecting portion  3022 ). Optionally, the first shape memory actuation element  3028   a , second shape memory actuation element  3028   b , and shuttle element  3030  can be located within a housing  3032 . The shuttle element  3030  can move within the housing  3032  to adjust the force on and/or the position of the connecting portion  3022  and vary the size of the loop portion  3020 , as described in greater detail below. 
     In some embodiments, the connecting portion  3022  can be received within the conduit  3034  (e.g., a flexible tube). The conduit  3034  can serve as a guide for the connecting portion  3022 . In some embodiments, the conduit  3034  also provides mechanical stabilization that impacts how the loop portion  3020  and aperture  3014  move in response to manipulation of the connecting portion  3022 . The conduit  3034  can be coupled to the housing  3032  or to another component of the system  3000  (e.g., in embodiments wherein the housing  3032  is omitted). 
     The movement of the shuttle element  3030  can be actuated by the first and second shape memory actuation elements  3028   a - b . For example, the first and second shape memory actuation elements  3028   a - b  can each be configured to change in shape in response to a stimulus such as heat or mechanical loading. In some embodiments, the first and second shape memory actuation elements  3028   a - b  are each manufactured or otherwise configured to approach (e.g., change in shape, deform, transform, etc.) a relatively lengthened configuration upon application of heat. In other embodiments, the first and second shape memory actuation elements  3028   a - b  are each manufactured or otherwise configured to approach a relatively shortened configuration upon application of heat. Optionally, one shape memory actuation element can approach a relatively lengthened configuration when heated, while the other shape memory actuation element can approach a relatively shortened configuration when heated. In some embodiments, at least one shape memory actuation element is manufactured so that, at a first temperature (e.g., body temperature), it is relatively more thermoelastically deformable in response to a fixed force or stress than it would be at a second temperature. The second temperature can be a higher temperature (e.g., a temperature resulting from the application of heat to an element) than the first temperature. 
     The shape change (e.g., due to deformation by externally-applied forces, due to heating that results in a deformation related to the shape memory effect, etc.) of the first and/or second shape memory actuation elements  3028   a - b  can actuate movement of the shuttle element  3030  relative to the housing  3032 . In some embodiments, the first and second shape memory actuation elements  3028   a - b , when at an unheated temperature (e.g., at or close to body temperature), are relatively more thermoelastically deformable as described above. In such embodiments, actuation (e.g., expansion/lengthening) of one shape memory actuation element via heating can move shuttle element  3030  in such a way that deforms/compresses the other shape memory actuation element. 
     Referring initially to  FIG. 30C , in a first stage of operation, the first and second shape memory actuation elements  3028   a - b  can reside in a neutral configuration, with both elements deformed from their original manufactured geometric configurations. As a result, the shuttle element  3030  can be positioned at or near the center of the housing  3032  and the loop portion  3020  can have a diameter D 1 . The size of the aperture (not shown) can be similar to the size of the loop portion  3020  (e.g., the aperture has a diameter equal or similar to D 1 ). The aperture size can permit a first amount of blood flow through the lumen of the shunting element (not shown). 
     Referring next to  FIG. 30D , in a different stage of operation, the first shape memory actuation element  3028   a  has changed in shape to a relatively shortened configuration and the second shape memory actuation element  3028   b  has changed in shape to a relatively lengthened configuration. For example, the second shape memory actuation element  3028   b  can be heated to induce a change in shape to a lengthened configuration (e.g., towards its original manufactured geometric configuration) relative to its shape in the neutral position shown in  FIG. 30C . This shape change can apply a force to the shuttle element  3030  that moves it along a first direction (e.g., away from the loop portion  3020 ). As a result, the shuttle element  3030  can apply an increased amount of tension to the connecting portion  3022  to retract it at least partially into the housing  3032 . The tension on the connecting portion  3022  can cause the loop portion  3020  to tighten and/or decrease in a size to a smaller diameter D 2  (e.g., by forcing a larger portion of the string element  3018  into the conduit  3034 ). The decrease in size of the loop portion  3020  can cause the aperture size to also decrease (e.g., to a diameter equal or similar to D 2 ). The decreased aperture size can permit a decreased amount of blood flow or no blood flow through the lumen. In some embodiments, the force applied by the shape change of the second shape memory actuation element  3028   b  can also cause the first shape memory actuation element  3028   a  (which is unheated and accordingly can be relatively more thermoelastically deformable than when at an elevated temperature) to change in shape to a relatively shortened configuration. 
     Referring to  FIG. 30E , in a further stage of operation, the first shape memory actuation element  3028   a  has changed in shape to a relatively lengthened configuration and the second shape memory actuation element  3028   b  has changed in shape to a relatively shortened configuration. For example, the first shape memory actuation element  3028   a  can be heated to induce a change in shape to a lengthened configuration (e.g., towards its original manufactured geometric configuration) relative to its shape in the neutral position shown in  FIG. 30C  and relative to its compressed shape shown in  FIG. 30D . This shape change can apply a force to the shuttle element  3030  that moves it along a second, opposite direction (e.g., towards the loop portion  3020 ). As a result, the shuttle element  3030  can apply a decreased amount of tension on the connecting portion  3022  to release it at least partially from the housing  3032 . The decreased tension on the connecting portion  3022  can cause the loop portion  3020  to loosen and/or increase in a size to a larger diameter D 3  (e.g., by allowing a larger portion of string element  3018  to reside outside the conduit  3034 ). The increase in size of the loop portion  3020  can cause the aperture size to also increase (e.g., to a diameter equal or similar to D 3 ). The increased aperture size can permit an increased amount of blood flow through the lumen. In some embodiments, the force applied by the shape change of the first shape memory actuation element  3028   a  can also cause the second shape memory actuation element  3028   b  (which is unheated and accordingly can be relatively more thermoelastically deformable than when at an elevated temperature) to change in shape to a relatively shortened configuration. 
     It will be appreciated that the system  3000  can be configured in a number of different ways. In some embodiments, for example, the system  3000  can include multiple membrane structures and/or materials. For example, a first membrane can interface with a first portion of the system  3000  (e.g., between first and second annular elements  3006   a - b ) and a second membrane can interface with a second portion of the system  3000  (e.g., between first annular element  3006   a  and a string element  3018 ). In such embodiments, the first and second membranes can be made of different materials having different material properties (e.g., flexibility, elasticity, permeability, tear strength, etc.). This approach is expected to be advantageous in embodiments where different material properties are optimal or otherwise beneficial for different regions of the system  3000 . For example, flexibility may be an important characteristic in one region of the system  3000 , while in a second region, lack of permeability may be more important than flexibility. The system  3000  can include any suitable number of membrane structure and/or materials. Optionally, some portions of the system  3000  can include multiple (e.g., overlapping) membranes made of the same material or different materials. 
