Techniques for blood pressure measurement by implantable device
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:
a sensing channel for generating signals reflective of cardiac electrical activity;
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 detected cardiac electrical activity 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 wherein the controller is programmed to align the collected blood pressure waveforms by simultaneously sampling and storing the blood pressure waveforms and the cardiac electrical activity signals with time stamps.
5. A method, comprising:
generating signals reflective of cardiac electrical activity;
generating blood pressure waveforms from an intravascular location;
collecting a plurality of blood pressure waveforms as digitized sample values and aligning the collected waveforms by making the time at which each corresponding sample value is collected the same with respect to detected cardiac electrical activity among the collected waveforms; and,
compute an average blood pressure waveform by averaging corresponding samples of the collected waveforms.
6. The method of claim 5 further comprising:
generating a spatial orientation signal indicative of the patient's posture; and,
collecting pressure waveforms for averaging only when the spatial orientation signal indicates the patient is in one or more specific postures.
7. The method of claim 5 further comprising downloading the collected and aligned pressure waveforms from an implantable device to an external device, wherein the averaging of the pressure waveforms is performed by the external device.
8. The method of claim 5 further comprising:
generating a spatial orientation signal indicative of the patient's posture; and,
calibrating the pressure waveforms before averaging in accordance with the spatial orientation signal in order to compensate for the effects of the patient's posture on the blood pressure waveforms.