Abstract:
Embodiments of the invention are related to devices and methods for modulating renal function, amongst other things. In an embodiment, the invention includes a method of modulating renal function in a patient including implanting an occlusive device in the patient, the occlusive device comprising a semi-permeable membrane and configured to expand or contract based on the passage of a fluid across the semi-permeable membrane. Other aspects and embodiments are provided herein.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional application of prior U.S. application Ser. No. 11/772,397, filed Jul. 2, 2007, the contents of which are herein incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This disclosure relates generally to devices and methods for modulating renal function and, more particularly, to occlusive devices and methods for modulating renal function, amongst other things. 
     BACKGROUND OF THE INVENTION 
     The kidneys function to rid the body of metabolic and ingested waste products and to maintain the volume and composition of bodily fluids. The maintenance of a constant extracellular fluid (ECF) composition by the kidneys is accomplished by various neural, hormonal, and intrinsic homeostatic mechanisms that control the rate at which blood is filtered by the glomerulis, referred to as the glomerular filtration rate (GFR), and the extent to which sodium and water are reabsorbed from the filtrate into the peritubular capillary blood. 
     The kidneys normally act to maintain both arterial blood pressure and ECF volume within desired normal ranges. However, in certain pathological situations, homeostatic mechanisms do not respond in an appropriate manner. One situation in which the homeostatic mechanisms of the kidneys may not respond in an optimal manner is during heart failure. Heart failure refers to a clinical syndrome in which an abnormality of cardiac function causes a below normal or normal ejection fraction and pathophysiological ventricular hypertrophy which often results in reduction in cardiac output. Such a reduction in cardiac output can fall below a level adequate to meet the metabolic demand of peripheral tissues. Reduced cardiac output has a depressing effect on renal function due to decreased renal perfusion, which causes a reduction in salt and water excretion by the pressure natriuresis mechanism. The renin-angiotensin-aldosterone system also promotes water and plasma volume retention to compensate for the reduced cardiac output. The increased sympathetic activity in response to low blood pressure and/or cardiac output may also depress renal function still further. 
     The increased fluid retention by the kidneys results in an increased blood volume and further increased venous return to the heart, thus increasing the heart&#39;s preload. This process is acutely beneficial in supplementing and maintaining adequate cardiac output, however this process can result in deleterious changes long-term. Increased fluid retention causes the progressive peripheral and pulmonary edema that characterizes overt congestive heart failure. As part of downward spiral, diastolic filling pressure becomes further elevated which causes the heart to become so dilated and edematous that its pumping function deteriorates even more. 
     One approach to treating heart failure is to modulate renal function through pharmacological means. For example, diuretic drugs can be used to decrease the tubular reabsorption of salt and water, leading to reduced fluid retention (increased fluid excretion). However, such pharmacological agents are not always effective and they may cause significant side effects. In addition, patient compliance with pharmacological regimens is a serious problem. 
     For at least these reasons, a need exists for devices and methods for modulating renal function. 
     SUMMARY OF THE INVENTION 
     Embodiments of the invention are related to modulating renal function, amongst other things. In an embodiment, the invention includes an implantable occlusive device including a wall member defining an enclosed volume, the wall member comprising a semi-permeable membrane. The device can also include a solution comprising a solvent and a solute disposed within the enclosed volume of the wall member. The semi-permeable membrane can be permeable to the solvent and impermeable to the solute. The enclosed volume can be configured to expand in response to decreases in osmolality of a bodily fluid and contract in response to increases in osmolality of a bodily fluid. The device can include a positioning member configured to maintain the position of the implantable occlusive device relative to a lengthwise axis of a lymphatic vessel. 
     In an embodiment, the invention includes a method of modulating renal function in a patient including implanting an occlusive device in the patient, the occlusive device comprising a semi-permeable membrane and configured to expand or contract based on the passage of a fluid across the semi-permeable membrane. The method can further include occluding a renal lymphatic vessel with the occlusive device. 
     In an embodiment, the invention includes a method of treating heart failure decompensation including implanting an occlusive device in the patient, the occlusive device comprising a semi-permeable membrane and configured to expand or contract or change its shape based on the passage of a fluid across the semi-permeable membrane. The method can further include occluding a renal lymphatic vessel with the occlusive device. 
