Gas station without pumps

2022 April 16

ECG: 2-electrode vs. 3-electrode

Filed under: Circuits course — gasstationwithoutpumps @ 12:23
Tags: , , , ,

In Lower PVC frequency, I said “I did not do direct comparisons of the 2-electrode and 3-electrode configurations—I’ll have to try that sometime soon.” So I did that earlier this week, recording resting ECGs first with a 3-electrode configuration (with the bias electrode on my sternum, halfway between the LA and RA electrodes) and then with a 2-electrode configuration (with the bias wire clipped to the RA electrode).  The 60 Hz noise was slightly higher with the 2-electrode configuration, but after filtering and signal averaging the two recordings were almost identical:


The waveforms after signal averaging were remarkably similar. The PVC burden was also similar (20.1% for the 3-electrode recording and 20.5% for the 2-electrode recording).


The pulse rate from looking at time between spikes worked well for the resting recordings, but the autocorrelation method failed completely, so I did not plot it. The rapid fluctuation in heart rate within a narrow range is real, not an artifact of the algorithm—the heart beats are not perfectly periodic, and the PVCs may be making them even less periodic. The 2-electrode recording probably started a little after 400 seconds—PteroDAQ only time stamps when the file was saved, not what the t=0s time was. I should probably fix PteroDAQ to change that, recording both.


I tried recording a session on the exercise bike also. The PVCs are mainly during resting at the beginning of the session and at the end of a recovery at the end of the session—the PVC burden was only 1.4%.


For the exercise recording, the noise really disrupted the spike-based pulse detection, but did not interfere as much with the autocorrelation-based pulse detection. My peak pulse rate was about 151.5 bpm, by the autocorrelation measure. I’m not sure whether the sudden changes in pulse rate at 100s (when I started pedaling) and around 556s (about 130s into the recovery time) are real or not—the noise in the recording makes it a little difficult to determine the “correct” pulse rate.

The noise during exercise was not 60Hz noise and seemed to vary with whether I was inhaling or exhaling, so I think that it was probably caused by EMG signals from the pectoral muscles or perhaps the diaphragm. The spike detector was clearly missing a lot of the spikes, but making it more sensitive would probably result in false triggering on the EMG noise. I’m wondering whether putting the electrodes on my back, over the scapulae, would reduce the EMG noise, but placing those electrodes and clipping to them would be difficult without an assistant.

The autocorrelation-based pulse detection seems more reliable when exercising, as my pulse is more periodic and has few PVCs, and the autocorrelation method is less susceptible to aperiodic noise.  The spike-based pulse detection seems more reliable when resting, when the pulse is not as periodic and PVCs disrupt the pattern.

I’m also wondering whether a more strenuous exercise session would raise my pulse rate, or whether I’m getting close to my maximum heart rate.  The standard formula for maximum heart rate by age suggests that this may be close to my maximum, but the exercise does not seem all that strenuous, and a couple of years ago I could routinely push to 170 bpm (though perhaps on a device that was an unreliable reporter—it was built into a treadmill at the gym).  So sometime in the next few weeks I’ll try using a higher power output and seeing where my heartbeat tops out.  I’ll probably need to increase the cadence, rather than the resistance, as I’ve been using about 70rpm and 28Nm to get about 205W.  Raising that to 80rpm or even 90rpm is probably easier than increasing the torque.

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