     The actuation mechanism  3016  can be configured in a number of different ways. For example, in some embodiments the first and/or second shape memory actuation elements  3028   a - b  can be manufactured or otherwise configured to approach a relatively shortened configuration rather than a relatively lengthened configuration when heated. As a result, heat can be applied to the first shape memory actuation element  3028   a  to retract more of the string element  3018  into the housing  3032 , and heat can be applied to the second shape memory actuation element  3028   b  to release more of the string element  3018  from the housing  3032 . Additionally, although  FIGS. 30C-30E  illustrate the first and second shape memory actuation elements  3028   a - b  as having a folded or zig-zag shape, in other embodiments the first and second shape memory actuation elements  3028   a - b  can have a different shape, such as a serpentine, curved, bent, or coiled shape. 
     In some embodiments, the first and second shape memory actuation elements  3028   a - b  are positioned on the same side of the shuttle element  3030 . In such embodiments, one shape memory actuation element can be manufactured such that when it is heated it moves towards a relatively lengthened/expanded configuration, and the second shape memory actuation element can be manufactured such that when it is heated it moves towards a relatively shortened/contracted configuration. In other embodiments, any number of shape memory actuation elements that have been manufactured to have similar or dissimilar original geometric configurations may be utilized. 
     In some embodiments, the string element  3018  itself acts as an actuation mechanism. In such embodiments, any additional actuation mechanism (e.g., actuation mechanism  3016 ) can be omitted. For example, an embodiment may consist of a string element  3018  that is composed entirely of a loop portion  3020  (e.g., there is no connecting portion  3022 ) that interfaces with openings or holes  3024  (e.g., eyelets). The loop portion  3020  may also interface directly or indirectly with membrane  3012  so as to form aperture  3014 . The string element  3018  can include a shape memory material (e.g., a nitinol wire or strut). In a mode of operation, the size and/or shape of the loop portion  3020  can be altered to vary the shape of the aperture  3014 . For example, a shape memory material comprising the loop portion  3020  can be manufactured to have a relatively small geometry (e.g., a small diameter). Prior to or following implantation, a force can be applied (e.g., a radial outward force provided by an expanding balloon) to the loop portion  3020  to deform it into a configuration with a relatively larger geometry. Subsequently, heat can be applied to the shape memory loop portion  3020  to induce a shape change towards its relatively smaller manufactured geometry. A series of similar operations can be performed over a period of time to allow a care provider to change an aperture size multiple times within a range of possible sizes. In other embodiments, the shape memory material comprising the loop portion  3020  can be manufactured to have a relatively large geometry. Prior to or following implantation, a force can be applied (e.g., a compressive force from a snare tool) to the loop portion  3020  to deform it into a configuration with a relatively smaller geometry. Subsequently, heat can be applied to the shape memory loop portion to induce a shape change towards its relatively larger manufactured geometry. 
     In some embodiments, the string element  3018  includes two or more shape memory elements that have been coupled together mechanically (e.g., with welds, sutures, glue/adhesives, rivets/crimps, etc.) in a way such that the two or more elements are electrically and/or thermally insulated from one another. In such embodiments, for example, a first shape memory element may be manufactured to have a relatively larger geometry, and a second shape memory element may be manufactured to have a relatively smaller geometry. As these elements are mechanically coupled, a heat-driven actuation of one element towards its original geometric configuration may drive a similar motion in the non-heated element, since the non-heated element will remain in a relatively more thermoelastically deformable material phase. As such, the size of the loop portion  3020 , and thereby the size of aperture  3014 , may be adjusted to be both larger and smaller using energy applied to different portions of the string element  3018 . In such embodiments, the size of the loop portion  3020  can also be altered by applying an external force (e.g., via an expandable balloon). 
     In embodiments of the present technology that utilize heat or another form of energy applied to a shape memory element or another component of the system, the energy/heat can be applied both invasively (e.g., via a catheter delivering laser, radiofrequency, or another form of energy, via an internal stored energy source such as a supercapacitor, etc.), non-invasively (e.g., using radiofrequency energy delivered by a transmitter outside of the body, by focused ultrasound, etc.), or through a combination of these methods. 
       FIGS. 31A and 31B  illustrate a portion of an interatrial shunting system  3100  configured in accordance with another embodiment of the present technology. More specifically,  FIG. 31A  is a closeup perspective view of the portion of the system  3100  and  FIG. 31B  is a closeup perspective view of an actuation mechanism  3101  and cross-section of adjustable structure  3102  of the system  3100 . The components of the system  3100  can be implemented in or combined with any of the other embodiments disclosed herein, e.g., the system  200  described with respect to  FIGS. 30A-30E . 
     Referring first to  FIG. 31A , the system  3100  includes an actuation mechanism  3101  coupled to an adjustable structure  3102 . The adjustable structure  3102  can be operably coupled to a membrane (e.g., membrane  3012  of  FIGS. 30A-30B —omitted for purposes of clarity) and an aperture  3104 . The aperture  3104  can at least partially overlap a lumen of a shunting element (not shown) to impact fluid flow therethrough, as previously described with respect to aperture  3014  of  FIGS. 30A-30E . In the illustrated embodiment, the adjustable structure  3102  is a band, ring or other annular structure that forms the perimeter of the aperture  3104 . The adjustable structure  3102  can be coupled to the portions of the membrane surrounding the aperture  3104  using fasteners, adhesives, sutures, or any other suitable technique known to those of skill in the art. 
