Figure 5: PRC curves and effective forcing.
From: In vivo cardiac phase response curve elucidates human respiratory heart rate variability
We show individual PRCs Z (a) and effective forcing I (b) for all ECG-based coupling functions with grey curves. In both panels blue lines show the average over all individual (grey) curves. Red curves are obtained by decomposition of the averaged coupling function, shown in Fig. 2e. Small panel on top of (a) shows for comparison the average ECG cycle as a function of its phase. One can clearly see the interval where PRC is not zero and, hence, the cardiac system is susceptible for the respiratory perturbation. Small panel on top of (b) shows the average respiratory cycle as a function of the phase, with marked epochs of inspiration and expiration (approximately). Intervals of positive (negative) effective forcing are the intervals where respiration is accelerating (decelerating) the heart rate. Panels (c,d) show error of the decomposition ||β||, where ||˙|| denotes the norm of the function. In (c) the relative error 
is shown (for the cases of the largest (red) and of the smallest (green) error) in dependence on the parameter ωe used in the decomposition procedure; finally the value of ωe yielding minimal error is chosen. In (d) all errors are presented, demonstrating quality of the decomposition.
