Batteryless wireless sensor blood flow monitoring

Abstract

A two-in-one device configured to provide both remote flow monitoring and mechanical reinforcement of an arteriovenous fistula (AVF) in a single, implantable device. The device is configured for mechanical structural support, wrapped around a vein adjacent to the anastomosis, e.g., a connection made surgically between adjacent blood vessels. The mechanical support is made using a conductive material that may also act as an antenna. A pressure sensor is mechanically, and electrically connected to the mechanical support portion to sense blood flow. The device receives wireless power via the conductive mechanical support portion from a data acquisition device that is also configured to measure a characteristic of the circuit formed by the pressure sensor and the mechanical support. Using the measurements, the system may determine pressure in the supported blood vessel, which may help with early detection and treatment of stenosis.

Description

BATTERYLESS WIRELESS SENSOR BLOOD FLOW MONITORING

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 548,766, filed February 1, 2024, the entire content of which is incorporated herein by reference.TECHNICAL FIELD

[0002] The disclosure relates to implantable medical devices, and more specifically blood flow sensing by an implantable medical device.BACKGROUND

[0003] End stage renal disease (ESRD) is a healthcare condition in which the kidneys cease to function. Chronic kidney disease is one precursor to end stage renal disease. A treatment for ESRD patients is hemodialysis, in which a patient’s circulation is connected to a hemodialysis machine to filter the blood. Hemodialysis is an ongoing treatment required several times a week to replace the lost kidney functionality. To enable ongoing hemodialysis, a vascular access is required in which an artery is connected to a vein to generate high volume flow which can be readily accessed, e.g., cannulated. Some examples of vascular access surgery include an arteriovenous fistula (AVF) or arteriovenous graft (AVG).SUMMARY

[0004] In general, the disclosure describes a two-in-one device configured to provide both remote flow monitoring and mechanical reinforcement of an arteriovenous fistula (AVF) in a single, implantable device. Unlike mechanical support devices located within a blood vessel, such as a stent, which provides an outward radial force, the device of this disclosure is configured for external mechanical structural support, wrapped around a vein adjacent to the anastomosis, e.g., a connection made surgically between adjacent blood vessels. Such external support of an AVF, particularly of the highly compliant venous branch, may act to limit turbulent flow and wall tension resulting from high volume arterial flow through the formed anastomosis that can induce the onset of neoimtimal hyperplasia (i.e., stenosis).

[0005] The mechanical support is made using a conductive material that may also act as an antenna. A pressure sensor is mechanically, and electrically connected to the mechanical support portion to sense blood flow. The device receives wireless power via the conductive mechanical support portion.

[0006] While AVFs and AVGs provide a lifeline for hemodialysis patients, these procedures present challenges and complications such as stenosis and thrombosis that may reduce flow through the access. Successful AVF and arteriovenous graft (AVG) maturation, and long term patency, may benefit from careful monitoring and ongoing reintervention. An occluded vascular access may become an emergent situation as it prevents delivery of dialysis therapy to the patient. Some examples of interventions to restore patency may include balloon angioplasty, stent placement, and thrombectomy. In some examples a stenosis may not be identified until it advances to the point that dialysis cannot be performed, e.g., because of lack of blood flow. The ongoing monitoring with the implantable device and the system of this disclosure may provide early indication of stenosis or other complications and allow for early intervention to prevent more serious conditions.

[0007] In one example, the disclosure describes a device comprising: a pressure sensor, configured to be located adjacent to a blood vessel and to sense pressure in the blood vessel; and a coil comprising a conductive material, wherein the coil is configured to: electrically and mechanically connect to the pressure sensor and be located external to and adjacent to the blood vessel; wirelessly receive electrical power and conduct the electrical power to the pressure sensor; and mechanically support the blood vessel.

[0008] In another example, the disclosure describes a system comprising: an implantable medical device comprising: a pressure sensor configured to be located adjacent to a blood vessel and to sense pressure in the blood vessel; and a coil comprising a conductive material, wherein the coil is configured to be located external to and adjacent to the blood vessel; and mechanically support the blood vessel; data acquisition circuitry comprising a signal source and an antenna, wherein the data acquisition circuitry is configured to: wirelessly transfer electrical power to the implantable medical device from the antenna located external to the coil, and measure a characteristic of the implantable medical device, wherein the measured characteristic comprises information indicating the pressure in the blood vessel.

[0009] In another example, the disclosure describes a method comprising: transmitting, by data acquisition circuitry, wireless power to an implantable medical device, wherein the implantable medical device comprises: a pressure sensor configured to be located adjacent to a blood vessel and to sense pressure in the blood vessel; and a coil comprising a conductive material, wherein the coil is configured to be located external to and adjacent to the blood vessel; and mechanically support the blood vessel; measuring, by the data acquisition circuitry, a characteristic of the implantable medical device, wherein the measured characteristic comprises information indicating the pressure in the blood vessel.

[0010] The details of one or more examples of the disclosure are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the disclosure will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF DRAWINGS

[0011] FIG. 1 is a conceptual diagram of an example hemodialysis system and a patient.

[0012] FIG. 2 is a conceptual diagram illustrating an example configuration of an AVF support device with one or more pressure sensors, according to one or more techniques of this disclosure.

[0013] FIG. 3 is a conceptual diagram illustrating an example system including an AVF support device and pressure sensor according to one or more techniques of this disclosure.

[0014] FIGS. 4A and 4B illustrate a compression device for flow restriction.

[0015] FIG. 5A illustrates a location for placement of a compression device.

[0016] FIG. 5B illustrates the location of FIG. 5A having the compression device.

