Acoustic physiological sensor

Abstract

This document describes, among other things, a body having at least one acoustically detectable property that changes in response to a change in a physiological condition, such as ischemia. The body is positioned with respect to a desired tissue region. At least one acoustic transducer is used to acoustically detect a change in physical property. In one example, the body is pH sensitive and/or ion selective. A shape or dimension of the body changes in response to pH and/or ionic concentration changes resulting from a change in an ischemia state. An indication of the physiological condition is provided to a user.

1 . An apparatus comprising:
 a physiological sensor including a biocompatible body sized and shaped to be implanted within a subject to contact tissue, at least a portion of the body including a material having at least one physical property that changes in response to a physiological condition predictive or indicative of a tachyarrhythmia when that portion of the body is implanted in contact with the tissue, wherein the change in the at least one physical property occurs because of the contact between that portion and the tissue, wherein the portion of the body is sized and shaped such that the change in the physical property is detectable using acoustic energy to provide an indication of the physiological condition.   
   
   
       2 . The apparatus of  claim 1 , wherein the change in the physical property of the body includes a change in size of the body. 
   
   
       3 . The apparatus of  claim 1 , wherein the change in the physical property of the body includes a change in an acoustic property of the body. 
   
   
       4 . The apparatus of  claim 1 , comprising an implantable transducer configured to supply the acoustic energy for providing the indication of the physiological condition. 
   
   
       5 . The apparatus of  claim 1 , wherein the body includes at least a portion of a catheter. 
   
   
       6 . The apparatus of  claim 1 , wherein the body includes a sphere. 
   
   
       7 . The apparatus of  claim 1 , wherein the change in the physical property of the body is responsive to a change in pH. 
   
   
       8 . A method comprising:
 introducing a physiological sensor including a biocompatible body into contact with a tissue, wherein the body includes at least one physical property that changes as a result of the contact with the tissue in response to a physiological change associated with the tissue, the physiological change predictive or indicative of a tachyarrhythmia;   transmitting acoustic energy to the body and the tissue;   receiving transmitted acoustic energy for detecting the change in the physical property of the body; and   detecting and providing an indication of the physiological change by detecting the change in the physical property of the body.   
   
   
       9 . The method of  claim 8 , wherein introducing the physiological sensor includes introducing a pH sensitive biocompatible body. 
   
   
       10 . The method of  claim 8 , wherein introducing the physiological sensor includes introducing an ion sensitive biocompatible body. 
   
   
       11 . The method of  claim 8 , wherein introducing the physiological sensor includes introducing a catheter. 
   
   
       12 . The method of  claim 8 , wherein introducing the physiological sensor includes introducing a sphere. 
   
   
       13 . The method of  claim 8 , comprising introducing a device for transmitting the acoustic energy. 
   
   
       14 . The method of  claim 8 , comprising introducing a device for receiving the transmitted acoustic energy. 
   
   
       15 . The method of  claim 8 , wherein transmitting the acoustic energy includes transmitting the acoustic energy using an implantable transducer. 
   
   
       16 . An apparatus comprising:
 a physiological sensor including a biocompatible body, the body sized and shaped to be implanted within a subject to contact tissue, at least a portion of the body including a material having at least one physical property that changes in response to a physiological condition of the tissue when that portion of the body is implanted in contact with the tissue, the change in the physiological condition being predictive or indicative of ischemia, wherein the change in the at least one physical property occurs because of the contact between that portion and the tissue, wherein the portion of the body is sized and shaped such that the change in the physical property is detectable using acoustic energy to provide an indication of the physiological condition.   
   
   
       17 . The apparatus of  claim 16 , comprising an implantable transducer configured to supply the acoustic energy for providing the indication of the physiological condition. 
   
   
       18 . The apparatus of  claim 16 , wherein the change in the physical property of the body includes a change in size of the body. 
   
   
       19 . The apparatus of  claim 16 , wherein the change in the physical property of the body includes a change in an acoustic property of the body. 
   
   
       20 . The apparatus of  claim 16 , wherein the change in the physical property of the body is responsive to a change in pH.