Table 2.

Summary of features extracted from each PPG cycle.

Feature	Description
DC value	Average value of the low-passed PPG signal
Peak value	Amplitude of the systolic peak [12]
Delta AC	Difference between the peak value and the trough on the left
Rise slope	Slope of the line between the trough on the left of the peak to the peak value
Rise time	Time difference between the trough on the left of the peak and the peak value
Fall level	Difference between the values of the peak and the trough on the right
Fall slope	Slope of the line between the trough on the right of the peak and the peak value
Fall time	Time between the trough on the right of the peak and the peak value
Width at 1/4 height	Value at 1/4 of the height of Delta AC
Width at 3/4 height	Value at 3/4 of the height of Delta AC
Base width	Difference between the trough on the right of the peak and the trough on its left
Area	Area enclosed between the two troughs
Optical density	$OD=log(1+\frac{deltaAC}{DC})$ [17]
TKEO mean	Mean, variance, standard
TKEO variance	deviation, skewness and
TKEO std	kurtosis of the TKEO calculated
TKEO skewness	from each cycle using:
TKEO kurtosis	$x\left[n\right]=x^2\left[n\right]-x[n+1]x[n-1]$