Patent Description:
The present invention relates generally to devices for altering flow in body lumens, such as devices for creating pressure differences and/or entrainment of fluid at lumens that branch off from other lumens for enhancing or modifying fluid flow to treat different disorders or diseases.

Heart failure is the physiological state in which cardiac output is insufficient to meet the needs of the body and the lungs. Patients suffering from any of a number of forms of heart failure are prone to increased fluid in the body. Congestive heart failure (CHF) occurs when cardiac output is relatively low and the body becomes congested with fluid. There are many possible underlying causes of CHF, including myocardial infarction, coronary artery disease, valvular disease, and myocarditis. Chronic heart failure is associated with neurohormonal activation and alterations in autonomic control. Although these compensatory neurohormonal mechanisms provide valuable support for the heart under normal physiological circumstances, they also have a fundamental role in the development and subsequent progression of CHF. For example, one of the body's main compensatory mechanisms for reduced blood flow in CHF is to increase the amount of salt and water retained by the kidneys. Retaining salt and water, instead of excreting it into the urine, increases the volume of blood in the bloodstream and helps to maintain blood pressure. However, the larger volume of blood also stretches the heart muscle, enlarging the heart chambers, particularly the ventricles. At a certain amount of stretching, the heart's contractions become weakened, and the heart failure worsens. Another compensatory mechanism is vasoconstriction of the arterial system. This mechanism, like salt and water retention, raises the blood pressure to help maintain adequate perfusion.

Glomerular filtration rate (GFR), the rate at which the kidney filters blood, is commonly used to quantify kidney function and, consequently, the extent of kidney disease in a patient. Individuals with normal kidney function exhibit a GFR of at least <NUM>/min with no evidence of kidney damage. The progression of kidney disease is indicated by declining GFR, wherein a GFR below <NUM>/min generally indicates that the patient has end stage renal disease (ESRD), which is the complete failure of the kidney to remove wastes or concentrate urine.

Cardiovascular problems, such as but not limited to, inadequate blood flow or chronic hypertension, may lead to fluid retention in the kidneys, chronic kidney disease, lowered GFR, renal failure or even ESRD. For example, hypertension is considered the second most prevalent cause for kidney failure (after diabetes). It is been estimated that hypertension causes nephrotic damage and lowers GFR.

Therefore, it would be desirable to provide apparatus to improve blood flow to prevent disease, improve body functionality, and/or treat conditions that would benefit from modified body fluid flow. For example, it would be desirable to treat heart failure, treat hypertension, prevent kidney disease, improve kidney functionality, and/or prevent blood clots from flowing through vasculature to sensitive portions of the body, such as the brain, in order to prevent strokes.

<CIT> discloses an implantable device intended generally for at least partially diverting flows of fluids within a body lumen to another lumen defined by a graft member. The device is made up of a stent, often radio-opaque, and a sheet-like member which is coupled to the stent and configured to form a side port through which fluids may be diverted.

The present invention seeks to provide devices for altering flow in body lumens, as is described more in detail hereinbelow. For example, devices are provided for creating pressure differences and/or fluid entrainment at lumens that branch off from other lumens for enhancing or modifying fluid flow to treat different disorders or diseases.

The devices of the present invention have many applications. For example, the device may be used to reduce pressure and improve flow, thereby improving flow in stenotic body lumens. It also may be used in the aortic arch to reduce peak systolic pressure in the brain or divert emboli to other portions of the body (e.g., the legs) and thereby reduce the risk of stroke. The device further may be installed in a bifurcation (e.g., in the brachiocephalic vessels) to reduce peak pressure gradients or to divert emboli with very little energy loss.

The devices of the present invention have particular application in treating blood flow to and from the kidneys. In accordance with one embodiment, the device is configured to be installed near one of the renal arteries or in the inferior vena cava near the branch off to the renal veins or in one of the renal veins.

When installed in the inferior vena cava or in the renal vein, the device can create (due to the Bernoulli effect or other factors) a region in the inferior vena cava or in the renal vein which has increased blood velocity and reduced pressure. In this manner, blood may be drawn from the kidneys to the renal veins and then to the inferior vena cava, thereby improving kidney functionality and reducing necrotic damage to the kidneys.

When installed in or near the renal vein, the devices of the present invention may improve renal function by improving net filtration pressure, which is glomerular capillary blood pressure - (plasma-colloid osmotic pressure + Bowman's capsule hydrostatic pressure), e.g., <NUM> Hg - (<NUM> Hg + <NUM> Hg) = <NUM> Hg. The devices and methods of the present invention thus provide an improvement over existing therapies, such as diuretics (although the invention can be used in addition to diuretics), angiotensinconverting enzyme inhibitors (ACEIs), and angiotensin receptor blockers (ARBs), which can have deleterious effects on kidney function. When used in conjunction with current modes of treatment such as diuretics, the devices and methods of the present invention are expected to improve the response for diuretics and reduce the dosage needed to obtain therapeutic benefit of such previously known therapies, without the disadvantages of these existing therapies.

The devices of the present invention may be used to divert flow from the kidneys to the inferior vena cava with little energy loss. For example, with a small energy loss due to pressure drop and other fluid factors, a significantly greater increase in blood flow may be achieved. This diversion of flow from the kidneys with little energy loss to increase blood flow is expected to treat conditions such as heart failure and/or hypertension.

It is noted that there is a significant difference between use of an upstream nozzle with no downstream flow decelerator, such as a diffuser. If only an upstream nozzle is placed in the flow path, there is significant energy loss downstream of the nozzle due to the sudden expansion of flow. However, by using a downstream flow decelerator, such as a diffuser, the energy loss is significantly reduced. This leads to another advantage: since the energy loss is significantly reduced, the additional flow that flows into the gap is efficiently added to the flow from the upstream flow accelerator.

In addition, the present invention is expected to provide optimal structure for an upstream flow accelerator when used together with a downstream flow decelerator. For example, the distance between the outlet of the upstream flow accelerator and the inlet of the downstream flow decelerator should be less than a predetermined length to reduce pressure at the gap between the outlet and the inlet.

When installed in the renal artery, the device can reduce pressure applied to the kidneys. Without being limited by any theory, high blood pressure can cause damage to the blood vessels and filters in the kidney, making removal of waste from the body difficult. By reducing the pressure in the renal artery, the filtration rate improves. Although there may be a reduction in the perfusion pressure, the filtration rate will increase because the overall kidney function is more efficient.

It is noted that the fluid flow modulator of the present invention may modulate fluid flow without any input from an external energy source, such as a fan, motor, and the like and without any moving parts. The structure of the device of the invention transfers energy from one lumen flow to another different lumen flow with minimal flow energy losses.

In accordance with one aspect of the present invention, an implantable device is provided for altering fluid flow through a body lumen (e.g., the inferior vena cava) that is coupled to a branch lumen(s) (e.g., a renal vein(s)). The implantable device includes a flow modulator configured to be implanted within the body lumen. The flow modulator preferably has an upstream component separated by a gap from a downstream component. The flow modulator may be formed as a single unit (e.g., from a single frame) or multiple units. The upstream component has an inlet, an outlet, and a cross-sectional flow area that preferably converges from the inlet towards the outlet. The downstream component has an entry, an exit, and a cross-sectional flow area that preferably diverges from the entry towards the exit. The gap defines a pathway that communicates with the branch lumen,.