[0017] FIG. 6 illustrates another compression device for flow restriction.

[0018] FIGS. 7A-7D illustrate balloon supports for directionally focusing pressure from balloon of compression device.

[0019] FIGS. 8A and 8B are conceptual diagrams illustrating an example external compression device with a plastic bead.

[0020] FIGS. 9A-9C are conceptual diagrams illustrating an example external compression device with an adjustable mechanism for compression.

[0021] FIG. lOA is a schematic diagram illustrating an example system including an AVF support device and pressure sensor according to one or more techniques of this disclosure.

[0022] FIG. 10B is a block diagram illustrating functional principles of the operation of the system of this disclosure.

[0023] FIGS. 11 A, 11B, 11C, and 11D are conceptual diagrams illustrating example implementations of the coil of the AVF support device of this disclosure.

[0024] FIG. HE is a conceptual diagram illustrating the support feature, and antenna, of the AVF support device of this disclosure.

[0025] FIGS. 12A and 12B illustrate options for the location of the pressure sensor of this disclosure relative to the support feature.

[0026] FIG. 12C is a conceptual diagram of the AVF support device of this disclosure in the open and planar shape before implantation.

[0027] FIGS. 13A, 13B, and 13C are conceptual diagrams illustrating different options for locating the AVF support device of this disclosure relative to the AVF of the patient.

[0028] FIGS. 14A and 14B are conceptual drawings illustrating an example structure for a capacitive pressure sensor.

[0029] FIG. 15 is a flow chart illustrating an example mode of operation of the system of this disclosure.DETAILED DESCRIPTION

[0030] This disclosure describes arteriovenous fistula (AVF) mechanical support with batteryless wireless sensor for enhanced patency, blood flow monitoring, and early stenosis detection. A system of this disclosure includes a device configured for mechanical structural support, wrapped around a vein adjacent to the anastomosis. The mechanical support is constructed of a conductive material that may also act as an antenna. A pressure sensor is mechanically, and electrically connected to the mechanical support portion to sense blood pressure. The implantable device receives wireless power via the conductive mechanical support portion and may be surgically implanted around the AVF outflow vein at the time of fistula creation. The structure of the implantable devicebecomes a permanent implant, providing mechanical support to the vessel over time to promote a laminar flow profile and prolonged patency by managing hemodynamic stresses (e.g., turbulent flow, oscillating wall shear stress) that can promote inward vascular remodeling. The system receives output pressure from sensors on the implantable device via inductive coupling, where the signal (phase and return loss of the internal circuit) may be transferred to external receivers, where pressure data and flow data can be calculated based on the signals. The collected data may be available to the clinician, or other caregiver, enabling the caregiver to track blood flow in the vein of the fistula over time. Changes in flow may be an indication for deeper diagnostic evaluation and intervention to clear developing stenosis or other issues before hemodialysis therapy is disrupted.

[0031] FIG. 1 is a conceptual diagram of an example hemodialysis system and a patient 10. Hemodialysis system 100 includes a hemodialysis device 12 and AVF 40. The dashed arrows indicate the direction of blood flow 22 during a hemodialysis session.

[0032] A clinician (or other user, such as patient 10 or a patient caretaker) may fluidically connect arterial line 14 to an inflow port (not shown) on hemodialysis device 12 and to vasculature of patient 10, e.g., via AV fistula 40 or a synthetic AV graft (not shown) in patient 10 that provide access to the vasculature of patient 10. AV fistula 40 or the synthetic AV graft in the patient may be accessed, for example, via a needle or cannula. Arterial line 14 may be configured to facilitate the transport of blood from a vein of patient 10 to hemodialysis device 12. For example, blood from patient 10 may contain high levels of waste products due to kidney failure or kidney disease.

[0033] The clinician may also fluidically connect a venous line 16 to an outflow port (not shown) of the hemodialysis device 12 and to the vasculature of patient 10 (e.g., via AV fistula 40 or the synthetic AV graft). Venous line 16 may be configured to return relatively cleaner blood from hemodialysis device 12 to a vein of patient 10. The fluidic connections between hemodialysis device 12 and the vasculature via arterial and venous lines 14, 16, may be made via one or more cannulas, needles, or the like, that are inserted into a blood vessel structure of the patient.

[0034] Hemodialysis device 12 is configured to remove waste products from the blood received via arterial line 14. For example, hemodialysis device 12 may include a dialyzer 26 and / or one or more filters that may remove waste products and excess fluid from theblood received via arterial line 14. In some examples, dialyzer 26 may use a dialysate solution to remove the waste products and excess fluid from the blood of patient 10.

[0035] FIG. 2 is a conceptual diagram illustrating an example configuration of an AVF support device with one or more pressure sensors, according to one or more techniques of this disclosure. In the example of FIG. 2, AVF support device 200 may be used for fistula support to limit vessel distention resultant from pulsatile arterial flow and may result in enhanced patency of the fistula, with a batteryless and wireless sensor for blood flow monitoring and early stenosis detection. AVF support device 200 may offer both remote flow monitoring and mechanical reinforcement of an AVF in a single, implantable device.

[0036] In the example of FIG. 2, AVF support device 200 includes mechanical support 202, which is configured to be wrapped around vein adjacent to the anastomosis.Mechanical support 202 is made of a conductive material that may also act as an antenna to wirelessly receive power from a power transmitting device (not shown in FIG. 2). In some examples, mechanical support 202 may be implemented using NiTi alloys or other shape memory material. NiTi alloys are nickel -titanium alloys that may also be referred to as nitinol. In other examples, mechanical support 202 may be implemented using drawn filled tubing (DFT) techniques (or similar multi-material wire fabrication technology) with a core made of any of platinum (Pt), platinum-iridium (Pt / Ir), gold (Au), silver (Ag), or other similar conductive material that also has high electrical conductivity. In other examples, mechanical support 202 may be implemented with multiple layers, such as DFT with another dielectric layer (polymer or ceramic layer) in between NiTi and the conductive core for the protection of short circuit. Mechanical support 202 may be fabricated as drawn, extruded, laser cut, or other similar techniques.