     This summary is an overview of some of the teachings of the present application and is not intended to be an exclusive or exhaustive treatment of the present subject matter. Further details are found in the detailed description and appended claims. Other aspects will be apparent to persons skilled in the art upon reading and understanding the following detailed description and viewing the drawings that form a part thereof, each of which is not to be taken in a limiting sense. The scope of the present invention is defined by the appended claims and their legal equivalents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more completely understood in connection with the following drawings, in which: 
         FIG. 1  is a schematic view of an occlusive device disposed within the lumen of a lymphatic vessel in accordance with an embodiment of the invention. 
         FIG. 2  is a schematic view of the occlusive device of  FIG. 1  in an expanded configuration. 
         FIG. 3  is a schematic view of portions of the renal lymphatic system. 
         FIG. 4  is a schematic view of an untethered occlusive device in accordance with an embodiment of the invention. 
         FIG. 5  is a cross-sectional schematic view as taken along line  5 - 5 ′ of  FIG. 4 . 
         FIG. 6  is a schematic view of the device of  FIG. 4  in a different configuration. 
         FIG. 7  is a schematic view of an occlusive device disposed within the lumen of a lymphatic vessel in accordance with another embodiment of the invention. 
         FIG. 8  is a schematic view of an occlusive device disposed within the lumen of a lymphatic vessel in accordance with another embodiment of the invention. 
         FIG. 9  is a schematic view of the occlusive device of  FIG. 8  is a different configuration. 
         FIG. 10  is a schematic view of an occlusive device with a sensor disposed within the lumen of a lymphatic vessel in accordance with another embodiment of the invention. 
         FIG. 11  is a schematic view of a monitoring device in conjunction with an occlusive device in accordance with an embodiment of the invention. 
         FIG. 12  is a schematic view of some aspects of a controller in accordance with an embodiment of the invention. 
         FIG. 13  is a schematic view of an occlusive device in accordance with another embodiment of the invention. 
         FIG. 14  is a cross-sectional view of the occlusive device of  FIG. 13  as taken along line  14 - 14 ′ of  FIG. 13 . 
         FIG. 15  is a schematic view of an occlusive device in accordance with another embodiment of the invention. 
         FIG. 16  is a schematic view of an occlusive device in accordance with another embodiment of the invention. 
         FIG. 17  is a schematic view of an occlusive device in accordance with another embodiment of the invention. 
         FIG. 18  is a schematic view of an occlusive device in accordance with another embodiment of the invention. 
         FIG. 19  is a schematic view of a multi-layer membrane structure in accordance with an embodiment of the invention. 
     
    
    
     While the invention is susceptible to various modifications and alternative forms, specifics thereof have been shown by way of example and drawings, and will be described in detail. It should be understood, however, that the invention is not limited to the particular embodiments described. On the contrary, the intention is to cover modifications, equivalents, and alternatives falling within the spirit and scope of the invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Blocking renal lymphatic flow can modulate renal function. Specifically, blocking renal lymphatic flow can decrease fluid retention by the kidneys, or stated differently, increase the amount of fluid excreted from the body as urine. This diuresis is typically the goal of diuretic pharmacological therapy. Embodiments of the invention can include devices that occlude the renal lymphatic vessels, thereby blocking or reducing renal lymphatic flow. As such, embodiments of the invention can be used to stimulate urine production and excretion by the kidneys (decrease fluid retention by the kidneys). Some embodiments can include treating disease states, such as heart failure and/or hypertension. 
     Embodiments of devices included herein can include those with an element that changes in physical dimensions through the process of osmosis. Osmosis is a physical process in which a solvent moves, without input of energy, across a semi-permeable membrane (permeable to the solvent, but not a solute) separating two solutions having different solute concentrations. Net movement of solvent is from the less-concentrated (hypotonic) solution, to the more-concentrated (hypertonic) solution. 
     Referring now to  FIG. 1 , a schematic view is shown of an occlusive device  100  disposed within the lumen  114  of a renal lymphatic vessel  108  in accordance with an embodiment of the invention. A wall member  102  including a semi-permeable membrane encloses an enclosed volume  106 . The wall member  102  is attached to a lead member  104  or tether. The lead member  104  can serve to maintain the position of the occlusive device  100  within the lymphatic vessel  108 . The lead member  104  can serve as one example of a positioning member since it can serve to maintain the position of the occlusive device relative to the lengthwise axis of the lymphatic vessel (axis of fluid flow) in which it can occlude fluid flow. The lengthwise axis of the renal lymphatic vessel  108  is indicated by arrowed line  101 . 
