Heart rate variability at the onset of efferent vagal stimulations in the rabbit

Vagal stimulations were performed in 6 anesthetized rabbits for single cardiac cycles. The distribution of effects over 6 consecutive cardiac cycles was described as a function of varying intervals between P waves and stimuli (P-St): the response on the first couple of cycles is affected by P-St whilst the effects decline regularly over successive cycles. Stimulation of 6 consecutive cycles showed rapid rise and subsequent slow increment of the response. Results interpreted as evidence for intracellular accumulation of a restraining factor for heart rate due to vagal stimulation.