Implantable systemic blood pressure measurement systems and methods

Abstract

Implantable systems, and methods for use therewith, for monitoring arterial blood pressure on a chronic basis are provided herein. A first signal indicative of electrical activity of a patient's heart, and a second signal indicative of mechanical activity of the patient's heart, are obtained using implanted electrodes and an implanted sensor. By measuring the times between various features of the first signal relative to features of the second signal, values indicative of systolic pressure and diastolic pressure can be determined. In specific embodiments, such features are used to determine a peak pulse arrival time (PPAT), which is used to determine the value indicative of systolic pressure. Additionally, a peak-to-peak amplitude at the maximum peak of the second signal, and the value indicative of systolic pressure, can be used to determine the value indicative of diastolic pressure.

1 . For use with an implantable system, a method for monitoring a patient's arterial blood pressure, the method comprising:
 (a) using implanted electrodes to obtain a first signal indicative of electrical activity of the patient's heart;   (b) using an implanted sensor to obtain a second signal indicative of mechanical activity of the patient's heart;   (c) detecting a ventricular depolarization in a portion of the first signal corresponding to a cardiac cycle;   (d) detecting a maximum peak amplitude in a portion of the second signal corresponding to the same cardiac cycle;   (e) determining a pulse arrival time (PAT) by determining a time t 1  from detection of the ventricular depolarization to the detection of the maximum peak amplitude in the second signal; and   (f) determining a value indicative of systolic pressure (SP) based on the PAT.   
     
     
         2 . The method of  claim 1 , further comprising calibrating the implantable system by:
 (i) obtaining accurate measures of the patient's systolic (SP) pressure using a non-implanted device and/or an acutely implanted device;   (ii) using the implanted electrodes and the implanted sensor to determine a pulse arrival time (PAT) corresponding each of a plurality of accurate measures of the patient's SP; and   (iii) using the accurate measures of SP and the corresponding PATs to determine one or more patient specific correlation factor that enables values indicative of the patient's SP to be calculated based on PAT; and   wherein step (h) includes using the one or more patient specific correlation factor when determining the value indicative of SP.   
     
     
         3 . The method of  claim 1 , further comprising:
 (g) determining a peak-to-peak amplitude a 1  in the second signal; and   (h) determining a value indicative of diastolic pressure (DP) based on the amplitude a 1  and the value indicative of SP.   
     
     
         4 . The method of  claim 3 , wherein step (h) includes:
 (h.1) determining a value indicative of pulse pressure (PP) based on the amplitude a 1 ; and   (h.2) determining the value indicative of DP by subtracting the value indicative of PP from the value indicative of SP.   
     
     
         5 . The method of  claim 3 , further comprising calibrating the implantable system by:
 (i) obtaining accurate measures of the patient's systolic pressure (SP) and diastolic pressure (DP) using a non-implanted device and/or an acutely implanted device;   (ii) using the implanted electrodes and the implanted sensor to determine a pulse arrival time (PAT) and a peak-to-peak amplitude a 1  corresponding each of a plurality of accurate measures of the patient's SP and DP; and   (iii) using the accurate measures of SP and DP and the corresponding PATs and peak-to-peak amplitudes a 1  to determine patient specific correlation factors that enable values indicative of the patient's SP and values indicative of the patient's DP to be to be calculated based on PAT and a 1 , and   wherein step (f) includes using at least one of the patient specific correlation factors when determining the value indicative of SP; and   wherein step (h) includes using at least one of the patient specific correlation factors when determining the value indicative of DP.   
     
     
         6 . An implantable system configured to monitor a patient's arterial blood pressure, comprising:
 a first detector configured to detect ventricular depolarizations in cardiac cycles represented in a first signal that is indicative of electrical activity of a patient's heart;   a second detector configured to detect maximum peak amplitudes in cardiac cycles represented in a second signal indicative of mechanical activity of the patient' heart;   an arterial blood pressure monitor configured to
 determine a time t 1  from a detected ventricular depolarization to a detected maximum peak amplitude in the second signal; 
 determine a pulse arrival time (PAT) based on the time t 1 ; and 
 determine a value indicative of systolic pressure (SP) based on the PAT. 
   
     
     
         7 . The implantable system of  claim 6 , wherein:
 the first signal comprises an intracardiac electrogram (IEGM) or an electrocardiogram (ECG); and   the second signal comprises a plethysmography signal.   
     
     
         8 . The implantable system of  claim 7 , further comprising:
 a sensing circuit to obtain the first signal using implantable electrodes; and   an implantable plethysmography sensor to obtain the second signal.   
     
     
         9 . The implantable system of  claim 8 , wherein the implantable plethysmography sensor comprises a photoplethymography sensor. 
     
     
         10 . The implantable system of  claim 6 , wherein the arterial blood pressure monitor is also configured to:
 determine a value indicative of pulse pressure (PP) based on the amplitude a 1 ; and   determine a value indicative of diastolic pressure (DP) by subtracting the value indicative of PP from the value indicative of SP.   
     
     
         11 . The implantable system of  claim 10 , wherein the arterial blood pressure monitor can track changes in SP and DP over time.