Fig. 4.

Significant reduction of approximately 40% in CRPS with age indicates decreased cardiorespiratory coupling in elderly subjects. The n∶m synchronization is obtained from each subject during 8 h of sleep without differentiating between sleep stages and is averaged over all subjects in each age group (error bars represent standard error). The same data as in Fig. 3 are analyzed (see Materials and Methods). Right bars show a surrogate test for the subjects in each age group based on synchronization between heartbeats and Fourier phase-randomized respiratory data, indicating statistical significance of the results for all age groups (Mann–Whitney rank sum test for all age groups, p < 10^-3). Dashed line (not a fit) highlights the decrease in synchronization with age.