The flow modulator preferably accelerates a fluid stream passing through the upstream component towards the downstream component to generate a low pressure region in the vicinity of the gap and to entrain additional fluid into the fluid stream as the fluid stream passes into the entry of the downstream component.

The outlet of the upstream component is preferably spaced apart from the entry of the downstream component a suitable distance for increasing flow within the branch lumen(s) while minimizing pressure loss. For example, the distance from the outlet to the entry may be less than <NUM>.

In accordance with one aspect, the cross-sectional flow area at the outlet of the upstream component is less than the cross-sectional flow area at the entry of the downstream component. The outlet of the upstream component may be positioned downstream from where the branch lumen first intersects with the body lumen. The gap may begin downstream from where the branch lumen first intersects with the body lumen. The upstream component and the downstream component may share a common, collinear flow axis with the body lumen's flow axis. The outlet of the upstream component may be positioned downstream from the entry of the downstream component.

In one example, the upstream component is coupled to the downstream component via a fluid flow structure that defines the gap. The upstream component, the downstream component, and the fluid flow structure may be formed from a single frame. The fluid flow structure may extend outward from the upstream component and from the downstream component such that the fluid flow structure contacts an inner wall of the body lumen. A junction between the fluid flow structure and the upstream component and/or the downstream component may have a curved shape such as an S-curve shape.

In accordance with one aspect, the downstream component's length is greater than the upstream component's length. The upstream component's average angle of convergence may be greater than the downstream component's average angle of divergence. The upstream component may include a nozzle that accelerates the fluid stream passing through the upstream component and the downstream component may include a diffuser that decelerates the fluid stream having the entrained additional fluid passing through the downstream component.

The flow modulator may be formed from a metal frame. The metal frame may be coated with a biocompatible material at the upstream component and at the downstream component. In one example, an uncoated portion of the metal frame between the upstream and downstream components defines the gap that allows fluid from the branch lumen(s) to entrain with the fluid stream flowing through the flow modulator.

In accordance with another aspect, a method (not part of the invention) for altering fluid flow through a body lumen coupled to a branch lumen is provided. The method may include implanting a flow modulator within a body lumen, the flow modulator including an upstream component separated by a gap from a downstream component, the upstream component being implanted in a first body lumen portion and having an inlet, an outlet, and a cross-sectional flow area that converges from the inlet towards the outlet, the downstream component being implanted in a second body lumen portion and having an entry, an exit, and a cross-sectional flow area that diverges from the entry towards the exit. The gap may be positioned where the branch lumen intersects with the body lumen and the outlet may be positioned downstream from where the branch lumen first intersects with the body lumen. The method may include accelerating a fluid stream passing through the upstream component towards the downstream component to generate a low pressure region in the vicinity of the gap and to entrain additional fluid into the fluid stream as the fluid stream passes into the entry of the downstream component.

Implanting the flow modulator within the body lumen may include implanting the upstream component in an inferior vena cava such that the inlet is upstream from a branch off to a renal vein(s) and the downstream component in the inferior vena cava such that the exit is downstream from the branch off to the renal vein(s), wherein the gap is at the branch to the renal vein(s), thereby drawing blood from the renal vein(s) to the inferior vena cava and improving kidney functionality. Drawing the blood from the renal vein(s) to the inferior vena cava to improve kidney functionality may further reduce excess fluid to treat heart failure.

The flow modulator may modulate fluid flow without any input from an external energy source. The flow modulator may modulate fluid flow without any moving parts.

There is thus provided in accordance with an embodiment of the present invention a system including a body-lumen fluid flow modulator including an upstream flow accelerator separated by a gap from a downstream flow decelerator, wherein the gap is a pathway to entrain additional fluid with fluid flowing from the upstream flow accelerator, to the downstream flow decelerator.

The gap may be located in a fluid flow structure that defines boundaries for the pathway to entrain the additional fluid to flow to the downstream flow decelerator. The upstream flow accelerator may have a flow cross-section that converges in a downstream direction. The downstream flow decelerator may have a flow cross-section that diverges in a downstream direction. The fluid flow structure may include one or more conduits that are not collinear with a direction of flow from the upstream flow accelerator to the downstream flow decelerator. The upstream flow accelerator and the downstream flow decelerator may share a common, collinear flow axis. The fluid flow structure may or may not connect the upstream flow accelerator to the downstream flow decelerator. The fluid flow structure may diverge outwards in a direction away from a central axis of the fluid flow structure. A junction between the fluid flow structure and at least one of the upstream flow accelerator and the downstream flow decelerator may be curved.

There is provided a method (not part of the invention) for altering fluid flow through a body lumen including installing a fluid flow modulator in a body, the fluid flow modulator including an upstream flow accelerator separated by a gap from a downstream flow decelerator, the upstream flow accelerator being installed in a first body lumen portion, the downstream flow decelerator being installed in a second body lumen portion and the gap being positioned at a branch lumen tilted with respect to the first and second body lumen portions, wherein when fluid flows from the upstream flow accelerator to the downstream flow decelerator, additional fluid is entrained into the gap and is added to the fluid flowing from the upstream flow accelerator to the downstream flow decelerator.

In one method (not part of the invention), the fluid flow modulator is installed near renal arteries to improve renal function by reducing renal perfusion pressure.

In one method (not part of the invention), the fluid flow modulator is installed near a bifurcation to divert emboli from the bifurcation.

In one method (not part of the invention), the fluid flow modulator is installed in an aortic arch to reduce peak systolic pressure.

Provided herein are devices and methods for altering flow in body lumens. For example, the devices and methods may be provided for creating pressure differences and/or fluid entrainment at lumens that branch off from other lumens for enhancing or modifying fluid flow to treat different disorders or diseases.

Reference is now made to <FIG>, which illustrates flow modulator <NUM>, constructed and operative in accordance with a non-limiting embodiment of the present invention.

Flow modulator <NUM> includes upstream component <NUM> separated by gap <NUM> from downstream component <NUM>. Gap <NUM> is a pathway to divert or entrain additional fluid into a stream of fluid flowing from upstream component <NUM> to downstream component <NUM>. As will be explained below, upstream component <NUM> and downstream component <NUM> create a lower pressure region in the vicinity of gap <NUM>, which preferably entrains fluid into the stream of fluid flowing across gap <NUM>. Fluid entrainment is fluid transport by shear-induced turbulent flux. In accordance with the principles of the invention, such entrainment may help transport blood or other body fluids to or from a region so as to promote better functionality of an organ (e.g., from the renal vein(s) to the inferior vena cava to promote better functionality of the kidney(s), thereby treating disorders and/or diseases such as heart failure).