     The adjustable structure  3102  can be made of a flexible and/or relatively malleable material (e.g., a metal or a polymer) configured to deflect and/or deform (e.g., elastically and/or plastically deform) when force is applied thereto. In one particular example, the adjustable structure  3102  can be an annealed stainless-steel wire. As another particular example, the adjustable structure  3102  can be a polyurethane string or suture. As a result, when force is applied to the adjustable structure  3102  (e.g., by actuation mechanism  3101 ), the adjustable structure  3102  can change in geometry (e.g., size and/or shape) to produce a corresponding change in geometry of the aperture  3104 . For example, as the size (e.g., diameter) of the adjustable structure  3102  decreases, the portions of the membrane surrounding the aperture  3104  can be cinched, stretched, loosened, or otherwise drawn together by the adjustable structure  3102  so that the size of the aperture  3104  decreases. Conversely, as the size of the adjustable structure  3102  increases, the portions of the membrane surrounding the aperture  3104  can be released, loosened, stretched, or otherwise allowed to move apart so that the size of the aperture  3104  increases. In some embodiments, the adjustable structure  3102  is transformable between a plurality of different configurations having different geometries, such as an expanded configuration having a relatively large size (e.g., as measured by diameter, cross-sectional area) and/or a compressed configuration having a relatively small size. When the adjustable structure  3102  is in the expanded configuration, the aperture  3104  can provide relatively lower resistance to fluid flow therethrough, thus permitting a greater amount of fluid flow. When the adjustable structure  3102  is in the compressed configuration, the aperture  3104  can provide relatively increased resistance to fluid flow therethrough, thus partially or completely inhibiting the volume of fluid flow. 
     Optionally, the adjustable structure  3102  can be made of a shape memory material such as nitinol. In such embodiments, for example, changes to the size and/or geometry of the adjustable structure  3102  (and therefore the aperture  3104 ) can be induced both by applying external stresses to the adjustable structure  3102  and/or by inducing internal stresses in the adjustable structure  3102  via the application of energy (e.g., heating the adjustable structure  3102  beyond a transition temperature that results in at least a temporary alteration of the material state). 
     The actuation mechanism  3101  can be configured to selectively change the geometry of the adjustable structure  3102  in order to modulate the size of the aperture  3104  and, accordingly, the relative volume of fluid flow therethrough. In some embodiments, the actuation mechanism  3101  is coupled to the adjustable structure  3102  via a lever element  3106 . The lever element  3106  can be any elongated structure (e.g., a strut, bar, rod, tube, etc.) configured to transmit a force and/or motion applied by the actuation mechanism  3101  to the adjustable structure  3102 . The lever element  3106  can be made of a superelastic material (e.g., nitinol) or another suitable material (e.g., stainless steel, cobalt chromium, a polymer, etc.). Optionally, the lever element  3106  can be made of a non-shape memory material. In other embodiments the lever element  3106  can be made of a shape memory material, but the shape memory properties of the material are not used during operation of the lever element  3106  (e.g., the lever element  3106  is not heated during operation). 
     In some embodiments, the lever element  3106  includes a first end portion  3108   a  coupled to the actuation mechanism  3101  and a second end portion  3108   b  coupled to the adjustable structure  3102 . The first end portion  3108   a  can be pivotally coupled to the actuation mechanism  3101  so that the lever element  3106  can pivot or otherwise rotate relative to the actuation mechanism  3101 . The second end portion  3108   b  can be pivotally coupled to the adjustable structure  3102  so that the lever element  3106  can pivot or otherwise rotate relative to the adjustable structure  3102 . The pivotal coupling(s) can be implemented in various ways known to those of skill in the art. For example, the first and/or second end portions  3108   a - b  can be pivotally coupled using a hinge or other rotational fastener. As another example, the first and/or second end portions  3108   a - b  can be configured to bend, e.g., by reducing the thickness and/or stiffness of these portions compared to other portions of the lever element  3106 . 
     In some embodiments, the actuation mechanism  3101  is configured to alter the geometry of the adjustable structure  3102  by pivoting the lever element  3106  (e.g., relative to the adjustable structure  3102  and/or the actuation mechanism  3101 ). For example, pivoting of the lever element  3106  in a first direction D 1  can apply an outwardly-directed and/or tensile force against the adjustable structure  3102  to increase the size thereof. Pivoting of the lever element  3106  in a second, opposite direction D 2  can apply an inwardly-directed and/or compressive force against the adjustable structure  3102  to decrease the size thereof. In other embodiments pivoting of the lever element  3106  in one direction (e.g., D 1  or D 2 ) can release a force that was applied to the adjustable structure  3102  via pivoting of the lever element  3106  in the opposite direction. Additional features of the actuation mechanism  3101  are described in detail below. 
     The adjustable structure  3102  can be coupled to one or more struts  3110  that connect the adjustable structure  3102  to the shunting element (not shown). The struts  3110  can each be made of a superelastic material (e.g., nitinol) or another suitable material (e.g., stainless steel, cobalt chromium, a polymer, etc.). Each strut can include a first end portion  3112   a  coupled to the adjustable structure  3102  and second end portion  3112   b  coupled to the shunting element or to another portion of the system  200 . The struts  3110  can be arranged radially around the perimeter (e.g., circumference) of the adjustable structure  3102  in a spoke-like configuration. The struts  3110  can be configured to restrict the extent to which the adjustable structure  3102  can move relative to the shunting element (e.g., along the longitudinal axis of the shunting element). As a result, when the lever element  3106  applies or releases force to the adjustable structure  3102 , the adjustable structure  3102  can expand or contract radially in a plane (e.g., a plane including the aperture  3104  or parallel thereto), rather than moving longitudinally (e.g., along the longitudinal axis of the shunting element). In some embodiments, the first and second end portions  3112   a - b  of each strut  3110  are pivotally coupled to the adjustable structure  3102  and the shunting element, respectively, such that each strut  3110  pivots (e.g., relative to the adjustable structure  3102  and/or shunting element) as the adjustable structure  3102  changes in geometry. The pivotal couplings of the struts  3110  can be implemented as hinges, bendable regions, or any other suitable structure known to those of skill in the art. Although  FIG. 31A  illustrates ten struts  3110 , in other embodiments the system  3100  can include a different number of struts (e.g., one, two, three, four, five, six, seven, eight, nine, eleven, fifteen, or twenty struts). 
