Using chest velocity to process physiological signals to remove chest compression artifacts
A method of analyzing a physiological (e.g., an ECG) signal during application of chest compressions. The method includes acquiring a physiological signal during application of chest compressions; acquiring the output of a sensor from which information on the velocity of chest compressions can be determined; and using the information on the velocity to reduce at least one signal artifact in the physiological signal resulting from the chest compressions.
1. A device for analyzing an impedance cardiographic (ICG) physiological signal during application of chest compressions, the device comprising:
circuitry for acquiring a impedance cardiographic physiological signal from a impedance cardiographic sensor applied to the chest during application of chest compressions;
circuitry for acquiring the output of a motion sensor applied to the chest from which information on the velocity of chest compressions can be determined, and
processing circuitry for using the information on the velocity to reduce at least one signal artifact in the impedance cardiographic signal resulting from the chest compressions.
2. A device for analyzing an impedance pneumographic physiological signal during application of chest compressions, the device comprising:
circuitry for acquiring a impedance pneumographic physiological signal from a impedance pneumographic sensor applied to the chest during application of chest compressions;
circuitry for acquiring the output of a motion sensor applied to the chest from which information on the velocity of chest compressions can be determined, and
processing circuitry for using the information on the velocity to reduce at least one signal artifact in the impedance pneumographic signal resulting from the chest compressions.
3. The device of claim 1 or 2 wherein the motion sensor is a velocity sensor, and the information on the velocity is determined from the velocity sensor.
4. The device of claim 1 or 2 wherein the motion sensor is an accelerometer, and the information on the velocity is determined from integration of the output of the accelerometer.
5. The device of claim 1 or 2 wherein using the information on the velocity to reduce at least one signal artifact in the physiological signal comprises time aligning the physiological signal with the velocity.
6. The device of claim 1 or 2 wherein using the information on the velocity to reduce at least one signal artifact in the physiological signal comprises using an adaptive filter that is adjusted to remove chest compression artifacts.
7. The device of claim 6 wherein the processing circuitry is configured to provide a preprocessing step that detects when chest compressions are applied and automatically initiates the adaptive filter.
8. The device of claim 6 wherein the processing circuitry is configured to produce a difference signal, the difference signal being representative of the difference between the physiological signal fed into the adaptive filter and the physiological signal after artifact reduction by the adaptive filter.
9. The device of claim 8 wherein the difference signal provides a measure of the amount of artifact in the physiological signal.
10. The device of claim 9 the difference signal is used to modify the subsequent processing of the physiological signal.
11. The device of claim 10 wherein spectral analysis is performed on the difference signal, and adjustments are made to filtering of the physiological signal based on the outcome of the spectral analysis.
12. The device of claim 6 wherein the velocity signal undergoes a normalization pre-processing prior to being fed to an adaptive filter.
13. The device of claim 6 wherein the adaptive filter comprises an FIR filter.
14. The device of claim 13 wherein the adaptive filter comprises a zero-th order filter.
15. The device of claim 6 wherein the adaptive filter comprises coefficients that are dynamically controlled by an estimate of the physiological signal.
16. The device of claim 6 wherein the adaptive filter comprises the capability of being automatically reset when the difference between the filter output and the measured physiological signal is beyond a threshold.
17. The device of claim 16 wherein the automatic reset comprises the capability of dynamically changing the step size and thus improving the relationship of convergence and stability of the filter.
18. The device of claim 1 or 2 further comprising a time-aligning process performed on the physiological and velocity signals, wherein the time aligning process aligns the two signals relative to the compressions.
19. The device of claim 18 further comprising adaptive filtering of the output of the time aligning process, wherein the adaptive filtering reduces the error between the physiological and velocity signals.
20. The device of claim 6 wherein the adaptive filter comprises a Kalman filter.
21. The device of claim 6 wherein the adaptive filter employs adaptive equalization.