AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 6 1932-R1945, Copyright © 1997 by American Physiological Society

ARTICLES

Nonlinear dynamics of the frequency locking of baroreceptor and sympathetic rhythms

G. L. Gebber, S. Zhong, S. Y. Zhou and S. M. Barman
Department of Pharmacology, Michigan State University, East Lansing 48824, USA.

We used phase plane analysis to identify modes of frequency locking of the 10-Hz rhythm in sympathetic nerve discharge (SND) to the cardiac cycle in urethan-anesthetized, baroreceptor-innervated cats. Frequency locking occurred in rational ratios predicted by a generic mathematical construct called the Farey tree. Both simple harmonic ratios (e.g., 1:3) and complex ratios (e.g., 2:5) comprised of relatively prime integers (no common divisor) were identified under natural conditions. Frequency locking in such ratios is attributed to forcing of the 10-Hz oscillator by pulse-synchronous baroreceptor afferent nerve activity (BNA). Ventricular pacing changed the frequency of the 10-Hz rhythm as well as heart rate so as to maintain or change the ratio of frequency locking in a predictable way. Intriguingly, frequency locking of the 10-Hz rhythm to medullary raphe sympathoinhibitory stimuli in simple harmonic ratios was accompanied by increased power in the 10-Hz band of SND, whereas locking in complex ratios led to decreased 10-Hz power. These findings raise the possibility that pulse-synchronous BNA also exerts divergent actions on the 10-Hz rhythm depending on the ratio of frequency locking. Augmented 10-Hz power can be attributed to the resonant properties of oscillators that are periodically forced at the same phase in their cycle.

This article has been cited by other articles:

				S. Zhong, G. L. Gebber, S.-Y. Zhou, and S. M. Barman Nonlinear interactions of slow and rapid rhythms in sympathetic nerve discharge Am J Physiol Heart Circ Physiol, August 1, 1998; 275(2): H331 - H340. [Abstract] [Full Text] [PDF]