     In some embodiments, the adjustable structure  3102  can be coupled to one or more structural members  3114 . The structural members  3114  can be arranged radially around the adjustable structure  3102  in a spoke-like configuration. In the illustrated embodiment, for example, each structural member  3114  is attached to the adjustable structure  3102  at or near a corresponding strut  3110 . In other embodiments, some or all of the structural members  3114  can be spaced apart from the struts  3110 . The structural members  3114  can be attached to, contact, or otherwise engage the membrane (not shown) to define the shape thereof. In the illustrated embodiment, for example, each structural member  3114  has a curved or bent shape and extends over the struts  3110 . As a result, when the membrane is attached to the structural members  3114 , the struts  3110  are positioned within the interior space enclosed by the membrane. In some embodiments, the structural members  3114  also extend over the actuation mechanism  3101  and lever element  3106  so that these components are also enclosed within the membrane. Although  FIG. 31A  illustrates seven structural members  3114 , in other embodiments the system  3100  can include a different number of structural members (e.g., one, two, three, four, five, six, eight, nine, ten, 15, or 20 structural members). 
     Referring to  FIG. 31B , in some embodiments, the actuation mechanism  3101  is a linear actuation mechanism including at least one linear actuator (e.g., a shuttle, slider, or other moveable component) configured to move linearly (e.g., translate) to actuate the adjustable structure  3102 . Translational movement of the linear actuator in a first direction can cause at least a portion of the adjustable structure to move (e.g., expand or contract) in a second, different direction (e.g., a direction oblique to the first direction, such as a radial direction). In the illustrated embodiment, for example, the actuation mechanism  3101  includes a shuttle element  3116  coupled (e.g., pivotally coupled) to the lever element  3106  (e.g., to the first end portion  3108   a ) so that movement of the shuttle element  3116  causes pivoting of the lever element  3106 . Translational movement of the shuttle element  3116  in a first direction (e.g., direction D 3 ) can pivot the lever element  3106  (e.g., forward to be relatively more perpendicular to the aperture  3104 ) to decrease the size (e.g., diameter d 3 ) of the adjustable structure  3102 , while translation of the shuttle element  3116  in a second, opposite direction (e.g., direction D 4 ) can pivot the lever element (e.g., backward to be relatively more parallel to the aperture  3104 ) to increase the size of the adjustable structure  3102 . As a result, the lever element  3106  can convert linear motion of shuttle element  3116  into radial motion of at least a portion of the adjustable structure  3102  that alters the size of the aperture  3104 . As described in greater detail below, the lever element  3106  can amplify the motion of the shuttle element  3116  such that the magnitude of the size change of the aperture  3104  is larger than the magnitude of the movement distance of the shuttle element  3116 . 
     The actuation mechanism  3101  can include one or more shape memory actuation elements configured to drive the movement of the shuttle element  3116 . In the illustrated embodiment, for example, the actuation mechanism  3101  includes a first shape memory actuation element  3118   a  and a second shape memory actuation element  3118   b  coupled to the shuttle element  3116 . The shuttle element  3116  can be positioned between and coupled to the first and second shape memory actuation elements  3118   a - b . In other embodiments one side of the shuttle element  3116  can be mechanically coupled to more than one shape memory actuation element (e.g., both the first and second shape memory actuation elements  3118   a - b ). Optionally, the first shape memory actuation element  3118   a , the second shape memory actuation element  3118   b , and the shuttle element  3116  can be located within a housing  320 . In such embodiments, the shuttle element  3116  can move (e.g., translate) within the housing  320  to pivot the lever element  3106 . In other embodiments the housing  320  can be omitted. 
     The movement of the shuttle element  3116  can be actuated by the first and second shape memory elements  3118   a - b . For example, the first and second shape memory elements  3118   a - b  can each be configured to change in shape in response to a stimulus, such as heat or mechanical loading. In some embodiments, the first and second shape memory elements  3118   a - b  are each manufactured or otherwise configured to approach (e.g., change in shape, deform, transform, etc.) a relatively lengthened configuration upon application of heat of sufficient heat to induce at least a temporary change in material state. In other embodiments, the first and second shape memory elements  3118   a - b  are each manufactured or otherwise configured to approach a relatively shortened configuration upon application of heat. Optionally, one shape memory element can approach a relatively lengthened configuration when sufficiently heated, while the other shape memory element can approach a relatively shortened configuration when sufficiently heated. In some embodiments, at least one shape memory element is manufactured so that, at a first temperature (e.g., body temperature), it is relatively more thermoelastically deformable in response to a fixed force or stress than it would be at a second temperature. The second temperature can be a higher temperature (e.g., a temperature resulting from the application of heat to an element) than the first temperature. 
     The shape change (e.g., due to deformation by externally-applied forces, due to heating that results in a deformation related to the shape memory effect, etc.) of the first and/or second shape memory elements  3118   a - b  can actuate movement of the shuttle element  3116  relative to the housing  320 . In some embodiments, the first and second shape memory elements  3118   a - b , when at an unheated temperature (e.g., at or close to body temperature), are relatively more thermoelastically deformable as described above. In such embodiments, actuation (e.g., expansion/lengthening) of one shape memory element via heating can move shuttle element  3116  in such a way that deforms (e.g., compresses or expands) the other shape memory element. 
     In a first stage of operation, the first and second shape memory elements  3118   a - b  can reside in a neutral configuration (e.g., as shown in  FIG. 31B ), with one or both elements deformed from their original manufactured geometric configurations. As a result, the shuttle element  3116  can be positioned at or near the center of the housing  320 , and the adjustable structure  3102  and aperture  3104  can have a first size permitting a first amount of blood flow through the lumen of the shunting element (not shown). 
     In a different stage of operation, the first shape memory actuation element  3118   a  can change in shape to a relatively shortened configuration and the second shape memory actuation element  3118   b  can changed in shape to a relatively lengthened configuration. For example, the second shape memory actuation element  3118   b  can be heated to induce a change in shape to a lengthened configuration (e.g., toward its original manufactured geometric configuration) relative to its shape in the neutral position shown in  FIG. 31B . This shape change can apply a force to the shuttle element  3116  that moves it along a first direction (e.g., direction D 3 ). As a result, the shuttle element  3116  can pivot the lever element  3106  to alter the size and/or geometry of the adjustable structure  3102  and aperture  3104  (e.g., to a decreased aperture size that permits a decreased amount of blood flow or no blood flow through the lumen). In some embodiments, the force applied by the shape change of the second shape memory actuation element  3118   b  can also cause the first shape memory actuation element  3118   a  (which is unheated and accordingly can be relatively more thermoelastically deformable than when at an elevated temperature) to change in shape to a relatively shortened configuration. 
