Implantable Sensors for Vascular Monitoring

Abstract

An implantable sensor for implantation in a vessel, comprising a plurality of electrodes for placement on, in or adjacent a vessel wall, means for providing a drive signal to the electrodes, means for measuring at least one of impedance and capacitance between at least two of the plurality of electrodes, and means for wirelessly communicating data from the sensor and a blood vessel monitoring system comprising same.

What is claimed is: 
     
         1 . An implantable sensor for implantation in a vessel, comprising:
 a plurality of electrodes for placement on, in or adjacent a vessel wall;   means for providing a drive signal to the electrodes;   means for measuring at least one of impedance and capacitance between at least two of the plurality of electrodes;   means for wirelessly communicating data from the sensor; and   means for processing the measured impedance or capacitance to monitor variations in the conductivity of the intervening media and to apply a correction factor accordingly.   
     
     
         2 . The implantable sensor of  claim 1 , further comprising means for calculating distance between the electrodes based on the measured impedance or the measured capacitance. 
     
     
         3 . The implantable sensor of  claim 1 , further comprising means for estimating vessel diameter or cross-sectional area of the vessel lumen based on measurements of impedance or capacitance between at least two of the plurality of electrodes. 
     
     
         4 . The implantable sensor of  claim 1 , further comprising means for selecting a pair of electrodes from the plurality of electrodes to which drive signals are to be delivered. 
     
     
         5 . The implantable sensor of  claim 2 , further comprising at least one of means for estimating pressure gradient, blood flow rate or blood velocity from the calculated distance between the electrodes. 
     
     
         6 . The implantable sensor of  claim 1 , further comprising at least one reference electrode maintained at a fixed distance from one of the electrodes and means for measuring at least one of impedance or capacitance between said electrode and said reference electrode. 
     
     
         7 . The implantable sensor of  claim 1 , further comprising means for biasing the plurality of electrodes against the vessel wall. 
     
     
         8 . The implantable sensor of  claim 1 , further comprising a support structure on which the electrodes are mounted, said support structure having sufficient elasticity to collapse and expand with the vessel without substantially altering the vessel's natural proportional shape changes in response to changes in fluid volume within the vessel. 
     
     
         9 . The implantable sensor of  claim 8 , wherein the support structure has an anchored part configured to engage the vessel wall and wherein each electrode is coupled to the support structure by a connecting strut extending from the anchored part of the support structure, the connecting strut being configured to bias the electrode into engagement with the vessel wall. 
     
     
         10 . The implantable sensor of  claim 9 , wherein at least one strut comprises an anchor for engagement directly with a vessel wall. 
     
     
         11 . An implantable sensor for implantation in a vessel, comprising:
 a plurality of electrodes for placement on, in or adjacent a vessel wall;   means for providing a drive signal to the electrodes;   means for measuring at least one of impedance and capacitance between at least two of the plurality of electrodes;   means for wirelessly communicating data from the sensor,   wherein at least part of the sensor is configured to endothelialize on a vessel wall, and at least one electrode has an anti-fouling surface to prevent endothelialization on a vessel wall.   
     
     
         12 . A vascular monitoring method, comprising:
 implanting a plurality of pairs of electrodes within a vessel, on, in or adjacent a vessel wall;   providing a drive signal to the electrodes;   measuring at least one of impedance and capacitance between at least two of the plurality of pairs of electrodes;   wirelessly communicating data from within the vessel;   wirelessly transmitting data representing measured impedance or capacitance to a control system comprising a processor and memory; and   determining vessel collapsibility or deformity over at least one respiratory cycle based on said measured impedance or capacitance between electrode pairs with steps executed on the processor.   
     
     
         13 . The method of  claim 12 , further comprising calculating the distance between plural pairs of said electrodes based on the measured impedance or the measured capacitance between said electrode pairs. 
     
     
         14 . The method of  claim 13 , further comprising estimating at least one of cross-sectional area of the vessel lumen or vessel diameter based on measurements of impedance or capacitance between at least one of the plurality of electrode pairs. 
     
     
         15 . The method of  claim 12 , further comprising:
 wirelessly transmitting data representing measured impedance or capacitance to a control system comprising a processor and memory; and   executing with the processor steps to correct the measurements for effects of fouling and/or endothelialisation on electrode surfaces.   
     
     
         16 . The method of  claim 15 , wherein said executing steps to correct the measurements comprise one or more of the steps of:
 impedance-to-distance calibration based on resting dimensions;   salinity recalibration with scales impedance measurements with reference change;   geometric reconstruction with elliptical assumption; and   fouling detection and rejection according to electrode geometry.   
     
     
         17 . The method of  claim 16 , wherein said fouling detection and rejection is performed using data from three or more electrodes to reconstruct an ellipse and additional data used to detect and reject fouling. 
     
