How can be obtain Power Spectral Density using FFT for foetal heart rate signal?

Hi! I want to find power spectral density for foetal heart rate signal sampled at 4Hz using FFT. I've learnt that we can also use STFT but even after trying, I'm not able to differentiate Frequency bands in it.I request the community to provide the code for this & also help me give a note on how can be obtain power from PSD at low frequency (0.03-0.2) and high frequency bands(0.02-1).

Answer 1

[Star Strider]

If you have the Signal Processing Toolbox, see the documentation section on Power Spectral Density Estimates Using FFT .

Note that for best results, the EKG should have a sampling frequency of at least 250 Hz. A 4 Hz sampling rate will likely give you the R-deflections, however little else, and no relevant detail.