Upstream component <NUM> has inlet <NUM> and outlet <NUM> and preferably has a cross-sectional flow area that converges in a downstream direction (indicated by arrow <NUM>) along part or all of the length of upstream component <NUM>, such as but not limited to, a nozzle. In this manner, upstream component <NUM> acts to accelerate flow of fluid through upstream component <NUM>. Downstream component <NUM> has entry <NUM> and exit <NUM> and preferably has a cross-sectional flow area that diverges in a downstream direction along part or all of the length of downstream component <NUM>, such as but not limited to, a diffuser. In this manner, downstream component <NUM> acts to decelerate flow of fluid through downstream component <NUM>. The distance between outlet <NUM> and entry <NUM> is selected to generate a low pressure region in the vicinity of gap <NUM> while minimizing pressure loss and reducing resistance to fluid flow at the branch lumen(s), e.g., renal flow. For example, as explained in the data below, a distance too great will create a significant pressure loss that actually sends flow in the wrong direction in a branched lumen. Applicant has discovered that using a maximum distance between outlet <NUM> and entry <NUM> (e.g., less than <NUM> and more preferably less than <NUM> when used at the renal veins) will improve flow rates in the branched vessel(s) with relatively low pressure loss. Gap <NUM> also permits flow modulator <NUM> to entrain additional fluid into the fluid stream as the fluid stream passes into entry <NUM> of downstream component <NUM>.

<CIT> and <CIT>, as well as <CIT> and <CIT>, describe several converging and diverging structures which may be utilized for creating flow modulator <NUM> in accordance with the principles described herein. Other non-limiting converging and diverging structures are shown in <FIG>. The invention may be carried out with different kinds of converging and diverging structures, such as but not limited to, Stratford ramp nozzles (e.g., in which flow through the nozzle is on the verge of separation, which gives the diffuser the best length to efficiency ratio), de Laval nozzles (e.g., asymmetric hourglass shape), variable cross-sectional area nozzles and venturis, ramped nozzles and venturis, and many others. The central axis of the diverging portion may be in-line with or offset from the central axis of the converging portion.

Gap <NUM> may be located in fluid flow structure <NUM> which defines boundaries for the pathway to divert or entrain the additional fluid to flow to downstream component <NUM>. Fluid flow structure <NUM> may include one or more conduits that are not collinear with a direction of flow (indicated by arrow <NUM>) from upstream component <NUM> to downstream component <NUM>. For example, the conduits of fluid flow structure <NUM> may be perpendicular to direction of flow or may be tilted at an angle, e.g., <NUM>° angle, <NUM>° angle or any other suitable configuration.

In the embodiment of <FIG>, upstream component <NUM> and downstream component <NUM> share a common, collinear flow axis <NUM>. However, the invention is not limited to this construction and upstream component <NUM> may be tilted with respect to downstream component <NUM>. Upstream component <NUM> and downstream component <NUM> may lie along a continuous curved path.

Fluid flow structure <NUM> may or may not connect upstream component <NUM> to downstream component <NUM>. For example, if fluid flow structure <NUM> employs conduits, then fluid flow structure <NUM> preferably connects upstream component <NUM> to downstream component <NUM>. However, fluid flow structure <NUM> as shown in <FIG> may not be conduits, but instead two walls that are not connected to each other. In such an example, fluid flow structure <NUM> does not connect upstream component <NUM> to downstream component <NUM>.

Upstream component <NUM>, downstream component <NUM>, and fluid flow structure <NUM> may be constructed as grafts, stents (coated or uncoated), stent grafts (coated or uncoated), catheters and the like, with known medically safe materials, such as stainless steel or nitinol. The outer contours of any of upstream component <NUM>, downstream component <NUM>, and fluid flow structure <NUM> may be sealed against the inner walls of the body lumen (such as by being expanded thereagainst), or alternatively may not be sealed, depending on the particular application.

Flow modulator <NUM> is sized and shaped to be implanted in a body lumen. Flow modulator <NUM> may be compressible for delivery (e.g., percutaneous delivery within a delivery sheath) and expandable upon deployment (e.g., self-expanding upon exposure from the end of the delivery sheath or balloon expandable). Flow modulator <NUM> may be inserted into the body lumen in an antegrade or retrograde manner and may be removed antegrade or retrograde. Flow modulator may be used as an acute device to be removed after few hours/days or a chronic permanent device or a device that can be retrieved after long-term implantation. When used as an acute device, flow modulator <NUM> may remain coupled to a delivery/retrieval device, e.g., sheath and/or wire/shaft, throughout the short-term implantation for ease of device delivery and retrieval. Flow modulator <NUM> may be compressible within a body lumen to allow washing of any stagnant flow zones created adjacent to flow modulator <NUM>. For example, flow modulator <NUM> may be partially or fully reduced in diameter within the body lumen to allow blood flow through a stagnant flow zone. Preferably, upon expansion, flow modulator <NUM> is sized to contact the inner wall of the body lumen to anchor flow modulator <NUM> in place. Flow modulator <NUM> preferably is formed from one or more frames and may be coated with one or more biocompatible materials. For example, the frame(s) may be formed of a metal (e.g., shape memory metal) or alloy or a combination thereof (e.g., a stent made of stainless steel or nitinol or cobalt chromium). For some applications, the frame(s) may be formed in the manner of a braided stent. In the case of more than one frame, the frames may be joined together by a suitable technique such as welding. For example, upstream component <NUM> and downstream component <NUM> may be formed from a common frame or two frames that may be joined prior to implantation. Flow modulator <NUM> may be at least partially coated with a biocompatible, covering material (although they may be used as bare metal, uncoated stents as well). The biocompatible material may be a fabric and/or polymer such as expanded polytetrafluoroethylene (ePTFE), woven, knitted, and/or braided polyester, polyurethane, DACRON (polyethylene terephthalate), silicone, polycarbonate urethane, or pericardial tissue from an equine, bovine, or porcine source. The biocompatible coating may impede or block fluid flow where applied to the frame. The order of the joining and coating processes may be joining before coating or coating before joining. The biocompatible material may be coupled to the frame(s) via stitching, spray coating, encapsulation, electrospinning, dip molding, and/or a different technique.

In a preferred embodiment, biocompatible material is fluid impermeable. However, for some applications, the surfaces need not be impermeable, but have a permeability that is sufficiently low as to substantially prevent any blood from flowing through the longitudinal portion of the body lumen, via any flow path other than through the flow channel defined by the inner surfaces of flow modulator <NUM>. For some applications, each of the surfaces has permeability per unit length of less than <NUM> micrometers (i.e., between <NUM> and <NUM> micrometers), where the permeability per unit length is defined based upon the following equation, which is based upon Darcy's Law: k/Δx = Vµ/Δp, where k is permeability, Δx is length (in meters), V is average velocity (in meters per second), µ is fluid viscosity (measured in Pascal-seconds), and ΔP is the pressure differential measured in Pascals).

Although the invention is not bound by any theory, a simplified engineering explanation is now provided to help understand how upstream component <NUM> and downstream component <NUM> operate to create reduced pressure at gap <NUM>.

The Bernoulli equation governs the relationship between fluid velocity and pressure (neglecting the height difference): <MAT>.

For example, if flow modulator <NUM> is installed near the kidneys with upstream component <NUM> in the inferior vena cava, then V<NUM> and A<NUM> are the renal velocity and flow area, respectively, at the inferior vena cava.