[0037] In the example of a shape memory material, mechanical support 202 may be a self wrapping device, configured to be planar, or nearly planar at low temperatures and to self wrap around the vein of the patient at body temperature. An average human body temperature may be approximately 98.6 °F (37 °C). But normal body temperature can range between 97 °F (36.1 °C) and 99 °F (37.2 °C) or more at rest. In other examples, mechanical support 202 may be implemented as a clamping assisted device, in which the device may be open and substantially planar prior to being surgically implanted. Mechanical support 202 may include one or more ancillary wrapping fixtures 208 to assist mechanical support 202 to wrap around the blood vessel and stay in place when implanted,as well as limit vessel distention under pulsatile flow. In some examples, the clamping assisted implementation of mechanical support 202 may be fabricated using cobaltchromium (Co-Cr) alloys such as MP35N and may also be drawn, extruded, laser cut or some similar fabrication process. In some examples, ancillary wrapping fixtures 208 may include hooks or some other type of clamp.

[0038] In some examples, mechanical support 202 may be arranged as a coil and the coil may be mechanically and electrically connected to one or more pressure sensors, e.g., 204 and 206. In some examples, AVF support device 200 may have a single pressure sensor, e.g., pressure sensor 204. In other examples, AVF support device 200 may include at least two pressure sensors, e.g., both pressure sensors 204 and 206. In the example of two or more pressure sensors, mechanical support 202 may have a single coil that is electrically connected to each of pressure sensors 204 and 206, where each sensor is connected to a portion of the full coil length. In other examples, each pressure sensor may be electrically connected to a respective separate coil, where each coil may be mechanically coupled, but separated electrically to separately power and register each separate pressure sensor. In some examples, collecting data from two different pressure sensors and two different locations on the vein of the AV fistula may deliver differential pressure information that may be used to calculate flow rate.

[0039] In some examples, pressure sensors 204 and 206 may change physical properties based on the pressure applied to the pressure sensor. For example, pressure sensors 204 and 206 may be implemented using pressure sensitive capacitance, such that as the pressure applied to either of pressure sensors 204 or 206 changes, the capacitance of pressure sensors 204 or 206 may change. Because mechanical support 206 is a conductor, mechanical support 202 may have some inherent resistance, as well as inherent inductance. Because mechanical support 202 may be formed as a coil antenna, mechanical support 202 may also have inductance based on the dimensions of the coil. In this manner the mechanical support 202, electrically connected to a pressure sensitive capacitance pressure sensor, e.g., pressor sensor 204, may form an LC circuit.

[0040] FIG. 3 is a conceptual diagram illustrating an example system including an AVF support device and pressure sensor according to one or more techniques of this disclosure. AVF support device 302 may support the maturation of an AVF for patient 10 to be used in hemodialysis as described above in relation to FIG. 1.

[0041] In the example of system 300 of FIG. 3, data acquisition circuitry 308 may be electrically connected to receiving antenna 306. Data acquisition circuitry 308 may also be electrically connected to computing device 310, which may include processing circuitry 312. Computing device 310 may further connect to user interface 314, which may include a display device. In the example of FIG. 3, computing device 310, data acquisition circuitry 308 and user interface 314 are shown as separate components. In other examples, not shown in FIG. 3, computing device 310, data acquisition circuitry 308 and user interface 314 may be combined into a single unit connected flexibly with antenna 306.

[0042] Data acquisition circuitry 308 is configured to output a signal via antenna 306 and measure of the return loss (SI 1) vs frequency, to obtain the phase and resonance frequency. At each single time point data acquisition circuitry 308 will have an output (e.g., an entire SI 1 vs f curve) The system may deduct the resonance frequency (e.g., fl, f2, f3), corresponding to each time. The resonant frequency of the internal circuit is associated with the capacitance of the pressure sensor (passive capacitive pressure sensor). Thus the local pressure can be calculated. The received signal has high time resolution, where data can be output as the pressure waveform vs. time. Characteristic pressure waveform may be associated with the disease states, including postimplantation complications such as lesion development. On the other hand, a standard pressure waveform without abnormal vessel compliance can be associated to fistula maturation.

[0043] Said another way, data acquisition circuitry 308 is configured to both wirelessly transfer power to AVF support device 302 and to measure the response of the pressure sensors electrically connected to the antenna portion of AVF support device 302, e.g., via inductive coupling. In some examples, data acquisition circuitry 308 may include network analyzer circuitry, such as vector network analyzer (VNA) circuitry. The “network” in network analyzer circuitry refers to an electrical network rather than a wired or wireless computer device network. The network analyzer circuitry of data acquisition circuitry 308 may be used to measure a characteristic of AVF support device 302, including impedance. At low frequencies, such as direct current (DC), impedance, or resistance may follow Ohm’s Law, e.g., Z = V / I, or impedance equals voltage divided by current. However, at higher frequencies network analyzer circuitry may measure both phase and magnitude related measurements by determining, in some examples, incidentwave, reflected wave and transmitted wave, and use these measurements to determine different parameters, such as S-parameters (Sil, SI 2, S21 and S22) and resonance frequency. In this manner, by transferring power to AVF support device 302, and measuring the response of the LC circuit comprising the pressure sensor and coil of AVF support device 302, system 300 may determine the pressure of the blood vessel supported by AVF support device 302.

