I'm working a project which tries to determine Blood Pressure from PPG signals.I'm trying to extract the features as shown below...

enter image description here

I'm having problem in finding the troughs and dicrotic notch for each cycle and also the cycle start and end duration. Are there any manual method methods which can be applied ( I'm a newbie to signal processing )thereby which we can extract the trough and notch location in each cycle ?

Much thanks in advance

  • $\begingroup$ i hadn't seen this question before. are you confident that the notch will always be there with a slight bump to the right of the notch? what if the derivative never quite reaches zero? then where to you want to mark the notch time to calculate the Peak to Notch Time? $\endgroup$ – robert bristow-johnson Oct 25 '18 at 18:41

Have you tried finding where the derivative of your signal is 0 (or crosses between positive and negative values)?

Simple, approximate, derivative filters are the first difference:

$y[n] = x[n] - x[n-1]$

and the central difference:

$y[n] = x[n] - x[n-2]$

You'll have to compensate for filter delay when mapping the zero crossings of the derivative back to the local minima and maxima of the original signal. For the first difference, the output is delayed by about half a sample period, and for the central difference, the output is delayed about a sample period.


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