Algorithm to calculated SBP from PPG and cuff pressure for a Ramp method
- Select PPG values during ramp
- Savgol filter the ppg signals.
- Find the troughs.
- Find the amplitude ratio of Dependent and Independent PPGs between these troughs.
- Savgol Filter the amplitude ratios.
- Square the amplitude ratio signal.
- Normalize it to 0 -100 %.
- Threshold = Standard deviation of signal less than X percent
- #Change this X percent value to suit data. I've observed Xpercent = 8% to be reasonable with the small datasets I've.
- Find the first instance of pressure at which the amplitude is less than threshold.
- This pressure is taken as systolic pressure.