The flow velocity at the gap (V<NUM>) is designed to achieve the desired pressure reduction. For example, without limitation, with a <NUM> meter per second velocity and <NUM> times area ratio, a suction of ~<NUM>-<NUM> mmHg can be achieved. In the case of installation near the kidney, this can improve renal function by improving renal perfusion pressure.

In another example, flow modulator <NUM> can be installed near a bifurcation to divert emboli from the bifurcation. In another example, flow modulator <NUM> can be installed in the aortic arch to reduce peak systolic pressure.

Reference is now made to <FIG>, which illustrates another version of flow modulator <NUM>, with like elements being designated by like numerals. In this version, fluid flow structure <NUM> includes central portion <NUM>, which may be cylindrical, that connects upstream component <NUM> to downstream component <NUM>. Fluid flow structure <NUM> extends outward from outlet <NUM> of upstream component <NUM> and from entry <NUM> of downstream component <NUM> such that fluid flow structure <NUM> is sized to contact an inner wall of the body lumen. Central portion <NUM> may be formed with one or more apertures <NUM> to define gap <NUM> for fluidly communicating with branch lumens such that additional fluid from the branch lumen or lumens flows into gap <NUM> and is added to the fluid flowing from upstream component <NUM> to downstream component <NUM>.

It is noted that junction <NUM> between fluid flow structure <NUM> and upstream component <NUM> and/or downstream component <NUM> is curved. This may help streamline the flow, and prevent creation of local turbulences or eddy currents that may adversely affect the pressure or flow characteristics. It is also noted that fluid flow structure <NUM> may diverge outwards (at numeral <NUM>) in a direction away from central axis <NUM> of fluid flow structure <NUM>. This diversion may be used to create different flow affects, depending on the application. The diversion also enables moving upstream component <NUM> and downstream component <NUM> closer to each other. For example, junction <NUM> between fluid flow structure <NUM> and upstream and downstream components <NUM> and <NUM> may be S-shaped to move outlet <NUM> closer to entry <NUM> to minimize the distance between those parts of fluid modulator <NUM>.

As best shown in <FIG>, fluid modulator <NUM> is formed from frame <NUM> and coated with biocompatible material <NUM>. The potential materials for frame <NUM> and biocompatible material <NUM> are described above. In <FIG>, fluid modulator <NUM> is formed of one frame that defines upstream component <NUM>, gap <NUM>, and downstream component <NUM>. Upstream component <NUM> is coated with biocompatible material <NUM> to define the fluid flow channel through upstream component <NUM> such that fluid flowing through a body lumen enters inlet <NUM>, accelerates through the converging portion of upstream component <NUM>, and exits out outlet <NUM> into the portion of fluid modulator <NUM> having gap <NUM>. At gap <NUM>, there is a low pressure region formed by the shapes of upstream component <NUM> and downstream component <NUM>. Also, additional fluid from the branch lumen(s) at gap <NUM> is entrained into the fluid stream passing from outlet <NUM> to entry <NUM>. Downstream component <NUM> also is coated with biocompatible material <NUM> to define the fluid flow channel through downstream component <NUM> such that the fluid stream from outlet <NUM> together with the additional fluid passing through gap <NUM> enter entry <NUM>, decelerate through the diverging portion of downstream component <NUM>, and exit out exit <NUM> back into the body lumen. In this example, gap <NUM> is created by an uncoated portion of frame <NUM>.

Upstream component <NUM> may have fixation area <NUM> sized for anchoring upstream component <NUM> within the body lumen. Fixation area <NUM> is sized to contact the inner wall of the body lumen and preferably has a diameter the size of, or slightly larger than, the diameter of the body lumen. Fixation area <NUM> may have a constant diameter for a length suitable for anchoring upstream component <NUM> in the body lumen. Similarly, downstream component <NUM> may have fixation area <NUM> sized for anchoring downstream component <NUM> within another portion of the body lumen. Fixation area <NUM> is sized to contact the inner wall of the other portion of the body lumen and preferably has a diameter the size of, or slightly larger than, the diameter of that portion of the body lumen. Fixation area <NUM> may have a constant diameter for a length suitable for anchoring downstream component <NUM> in the body lumen. Preferably fixation areas <NUM> and <NUM> are configured to seal fluid modulator <NUM> within the body lumen so that fluid only flows into the fluid channels created by fluid modulator <NUM> and does not flow around fixation area <NUM> or fixation area <NUM>. In <FIG>, fluid flow structure <NUM> has the same diameter as fixation areas <NUM> and <NUM>, which may enhance anchoring immediately proximal and distal to the branch lumen(s) while positioning gap <NUM> at the intersection between the body lumen and the branch lumen(s). In this manner, fluid flow structure <NUM> forms one or more additional fixation areas (illustratively, two additional fixation areas) between fixation areas <NUM> and <NUM>. As shown, the portions of fluid flow structure <NUM> coated with biocompatible material <NUM> (on opposing sides of uncoated frame <NUM> that defines gap <NUM>) act as fixation/sealing areas. Fluid flowing in the body lumen may be trapped between the outer surface of upstream component <NUM> and the body lumen wall between fixation area <NUM> and the upstream portion of fluid flow structure <NUM>. In addition, or alternatively, fluid flowing in the body lumen may be trapped between the outer surface of downstream component <NUM> and the body lumen wall between fixation area <NUM> and the downstream portion of fluid flow structure <NUM>.

Referring now to <FIG>, an exemplary flow modulator is shown with symbols depicting dimensions of flow modulator <NUM> in accordance with a preferred embodiment. The dimensions provided with respect to <FIG> are for an embodiment where flow modulator <NUM> is configured for implantation in the inferior vena cava such that inlet <NUM> of upstream component <NUM> is upstream from a branch off to a renal vein(s) and downstream component <NUM> is in the inferior vena cava such that exit <NUM> is downstream from the branch off to the renal vein(s) and gap <NUM> is at the branch to the renal vein(s). d1 is the diameter of outlet <NUM> of upstream component <NUM>. d1 is selected to create a jet velocity for a given device resistance. In the example of chronic cases, d1 may be in a range from <NUM>-<NUM>. In acute cases, d1 preferably is in a range from <NUM>-<NUM>. d2 is the diameter of inlet <NUM> in the deployed, expanded state and may be in a range from <NUM>-<NUM>. <NUM> is the length of fixation area <NUM> and may be in a range from <NUM>-<NUM>. l2 is the overall length of upstream component <NUM> and may be in a range from <NUM>-<NUM>. x is the distance from outlet <NUM> of upstream component <NUM> to entry <NUM> of downstream component. For x, a minimum distance from outlet <NUM> to entry <NUM> will provide better performance for downstream component <NUM>, but the renal flow will be lower because there is a greater resistance to flow from the renal vein(s) to downstream component <NUM>. Thus, distance x preferably is selected (e.g., in a range from -<NUM>-<NUM>) to provide improved renal flow rate with minimal pressure loss.

