Fig. 6.

Three different cases of the process of DN detection using the IEM algorithm in PPG input signal: (i) where the DN is clearly observable within a cardiac cycle of PPG input signal; (ii) where DN is less evident within a cardiac cycle of PPG input signal; and (iii) where DN is absent within a cardiac cycle of PPG input signal. Plots labeled (a) depict the curves for 4-s PPG input signal window with marked DN locations by an experienced researcher in cases i and ii and with marked DN locations revealed by the IEM method in case iii, plots labeled as (b) depict the curves for the normalized input signal, plots labeled as (c) show the curves for the non-stationary component of the IEM method, and plots labeled as (d) display the curves for the stationary component of the IEM method.