Myogram determination from ECG signal

1. A method of measuring signals representative of muscle activity, the method comprising:

detecting, using a processing circuit, an electrocardiogram (ECG) signal through a plurality of electrodes, wherein the ECG signal comprises a plurality of ECG sample signals, wherein each ECG sample signal is a bipolar signal associated with two of the plurality of electrodes and comprises a cardiac signal component and a myographic signal component representative of muscle contractions relating to the muscle activity;

filtering, using the processing circuit, each of the ECG sample signals to remove at least a portion of the cardiac signal component and generate a combined myographic power signal for the two of the plurality of electrodes with which the ECG sample signal is associated, wherein each combined myographic power signal represents a myographic potential between the two electrodes; and

calculating, using the processing circuit, individual myographic power signals for each of the plurality of electrodes by applying the combined myographic power signals within a covariance matrix;

wherein:

the method further comprises designating one of the plurality of electrodes to be a reference electrode and the others of the plurality of electrodes to be recording electrodes;

detecting the ECG signal comprises detecting a first set of ECG sample signals comprising an ECG sample signal for each recording electrode with respect to the reference electrode;

filtering each of the ECG sample signals comprises filtering each of the first set of ECG sample signals to generate a first set of combined myographic power signals, wherein the first set of combined myographic power signals comprises a combined myographic power signal for each recording electrode with respect to the reference electrode; and

calculating the individual myographic power signals comprises applying the first set of combined myographic power signals within the covariance matrix and calculating the individual myographic power signal for the reference electrode.

2. The method of claim 1 , wherein the individual myographic power signal for the reference electrode is calculated based on one or more off-diagonal combined myographic power signals within the covariance matrix.

3. The method of claim 1 , further comprising:

changing the reference electrode to another of the plurality of electrodes to designate a new reference electrode;

designating the electrodes of the plurality of electrodes other than the new reference electrode to be new recording electrodes;

determining a second set of combined myographic power signals comprising a combined myographic power signal for each new recording electrode with respect to the new reference electrode; and

calculating the individual myographic power signal for the new reference electrode by applying the second set of combined myographic power signals within the covariance matrix.

4. The method of claim 3 , further comprising repeating the changing, designating, determining, and calculating operations until the individual myographic power signals have been calculated for each of the plurality of electrodes.

5. The method of claim 1 , wherein filtering each of the ECG sample signals to generate a combined myographic power signal for the two of the plurality of electrodes with which the ECG sample signal is associated comprises applying a high pass filter to the ECG sample signals to remove low frequency components of the ECG sample signals.

6. The method of claim 5 , wherein filtering each of the ECG sample signals to generate a combined myographic power signal for the two of the plurality of electrodes with which the ECG sample signal is associated further comprises:

determining a presence of at least one of a QRS wave or a P wave within a portion of the ECG sample signals; and

replacing the portion of the ECG sample signals including the at least one of the QRS wave or the P wave with a corresponding portion of the ECG sample signals from a previously detected sample.

7. The method of claim 5 , wherein filtering each of the ECG sample signals to generate a combined myographic power signal for the two of the plurality of electrodes with which the ECG sample signal is associated further comprises filtering out at least a portion of the ECG sample signals corresponding to a frequency of at least one of 50 Hz or 60 Hz.

8. A system for measuring signals representative of muscle activity, the system comprising:

a circuit configured to:

detect an electrocardiogram (ECG) signal through a plurality of electrodes, wherein the ECG signal comprises a plurality of ECG sample signals, wherein each ECG sample signal is a bipolar signal associated with two of the plurality of electrodes and comprises a cardiac signal component and a myographic signal component representative of muscle contractions relating to the muscle activity;

filter each of the ECG sample signals to remove at least a portion of the cardiac signal component and generate a combined myographic power signal for the two of the plurality of electrodes with which the ECG sample signal is associated, wherein each combined myographic power signal represents a myographic potential between the two electrodes; and

calculate individual myographic power signals for each of the plurality of electrodes by applying the combined myographic power signals within a covariance matrix;

wherein the circuit is configured to:

designate one of the plurality of electrodes to be a reference electrode and the others of the plurality of electrodes to be recording electrodes;

detect a first set of ECG sample signals comprising an ECG sample signal for each recording electrode with respect to the reference electrode;

filter each of the first set of ECG sample signals to generate a first set of combined myographic power signals, wherein the first set of combined myographic power signals comprises a combined myographic power signal for each recording electrode with respect to the reference electrode; and

apply the first set of combined myographic power signals within the covariance matrix and calculate the individual myographic power signal for the reference electrode.

9. The system of claim 8 , wherein the individual myographic power signal for the reference electrode is calculated based on one or more off-diagonal combined myographic power signals within the covariance matrix.

10. The system of claim 8 , wherein the circuit is configured to:

change the reference electrode to another of the plurality of electrodes to designate a new reference electrode;

designate the electrodes of the plurality of electrodes other than the new reference electrode to be new recording electrodes;

determine a second set of combined myographic power signals comprising a combined myographic power signal for each new recording electrode with respect to the new reference electrode; and

calculate the individual myographic power signal for the new reference electrode by applying the second set of combined myographic power signals within the covariance matrix.

11. The system of claim 10 , wherein the circuit is configured to repeat the changing, designating, determining, and calculating operations until the individual myographic power signals have been calculated for each of the plurality of electrodes.

12. The system of claim 8 , wherein the circuit is configured to apply a high pass filter to the ECG sample signals to remove low frequency components of the ECG sample signals.

13. The system of claim 12 , wherein the circuit is configured to:

determine a presence of at least one of a QRS wave or a P wave within a portion of the ECG sample signals; and

replace the portion of the ECG sample signals including the at least one of the QRS wave or the P wave with a corresponding portion of the ECG sample signals from a previously detected sample.

14. The system of claim 12 , wherein the circuit is configured to filter out at least a portion of the ECG sample signals corresponding to a frequency of at least one of 50 Hz or 60 Hz.