     A solution including a solvent and a solute is disposed within the enclosed volume  106 . In some embodiments, the solvent is water. The solute can include many different types of chemical compounds. In an embodiment, the solute is a biocompatible chemical compound. In an embodiment, the solute is a chemical compound naturally occurring within the body. In an embodiment, the solute is sodium chloride. In an embodiment, the solute is glucose. Further examples of solutes are described below. 
     The enclosed volume  106  can change in size as a result of osmosis. Specifically, where the solution within the enclosed volume  106  has a higher osmolality than the bodily fluid within the lumen  114  of the lymphatic vessel  108 , fluid can diffuse across the semi-permeable membrane and into the enclosed volume  106 , causing the same to enlarge. Conversely, where the solution within the enclosed volume  106  has a lower osmolality than the bodily fluid within the lumen  114  of the lymphatic vessel  108 , fluid can diffuse across the semi-permeable membrane and out of the enclosed volume  106 , causing the same to become smaller. Between about 280 and 303 mOsm/kg is a normal value of osmolality in fluids of the body. As such, in some embodiments, the solution within the enclosed volume has a starting osmolality of between about 280 and 303 mOsm/kg when the device is implanted within a patient. In other embodiments, the solution within the enclosed volume can have a starting osmolality outside of that range. 
     Though units of osmolality are used herein to describe concentrations of solutions, it will be appreciated that units of osmolarity could also be used. 
     In some embodiments, the enclosed volume  106  can swell from a first diameter  110  to a second diameter  112 . The closer the enclosed volume  106  approaches the size of the lymphatic vessel lumen  114 , the more it occludes the flow of fluid through the renal lymphatic vessel  108 . Complete or partial occlusion of the lymphatic vessel lumen  114  can result in modulating renal function so as to excrete more fluid, achieving a result similar to the administration of diuretic therapeutic agents. 
     Referring now to  FIG. 2 , a schematic view of the occlusive device of  FIG. 1  is shown in an expanded configuration. In this view, the enclosed volume  106  is expanded to a degree that the occlusive device  100  is now occluding substantially the entire lumen  114  of the renal lymphatic vessel  108 . It will be appreciated that the device  100  can be configured so that maximal expansion of the enclosed volume  106  occludes a particular percentage of the lumen of the renal lymphatic vessel  108 . For example, in some embodiments, the device can be configured so that it occludes a maximum of approximately 50% of the cross-sectional area of the lumen  114  of the renal lymphatic vessel when the enclosed volume  106  is fully expanded. In some embodiments, the device can be configured so that it occludes a maximum of approximately 70% of the cross-sectional area of the lumen  114  of the renal lymphatic vessel when the enclosed volume  106  is fully expanded. In some embodiments, the device can be configured so that it occludes a maximum of approximately 90% of the cross-sectional area of the lumen  114  of the renal lymphatic vessel when the enclosed volume  106  is fully expanded. In some embodiments, the device can be configured so that it occludes approximately 100% of the cross-sectional area of the lumen  114  of the renal lymphatic vessel when the enclosed volume  106  is fully expanded. 
     Occlusive devices in accordance with embodiments of the invention can be placed into various locations in the body in order to modulate renal function. Referring now to  FIG. 3 , a schematic view is shown of portions of the renal lymphatic system.  FIG. 3  shows a right kidney  152  and a left kidney  154 . Renal lymphatic vessels  158  can emerge from the kidney near the Hilar region  156  of the kidney. The renal lymphatic vessels  158  can serve to carry lymphatic fluid. The renal lymphatic vessels  158  can join together to form a renal lymphatic vessel trunk  160 . The renal lymphatic vessel trunk  160  passes the lymphatic fluid on to the thoracic duct  162 . One or more occlusive devices, as described herein, can be positioned appropriately to block or reduce the flow of lymphatic fluid through the renal vessels including individual vessels  158  and the vessel trunk  160  as well as the thoracic duct  162  itself. As used herein, the term “renal lymphatic vessel” shall include both the individual vessels and the vessel trunk. The occlusive devices can be placed inside of or adjacent to the individual vessels  158  or the trunk  160 . In some embodiments, an occlusive device can be positioned on or within the thoracic duct  162 . 
