Techniques for blood pressure measurement by implantable device

Abstract

An implantable cardiac device is configured and programmed to collect blood pressure waveforms from one or more implantable pressure sensors. Techniques are described for extracting features and reducing noise in the pressure waveforms by averaging waveforms which are aligned with a detected cardiac cycle. Noise can also be reduced by gating and calibration functions performed in accordance with other sensor data.

1 . A device, comprising:
 an intravascular pressure sensor for generating blood pressure waveforms;   a controller interfaced to the sensing channel and the intravascular pressure sensor; and,   wherein the controller is programmed to collect a plurality of blood pressure waveforms as digitized sample values, align the collected waveforms by making the time at which each corresponding sample value is collected the same with respect to a detected event among the collected waveforms, and compute an average blood pressure waveform by averaging corresponding samples of the collected waveforms.   
     
     
         2 . The device of  claim 1  further comprising:
 a posture sensor interfaced to the controller for generating a spatial orientation signal indicative of the patient's posture; and,   wherein the controller is programmed to calibrate the pressure waveforms in accordance with the spatial orientation signal in order to compensate for the effects of the patient's posture on the blood pressure waveforms.   
     
     
         3 . The device of  claim 1  further comprising:
 a posture sensor interfaced to the controller for generating a spatial orientation signal indicative of the patient's posture; and,   wherein the controller is programmed to collect pressure waveforms only when the spatial orientation signal indicates the patient is in one or more specific postures.   
     
     
         4 . The device of  claim 1  further comprising:
 a temperature sensor interfaced to the controller for generating a temperature signal indicative of the patient's present body temperature; and,   wherein the controller is programmed to calibrate the pressure waveforms in accordance with the temperature signal in order to compensate for the effects of the patient's body temperature on the pressure sensor.   
     
     
         5 . The device of  claim 1  further comprising:
 a temperature sensor interfaced to the controller for generating a temperature signal indicative of the patient's present body temperature; and,   wherein the controller is programmed to collect pressure waveforms only when the temperature signal indicates the patient's body temperature is within a specified range.   
     
     
         6 . The device of  claim 1  further comprising:
 an exertion level sensor interfaced to the controller for generating a signal indicative of the patient's present level of exertion; and,   wherein the controller is programmed to collect a pressure waveform along with a corresponding signal indicating the patient's exertion level when the pressure waveform was collected.   
     
     
         7 . The device of  claim 1  further comprising:
 an exertion level sensor interfaced to the controller for generating a signal indicative of the patient's present level of exertion; and,   wherein the controller is programmed to collect pressure waveforms only when the exertion level signal indicates the patient's exertion level is within a specified range.   
     
     
         8 . The device of  claim 1  further comprising:
 an intravascular flow sensor interfaced to the controller for producing a signal indicative of blood flow; and,   wherein the controller is programmed to use the blood flow signal and a pressure waveform to calculate a flow resistance value.   
     
     
         9 . The device of  claim 1  further comprising:
 a sensor for generating a phonocardiogram signal;   wherein the detected event with which the collected pressure waveforms are aligned is the occurrence of intrinsic cardiac activity as indicated by the phonocardiogram signal.   
     
     
         10 . The device of  claim 1  further comprising:
 a sensing channel for detecting cardiac electrical activity;   a pacing channel for pacing a heart chamber; and,   wherein the detected event with which the collected pressure waveforms are aligned is the occurrence of cardiac activity as indicated from the sensing channel or a corresponding delivery of a pace through the pacing channel.   
     
     
         11 . A method, comprising:
 generating blood pressure waveforms from an intravascular location in a patient;   collect a plurality of blood pressure waveforms as digitized sample values;   aligning the collected waveforms by making the time at which each corresponding sample value is collected the same with respect to a detected event among the collected waveforms; and,   computing an average blood pressure waveform by averaging corresponding samples of the collected waveforms.   
     
     
         12 . The method of  claim 11  further comprising:
 generating a spatial orientation signal indicative of the patient's posture; and,   calibrating the pressure waveforms in accordance with the spatial orientation signal in order to compensate for the effects of the patient's posture on the blood pressure waveforms.   
     
     
         13 . The method of  claim 11  further comprising:
 generating a spatial orientation signal indicative of the patient's posture; and,   collecting pressure waveforms only when the spatial orientation signal indicates the patient is in one or more specific postures.   
     
     
         14 . The method of  claim 11  further comprising:
 generating a temperature signal indicative of the patient's present body temperature; and,   calibrating the pressure waveforms in accordance with the temperature signal in order to compensate for the effects of the patient's body temperature on the pressure sensor.   
     
     
         15 . The method of  claim 11  further comprising:
 generating a temperature signal indicative of the patient's present body temperature; and,   collecting pressure waveforms only when the temperature signal indicates the patient's body temperature is within a specified range.   
     
     
         16 . The method of  claim 11  further comprising:
 generating a signal indicative of the patient's present level of exertion; and,   collecting a pressure waveform along with a corresponding signal indicating the patient's exertion level when the pressure waveform was collected.   
     
     
         17 . The method of  claim 11  further comprising:
 generating a signal indicative of the patient's present level of exertion; and,   collecting pressure waveforms only when the exertion level signal indicates the patient's exertion level is within a specified range.   
     
     
         18 . The method of  claim 11  further comprising:
 producing a signal indicative of blood flow; and,   using the blood flow signal and a pressure waveform to calculate a flow resistance value.   
     
     
         19 . The method of  claim 11  further comprising:
 generating a phonocardiogram signal;   wherein the detected event with which the collected pressure waveforms are aligned is the occurrence of intrinsic cardiac activity as indicated by the phonocardiogram signal.   
     
     
         20 . The method of  claim 11  further comprising:
 detecting cardiac electrical activity;   pacing a heart chamber; and,   wherein the detected event with which the collected pressure waveforms are aligned is the occurrence of cardiac activity as indicated from the sensing channel or a corresponding delivery of a pace through the pacing channel.