     In a further stage of operation, the first shape memory actuation element  3118   a  can change in shape to a relatively lengthened configuration and the second shape memory actuation element  3118   b  can change in shape to a relatively shortened configuration. For example, the first shape memory actuation element  3118   a  can be heated to induce a change in shape to a lengthened configuration (e.g., toward its original manufactured geometric configuration) relative to its shape in the neutral position shown in  FIG. 31B . This shape change can apply a force to the shuttle element  3116  that moves it along a second, opposite direction (e.g., direction D 4 ). As a result, the shuttle element  3116  can pivot the lever element  3106  to alter the size and/or geometry of the adjustable structure  3102  and aperture  3104  (e.g., to an increased aperture size that permits an increased amount of blood flow through the lumen). In some embodiments, the force applied by the shape change of the first shape memory actuation element  3118   a  can also cause the second shape memory actuation element  3118   b  (which is unheated and accordingly can be relatively more thermoelastically deformable than when at an elevated temperature) to change in shape to a relatively shortened configuration. 
     The actuation mechanism  3101  can be configured in a number of different ways. For example, in some embodiments the first and/or second shape memory actuation elements  3118   a - b  can be manufactured or otherwise configured to approach a relatively shortened configuration rather than a relatively lengthened configuration when sufficiently heated. Additionally, although  FIGS. 31A and 31B  illustrate the first and second shape memory actuation elements  3118   a - b  as having a serpentine or zig-zag shape, in other embodiments the first and second shape memory actuation elements  3118   a - b  can have a different shape, such as a folded, curved, bent, or coiled shape. 
     In some embodiments, the first and second shape memory actuation elements  3118   a - b  are positioned on the same side of the shuttle element  3116 . In such embodiments, one shape memory actuation element can be manufactured such that when it is heated it moves towards a relatively lengthened/expanded configuration, and the second shape memory actuation element can be manufactured such that when it is heated it moves towards a relatively shortened/contracted configuration. In other embodiments, any number of shape memory actuation elements that have been manufactured to have similar or dissimilar original geometric configurations may be utilized. 
     In embodiments of the present technology that utilize heat or another form of energy applied to a shape memory actuation element or another component of the system, the energy/heat can be applied both invasively (e.g., via a catheter delivering laser, radiofrequency, or another form of energy, via an internal stored energy source such as a supercapacitor, etc.), non-invasively (e.g., using radiofrequency energy delivered by a transmitter outside of the body, by focused ultrasound, etc.), or through a combination of these methods. 
     Although  FIGS. 31A-31B  illustrate a single actuation mechanism  3101 , in other embodiments the system  3100  can include a different number of actuation mechanisms (e.g., two, three, four, five, or more actuation mechanisms). The actuation mechanisms can be arranged radially around the adjustable structure  3102 . Each actuation mechanism can be coupled to the adjustable structure  3102  via a respective lever element. The actuation mechanisms can operate simultaneously or sequentially to adjust the geometry of the adjustable structure  3102  and aperture  3104 . This approach may be beneficial in embodiments in which a greater amount of force is used to alter the geometry of the adjustable structure  3102  and aperture  3104 . 
       FIG. 32  is a closeup perspective view of a portion of an interatrial shunting system  3200  configured in accordance with a further embodiment of the present technology. The system  3200  can be generally similar to the system  3100  described with respect to  FIGS. 31A-31B , such that like reference numbers (e.g., actuation mechanism  3201  versus actuation mechanism  3101 ) indicate similar or identical components. Accordingly, the following discussion of system  3200  will be limited to those features that differ from system  3100  of  FIGS. 31A-31B . Additionally, the components of the system  3200  can be implemented in or combined with any of the other embodiments disclosed herein. 
     The system  3200  includes an actuation mechanism  3201  coupled to an adjustable structure  3202 . In some embodiments, the adjustable structure  3202  can be operably coupled to a membrane (not shown) and an aperture  3204 . The aperture  3204  can at least partially overlap a lumen of a shunting element (not shown) to control fluid flow therethrough, as previously described. Optionally, the adjustable structure  3202  can itself serve as a shunting element defining a lumen for blood flow. In the illustrated embodiment, the adjustable structure  3202  is a stent (e.g., a laser-cut metal stent) positioned at the perimeter of the aperture  3204 . The stent can be configured to transform between multiple different geometries (e.g., an expanded configuration, a compressed configuration, and configurations therebetween) when force is applied thereto by the actuation mechanism  3201  and lever element  3206 . As shown in  FIG. 4 , for example, the stent can include a first annular structure  3230   a  and a second annular structure  3230   b  connected to each other to form a plurality of cells  3232 . The first and second annular structures  3230   a - b  can each have a curved and/or serpentine shape having a plurality of apices or bend regions  3234 . The first and second annular structures  3230   a - b  can be connected to each other at the apices  3234 , e.g., directly and/or via connectors  3236 . When the adjustable structure  3202  is in an expanded configuration, the first and second annular structures  3230   a - b  can deflect, deform, and/or otherwise move apart from each other so that the size of the cells  3232  increases. Conversely, when the adjustable structure  3202  is in a compressed configuration, the first and second annular structures  3230   a - b  can deflect, deform, and/or otherwise move closer together so that the size of the cells  3232  decreases. The size of the aperture  3204  can increase or decrease correspondingly to modulate the amount of fluid flow therethrough, as previously described. 
       FIG. 33  is a graph  3300  illustrating an example relationship between aperture diameter and movement of a linear actuation mechanism in an interatrial shunting system configured in accordance with embodiments of the present technology. The actuation mechanisms described herein (e.g., with respect to  FIGS. 30A-32 ) can be configured such that relatively small translational and/or linear movements of a shuttle element or other linear actuator produce relatively large changes in aperture geometry (e.g., size). In the illustrated embodiment, for example, a change in aperture diameter from 10 mm to 9 mm can be produced by a linear translation of the shuttle element over a distance of 0.13 mm; a change in aperture diameter from 9 mm to 8 mm can be produced by a translation distance of 0.23 mm; and so on. The change in the aperture size can be greater than the translation distance of the shuttle element. For example, the ratio of the change in aperture diameter to the translation distance of the shuttle element can be at least 1:1, 2:1, 3:1, 4:1, 5:1, 10:1, 15:1, or 20:1. In some embodiments, the ratio varies over the size range of the aperture (e.g., the ratio decreases as the aperture size decreases as shown in  FIG. 33 ). In other embodiments the ratio can be generally constant over the size range of the aperture. Optionally, the shuttle element can be coupled to an adjustable structure defining the aperture via a lever element, and the angle of the lever element relative to the shuttle element (e.g., as measured from the axis of movement of the shuttle element) can determine the extent to which incremental movements of the shuttle element affect the size of the aperture. For example, the angle of the lever element relative to the shuttle element can be equal or approximately equal to 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, or 90°. 