[0044] In some examples, AVF support device 302 may include two or more pressure sensors. In other examples, two or more AVF support devices 302 may be implanted to support the vein of the AVF for patient 10. By determining the pressure of two or more pressure sensors, system 300 may determine a pressure differential and calculate a blood flow rate through the supported vein of the AVF.

[0045] Computing device 310 may include processing circuitry 312 and memory 316 and be configured to communicate with data acquisition circuitry 308. In some examples, processing circuitry of computing device 310 may receive data from data acquisition circuitry 308 and determine pressure, blood flow rate, and other biological parameters of patient 10. Computing device 310 may communicate with user interface 314 to display measured parameters from patient 10. In some examples, computing device 310 may also calculate and display measured parameters trends, charts, may compare measurements to one or more thresholds and output an alert if the measurements fall outside of a predetermined range, and perform other functions related to the measurements from patient 10. In some examples, the computing device may output an alert to a caregiver for patient 10 via servers 318 in response to the comparison satisfying a threshold. In this disclosure, to “satisfy” a threshold may include a measurement that exceeds the threshold, is less than a threshold, within a predetermined range, or outside of a predetermined range.

[0046] Examples of processing circuitry 312 in computing device 310 may include any one or more of a microcontroller (MCU), e.g. a computer on a single integrated circuit containing a processor core, memory, and programmable input / output peripherals, a microprocessor (pP), e.g. a central processing unit (CPU) on a single integrated circuit (IC), a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a system on chip (SoC) or equivalent discrete or integrated logic circuitry. A processor may be integrated circuitry, i.e., integrated processing circuitry, and that the integrated processing circuitry may berealized as fixed hardware processing circuitry, programmable processing circuitry and / or a combination of both fixed and programmable processing circuitry. Accordingly, the terms "processing circuitry," “processor” or “controller,” as used herein, may refer to any one or more of the foregoing structures or any other structure operable to perform techniques described herein.

[0047] Examples of memory 316 may include any type of computer-readable storage media. Some examples may include random access memory (RAM), read only memory (ROM), programmable read only memory (PROM), erasable programmable read only memory (EPROM), one-time programable (OTP) memory, electronically erasable programmable read only memory (EEPROM), flash memory, or another type of volatile or non-volatile memory device. In some examples the computer readable storage media may store instructions that cause the processing circuitry to execute the functions described herein. In some examples, the computer readable storage media may store data, such as configuration information, temporary values and other types of data used to perform the functions of this disclosure.

[0048] In some examples, data acquisition circuitry 308 and servers 318 may also include processing circuitry and memory (not shown in FIG. 3). Computing device 310 may be configured to communicate with servers 318. Servers 318 may include one or more computing devices configured to communicate via wired or wireless networking and may include offsite computing devices. In some examples, servers 318 may receive the measurements, alerts, trends and other information from computing device 310 and transmit the information to a caregiver for patient 10.

[0049] In some examples, system 300 may include a fixation device, such as compression bandage 304. In some examples, antenna 306 may be part of compression bandage 304 or be configured to attach to compression bandage 304 while measuring patient parameters from AV support device 302. In this manner, patient 10 need not hold antenna 306 proximal to the location of AV support device 302.

[0050] In some examples, compression bandage 304 may also perform the function of diverting blood flow from one blood vessel to another. In this manner, may improve the maturation of a new AVF for patient 10. Compression bandage 304 may also be useful during dialysis, e.g., described above in relation to FIG. 1, to adjust blood flow.

[0051] Split flow between superficial outflow veins enhances long term patency of the fistula by reducing the shear stress on the walls of the outflow veins and lowering the pressure within the fistula circuit. While there are documented benefits of split outflow, the reduced shear stress may delay or impair maturation of a single target vessel in a newly created AVF. Sufficient blood flow through the maturing vein may be desirable to achieve flow-driven vascular remodeling to enable hemodialysis therapy. In some examples, compression bandage 304 of this disclosure may increase the success rate of fistula maturation in fistulas with multiple outflows without the need for secondary interventions. As noted above, in some examples, compression bandage 304 may temporarily divert flow into a single vessel to promote maturation but spare alternative vessels for potential future vascular access (e.g., avoid fully shutting off blood vessels such that flow cannot be restored). Once a vessel is matured, flow in the secondary vessel(s) may be restored by removing or reconfiguring compression bandage 304, which may enable dual outflow and limiting stresses on the new fistula.

[0052] In some examples, compression bandage 304 may restrict flow through a target vessel or vessels to facilitate maturation of an AVF by promoting greater blood flow through the intended outflow vessel. The greater blood flow may drive flow-driven vascular remodeling.

[0053] In some examples, compression bandage 304 may be applied external to the skin, such that it is non-invasive. Compression bandage 304 may be placed, manipulated, and removed by a clinician or patient. External application in this manner may enable temporary and reversible flow reduction. In addition to the antenna fixation function described above, compression bandage 304 may include a flow restriction element and a securement element, which may be any of several forms.

[0054] FIGS. 4A and 4B are examples of compression device 320 for flow restriction. Compression device 320 is an example of compression bandage 304 of FIG. 3. As illustrated, compression device 320 includes adhesive patches 321A and 321B for attaching compression device 320 to the patient. Compression device 320 includes inflatable balloon 325, illustrated in a deflated state in FIG. 4A and in an inflated state in FIG. 4B. As illustrated in FIG. 4B, when inflated, inflatable balloon 325 applies a force F against the skin of the patient. Compression device 320 may also include a rigid balloon support 322 to support the balloon 325 being in the inflated state.