     In some embodiments, the occlusive device can be untethered. For example, the occlusive devices themselves can include a retention member to maintain their position within the lumen of a renal lymphatic vessel. Referring now to  FIG. 4 , an embodiment of an untethered occlusive device  200  is shown in accordance with an embodiment of the invention. The occlusive device  200  includes a wall member  202  that includes a semi-permeable membrane. The wall member  202  surrounds an enclosed volume  206 , separating the enclosed volume  206  from the lumen  214  of the renal lymphatic vessel  208 . A retention member  216  can be coupled to the wall member  202 . The retention member  216  can be configured to engage the inside surfaces  209  of the renal lymphatic vessel  208 . The retention member  216  can include one or more arms  217  or appendages. 
     Referring now to  FIG. 5 , a cross-sectional schematic view of the renal lymphatic vessel is shown as taken along line  5 - 5 ′ of  FIG. 4 . In this view, the retention member  216  can be seen engaging the inside surface  209  of the renal lymphatic vessel  208 . In some embodiments, the retention member  216  can be configured so that it exerts a force against the inside surface  209  of the renal lymphatic vessel  208 . 
     Referring now to  FIG. 6 , the retention member  216  can exhibit a degree of elasticity so that the arms  217  or appendages of the retention member  216  can be disposed against the wall member  202  to facilitate inserting the occlusive device  200  into a desired location within the renal lymphatic vessel system. For example, a sheath (not shown) can be disposed over the arms  217  when the occlusive device  200  is being inserted into the proper position. In this configuration, the effective diameter of the retention member is smaller than the diameter of the lumen  214 . Then, after the occlusive device has been maneuvered into the desired position, the sheath can be removed allowing the arms  217  to flex outwardly and engage the inside surface  209  of the renal lymphatic vessel  208 . 
     The retention member  216  can include many different materials. By way of example, the retention member  216  can include polymers, metals, metal alloys, ceramics, and the like. In some embodiments, the retention member  216  is a shape memory material, such as a shape memory metal. In an embodiment, the retention member  216  is the alloy nitinol. In the embodiment shown in  FIGS. 4-6 , the retention member  216  has two arms. However, it will be appreciated that in other embodiments the retention member can have a different number of arms. By way of example, the retention member can include three arms, four arms, or more than four arms. It will be appreciated that the retention member can also take on different shapes. By way of example, in some embodiments, the retention member can have a substantially annular shape. The retention member can also include a tubular mesh configuration similar to shape of vascular stents. The retention member can serve as an example of a positioning member since it can serve to maintain the position of the occlusive device relative to the lengthwise axis of the renal lymphatic vessel (axis of fluid flow) in which it can occlude fluid flow. 
     In some embodiments, the wall member of the occlusive device can include a non-permeable membrane (non-permeable to both solvents and solutes) in addition to the semi-permeable membrane. For example, the wall member can include a semi-permeable membrane in areas where it is desired to have fluids diffuse through and can include a non-permeable membrane in other areas. In some embodiments, a non-permeable portion of the wall member can be used to enhance the structural characteristics of the device. In addition, a non-permeable portion of the wall member can be used to control how the enclosed volume of the occlusive device expands, such as the direction in which it expands. 
     Referring now to  FIG. 7 , a schematic view is shown of an occlusive device disposed within the lumen  314  of a lymphatic vessel  308  in accordance with another embodiment of the invention. A wall member  302  including a semi-permeable membrane encloses an enclosed volume  306 . The wall member  302  is attached to a lead member  304 . The lead member can serve to maintain the position of the occlusive device. A solution including a solvent and a solute is disposed within the enclosed volume  306 . The wall member  302  can include a non-permeable portion  318  or patch (impermeable to both the solvent and the solute). In some embodiments, the non-permeable portion  318  is joined at its perimeter to the semi-permeable membrane. In some embodiments, the non-permeable portion  318  is disposed on top of the semi-permeable membrane. In some embodiments, the non-permeable portion  318  is adhered to the semi-permeable membrane, such as with an adhesive. In some embodiments, the non-permeable portion  318  is welded to the semi-permeable membrane. 