     E. Anchors 
       FIGS. 34A-34D  show various embodiments of anchoring scaffolds  3420  configured in accordance with select embodiments of the present technology. As one skilled in the art will appreciate, the various shunting systems described herein can incorporate various anchoring scaffolds, such as anchoring scaffolds  3420 , although other suitable anchoring mechanisms are possible. As illustrated, the anchoring scaffolds  3420  generally include right atrium elements  3422  and left atrium elements  3434 . The right atrium elements  3422  and the left atrium elements  3434  engage the septal wall to secure the interatrial shunt device in position. In some embodiments, the anchoring scaffolds  3420  are configured to minimize the squeezing force on the septal wall. In some embodiments, the right atrium elements  3422  are symmetrical with the left atrium elements  3434 . In other embodiments, the right atrium elements  3422  are not symmetrical with the left atrium elements. The anchoring scaffolds  3420  can be partially or completely covered by a biocompatible and/or anti-thrombogenic material (e.g., ePTFE). 
     The anchoring scaffolds  3420  can also define chambers. As illustrated in  FIG. 34A , the right atrium elements  3422   a  can extend into the right atrium such that they define a chamber  3426   a . The chamber  3426   a  can be partially or completely enclosed by the right atrium elements  3422   a  and the septal wall. In some embodiments, the chamber  3426   a  can house electronic components of the interatrial shunt devices, including motors, batteries, capacitors, electronics board and the like. Housing the electronic components within the chamber  3426   a  can mitigate thrombosis risks and protect the electronic components from excess exposure. 
     The anchoring scaffolds  3420  can be composed of a superelastic material such as nitinol or another suitable material (e.g., an alloy derivative of nitinol, cobalt chromium, stainless steel, etc.). In embodiments in which the anchoring scaffolds  3420  are composed of nitinol, the nitinol has a transition temperature less than body temperature such that the nitinol is in an austenitic material state when implanted, and thus the anchoring scaffolds  3420  are resistant to geometric changes, even if heated. 
     F. Shunting Assemblies Having Superelastic and Shape Memory Properties 
     As previously described, in many embodiments described herein the interatrial shunting systems include a nitinol-based actuation element manufactured so as to intentionally utilize the shape-memory properties of the material in vivo rather than the superelastic properties. For example, in some embodiments at least some components utilized will have an austenite finish temperature above body temperature (e.g., above 37 degrees C.). Consequently, the microstructure of these components exists largely in the thermally-induced martensitic material state and/or the R-phase material state throughout assembly, catheterization, deployment, and at least some periods of post-implantation in vivo operation. When deployed from the catheter during a percutaneous delivery to the target organ (e.g., the septal wall of a heart), these components will not generally exhibit self-expanding attributes like traditional superelastic nitinol components. Instead, they may behave similar to a balloon-expandable device (e.g., a cobalt chromium stent) whereby the shape memory component may recover some small amount of elastic recoil when deployed, but the vast majority of the shape change is achieved by applying a force to the component (e.g., a balloon expansion force). However, unlike traditional balloon-expandable devices which achieve this macroscopic shape change via a microstructural non-reversible plastic deformation, the shape memory components achieve their macroscopic shape change via a microstructural reversible thermoelastic deformation. As disclosed above, further deformation of these shape memory elements may be achieved by subsequently applying energy (e.g., heat) to the elements to partially or fully recover the thermoelastic deformation. In some embodiments, an interatrial shunting device may include both nitinol components manufactured to exhibit largely superelastic properties (e.g., anchor elements of the device) and nitinol components manufactured to exhibit largely shape memory properties (e.g., all or portions of actuation elements) at temperature ranges encountered during delivery/deployment and/or post-implantation use. 
     For example,  FIGS. 35A and 35B  illustrate an interatrial shunting system/device  3500  configured in accordance with select embodiments of the present technology. The interatrial shunting system  3500  includes portions that have been manufactured to exhibit largely superelastic material properties and portions that have been manufactured to exhibit largely shape memory material properties. Referring to  FIG. 35A , the interatrial shunting system  3500  includes a body element or frame  3510 . The body element  3510  can have a generally cylindrical shape, although other shapes and configurations are within the scope of the present technology. The body element  3510  is configured to extend generally between the LA and RA of a heart when implanted in the patient, and can include a lumen  3501  extending therethrough for shunting blood from the LA to the RA. 
     The interatrial shunting system  3500  can further include a first plurality of anchors  3512  extending from a first side (e.g., the right atrial side) of the body element  3510  and a second plurality of anchors  3514  extending from an opposing side (e.g., the left atrial side) of the body element  3510 . When implanted in the heart, the first plurality of anchors  3512  can engage the septal wall from the right atrial side of the heart and the second plurality of anchors  3514  can engage the septal wall from the left atrial side of the heart. The anchors  3512 / 3514  can have any suitable shape configured to secure the system  3500  to the septal wall, including, for example a flower petal configuration, a flange configuration, or the like. As illustrated, the first plurality of anchors  3512  can have a different (e.g., larger) size than the second plurality of anchors  3514 , although in other configurations the first plurality of anchors  3512  are smaller than or have the same size as the second plurality of anchors  3514 . 
     Referring to  FIG. 35B , which is a cross-sectional view of the system  3500 , the body element  3510  can comprise a first body element  3510   a  (e.g., a right atrial body element) and a second body element  3510   b  (e.g., a left atrial body element). The first body element  3510   a  includes the first plurality of anchors  3512  and is generally positionable at least partially in and/or adjacent the RA when the system  3500  is implanted. The second body element  3510   b  includes the second plurality of anchors  3514  and is generally positionable at least partially in and/or adjacent the LA when the system  3500  is implanted. The first body element  3510   a  and the second body element  3510   b  can be joined together to form the body element  3510  illustrated in  FIG. 35A . The first body element  3510   a  and the second body element  3510   b  can be joined via suturing, riveting, gluing, welding, or other suitable techniques. In some embodiments, the first body element  3510   a  and the second body element  3510   b  are a single unitary component, rather than two modular components secured together. In some embodiments, the first body element  3510   a  and the second body element  3510   b  are electrically and/or thermally isolated. 