[0055] FIG. 5A illustrates a location for placement of a compression device. For instance, FIG. 5A illustrates target flow restriction zone 326 which is an area on the patient where compression is to be applied. FIG. 5B illustrates the location of FIG. 5A having compression device 320. For instance, balloon 325 may be inflated to apply pressure at target flow restriction zone 326.

[0056] FIG. 6 illustrates compression device 327. Compression device 327 may be substantially similar to compression device 320 of FIGS. 4A and 4B, but may include two inflatable balloons 328A and 328B. To support inflation, compression device 327 may include two rigid balloon supports 329A and 329B to support balloons 328A and 328B, respectively, being in an inflated state.

[0057] FIGS. 7A-7D illustrate balloon supports for directionally focusing pressure from balloon of compression device. For example, in FIGS. 7A and 7B, balloon support 330A may be configured to support the inflation of balloon 325. In FIG. 7A, ballon 325 is in a deflated state, and when inflated, as illustrated in FIG. 7B, balloon support 330A causes balloon 325 to exert force F, as illustrated. In FIGS. 7C and 7D, balloon support 330B may be configured to support the inflation of balloon 325. In FIG. 7C, ballon 325 is in a deflated state, and when inflated, as illustrated in FIG. 7D, balloon support 330B causes balloon 325 to exert force F, as illustrated.

[0058] FIGS. 8A and 8B are conceptual diagrams illustrating an example external compression device with a plastic bead. For instance, FIG. 8 A illustrates compression device 331 that includes a plastic bead 332. As illustrated in FIG. 8B, plastic bead 332 may exert a force F.

[0059] FIGS. 9A-9C are conceptual diagrams illustrating an example external compression device with an adjustable mechanism for compression. For instance, FIG. 9A illustrates compression device that includes adjustable mechanism 334. As illustrated in FIGS. 9B and 9C, adjustable mechanism 334 may be a screw. In FIG. 9B, adjustable mechanism 334 is illustrated in an unscrewed state. In FIG. 9C, adjustable mechanism 334 is illustrated in a screwed state, and illustrated as applying a force F.

[0060] Accordingly, in some examples, flow restriction elements may be any of an inflatable balloons 325, 328A, or 328B enabling directionally focused pressure (FIGS. 4A, 6, and 7A-7D), a plastic bead 332 for direct mechanical compression (FIGS. 8A and 8B), or an adjustable screw 334 (FIGS. 9A-9C), or cam mechanism. Attachment elements maybe any one of an elastic band secured around the wrist or arm, an adjustable cuff, or an adhesive patch.

[0061] In some examples, after vascular remodeling has occurred and the AVF has matured, a patient may begin routine hemodialysis therapy. Administration of hemodialysis may benefit from a minimum flow rate to effectively filter the blood. In an example in which there is insufficient flow into the intended cannulation vessel, compression bandage 304 could be applied in the manner described above to temporarily divert flow away from other vessels and into the target vessel. This temporary application could be removed once the dialysis session is completed to restore the baseline flow.

[0062] In other examples, compression bandage 304 may be used for the treatment of steal syndrome, in which the AVF access diverts too much arterial flow and causes insufficient perfusion of blood to the forearm and hand, leading to distal ischemia. In this instance, the compression bandage 304 may be applied to the AV access to reduce the arterial steal and maintain a sufficient flow volume into the distal arteries, limiting symptoms.

[0063] FIG. lOA is a schematic diagram illustrating an example system including an AVF support device and pressure sensor according to one or more techniques of this disclosure. System 400 in the example of FIG. 10A is an example of system 300 described above in relation to FIG. 3. In some examples, external detector 408 may connect to a computing device as shown in FIG. 3 (not shown in FIG. 10 A).

[0064] External detector 408 is an example implementation of data acquisition circuitry shown in FIG. 3. Antenna 406 is an example of antenna 306 of FIG. 3. External detector 408 includes signal source 410 connected to antenna 406 through a modeled detector resistance 404. Signal source 410 may be an alternating current (AC) source and may cause antenna 406 to generate a magnetic field. As with any circuit that operates at some frequency above DC, external detector 408 may also include some parasitic capacitance (not shown in FIG. 10A).

[0065] Electrical power from signal source 410 may inductively couple to coil 412 of fistula support and pressure sensor 402. Fistula support and pressure sensor 402 is an example of AVF support device 200 and 302 described above in relation to FIGS. 2 and 3. In the example of FIG. 10A, fistula support and pressure sensor 402 includes a single pressure sensitive capacitance 416 electrically connected to coil 412. As described abovein relation to FIGS. 2 and 3, in addition to acting as an antenna to receive the wireless power from external detector 408, coil 412 may be arranged surrounding a vein of a fistula to provide support for the fistula (not shown in FIG. 10A).

[0066] Pressure sensitive capacitance 416 may be located adjacent to the vein such that changes in venous pressure may change the amount of pressure felt by pressure sensitive capacitance 416, and cause a change in the capacitance of pressure sensitive capacitance 416. External detector 408 includes circuitry configured to detect changes in resonant frequency of fistula support and pressure sensor 402 via coil 412 and determine a pressure in the vein of the patient based on the frequency of the LC circuit of fistula support and pressure sensor 402.

[0067] FIG. 10B is a block diagram illustrating functional principles of the operation of the system of this disclosure. The example of FIG. 10B illustrates functional principles of system 300 and system 400 described above in relation to FIGS. 3 and 10A. The blocks of FIG. 10B will be described in terms of FIG. 10 A.