As illustrated below, distance x may be negative as outlet <NUM> of upstream component <NUM> may be positioned downstream from entry <NUM> of downstream component <NUM>. a is the distance from outlet <NUM> of upstream component <NUM> to the center line of the branched lumen, e.g., the right renal vein, and may be in a range from -<NUM>-<NUM>. L1 is the length of fixation area <NUM> and may be in a range from <NUM>-<NUM>. L2 is the overall length of downstream component <NUM>. L2 is preferably greater than l2 because a diverging shape creates a much higher pressure loss than a converging shape. The ratio of L2:l2 may be from <NUM>: <NUM> to <NUM>:<NUM>. D1 is the diameter at entry <NUM> of downstream component <NUM> and is preferably larger than d1. Thus, the cross-sectional flow area at outlet <NUM> of upstream component <NUM> is less than the cross-sectional flow area at entry <NUM> of downstream component <NUM>. D1 is selected to receive all the fluid jetted from outlet <NUM>. The ratio of D1:d1 may be from <NUM>:<NUM> to <NUM>:<NUM>. In addition, D1 should be greater for larger distances x to ensure receipt of the fluid jetted from upstream component <NUM>. D2 is the diameter of exit <NUM> in the deployed, expanded state and may be in a range from <NUM>-<NUM>. α is the average angle of divergence in downstream component <NUM> and may be in a range from <NUM>-<NUM> degrees. Preferably, the angle of divergence in downstream component <NUM> is less than the angle of convergence in upstream component <NUM>, as illustrated. Such structure is expected to prevent pressure loss. In addition, downstream component <NUM> should have slow change in area adjacent to entry <NUM> (closer to the renal vein) - any additional pressure loss will reduce the inferior vena cava flow rate and thus will reduce the effectiveness of the device. The angle of divergence in downstream component <NUM> may be constant or may change along the length of downstream component <NUM>. When the angle of divergence changes along the length (as shown in <FIG>, for example) the angle of divergence is preferably smallest (e.g., in a range from <NUM>-<NUM> degrees) adjacent to entry <NUM>. A slow change in the cross-sectional flow area adjacent to entry <NUM> is preferable because the fluid velocity decreases as the cross-sectional flow area increases, hence the pressure loss. Accordingly, the angle of divergence is smallest at entry <NUM> where the fluid flow is at maximum velocity within downstream component <NUM>.

Fluid modulator <NUM> of <FIG> may be formed from one frame that defines upstream component <NUM>, gap <NUM>, and downstream component <NUM>. In this example, upstream component <NUM> and downstream component <NUM> are each coated with a biocompatible material while gap <NUM> is created by an uncoated portion of the frame.

<FIG> shows flow modulator <NUM> of <FIG> implanted in the inferior vena cava at the renal veins. Upstream component <NUM> is in the inferior vena cava such that inlet <NUM> is upstream from a branch off to the left and right renal veins and downstream component <NUM> is in the inferior vena cava such that exit <NUM> is downstream from the branch off to the renal veins. While the right and left renal veins are usually at different heights along the inferior vena cava, gap <NUM> is generally positioned in the vicinity of the branches to the renal veins (or other branch lumens when used for other indications). For example, gap <NUM> may begin downstream from where the renal veins first intersect with the inferior vena cava, as illustrated. In addition, gap <NUM> may be entirely disposed within the intersection between the renal veins and the inferior vena cava, as illustrated. Outlet <NUM> of upstream component <NUM> may be positioned downstream from where the renal veins first intersect with the inferior vena cava, as shown. Accordingly, blood only enters fluid modulator <NUM> at inlet <NUM> and gap <NUM>, which is downstream from where the branch lumen first intersects the main lumen. Entry <NUM> of downstream component <NUM> may be positioned upstream from where the intersection of the renal veins and the inferior vena cava ends, as shown. Flow modulator <NUM> creates reduced pressure at gap <NUM> and increases blood flow velocity to gap <NUM>. Entrainment may also help transport blood to gap <NUM> from the kidneys. In this manner, the invention may draw blood from the kidneys to the renal veins and then to the inferior vena cava, thereby improving kidney functionality, reducing necrotic damage to the kidneys, and/or treating heart failure.

Reference is now made to <FIG>, which illustrate different flow modulators of the invention, in accordance with non-limiting embodiments of the present invention. Once again, like elements are designated by like numerals.

In <FIG>, flow modulator <NUM> is constructed similarly to fluid modulator of <FIG> although flow modulator <NUM> of <FIG> includes one or more openings <NUM> to prevent stagnant flow zones. Fluid entering fluid modulator <NUM> flows out of openings <NUM> and into the body lumen. Openings <NUM> act as flashing flow channels for fluid and may encompass the entire circumference of fluid modulator <NUM> or be ports. Upstream component <NUM> or downstream component <NUM> or both (as illustrated) may include one or more openings <NUM>. As shown, openings <NUM> may be on the converging portion of upstream component <NUM> and/or on the diverging portion of downstream component <NUM>. When openings <NUM> are utilized, they are preferably at least on downstream component <NUM> as downstream component <NUM> is preferably longer than upstream component <NUM>, making downstream component <NUM> more prone to a larger stagnant flow zone.

<FIG> is a cross-sectional view of fluid modulator <NUM> with a plurality of openings <NUM> that act as flashing flow channels.

<FIG> illustrates fluid modulator <NUM> where outlet <NUM> of upstream component <NUM> is positioned downstream from entry <NUM> of downstream component <NUM>. In this example, distance x is negative and D1 is larger than d1, e.g., at least <NUM> larger. As shown, outlet <NUM> and entry <NUM> may both be positioned downstream past the intersection of the branch lumen(s) and the body lumen.

<FIG> shows a manner for selecting the diameter D1 at entry of the downstream component <NUM> relative to the distance x from outlet <NUM> of upstream component <NUM> so as to receive all the fluid jetted from outlet <NUM>. As shown, D1 is greater for larger distances x to ensure receipt of the fluid jetted from upstream component <NUM>.

<FIG> illustrates fluid modulator <NUM> constructed similarly to fluid flow modulators <NUM> of <FIG> and <FIG>, although gap <NUM> is along a portion that extends radially outward from outlet <NUM> of upstream component <NUM>. Gap <NUM> is formed along a curved portion (e.g., S-shaped) between fluid flow structure <NUM> and outlet <NUM>. This curved portion allows downstream component <NUM> to be close to the branched lumen(s). In addition, fluid flow structure <NUM> is positioned downstream from the intersection between the branched lumen(s) and the body lumen for simplicity and additional anchoring support. Fluid modulator <NUM> may be formed from a common frame (e.g., a single stent design), which facilitates control of the distance x between outlet <NUM> and entry <NUM>. A single structure also facilitates co-axial orientation, especially for eccentric upstream and downstream components.

<FIG> illustrates flow modulator <NUM> constructed similarly to flow modulator <NUM> of <FIG>, although downstream component <NUM> includes curved portion <NUM> (e.g., S-shaped) that extends radially outward to contact the inner wall of the body lumen. A second curved portion downstream in downstream component <NUM> provides further radially force to enhanced anchoring within the body lumen and also gives a longer diffuser for a given length. Flow modulator <NUM> also may include an additional gap(s) so as to not block fluid flowing from other branched vessels, such as gap <NUM> at the downstream end of downstream component <NUM>.

