Table 4.

A list of typical feature extracted from the PPG and its derivatives.

Feature		Description
Time domain	Amplitude	Amplitude of the fiducial points in Figure 2 (e.g., systolic peak, diastolic peak, and dicrotic notch)
	Time	Time interval between the fiducial points in Figure 2 (e.g., systolic peak, diastolic peak, dicrotic notch, and onset)
	Width	Systolic width at 10%, 25%, 33%, 50%, 66%, and 75% and diastolic width at 10%, 25%, 33%, 50%, 66%, and 75%, as shown in Figure 3
	Area	Systolic area, diastolic area, and their ratios
	Derivatives	Ratio of amplitude of fiducial points on first-order derivative and second-order derivative in Figure 2
Frequency domain		Amplitude and frequency of the first, second, and third peaks of the frequency domain signal
Demographic information		Age, gender, height, weight, body mass index (BMI), etc.
Entropy		Shannon entropy, spectral entropy, approximate entropy, sample entropy, etc.
Statistical characteristics		Mean, standard deviation, skewness, kurtosis, etc.
Others		K value, PIR, ASI, etc.