[0068] A signal source, e.g., signal source 410, may output an AC signal that causes transcutaneous wireless power transfer to the AVF support device of this disclosure, e.g., AVF support device 200 of FIG. 2 via inductive coupling. The electrical power received by the AVF support device, e.g., fistula support and pressure sensor 402 of system 400, powers the operation of pressure sensitive capacitance 402 for FIG. 10 A.

[0069] As the vessel pressure (450) changes, pressure sensitive capacitance (452) changes. In an example in which two pressure sensors are located on the AVF vein (not shown in FIG. 4B), the pressure difference may also allow detection of blood flow, as described above in relation to FIG. 3.

[0070] As the pressure sensitive capacitance (452) changes, the LC circuit resonance frequency (454) will change. External detector 408, e.g., data acquisition circuitry 308 of FIG. 3, may detect the resonance frequency change. System 300 of FIG. 3 may use the measured resonance frequency to determine the blood pressure at the pressure sensor.

[0071] FIGS. 11 A, 1 IB, 11C and 1 ID are conceptual diagrams illustrating example implementations of the coil of the AVF support device of this disclosure. FIG. 11 A illustrates an octagonal coil, FIG. 1 IB illustrates a hexagonal coil, FIG. 11C illustrates a rectangular coil and FIG. 1 ID illustrates a circular coil. All these implementations may have associated dimensions, including outside diameter, Dout 502, inside diameter Din508, spacing between wraps S 506, and width 504, which is only shown on FIG. 1 ID to simplify the description.

[0072] FIG. HE is a conceptual diagram illustrating the support feature, and antenna, of the AVF support device of this disclosure. As described above in relation to FIG. 2, the AVF support device may be implemented using a variety of materials. Some examples of materials include memory materials that take the wrapped shape shown in FIG. 1 IE at body temperature, but may be open and planar, e.g., flat, as shown in FIGS. 11 A - 1 ID at different temperatures. In some examples, the AVF support device of this disclosure may include one or more fasteners 510 used to hold the support feature in the wrapped shape around the vein of the AVF of the patient.

[0073] FIGS. 12A and 12B illustrate options for the location of the pressure sensor of this disclosure relative to the support feature. Pressure sensor 600 is electrically connected to both ends of the coil. FIG. 12A depicts pressure sensor 600 located near the center of the coil. FIG. 12B depicts the pressure sensor 600 located near the outside of the coil.

[0074] FIG. 12C is a conceptual diagram of the AVF support device of this disclosure in the open and planar shape before implantation. FIG. 12C is an edge view of the top down view FIG. 12B described above. FIGS. 11 A - 1 ID and FIG. 12A also depict the AVF support device of this disclosure in the open and planar shape. In contrast, FIGS. 2 and 1 IE show the AVF support device in a shape configured to conform to the shape of the outer surface of a blood vessel, e.g., as shown in FIG. 8B. In this disclosure, the coil portion 604 of the AVF support device when “open and planar” may be described as flat, or approximately flat and within a plane 608. In some examples plane 608 may have a flatness from about ten micrometers to about three millimeters, where flatness includes the difference between the highest and lowest point on a plane after best fitting all points to a perfect plane.

[0075] FIGS. 13A, 13B, and 13C are conceptual diagrams illustrating different options for locating the AVF support device of this disclosure relative to the AVF of the patient. FIG. 13 A illustrates AVF support device 702 located to support the vein of an end-to-end AVF. FIG. 13B illustrates AVF support device 704 located to support the vein of a side to end AVF. In the example of FIG. 13B, AVF support device 704 may have tapered geometry 710 to conform to the orientation of the AVF. In all three figures, the support device is depicted wrapped around the vein rather than the artery. This is because thevenous segment is the portion requiring vascular remodeling to support hemodialysis (i.e., AVF maturation) and is the portion more prone to developing stenosis based on the hemodynamic profile of the arterial inflow. In some cases, a separate structure may also be placed around the arterial segment. As described above in relation to FIGS. 2 - 12B, the AVF support device of FIGS. 13A - 13C also includes at least one pressure sensor (not shown in FIGS. 13 A - 13C). The example of FIG. 13C shows a side to end AVF with an extra securement device 706 to retain AVF support device 708 in place.

[0076] FIGS. 14A and 14B are conceptual drawings illustrating an example structure for a capacitive pressure sensor. FIG. 14A is a conceptual diagram illustrating an example capacitive pressor sensor 802A that includes fins 804. Pressure sensor 802A and pressure sensor 802B are examples of pressure sensors 204 and 206 of FIG. 2. An increasing of distance between fins can increase capacitance of the sensor.

[0077] FIG. 14B shows pressure sensor 802B located adjacent to blood vessel 810. As the pressure in blood vessel 810 changes, the wall of blood vessel 810 may press against pressure sensor 802B. As shown in FIG. 14A, as blood vessel 810 pushes against pressure sensor 802A, length 806 may change, which may change the relative location of fins 804. As length 806 changes, fins 804 may move causing a change in capacitance, which may affect the frequency of the LC circuit to which pressure sensor 802A connects. Data acquisition circuitry 308 may detect the changes in frequency and determine a pressure in blood vessel 810, as described above in relation to FIGS. 3, 10A, and 10B.

[0078] FIG. 15 is a flow chart illustrating an example mode of operation of the system of this disclosure. The blocks of FIG. 15 will be described in terms of system 300 of FIG. 3, unless otherwise noted.

[0079] Data acquisition circuitry 308 may transmit wireless power to implantable AVF support device 302 (90). As described above in relation to FIG. 2, AVF support device 302 includes a pressure sensor configured to be located adjacent to a blood vessel and to sense pressure in the blood vessel. The pressure sensor is electrically and mechanically connected to a coil comprising a conductive material. Both the coil and the pressure sensor are configured to be located external to and adjacent to the blood vessel and the coil mechanically supports the blood vessel.

