Table 3.

Features extracted only from S1 and S2 intervals of the heartbeat cycle (tagged as S1 and S2, respectively).

Index	Tag	Description
Absolute extrema:
26	a_max	maximum value (positive amplitude)
27	t_max	relative time location of a_max
28	a_min	the minimum value (negative amplitude)
29	t_min	relative time location of a_min
30	max_a	maximum absolute value
31	max_t	relative time location of max_a
Local extrema:
32	mean_t_max	mean time across all relative maxima
33	mean_dt_max	mean-time difference across all relative maxima
34	std_t_max	standard deviation over the time of all relative maxima
35	std_dt_max	standard deviation over the time difference between all relative maxima
36	n_max	number of local maxima
37	mean_t_min	mean-time across all relative minima
38	mean_dt_min	mean-time difference across all relative minima
39	std_t_min	standard deviation over the time of all relative minima
40	std_dt_min	standard deviation over the time difference between all relative minima
41	n_min	number of local minima
42	mean_t_zero	mean-time across all zero-crossing
43	std_t_zero	standard deviation over the time of all zero-crossing
44	mean_dt_zero	mean-time difference across all zero-crossing
45	std_dt_zero	standard deviation over the time difference between all zero-crossing
46	mean_t_max	mean-time across all relative maxima
Structural:
47	n_broken	number of discontinuities on the derivative of the signal
48	skewness	the relative position of the maximum absolute value of the signal around the middle point of the interval