NONLINEAR-INTERACTIONS OF SLOW AND RAPID RHYTHMS IN SYMPATHETIC-NERVEDISCHARGE

We used bispectral analysis to characterize the nonlinear interactions of the respiratory-related (RR), cardiac-related (CR), or 10-Hz rhyth ms in sympathetic nerve discharge (SND) of urethan-anesthetized cats. Bispectral analysis investigates relationships among frequency triples in the same signal (inferior cardiac postganglionic SND) where the th ird frequency is the sum of the other two due to quadratic nonlinear c oupling. Coupling of the RR and CR rhythms leading to the generation o f new components (i.e., modulated frequencies) in SND occurred in 84% of the total cases, whereas the incidence was 71% for the RR and 10-Hz rhythms. The occurrence of such nonlinear interactions implies that t he RR, CR, and 10-Hz rhythms are carried to common targets by the same postganglionic sympathetic neurons. Furthermore, we suggest that nonl inear interactions leading to the generation of new frequencies in SND may affect end-organ function beyond the level expected in simple cas es of linear superposition of the primary rhythms. This suggestion is supported by our observation that strong coupling of the RR and CR rhy thms resulted in appreciable power at the modulated frequencies.