[0080] Data acquisition circuitry 308, while transmitting wireless power via antenna 306 to the coil of AVF support device 302 may also measure one or more characteristicsof the circuitry of AVF support device 302, which may include a resonance frequency. Because the pressure sensor changes capacitance based on the amount of pressure in the blood vessel, the measured characteristic includes information indicating the pressure in the blood vessel. As described above in relation to FIG. 3, in some examples, data acquisition circuitry 308 may calculate the blood pressure, while in other examples computing device 310 may calculate the blood pressure, and other measurements, based on the one or more measured characteristics from data acquisition circuitry 308.

[0081] The techniques of this disclosure may also be described in the following examples.

[0082] Example 1. A device comprising: a pressure sensor, configured to be located adjacent to a blood vessel and to sense pressure in the blood vessel; and a coil comprising a conductive material, wherein the coil is configured to: electrically and mechanically connect to the pressure sensor and be located external to and adjacent to the blood vessel; wirelessly receive electrical power and conduct the electrical power to the pressure sensor; and mechanically support the blood vessel.

[0083] Example 2. The device of example 1, wherein the blood vessel is a vein of an arteriovenous fistula (AVF), and wherein the coil is wrapped around a vein adjacent to an anastomosis that includes the vein for the coil to mechanically support the vein.

[0084] Example 3. The device of examples 1 or 2, wherein the coil is configured to be open and planar before implantation, and wherein the coil is configured to conform to an outer surface of the blood vessel after implantation.

[0085] Example 4. The device of any of examples 1 - 3, wherein the device further comprises a retention device configured to clamp the coil such that the coil conforms to the outer surface of the blood vessel after implantation.

[0086] Example 5. The device of any of examples 1 - 4, wherein the coil comprises a memory metal configured to change shape at body temperature to conform to an outer surface of the blood vessel.

[0087] Example 6. The device of any of examples 1 - 5, wherein the pressure sensor defines a pressure sensitive capacitance, wherein the pressure sensitive capacitance depends on the pressure in the blood vessel, wherein changes in the pressure sensitive capacitance change a resonant frequency of a circuit comprising the pressure sensor andthe coil, and wherein the sensed blood pressure is based on a measured characteristic that comprises the resonant frequency of the circuit.

[0088] Example 7. The device of any of examples 1 - 6, wherein the pressure sensor is a first pressure sensor, and wherein the device further comprises a second pressure sensor.

[0089] Example 8. A system comprising: an implantable medical device comprising: a pressure sensor configured to be located adjacent to a blood vessel and to sense pressure in the blood vessel; and a coil comprising a conductive material, wherein the coil is configured to be located external to and adjacent to the blood vessel; and mechanically support the blood vessel; data acquisition circuitry comprising a signal source and an antenna, wherein the data acquisition circuitry is configured to: wirelessly transfer electrical power to the implantable medical device from the antenna located external to the coil, and measure a characteristic of the implantable medical device, wherein the measured characteristic comprises information indicating the pressure in the blood vessel.

[0090] Example 9. The system of example 8, further comprising a computing device including processing circuitry, the computing device configured to: receive the information indicating the pressure in the blood vessel from the data acquisition circuitry; based on the received information, compute the pressure in the blood vessel; compare the computed pressure to a threshold; in response to the computed pressure satisfying the threshold, cause an alert to output.

[0091] Example 10. The system of examples 8 or 9, wherein the blood vessel is a vein of an arteriovenous fistula (AVF), the system further comprising a fixation device, wherein the fixation device is configured to hold the antenna in place proximal to the implantable medical device.

[0092] Example 11. The system of any of examples 8 - 10, wherein the coil is configured to be open and planar before implantation, and wherein the coil is configured to conform to an outer surface of the blood vessel after implantation.

[0093] Example 12. The system of any of examples 8 - 11, wherein the implantable medical device further comprises a retention device configured to clamp the coil such that the coil conforms to the outer surface of the blood vessel after implantation.

[0094] Example 13. The system of any of examples 8 - 12, wherein the coil comprises a memory metal configured to change shape at body temperature to conform to the outer surface of the blood vessel.

[0095] Example 14. The system of any of examples 8 - 13, wherein the pressure sensor defines a pressure sensitive capacitance, wherein the pressure sensitive capacitance depends on the pressure in the blood vessel, wherein changes in the pressure sensitive capacitance change a resonant frequency of a circuit comprising the pressure sensor and the coil, wherein the measured characteristic comprises the resonant frequency.

[0096] Example 15. The system of any of examples 8 - 14, wherein the implantable medical device is a first implantable medical device and the measured characteristic of the first implantable medical device is a first measured characteristic, the system comprising a second implantable medical device including a second pressure sensor, wherein the data acquisition circuitry is configured to measure a second characteristic of the second implantable medical device, wherein the system is configured to determine a blood flow based on a difference between the first measured characteristic and the second measured characteristic.

[0097] Example 16. A method comprising: transmitting, by data acquisition circuitry, wireless power to an implantable medical device, wherein the implantable medical device comprises: a pressure sensor configured to be located adjacent to a blood vessel and to sense pressure in the blood vessel; and a coil comprising a conductive material, wherein the coil is configured to be located external to and adjacent to the blood vessel; and mechanically support the blood vessel; measuring, by the data acquisition circuitry, a characteristic of the implantable medical device, wherein the measured characteristic comprises information indicating the pressure in the blood vessel.