Reference is now made to <FIG>, which illustrate flow modulators <NUM> with gap <NUM> positioned asymmetrically with respect to upstream component <NUM> and downstream component <NUM>. In other words, gap <NUM> is not positioned along the axis of the major vessel between upstream component <NUM> and downstream component <NUM>, but instead is offset towards one of upstream component <NUM> and downstream component <NUM>.

The left side structure of <FIG> may be the upstream or downstream direction, depending on the application; thus, the left side structure is labeled <NUM> or <NUM> and the right side structure is labeled <NUM> or <NUM>.

<FIG> illustrates a construction of either upstream component <NUM> or downstream component <NUM>, depending on the direction of flow. The structure includes relatively wide portion <NUM> which converges into relatively narrow portion <NUM>. Relatively narrow portion <NUM> extends into diverging portion <NUM> which serves as a sealing portion.

<FIG> illustrates another construction of either upstream component <NUM> or downstream component <NUM>, depending on the direction of flow. The structure of converging portion <NUM> includes surfaces that curve backward in the opposite direction.

<FIG> illustrate another construction of either upstream component <NUM> or downstream component <NUM>. In this construction, first stent member <NUM> may be installed with converging and diverging portions (<FIG>) and afterwards second stent member <NUM> may be installed over first stent member <NUM> to define a final converging and diverging shape. <FIG> may also be used as is, without the additional stent member. It is noted that the first stent member does not have to touch the second stent member (diffuser stent) and can be shorter than that shown in the drawings.

<FIG> illustrates an alternative design in which upstream component <NUM> is constructed of a plurality of discrete objects <NUM>, such as but not limited to, spheres, balloons, rods, and the like, which gradually increase in size to create the converging effect. Similarly, downstream component <NUM> may be constructed of a plurality of discrete objects <NUM>, such as but not limited to, spheres, balloons, rods, and the like, which gradually decrease in size to create the diverging effect. Discrete objects <NUM> may be optionally covered with membrane <NUM> to provide a smooth flow surface.

<FIG> illustrates flow modulator <NUM> of <FIG> installed in a body lumen <NUM>, such that gap <NUM> is situated at a bifurcation <NUM>.

<FIG> illustrates another embodiment of flow modulator <NUM> installed in the body lumen <NUM>, such that gap <NUM> is situated at bifurcation <NUM>. In this embodiment, fluid flow structure <NUM> includes extension <NUM> that is deployed in bifurcation <NUM>. The opening in the stent graft at the bottom of the device (in the sense of <FIG>; of course, it could be situated in a different location other than "bottom"), may be used instead of sleeve-like extension <NUM>. Alternatively, extension <NUM> may be used both at the top and the bottom, or an opening may be used at the top and bottom or any other combination.

<FIG> illustrates the flow modulator of one of the embodiments installed in the aortic arch, such that gap <NUM> is situated at the bifurcation of the carotid arteries. This installation may be used to reduce peak pressure gradients or to divert emboli away from the carotid arteries with very little pressure loss.

<FIG> illustrates a flow modulator installed near the kidneys. For example, upstream component <NUM> may be installed in the inferior vena cava just below (upstream to) the branch off to the renal vein and the downstream component <NUM> may be installed in the inferior vena cava just above (downstream to) the branch off to the renal vein. Gap <NUM> is at the branch to the renal vein. Flow modulator <NUM> creates a reduced pressure region in the vicinity of gap 14and increases blood flow velocity at gap <NUM>. Entrainment may also help draw blood into the gap from the kidneys. In this manner, the invention can draw blood from the kidneys to the renal veins and then to the inferior vena cava, thereby improving kidney functionality and reducing necrotic damage to the kidneys.

Reference is now made to <FIG>, which illustrates another construction of either upstream component or downstream component, depending on the direction of flow. The structure includes outer stent <NUM> and inner stent <NUM>. Outer stent <NUM> may be cylindrical. Inner stent <NUM> may include relatively wide portion <NUM> which converges into relatively narrow portion <NUM>. Relatively narrow portion <NUM> extends into slightly diverging portion <NUM> with very little energy losses. The two stents may be joined together (such as, but not limited to, by welding or other suitable technique) and at least partially coated with coating <NUM> (although they may be used as bare metal, uncoated stents as well). The order of the joining and coating processes may be joining before coating or coating before joining.

Reference is now made to <FIG>, which illustrates another version of the embodiment of <FIG>. In this version, outer stent <NUM> is shorter so that coating <NUM> coats over the end of outer stent <NUM>.

Reference is now made to <FIG>, which illustrates flow modulator <NUM>, in accordance with another non-limiting embodiment of the present invention. Flow modulator <NUM> includes pump <NUM>, such as but not limited to, an axial flow pump, centrifugal pump, booster pump, chopper pump and many others. Pump <NUM> may be secured in place by a stent or may be coupled to a portion of the upstream component <NUM> or downstream component <NUM>. Pump <NUM> may be located either downstream or upstream, depending on the particular application. Pump <NUM> may be used to augment blood flow and filtration, for example.

Any of the embodiments of the invention may serve to divert emboli or other debris, so there is no need to use an extra filtration device. One example is using the upstream component or downstream component at or near the carotid arteries to divert emboli or other debris.

Reference is now made to <FIG>, which illustrates flow modulator <NUM> (or any other flow modulator of the invention) installed in an aneurysm <NUM>. The flow modulator is installed through the blood vessel and lowers pressure at the aneurysm site, so as to help prevent the aneurysm from increasing in size or bursting, and perhaps decreasing the size of the aneurysm. The flow modulator works even without sealing against the aneurysm.

If there are one or more side branch lumens at or near the aneurysm site, the device reduces the pressure but also permits blood to flow to the side branches. This is in contrast to circular stent grafts of the prior art which disadvantageously block the side branches. If there are no side branches, then the device just reduces the pressure without increasing the blood flow.

A filter may be optionally used with the flow modulator to prevent embolic debris from flowing from the aneurysm to other blood vessels.

Reference is now made to <FIG>, which illustrates flow modulator <NUM>, in accordance with another non-limiting embodiment of the present invention. Flow modulator <NUM> includes upstream component <NUM> with outlet <NUM> and downstream component <NUM> which has an upstream divergent mouth entry <NUM>. Outlet <NUM> enters entry <NUM> and this area serves as gap <NUM>. Outlet <NUM> may be coupled with support <NUM> to a portion of downstream component <NUM>, for example, to center outlet <NUM> with respect to entry <NUM>. Alternatively, a separate stent structure (which does not hinder flow) may be used to support outlet <NUM>.

The straight portion in downstream component <NUM> may help straighten the flow before it is diffused and reduce flow separation form the diffuser wall, thereby reducing pressure losses.

<FIG> shows one example of flow modulator <NUM> installed in a renal application. In this example, upstream component <NUM> may be installed in the inferior vena cava upstream to the branch off to the renal vein and the downstream component <NUM> may be installed in the inferior vena cava downstream to the branch off to the renal vein. Outlet <NUM> is also downstream to the branch off to the renal vein. Similar to the embodiment of <FIG>, flow modulator <NUM> creates reduced pressure at outlet <NUM> in gap <NUM>, which increases blood flow velocity from the renal vein to the gap.

