Fundamental Rhythm of Cardiac Sympathetic Nerve Activity in Awake Cats at Rest and during Body Movement

Abstract

Cardiac sympathetic nerve activity (CSNA in imp/s) was measured in the postganglionic fibers of awake cats at rest, during body movement, and with excitement. The CSNA showed synchronized discharges with various periodicities. Rhythms of the synchronized CSNA were analyzed by an interval histogram (IIH). The IIH showed a multimodal distribution. The first model interval (T_c) was in a range of 75 to 125ms. An 8-12 cycle/s T_c rhythm, i.e., inverse value of T_c, was always observed in the awake cat at rest and during body movements. Probability of the 8-12 cycle/s T_c rhythm was smallest at rest, increased during body movement, and was largest with excitement. These results suggested that the 8-12 cycle/s T_c rhythm, observed in all states in the conscious cat, is a fundamental rhythm of central cardiovasomotor origin. The subsequent model distribution (T_b=2×T_c, 3×T_c, 4×T_c, or 5×T_c) ranged from 150 to 700ms, mostly 200 to 500ms. A 2-5 cycle/s T_b rhythm, i.e., inverse value of T_b, appeared more frequently at rest than that during body movement or with excitement. A new model concerning a mechanism to cause the 2-5 cycle/s T_b rhythm is suggested.