     
         18 . The method of  claim 17 , further comprising performing with the processor at least one of data correction with parallelogram edge and diagonal correction, by averaging opposed parallelogram sides, or ellipse reconstruction to model a vessel shape, based on chordal lengths. 
     
     
         19 . The method of  claim 18 , further comprising executing with the processor a step of applying a correction to compensate for change from a round to elliptical cross-sectional shape of the vessel. 
     
     
         20 . The method of  claim 12 , further comprising delivering a sinusoidal waveform and cycling through each electrode pair taking impedance measurements or capacitive measurements. 
     
     
         21 . A sensor system for monitoring parameters in a vessel, comprising:
 an implantable support structure configured to move with natural movement of the vessel wall;   a plurality of pairs of electrodes coupled to the support structure and configured to be positioned circumferentially spaced around the vessel interior on, in or adjacent a wall of the vessel so as to move with natural movement of the vessel wall when the support structure moves therewith;   a drive circuit configured to provide a drive signal to the electrodes;   measurement circuitry configured to measure at least one of impedance and capacitance between at least two of the plurality of pairs of electrodes; and   a communications circuit configured to wirelessly communicate data from the sensor.   
     
     
         22 . The sensor system of  claim 21 , further comprising an external console, the communications circuit being configured to wirelessly communicate data to the external console. 
     
     
         23 . The sensor system of  claim 22 , further comprising a signal processing circuit in at least one of the implantable sensor and the external console, wherein the signal processing circuit is configured to calculate distance between the electrodes based on the measured impedance or the measured capacitance. 
     
     
         24 . The sensor system of  claim 23 , wherein the signal processing circuit is further configured to estimate at least one of cross-sectional area of the vessel lumen or vessel lumen diameter based on measurements of impedance or capacitance between at least two of the plurality of electrodes. 
     
     
         25 . The sensor system of  claim 23 , wherein the signal processing circuit is further configured to estimate at least one of a pressure gradient or blood velocity from the calculated distance between the electrodes. 
     
     
         26 . The sensor system of  claim 21 , further comprising at least one reference electrode maintained at a fixed distance from one of the electrodes and wherein the measurement circuitry is configured to measure at least one of impedance or capacitance between said one of the electrodes and said reference electrode. 
     
     
         27 . The sensor system of  claim 26 , wherein the processing circuitry is configured to calibrate distance measurements between the plurality of electrodes using a measurement of impedance or capacitance between said one of the electrodes and said reference electrode. 
     
     
         28 . The sensor system of  claim 21 , wherein the support structure comprises an anchor part configured to engage the vessel wall and wherein each electrode is coupled to the support structure by a connecting strut extending from the anchored part of the support structure, the connecting strut being configured to bias the electrode into engagement with the vessel wall. 
     
     
         29 . The sensor system of  claim 23 , wherein the signal processing circuit comprises a processor configured to execute instructions stored in a memory to reduce effects of fouling and/or endothelialisation on electrode surfaces. 
     
     
         30 . The sensor system of  claim 29 , wherein said instructions include one or more of the steps of:
 performing impedance-to-distance calibration based on resting dimensions;   salinity recalibration with scales impedance measurements with reference change;   geometric reconstruction with elliptical assumption; and   fouling detection and rejection according to electrode geometry based on data from three or more electrodes to reconstruct an ellipse, and additional data used to detect and reject fouling.   
     
     
         31 . The sensor system of  claim 26 , further comprising a signal processing circuit in at least one of the implantable sensor and the external console, wherein the signal processing circuit is configured to calculate distance between the electrode pairs based on the measured impedance or the measured capacitance, and wherein the signal processing circuit comprises a processor configured to execute instructions stored in a memory configured to perform one or more steps of:
 data correction with parallelogram edge and diagonal correction, by averaging opposed parallelogram sides;   ellipse reconstruction to model a vessel shape, based on chordal lengths using parallelogram side calculations; and   apply a correction to compensate for change from a round to elliptical cross-sectional shape of the vessel.   
     
     
         32 . An implantable sensor system for monitoring area of elliptical vessels, comprising:
 an implantable sensor comprising a plurality of electrodes for placement on, in or adjacent a vessel wall;   means for providing a drive signal to the electrodes;   means for measuring at least one of impedance and capacitance between the plurality of electrodes; and   means for determining the elliptical area of the vessel based on said impedance or capacitance measurements between the plurality of electrodes.   
     
     
         33 . The implantable sensor system of  claim 32 , wherein said means for determining the elliptical area comprises a processing system configured to execute instructions for ellipse reconstruction based on distances measured between the plurality of electrodes. 
     
     
         34 . The implantable sensor system of  claim 32 , wherein said instructions comprise instructions for parallelogram construction based on distances measured with parallel edge correction and instructions for ellipse reconstruction based on the constructed parallelogram.