I'm doing a comparison of heart rate variability in awake and sleeping humans and your research interests me. When working with your dataset, I'm having some questions:
1) what is the dimension of the signal H. R.? Is it milliseconds?
2) is it possible to extract RR-intervals from your data?
3) is it possible to know the time of the sleep/awake?
4) at what point of time the recording starts? When the surveyed goes to sleep or turns off when light?
Hello Pavel, thanks for your questions! I've pinged the team locally, to see who may have insights into your questions.
Which specific datasets are you working with?
1) In general, the units for the heart rate variability indices are milliseconds for the time domain variables: AVNN, SDNN, SDANN, SDNNIDX, rMSSD. pNN50 is a %.; the unites for instantaneous heart rate IHR is bpm; the units for the frequency domain variables: total power, ultra-low frequency, very low frequency, low frequency and high frequency power are millisecond square (ms2). The ratio LF/HF is unitless.
2) If you have the ECG signal you can extract the RR intervals using a open-source QRS detector. One is available here: https://www.physionet.org/physiotools/wag/wqrs-1.htm
3) The xml files, if available, contain the sleep stage annotations: 0 for awake, 1 for N1, 2 for N2, 3 for N3, 4 for N4 and 5 for REM. Usually the annotation window is 30 secs. The time of occurrence of the first "non-zero" symbol is sleep onset. The time of occurrence of the last "non-zero" symbol is sleep-offset.
4) The answer to that question depends on the protocol followed by a particular study.