     In some applications it may be desirable to ensure that some percentage of the lymphatic vessel remains open to the flow of lymphatic fluid. As such, in some embodiments, an occlusive device can include a central lumen or channel that provides a passageway for lymphatic fluid, regardless of the state of expansion of the occlusive device. Referring now to  FIG. 8 , an embodiment of an occlusive device  350  with a channel is shown disposed within the lumen  364  of a lymphatic vessel  358  in accordance with an embodiment of the invention. A wall member  352  including a semi-permeable membrane encloses an enclosed volume  356 . A solution including a solvent and a solute is disposed within the enclosed volume  356 . 
     The wall member  352  is coupled to a channel member  362  defining a device lumen  366 . The channel member  362  can include a cylindrical-type shape, resisting deformation when the enclosed volume  356  expands and contracts. For example, the channel member  362  can include a polymeric or metallic tube. The device lumen  366  can serve as a passageway for lymphatic fluid regardless of the degree of expansion of the enclosed volume  356 . Referring now to  FIG. 9 , the occlusive device  350  of  FIG. 8  is shown in an expanded configuration. In this view it can be seen that enclosed volume  356  has expanded to the bounds of the interior of the lymphatic vessel  358  and that the device lumen  366  still provides a passageway for lymphatic fluid. The device lumen  366  can have a cross-sectional area as large as is desired for the specific application. In some embodiments, the device lumen  366  includes a cross-sectional area equal to at least about 5% of the total cross-sectional area of the lumen  364  of the lymphatic vessel  358 . In some embodiments, the device lumen  366  includes a cross-sectional area equal to at least about 10% of the total cross-sectional area of the lumen  364  of the lymphatic vessel  358 . 
     In some circumstances, it can be desirable to monitor the status of the occlusive device in vivo. In some embodiments, the occlusive device includes a sensor so that the status and degree of expansion of the occlusive device can be monitored. Referring now to  FIG. 10 , an occlusive device with a sensor  420  is shown disposed within the lumen  414  of a lymphatic vessel  408  in accordance with another embodiment of the invention. A wall member  402  including a semi-permeable membrane encloses an enclosed volume  406 . A solution including a solvent and a solute is disposed within the enclosed volume  406 . A sensor  420  can be in communication with the enclosed volume  406 . The wall member  402  is coupled to a lead member  404 . The lead member  404  can serve to maintain the position of the occlusive device. The lead member  404  can also include an electrical or an optical conductor in order to convey signals to or from the sensor  420 . 
     The sensor  420  can be configured to sense various properties that are indicative of the status and performance of the occlusive device. In some embodiments, the sensor  420  can be configured to sense pressure within the enclosed volume  406  of the occlusive device. The sensor  420  can include any type of pressure sensor, for example an electrical, mechanical, or optical pressure sensor, that generates a signal in response to pressure. By way of example, exemplary pressure sensors are described in U.S. Pat. No. 6,237,398, the content of which is herein incorporated by reference. 
     In some embodiments, the sensor  420  can be configured to sense the osmolality within the enclosed volume  406 . Generally, it is expected that the osmolality within the enclosed volume  406  will reflect the osmolality of the bodily fluid surrounding the occlusive device since fluid can diffuse through the semi-permeable membrane in order to equalize osmolalities. However, sudden large changes in osmolality can be indicative of dysfunction of the patient or of the device itself. As such, in some embodiments, signals from the sensor  420  can pass through the lead member  404  to a monitoring device which can be configured to monitor for changes in sensed osmolality. Many different types of osmolality sensors can be used. One example of an osmolality sensor is described in U.S. Pat. No. 5,388,449, the contents of which is herein incorporated by reference. 
