Dear all,
I want to measure mental stress through HRV (from PPG data) for biofeedback purposes, in real time. Which method do you recommend for HRV measurement and which is the minimum time interval suggested for good accuracy?
Thank you very much in advance.
Best regards from Brazil,
Fernando
This is the answer kindly proposed by Prof. Paul Lehrer,
One of the measures is based on spectral analysis, you will need 10 cycles of the frequency you are looking at. For 6/min breathing, that would be about a minute and a half. But be sure that you are measuring it during a period of stable signal. This sometimes take as a minute or so to achieve, particularly since the program will compute spectral values over a period of time in the past, usually between 30 sec and 1 minute. You don't want to look at values computed at periods before the individual was breathing at the assigned frequency.
The short time intervals probably use wavelet analysis. Probably it is ok but I have not seen a correlational study showing the relationship to other HRV measures. There might have been such work, but I haven't seen it. See how this device correlates with devices using longer time intervals.
RMSSD is a good measure, quite robust against various kinds of artifact. However it isn't quite as sensitive to vagal effects as HF HRV.
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