Figure 2: Coupling functions for the human cardiorespiratory system.
From: In vivo cardiac phase response curve elucidates human respiratory heart rate variability
The reconstructed functions provide the dependence of the instantaneous cardiac frequency, measured in radians per second, on the cardiac and respiratory phases. Red regions mean higher frequencies (acceleration), whereas blue regions correspond to lower frequencies (deceleration). Functions Qe(φe,φr) (a,c,e) are obtained from the ECG and the respiration, whereas functions Qp(φp,φr) (b,d,f) are computed from arterial pulse and respiration. Using these two very different observables for the cardiovascular system, we nevertheless obtain highly correlated results, as is expected for the invariant approach. The functions for the subject with the lowest correlation between Qe and Qp are shown in (a,b), and for the subject with the highest correlation in (c,d). Panels (e,f) present the averaged (over all measurements for all subjects) coupling functions Qe and Qp.