     In some embodiments, the sensor  420  can be configured to sense the physical dimensions of enclosed volume  406 . For example, the sensor  420  can be configured to sense the diameter of the enclosed volume  406  and/or the length of the enclosed volume  406 . Specifically, the sensor  420  can include photosensor with a light source, such as a light emitting diode (LED), and a light receiver, such as a charge-coupled device (CCD), photodiode, a junction field effect transistor (JFET) type optical sensor, or a complementary metal-oxide semiconductor (CMOS) type optical sensor. The light source can generate an emission of light within the enclosed volume  406  that reflects off an opposing part of the wall member before being received by the light receiver. The larger the size of the enclosed volume  406 , the farther the light must travel and the greater the loss of light intensity due to diffusion. Therefore, the intensity of light received by the light receiver can be correlated to the size of the enclosed volume. It will be appreciated that this is merely one example of a sensor for detecting the physical dimensions of the enclosed volume and that there are also many other types of sensors that can also be used to sense the size of the enclosed volume. 
     In some embodiments, signals from the sensor can pass through the lead member to a monitoring device. Referring now to  FIG. 11  a schematic view of a system  500  including a monitoring device  530  in conjunction with an occlusive device  502  is shown in accordance with an embodiment of the invention. The monitoring device  530  can include a controller module  532 . The monitoring device  530  can be coupled to a lead  504  which is in turn coupled to an occlusive device  502  that includes a sensor. However, it will be appreciated that in some embodiments, the monitoring device  530  and the occlusive device  502  can be in wireless communication. 
     A remote monitoring device  534  can also be included and can be in wireless communication with the monitoring device  530 . For example, data regarding the occlusive device  502 , as stored by the controller  532 , can be wirelessly transmitted to the remote monitoring device  534 . The remote monitoring device  534  can be a patient management system. An exemplary patient management system includes the LATITUDE® patient management system, commercially available from Boston Scientific Corporation, Natick, Mass. Aspects of an exemplary patient management system are described in U.S. Pat. No. 6,978,182, the contents of which are herein incorporated by reference. 
     The controller  532  can include various electronic components and can be configured to process signals from a sensor within an occlusive device, including analyzing the signals and storing data regarding the signals. Referring now to  FIG. 12 , some aspects of a controller  532  are schematically illustrated. In this embodiment, the controller  532  includes a microprocessor  552  that communicates with memory  554  via a bidirectional data bus. The memory  554  typically comprises ROM or RAM for program storage and a RAM for data storage. The controller  532  can include a bidirectional occlusive device sensor channel interface  556 . In addition, the controller  532  can include a clock circuit  562 . The controller  532  can also include a telemetry interface module  564  for wireless communication of data into and out of the controller  532 . 
     In some embodiments, the invention can include occlusive devices configured to be disposed on the outside of renal lymphatic vessels. Referring now to  FIG. 13 , an embodiment of an occlusive device is shown in accordance with another embodiment of the invention. The occlusive device can include a wall member  602  defining an enclosed volume  606  (shown in  FIG. 14 ). The wall member  602  can include a semi-permeable membrane, examples of which are described in greater detail below. A semi-rigid support member  622  can be disposed around the outer perimeter of the wall member  602 . The semi-rigid support member  622  can serve to maintain the occlusive device in position around the renal lymphatic vessel  608 . The semi-rigid support member  622  can also serve as an example of a positioning member since it can serve to maintain the position of the occlusive device relative to the lengthwise axis of the renal lymphatic vessel  608  (axis of fluid flow) in which it can occlude fluid flow. 
     In some embodiments, the wall member  602  and the semi-rigid support member  622  can both have a shape similar to a ring with a gap  624  in the perimeter of the ring. This shape can also be referred to as a discontinuous annular shape. The occlusive device can be wrapped around a renal lymphatic vessel  608 . The gap  624  in the wall member  602  and the semi-rigid support member  622  can allow the ring-shaped device to be opened so that it can be positioned around the renal lymphatic vessel  608 . 
     Referring now to  FIG. 14 , a cross-sectional view of the occlusive device of  FIG. 13  is shown as taken along line  14 - 14 ′ of  FIG. 13 . As the support member  622  is semi-rigid, it serves to direct expansion of the enclosed volume  606  inward toward the lumen  614  of the renal lymphatic vessel  608 . In some embodiments, the support member can be made of a polymer or a metal. 
     However, some embodiments of occlusive devices configured to be disposed outside of renal lymphatic vessels can lack support members. For example, referring now to  FIG. 15 , an embodiment of an occlusive device is shown lacking a support member. The occlusive device can include a wall member  702  defining an enclosed volume. The wall member  702  can include a semi-permeable membrane, examples of which are described in greater detail below. The occlusive device can be wrapped around a renal lymphatic vessel  708 . A gap  724  in the wall member  706  can allow the device to be opened so that it can be wrapped around the renal lymphatic vessel  708 . 