     The body element  3510 , the first plurality of anchors  3512 , and the second plurality of anchors  3514  may be composed of a material (e.g., nitinol) and that has been manufactured such that it exhibits superelastic material properties at and above body temperature. For example, during manufacturing the body element  3510 , the first plurality of anchors  3512 , and the second plurality of anchors  3514  can be shape set using processes (e.g., high temperatures) that produce a material state transition temperature (e.g., an austenite start temperature, an austenite finish temperature) in these sections of the device that is below body temperature (e.g. below 37 degrees C.). As such, the body element  3510 , the first plurality of anchors  3512 , and the second plurality of anchors  3514  exhibit superelastic material properties upon implantation into the body. For example, the foregoing sections of the device may be in an austenitic material state while at or above body temperature. Because they are already in an austenitic material state at or above body temperature, applying additional energy (e.g., heat) to the body element  3510 , the first plurality of anchors  3512 , and the second plurality of anchors  3514  after the system  3500  is implanted in the heart will not change the shape or other dimension of these sections of the device. As a result, the body element  3510 , the first plurality of anchors  3512 , and the second plurality of anchors  3514  are configured to retain a relatively stable geometry in the heart (e.g., an outer diameter of the body element  3510  does not change, even in response to heat). 
     Referring to both  FIGS. 35A and 35B , the system  3500  can include a first actuation element  3520  and a second actuation element  3522 . The first actuation element  3520  and the second actuation element  3522  can be positioned within the body element  3510  and can at least partially define an actuation assembly configured to selectively adjust a dimension of the lumen  3501 . In some embodiments, the first actuation element  3520  and the second actuation element  3522  can be comprised of a material (e.g., nitinol) that has been manufactured to exhibit shape memory material properties at temperatures close to body temperature. In the illustrated embodiment, the first actuation elements  3520  and the second actuation elements  3522  are interlocked actuation elements and can function in a manner similar to the embodiments shown in  FIGS. 5A-7 . However, the system  3500  can alternatively (or additionally) include an actuation assembly that comprises nested stents in a manner similar to the embodiment shown in  FIGS. 3-4 , elongated or serially arranged actuation elements (e.g., rings) in a manner similar to the embodiment shown in  FIGS. 8-12 , or other suitable arrangements. The first actuation elements  3520  and the second actuation elements  3522  can have a transition temperature (e.g., an austenite start temperature, an austenite final temperature, etc.) that is above body temperature (e.g., 37 degrees Celsius). Accordingly, when the system  3500  is implanted in the heart, the first actuation elements  3520  and the second actuation elements  3522  are in a relatively malleable or deformable state (e.g., a martensitic material state and/or a R-phase material state). 
     A dimension of the lumen  3501  can be adjusted by selectively heating either the first actuation elements  3520  or the second actuation elements  3522 , as described in detail previously. For example, heating (e.g., resistively heating) the first actuation elements  3520  above their transition temperature decreases a diameter or other dimension of the lumen  3501 , and heating the second actuation elements  3522  above their transition temperature increases a diameter or other dimension of the lumen  3501 . However, because the body element  3510  and the anchors  3512 ,  3514  are partially or entirely in an austenitic material state at body temperature, incidental (or purposeful, as described below) heating of the body element  3510  and/or the anchors  3512 ,  3514  during actuation of the first actuation elements  3520  and/or the second actuation elements  3522  does not induce a geometry or other dimensional change in the body element  3510  or anchors  3512 ,  3514 . Accordingly, the body element  3510  will maintain a relatively constant outer diameter even during actuation of the first actuation elements  3520  and/or the second actuation elements  3522 , and the anchors  3512 ,  3514  will remain in a desired orientation. 
     In some embodiments, the first actuation elements  3520  are electrically coupled to and/or integral with the first body element  3510   a  and/or the first anchors  3520 . Because the first body element  3510   a  and the first anchors  3520  are manufactured such that they are partially or entirely in an austenitic material state at and above body temperature, energy (e.g., an electric current which induces resistive heating) can be applied to any of the foregoing components to help heat, and thereby induce a shape change in, the first actuation elements  3520 . For example, heat applied to the first body element  3510   a  may be passively and/or actively transferred to, and drive actuation of, the first actuation element  3520 . Likewise, the second actuation elements  3522  can be electrically coupled to and/or integral with the second body element  3510   b  and/or the second anchors  3522 . Because the second body element  3510   b  and the second anchors  3522  are also manufactured such that they are partially or entirely in an austenitic material state at and above body temperature, energy can be applied to any of the foregoing components to heat, and thereby induce a shape change in, the second actuation elements  3522 . For example, heat applied to the second body element  3510   b  may be passively and/or actively transferred to, and drive actuation of, the second actuation element  3522 . Accordingly, rather than solely applying heat to the actuation elements themselves, heat can be applied to portions of the desired system that surround and/or are in thermal communication with the actuation elements. 
     G. Operation of Adjustable Interatrial Shunting Systems 
     Without wishing to be bound by theory, the adjustability of the shunting systems provided herein are expected to advantageously address a number of challenges associated with heart failure treatment. First, heart failure is a heterogenous disease and many patients have various co-morbidities, and the resulting disease presentation can be diverse. Accordingly, a “one size fits all” approach to heart failure treatment will not provide the same therapeutic benefit to each patient. Second, heart failure is a chronic and progress disease. Use of a non-adjustable (i.e., static) device does not permit treatment to be adapted to changes in disease progression. The adjustable shunting systems described herein, however, are expected to advantageously provide increased flexibility to better tailor treatment to a particular patient and/or to various disease stages. 
     For example, the shunting systems described can enable a clinician to periodically (e.g., monthly, bi-monthly, annually, as needed, etc.) adjust the diameter of a lumen to improve patient treatment. For example, during a patient visit, the clinician can assess a number of patient parameters and determine whether adjusting the geometry and/or size of the lumen, and thus altering blood flow between the LA and the RA, would provide better treatment and/or enhance the patient&#39;s quality of life. Patient parameters can include, for example, physiological parameters (e.g., left atrial blood pressure, right atrial blood pressure, the difference between left atrial blood pressure and right atrial blood pressure, flow velocity, heart rate, cardiac output, myocardial strain, etc.), subjective parameters (e.g., whether the patient is fatigued, how the patient feels during exercise, etc.), and other parameters known in the art for assessing whether a treatment is working. If the clinician decides to adjust the diameter of the lumen, the clinician can adjust the device lumen using the techniques described herein. 