Reference is now made to <FIG>, which illustrates flow modulator <NUM>, in accordance with another non-limiting embodiment of the present invention. Flow modulator <NUM> includes upstream component <NUM> with outlet <NUM> and downstream component <NUM>. Upstream component <NUM> has first portion <NUM> which is not in-line with downstream component <NUM>, but is instead tilted relative thereto and which may be installed in a branch lumen, as shown in <FIG>. Outlet <NUM> may be directed to the center of the inlet to downstream component <NUM>. Outlet <NUM> may be coupled with support <NUM> to a portion of downstream component <NUM>, for example, to center the nozzle with respect to the inlet. Alternatively, a separate stent structure (which does not hinder flow) may be used to support outlet <NUM>.

Reference is now made to <FIG>, which illustrates lumen support member <NUM> installed with flow modulator <NUM>, in accordance with another non-limiting embodiment of the present invention. Lumen support member <NUM>, which may be a stent body, helps support the body lumen from collapsing inwards during reduced pressure.

Reference is now made to <FIG>, which illustrates that in any of the embodiments, upstream component <NUM> and/or downstream component <NUM> may not seal against the inner contour of the body lumen, but instead may be spaced from the inner contour of the body lumen. For example, this arrangement prevents blocking flow from a side branch <NUM>. Although this may create pressure losses, it still reduces pressure as compared to just using a nozzle, and it may improve flow out of the body lumen, such as improving flow out of a vein.

Reference is now made to <FIG>, which illustrates that the transition between upstream component <NUM> to downstream component <NUM> (the region of gap <NUM>) may be offcenter from the center line C-C of the body lumen. In such an embodiment, the transition between upstream component <NUM> to downstream component <NUM> is asymmetric with respect to the center line of the body lumen. For example, this may be used advantageously if there is only one side branch - the asymmetry will favor flow from the side branch; if there are two side branches, the asymmetry will favor flow from one of the side branches.

Reference is now made to <FIG>, which illustrate upstream component or downstream component <NUM>, whose shape is changeable in accordance with another non-limiting embodiment of the present invention. Upstream component and downstream component <NUM> may be combined to create a nozzle/diffuser configuration with a gap therebetween similar to the structures described throughout this disclosure.

Accelerator or decelerator <NUM> may include one or more inflatable members, such as end faces <NUM> and <NUM> coupled by intermediate member <NUM>, such as but not limited to, inflatable balloons or bladders, which can be inflated or deflated by introducing or extracting fluid into or from inflatable members <NUM> and <NUM> (connected to a suitable fluid source, such as water, saline, air, etc. Intermediate member <NUM> may be a cover material and/or may be preshaped (e.g., a cylindrical shape like a stent) thereby creating radial force on inflatable members <NUM> and/or <NUM> to create better sealing. Changing the size of inflatable members <NUM> and <NUM> changes the flow characteristics through the device. For example, one can change how much the device diverges or converges. Inflatable members <NUM> and <NUM> may be connected by longitudinal members <NUM>, which may also be inflatable and thus changeable in size, such as changeable in length or thickness.

The device may be deployed in the deflated state and then inflated in-situ. In the example where the upstream component and the downstream component are combined into one device, the respective inflatable members may be inflated/deflated simultaneously with a common lumen in a catheter or individually using a multi-lumen catheter. After the patient has reached a stable condition, the device may be deflated or inflated as needed to adapt to changing conditions. The device may be deflated for removal from the body. A reservoir of fluid may be implanted with the device for use in inflating the device after installation in the body. The device may be held against the inner walls of the body lumen or may be separated from them, as described above for other embodiments.

As is explained above, flow modulator <NUM> is sized and shaped to be implanted in a body lumen. Flow modulator <NUM> may be compressible for delivery (e.g., percutaneous delivery within a delivery sheath) and expandable upon deployment (e.g., self-expanding upon exposure from the distal end of the delivery sheath or balloon expandable).

Referring now to <FIG>, flow modulator <NUM> is shown in the compressed, delivery configuration within sheath <NUM> in accordance with another non-limiting embodiment of the present invention. Flow modulator <NUM> may be coupled to transition portion <NUM> and/or wire <NUM> to facilitate delivery to the body lumen and retrieval from the body lumen. Transition portion <NUM> illustratively has a non-concentric cone shape to facilitate compression into sheath <NUM> and is coupled to upstream component <NUM> although it may be coupled to downstream component <NUM>. Wire <NUM> is coupled to transition portion.

<FIG> show flow modulator <NUM> in the expanded, deployed configuration outside of sheath <NUM>. Flow modulator <NUM> may transition to the expanded, deployed configuration when exposed past the distal end of sheath <NUM>. For example, sheath <NUM> may be pulled proximally against a fixed stopper in sheath <NUM> to unsheath flow modulator <NUM> at a target location within a body lumen, e.g., where the renal veins intersect with the inferior vena cava.

Flow modulator <NUM> may be retrieved from the body lumen (e.g., inferior vena cava). For example, a sheath may be threaded over wire <NUM> and wire <NUM> may be fixed in place (e.g., ex vivo fixation of the proximal end of the wire). Then, the sheath is pushed against transition portion <NUM> to compress flow modulator <NUM> within the sheath. Flow modulator <NUM> and the sheath are then removed from the patient.

Referring now to <FIG>, flow modulator <NUM> is shown in accordance with another non-limiting embodiment of the present invention. Flow modulator <NUM> is similar to flow modulator <NUM> of <FIG>, although flow modulator <NUM> of <FIG> further includes retrieval mechanism <NUM>. Retrieval mechanism <NUM> may be coupled to the proximal end of upstream component <NUM> as illustrated. In this manner a retrieval device, e.g., hook <NUM>, may be coupled to retrieval mechanism <NUM> to pull retrieval mechanism towards sheath <NUM> to compress flow modulator <NUM> into sheath <NUM> for retrieval. For example, retrieval mechanism <NUM> may be configured like a snare with a plurality of arms coupled to the end of upstream component <NUM> and coupled together near the center of the flow path within upstream component <NUM>. Flow component <NUM> may be implanted with retrieval mechanism <NUM> coupled thereon or retrieval mechanism <NUM> may be coupled to flow modulator <NUM> during the retrieval process. Flow modulator <NUM> in <FIG> also includes retrieval mechanism <NUM> at an opposing end of flow modulator, e.g., coupled to the end of downstream component <NUM>. Retrieval mechanism <NUM> works in the same manner as retrieval mechanism <NUM>. Use of two retrieval mechanisms may be particularly helpful when flow modulator <NUM> is formed from a braided structure since the diameter of the structure decreases as the braid is lengthened. Retrieval mechanisms <NUM> and/or <NUM> may also be used for partial retrieval. For example, retrieval mechanism <NUM> and/<NUM> may be pulled (simultaneously or at different times) in a direction(s) away gap <NUM> to partially or fully reduce the diameter of flow modulator <NUM> within a body lumen. Such reduction would allow for washing of any stagnant flow zones created adjacent to flow modulator <NUM>. Flow modulator <NUM> could then be fully removed, repositioned within the body lumen and expanded, or expanded in the prior deployment location within the body lumen.

<FIG> show hook <NUM> coupled to retrieval mechanism <NUM> in the compressed state within sheath <NUM> and in the expanded state outside of sheath <NUM>.