[0098] Example 17. The method of example 16, wherein the pressure sensor defines a pressure sensitive capacitance, wherein the pressure sensitive capacitance depends on the pressure in the blood vessel, wherein changes in the pressure sensitive capacitance change a resonant frequency of a circuit comprising the pressure sensor and the coil, and wherein the measured characteristic comprises the resonant frequency of the circuit.

[0099] Example 18. The method of examples 16 or 17, wherein the implantable medical device is a first implantable medical device and the measured characteristic of thefirst implantable medical device is a first measured characteristic, the method further comprising: measuring, by the data acquisition circuitry, a second characteristic of a second implantable medical device including a second pressure sensor, determining a blood flow based on a difference between the first measured characteristic and the second measured characteristic.

[0100] Example 19. The method of any of examples, further comprising applying focused extrinsic compression of a targeted superficial outflow vein to force flow into the blood vessel using an external compression device, wherein the blood vessel is a vein of an arteriovenous fistula (AVF), wherein the external compression device is configured to occlude only the targeted superficial outflow vein and without limiting inflow to the blood vessel, and wherein applying the external compression device reduces an amount of time to mature the AVF with multiple outflows vessels by temporarily occluding an outflow vein through extrinsic compression.

[0101] Example 20. The method of any of examples 16 - 19, wherein reducing the amount of time to mature the AVF by temporarily occluding the targeted superficial outflow vein through extrinsic compression is based on directing flow into the blood vessel thereby increasing shear stress and pressure in the blood vessel, thereby causing it to increase in diameter and wall thickness.

[0102] Various examples of the disclosure have been described. These and other examples are within the scope of the following claims.

Claims

WHAT IS CLAIMED IS:

1. A devi ce compri sing : a pressure sensor, configured to be located adjacent to a blood vessel and to sense pressure in the blood vessel; and a coil comprising a conductive material, wherein the coil is configured to: electrically and mechanically connect to the pressure sensor and be located external to and adjacent to the blood vessel; wirelessly receive electrical power and conduct the electrical power to the pressure sensor; and mechanically support the blood vessel.

2. The device of claim 1, wherein the blood vessel is a vein of an arteriovenous fistula (AVF), and wherein the coil is wrapped around a vein adjacent to an anastomosis that includes the vein for the coil to mechanically support the vein.

3. The device of any of claims 1 and 2, wherein the coil is configured to be open and planar before implantation, and wherein the coil is configured to conform to an outer surface of the blood vessel after implantation.

4. The device of any of claims 1-3, wherein the device further comprises a retention device configured to clamp the coil such that the coil conforms to the outer surface of the blood vessel after implantation.

5. The device of any of claims 1-4, wherein the coil comprises a memory metal configured to change shape at body temperature to conform to an outer surface of the blood vessel.

6. The device of any of claims claim 1-5, wherein the pressure sensor defines a pressure sensitive capacitance,wherein the pressure sensitive capacitance depends on the pressure in the blood vessel, wherein changes in the pressure sensitive capacitance change a resonant frequency of a circuit comprising the pressure sensor and the coil, and wherein the sensed blood pressure is based on a measured characteristic that comprises the resonant frequency of the circuit.

7. The device of any of claims 1-6, wherein the pressure sensor is a first pressure sensor, and wherein the device further comprises a second pressure sensor.

8. A system comprising: an implantable medical device comprising: a pressure sensor configured to be located adjacent to a blood vessel and to sense pressure in the blood vessel; and a coil comprising a conductive material, wherein the coil is configured to be located external to and adjacent to the blood vessel, and mechanically support the blood vessel; data acquisition circuitry comprising a signal source and an antenna, wherein the data acquisition circuitry is configured to: wirelessly transfer electrical power to the implantable medical device from the antenna located external to the coil, and measure a characteristic of the implantable medical device, wherein the measured characteristic comprises information indicating the pressure in the blood vessel.

9. The system of claim 8, further comprising a computing device including processing circuitry, the computing device configured to: receive the information indicating the pressure in the blood vessel from the data acquisition circuitry; based on the received information, compute the pressure in the blood vessel; compare the computed pressure to a threshold;in response to the computed pressure satisfying the threshold, cause an alert to output.

10. The system of any of claims 8 and 9, wherein the blood vessel is a vein of an arteriovenous fistula (AVF), the system further comprising a fixation device, wherein the fixation device is configured to hold the antenna in place proximal to the implantable medical device.

11. The system of any of claims 8-10, wherein the coil is configured to be open and planar before implantation, and wherein the coil is configured to conform to an outer surface of the blood vessel after implantation.

12. The system of any of claims 8-11, wherein the implantable medical device further comprises a retention device configured to clamp the coil such that the coil conforms to the outer surface of the blood vessel after implantation.

13. The system of any of claims 8-12, wherein the coil comprises a memory metal configured to change shape at body temperature to conform to the outer surface of the blood vessel.

14. The system of any of claims 8-13, wherein the pressure sensor defines a pressure sensitive capacitance, wherein the pressure sensitive capacitance depends on the pressure in the blood vessel, wherein changes in the pressure sensitive capacitance change a resonant frequency of a circuit comprising the pressure sensor and the coil, wherein the measured characteristic comprises the resonant frequency.

15. The system of any of claims 8-15, wherein the implantable medical device is a first implantable medical device and the measured characteristic of the first implantable medical device is a first measuredcharacteristic, the system comprising a second implantable medical device including a second pressure sensor, wherein the data acquisition circuitry is configured to measure a second characteristic of the second implantable medical device, wherein the system is configured to determine a blood flow based on a difference between the first measured characteristic and the second measured characteristic.

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