     In some embodiments, the systems described herein can include or be operably coupled to one or more sensors. The sensor(s) can measure one or more physiological parameters related to the system or the environment proximate to the sensor(s), such as left atrial pressure, right atrial pressure, and/or a pressure differential between the LA and RA. The system can adjust the size or geometry of the lumen and/or lumen orifice based on the physiological parameter(s). For example, the sensor(s) can be operably coupled to the actuation assembly such that the actuation assembly adjusts the lumen and/or lumen orifice in response to the sensor data. 
     Some embodiments of the present technology adjust the relative size and/or shape of the lumen and/or lumen aperture consistently (e.g., continuously, hourly, daily, etc.). Consistent adjustments might be made, for example, to adjust the flow of blood based on a blood pressure level, respiratory rate, heart rate, and/or another parameter of the patient, which changes frequently over the course of a day. For example, the systems described herein can have a baseline state in which the lumen or lumen orifice is substantially closed and does not allow substantial blood flow between the LA and RA, and an active state in which the lumen and lumen orifice are open and allows blood to flow between the LA and RA. The system can transition between the baseline state and the active state whenever one or more patient status parameters change due to exercise, stress, or other factors. In other embodiments, consistent adjustments can be made based on, or in response to, physiological parameters that are detected using sensors, including, for example, sensed left atrial pressure and/or right atrial pressure. If the left atrial pressure increases, the systems can automatically increase a diameter of the lumen and/or lumen orifice to decrease flow resistance between the LA and the RA and allow increased blood flow. In another example, the systems can be configured to adjust based on, or in response to, an input parameter from another device such as a pulmonary arterial pressure sensor, insertable cardiac monitor, pacemaker, defibrillator, cardioverter, wearable, external ECG or PPG, and the like. 
     Some embodiments of the present technology adjust the relative size and/or shape of the lumen and/or lumen orifice only after a threshold has been reached (e.g., a sufficient period of time has elapsed). This may be done, for example, to avoid unnecessary back and forth adjustments and/or avoid changes based on clinically insignificant changes. In some embodiments, adjustments may occur occasionally as a patient&#39;s condition changes. For example, the lumen and/or lumen orifice may gradually open if a patient experiences a sustained rise in left atrial pressure (e.g., rate of change is above a predetermined threshold, and/or the left atrial pressure remains higher than a predetermined threshold for longer than a predetermined amount of time), pulmonary artery pressure, weight, or another physiologically relevant parameters. Additionally or alternatively, adjustments can occur if pressure exceeds a threshold or increases by a threshold amount over a period of time (e.g., several days or more). The diameter of the lumen and/or lumen orifice can then be increased to increase blood flow between the LA and RA and to avoid decompensation. 
     In some embodiments, the adjustable interatrial shunting systems described herein can include additional or alternative features, such as those described in PCT Patent Application No. PCT/US20/38549, titled ADJUSTABLE INTERATRIAL SHUNTS AND ASSOCIATED SYSTEMS AND METHODS, filed Jun. 18, 2020, the disclosure of which is incorporated by reference herein in its entirety. 
     CONCLUSION 
     Embodiments of the present disclosure may include some or all of the following components: a battery, supercapacitor, or other suitable power source; a microcontroller, FPGA, ASIC, or other programmable component or system capable of storing and executing software and/or firmware that drives operation of an implant; memory such as RAM or ROM to store data and/or software/firmware associated with an implant and/or its operation; wireless communication hardware such as an antenna system configured to transmit via Bluetooth, WiFi, or other protocols known in the art; energy harvesting means, for example a coil or antenna which is capable of receiving and/or reading an externally-provided signal which may be used to power the device, charge a battery, initiate a reading from a sensor, or for other purposes. Embodiments may also include one or more sensors, such as pressure sensors, impedance sensors, accelerometers, force/strain sensors, temperature sensors, flow sensors, optical sensors, cameras, microphones or other acoustic sensors, ultrasonic sensors, ECG or other cardiac rhythm sensors, SpO2 and other sensors adapted to measure tissue and/or blood gas levels, blood volume sensors, and other sensors known to those who are skilled in the art. Embodiments may include portions that are radiopaque and/or ultrasonically reflective to facilitate image-guided implantation or image guided procedures using techniques such as fluoroscopy, ultrasonography, or other imaging methods. Embodiments of the system may include specialized delivery catheters/systems that are adapted to deliver an implant and/or carry out a procedure. Systems may include components such as guidewires, sheaths, dilators, and multiple delivery catheters. Components may be exchanged via over-the-wire, rapid exchange, combination, or other approaches. 
     The above detailed description of embodiments of the technology are not intended to be exhaustive or to limit the technology to the precise forms disclosed above. Although specific embodiments of, and examples for, the technology are described above for illustrative purposes, various equivalent modifications are possible within the scope of the technology as those skilled in the relevant art will recognize. For example, although steps are presented in a given order, alternative embodiments may perform steps in a different order. The various embodiments described herein may also be combined to provide further embodiments. For example, although this disclosure has been written to describe devices that are generally described as being used to create a path of fluid communication between the LA and RA, the LV and the right ventricle (RV), or the LA and the coronary sinus, it should be appreciated that similar embodiments could be utilized for shunts between other chambers of heart or for shunts in other regions of the body. 
     Unless the context clearly requires otherwise, throughout the description and the examples, the words “comprise,” “comprising,” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.” As used herein, the terms “connected,” “coupled,” or any variant thereof, means any connection or coupling, either direct or indirect, between two or more elements; the coupling of connection between the elements can be physical, logical, or a combination thereof. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. As used herein, the phrase “and/or” as in “A and/or B” refers to A alone, B alone, and A and B. Additionally, the term “comprising” is used throughout to mean including at least the recited feature(s) such that any greater number of the same feature and/or additional types of other features are not precluded. It will also be appreciated that specific embodiments have been described herein for purposes of illustration, but that various modifications may be made without deviating from the technology. Further, while advantages associated with some embodiments of the technology have been described in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the technology. Accordingly, the disclosure and associated technology can encompass other embodiments not expressly shown or described herein.