Referring now to <FIG>, flow modulator <NUM> is shown in accordance with another non-limiting embodiment of the present invention. Flow modulator <NUM> is similar to flow modulator <NUM> of <FIG>, although flow modulator <NUM> of <FIG> further includes ring <NUM>. In this illustration, frame <NUM> is formed from a plurality of ribs and defines upstream component <NUM> and downstream component <NUM>. Frame <NUM> may be formed from a shape memory material such as shape memory metal. Frame <NUM> is coated with biocompatible material <NUM> at upstream component <NUM> and downstream component <NUM> to define the flow channels and the uncoated portion of frame <NUM> therebetween defines gap <NUM>. Ring <NUM> is disposed around a portion of frame <NUM> and maintains the portion disposed therein in a compressed configuration. For example, in the deployed state down in <FIG>, ring <NUM> is disposed around the portion of fluid modulator between upstream component <NUM> and downstream component <NUM> to cause frame <NUM> to form a converging cross-sectional flow area at upstream component <NUM> and a diverging cross-sectional flow area at downstream component <NUM>. Ring <NUM> is configured to move along frame <NUM> to transition the portions of frame <NUM> disposed within ring <NUM> from an expanded state to a contracted state. Shaft <NUM> may be coupled to ring <NUM> such that movement of shaft <NUM> moves ring <NUM> along frame <NUM>.

Flow modulator <NUM> is deliverable in a compressed state within a sheath to a target location within a body lumen. Once suitably positioned, flow modulator <NUM> is exposed from the sheath (e.g., by pulling the sheath proximally while flow modulator <NUM> remains in place) and flow modulator <NUM> self-expands to the deployed configuration. Flow modulator <NUM> may be partially retrieved (e.g., compressed to allow for washing) and/or fully retrieved by moving ring <NUM> proximally (e.g., by pulling shaft <NUM> proximally) to compress upstream component <NUM> or downstream component <NUM> to a diameter suitable for insertion within a sheath. The remaining portion of flow modulator <NUM> may then be compressed within the sheath and removed from the body via the sheath.

<FIG> illustrates a bench test used for determining the optimal configuration for a flow modulator constructed in accordance with the present invention. In the bench test, a flow modulator was placed in a main lumen (to simulate the inferior vena cava) such that the gap was positioned at a branch lumen (to simulate a renal vein). The bench model utilized a constant steady flow in the main branch and was connected to an over flow bath to maintain constant physiological pressure. Water was used for the fluid and blood analogue was used to verify the trends. A side branch pipe with a controlled resistance was connected to a lifted reservoir (to simulate renal filtration pressure). The resistance in the side branch was fixed in a rate to create a normal renal flow with a normal net filtration pressure. As a result, fluid flow was low when the pressure gradient between the renal bath to the main lumen was smaller.

Three pressure sensors (shown as P1, P2, and P3 in <FIG>) were connected to the simulated IVC (upstream to the side branch, at the side branch level, and downstream to side branch). A magnetic flow sensor was used to measure IVC flow. Renal flow was measured with a digital weight scale with a computer interface via rs232. Thus, mass flow rate can be measured (or flow rate since the density can be calculated) without creating additional pressure loss.

<FIG> is a graph showing the results for one representatives IVC flow rate (<NUM> liters per minute (L/min)). The graph shows renal flow in mL/min versus pressure difference in mmHg for various configurations shown in <FIG>. Data points <NUM> are for a nozzle and diffuser configuration (shown in <FIG>) based on the flow modulator principles described herein. In this example, the upstream nozzle has an outlet inner diameter of <NUM> and the downstream diffuser has an entry inner diameter of <NUM>. As shown in <FIG>, the renal flow is highest for this configuration and the table below shows that this nozzle and diffuser configuration create significantly less pressure loss than all other configurations. Data points <NUM> are for a single nozzle configuration (shown in <FIG>). The same upstream nozzle was used as the upstream nozzle in the nozzle and diffuser configuration. As shown in <FIG>, the renal flow is lower than the nozzle/diffuser configuration, but higher than the other configurations and the pressure loss of <NUM> mmHg shown in the table below is significantly larger than the pressure loss of the nozzle and diffuser configuration. Data points <NUM> are for baseline, meaning no device is used (shown in <FIG>). As shown in <FIG>, only the nozzle and diffuser configuration based on the principles of the present invention is significantly better than baseline. Data points <NUM> are for two nozzles in the same direction (shown in <FIG>). As shown in <FIG>, renal flow is actually negative, which would send blood flow in the renal veins in the wrong direction. In addition, the table below confirms the pressure loss of <NUM> mmHg is high. The same upstream nozzle was used as above and the downstream nozzle has an outlet inner diameter of <NUM>. Data points <NUM>, <NUM>, and <NUM> are for two nozzles in opposite directions for distances between the outlet of the upstream nozzle and the inlet of the downstream nozzle of <NUM> (shown in <FIG>), <NUM>, and <NUM>, respectively. The same upstream nozzle was used as above and the downstream nozzle has an inlet inner diameter of <NUM>. For data points <NUM> where the distance is <NUM>, similar to data points <NUM>, renal flow is actually negative, which would send blood flow in the renal veins in the wrong direction. In addition, the table below confirms the pressure loss of <NUM> mmHg is high. For data points <NUM> and <NUM>, the renal flow is around or worse than baseline and the pressure loss is high at <NUM> mmHg.

Thus, Applicant has discovered that using a maximum distance between the outlet of the upstream component and the entry to the downstream component will improve flow rates in the branched vessel(s) with relatively low pressure loss. A distance too great will create a significant pressure loss that actually sends flow in the wrong direction in the renal vein(s). In addition, other structural characteristics of the downstream component improve renal flow with low pressure loss such as a greater inner diameter at the entry of the downstream component than the inner diameter at the outlet of the upstream component, a greater length of the diverging area of the downstream component than the length of the converging area of the upstream component, and/or a lesser average angle of divergence of the downstream component than the average angle of convergence of the upstream component.

Claim 1:
An implantable device for altering fluid flow through a body lumen, the body lumen coupled to a branch lumen, the implantable device comprising:
a flow modulator (<NUM>, <NUM>, <NUM>) configured to be implanted within the body lumen, the flow modulator comprising an upstream component (<NUM>, <NUM>, <NUM>) separated by a gap (<NUM>, <NUM>) from a downstream component (<NUM>, <NUM>, <NUM>), the upstream component having an inlet (<NUM>), an outlet (<NUM>, <NUM>, <NUM>), and a cross-sectional flow area that converges from the inlet towards the outlet, the downstream component having an entry (<NUM>, <NUM>), an exit (<NUM>), and a cross-sectional flow area that diverges from the entry towards the exit, wherein the gap defines a pathway that communicates with the branch lumen,
wherein the flow modulator is configured to accelerate a fluid stream passing through the upstream component towards the downstream component to generate a low pressure region in the vicinity of the gap and to entrain additional fluid into the fluid stream as the fluid stream passes into the entry of the downstream component,
characterized in that, the cross-sectional flow area at the outlet of the upstream component is less than the cross-sectional flow area at the entry of the downstream component.