     In some embodiments, the enclosed volume of the occlusive device can be filled with a solution including a solvent and a solute when the device is first manufactured. For example, in some embodiments, a solution with an osmolality of between about 280 and about 303 mOsm/kg is disposed within the enclosed volume when the device is initially manufactured. However, in other embodiments, the device can be configured so that it can be filled up with a solution having a desired solute concentration just before insertion into the patient. For example, in general, the use of solutions with higher concentrations of solute will result in greater initial swelling or enlargement of the enclosed volume of the device after it is positioned within the patient. As such, in some embodiments, the solute concentration of the solution can be manipulated by the clinician before implantation. For example, if the device is to be disposed within or around a particularly large renal lymphatic vessel, the starting osmolality of the solution within the enclosed volume can be increased so that there will be greater initial swelling or enlargement of the occlusive device. However, in other circumstances, where a smaller size is desired, a solution with a lesser concentration of solute can be inserted into the device before implantation into a patient. In some embodiments, a kit is provided including an occlusive device as described herein and a set of solutions with different solute concentrations, from which a health professional can select for use. 
     Referring now to  FIG. 16 , an embodiment of an occlusive device with an injection port is shown. The occlusive device can include a wall member  802  defining an enclosed volume. The wall member  802  can include a semi-permeable membrane, examples of which are described in greater detail below. A semi-rigid support member  822  can be disposed around the outer perimeter of the wall member  802 . An injection port  826  can be disposed on the wall member  802 . The injection port  826  can allow a syringe  828  to be inserted into the device to deliver a solution into the enclosed volume of the device. The injection port  826  can include a plug of material that self-seals to prevent leakage once the needle of the syringe  828  is withdrawn. For example, in an embodiment the injection port  826  can include a polymer with elastomeric properties. In an embodiment, the injection port  826  can include a polysiloxane polymer. 
     In some embodiments, an occlusive device can be disposed adjacent to a renal lymphatic vessel and can be configured to expand in a direction that results in occlusion of the renal lymphatic vessel. Referring now to  FIG. 17 , an occlusive device  850  is shown in accordance with another embodiment of the invention. The occlusive device  850  can include a wall member  852  defining an enclosed volume. The wall member  852  can include a semi-permeable membrane, examples of which are described in greater detail below. A semi-rigid support member  876  can be disposed around the inner perimeter of the wall member  852 . In some embodiments, the semi-rigid support member  876  can include a semi-permeable membrane. The occlusive device  850  can be wrapped around a first vessel  858 , which could be any type of vessel-like structure such as an artery or a vein. The enclosed volume can expand in the direction of arrow  878  as a result of changes in osmolality in the bodily fluid surrounding the device  850 . Expansion can occur to an extent that the device  850  exerts a force on an adjacent renal lymphatic vessel  880  and occludes the same. The semi-rigid support member  876  can prevent expansion of the enclosed volume from occluding the first vessel  858  and focus expansion in an outward direction. A harness  882  or strap can be included so as to prevent the adjacent renal lymphatic vessel  880  from simply moving away when the device  850  expands. The harness  882  can include a loop of material wrapped around the adjacent renal lymphatic vessel  880 . The harness  882  can also serve as an example of a positioning member since it can serve to maintain the position of the occlusive device relative to the lengthwise axis of the lymphatic vessel (axis of fluid flow) in which it can occlude fluid flow. 
     In some cases, it may be desirable to configure the device to be more directly responsive to changes in osmolality within arteries and/or veins. In some embodiments, the occlusive device can include a finger like projection or protruding member that passes from a wall member, through an aperture in the wall of an artery or vein, and into the interior lumen of the artery or vein. The projection can include a semi-permeable membrane and can be in fluid communication with an enclosed volume of the occlusive device. In some embodiments, other portions of the occlusive device are impermeable. As such, expansion and contraction of the occlusive device can be made to be particularly sensitive to changes in osmolality in plasma within the lumen of an artery or vein. 
     In some embodiments, over-expansion of the device can be controlled for purposes of safety. Various techniques and structures can be used to prevent over-expansion. For example, in an embodiment, an inflexible band can be disposed over the device, the inflexible band having a circumference corresponding to the maximum allowable size of the occlusive device. In another embodiment, the device can include a pressure release valve, the valve configured to open when a certain threshold pressure is reached inside of the occlusive device. Referring now to  FIG. 18 , an embodiment of an occlusive device with a pressure release valve is shown. The occlusive device can include a wall member  902  defining an enclosed volume. The wall member  902  can include a semi-permeable membrane, examples of which are described in greater detail below. A pressure release valve  926  can be disposed on the wall member  902 . The pressure release valve  926  can be configured to open when the pressure in the area enclosed by the wall member  902  exceeds a threshold amount. As such, the pressure inside of the enclosed volume is prevented from becoming so high that the wall member  902  could rupture or that the area enclosed by the wall member  902  becomes undesirably large. Many different types of pressure release valves  926  are known to those of skill in the art and can be used. 
     Semi-Permeable Membranes 
     Embodiments of the invention can include a semi-permeable membrane. The term “semi-permeable membrane” as used herein shall refer to a membrane that is permeable to a solvent but impermeable to one or more solutes, such that the semi-permeable membrane can be used in the process of osmosis. Exemplary solutes can include chemical compounds found within bodily fluids such as salts and their ions including calcium ions, sodium ions, potassium ions, chlorine ions, glucose and other carbohydrates, proteins (such as albumin), glycosaminoglycans, and the like. The term “impermeable” as applied to an article, such as a membrane, shall refer to one that substantially blocks the passage of one or more compounds through its substance. 
     It will be appreciated that semi-permeable membranes can be constructed of many different types of materials. For example, semi-permeable membranes can include polymers such as cellulose, cellulose derivatives, polyacrylonitrile, polysulfone, polycarbonates, polyamides, polymethylmethacrylate (PMMA), polyethylenes, polytetrafluoroethylene (PTFE), and polysiloxanes. In some embodiments, the semi-permeable membrane can include a hydrogel. The specific choice of material can depend on factors such as desired tear strength, desired flexibility, and the like. In an embodiment, the semi-permeable membrane includes a biocompatible material. 
     In some embodiments, the semi-permeable membrane can be porous. The pores can have a diameter large enough to allow for the passage of water molecules but small enough to prevent the passage of various solutes found in bodily fluids. 
     The semi-permeable membrane can have a thickness that is sufficient to provide strength to prevent tearing under the conditions of use. However, the semi-permeable membrane can be thin enough to maintain flexibility. In some embodiments, the semi-permeable membrane is between about 1 nanometer and about 2 millimeters in thickness. In some embodiments, a semi-permeable membrane can include multiple layers of material. For example, referring to  FIG. 19 , an embodiment of a multi-layer semi-permeable membrane  950  structure is shown. A first layer  972  is disposed beneath a second layer  974 . The first layer  972  and second layer  974  can include the same materials or different materials. In some embodiments, the first layer  972  is fastened to the second layer  974 . For example, an adhesive can be disposed between the first layer  972  and the second layer  974 . In some embodiments, the first layer  972  and the second layer  974  are thermally welded together, such as through ultrasonic welding or a similar technique. 
     In some embodiments, the semi-permeable membrane can have an irregularly shaped surface or various types of surface features such as dimples in order to increase its effective surface area. 
     It should be noted that, as used in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the content clearly dictates otherwise. It should also be noted that the term “or” is generally employed in its sense including “and/or” unless the content clearly dictates otherwise. 
     It should also be noted that, as used in this specification and the appended claims, the phrase “configured” describes a system, apparatus, or other structure that is constructed or configured to perform a particular task or adopt a particular configuration. The phrase “configured” can be used interchangeably with other similar phrases such as “arranged”, “arranged and configured”, “constructed and arranged”, “constructed”, “manufactured and arranged”, and the like. 
     All publications and patent applications in this specification are indicative of the level of ordinary skill in the art to which this invention pertains. All publications and patent applications are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated by reference. 
     This application is intended to cover adaptations or variations of the present subject matter. It is to be understood that the above description is intended to be illustrative, and not restrictive. The scope of the present subject matter should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.