Paradoxical Effect of Vagus Nerve Stimulation on Heart Rate in Dogs

• Published in: Circulation research 1969-09, Vol.25 (3), p.303-314
• Main Authors: Levy, Matthew N, Martin, Paul J, Iano, Thelma, Zieske, Harrison
• Format: Article
• Language: English
• Subjects: Animals; Dogs; Electric Stimulation; Heart Conduction System - physiology; Heart Rate; Pacemaker, Artificial; Sinoatrial Node - physiology; Vagus Nerve - physiology
• ISSN: 0009-7330; 1524-4571
• DOI: 10.1161/01.RES.25.3.303

ABSTRACTIn the anesthetized, open-chest dog, electrical stimulation of the cardiac ends of the transected cervical vagus nerves produced effects on heart rate and A-V transmission that were dependent upon the P-St interval, i.e., the time from the beginning of the P wave to the beginning of the stimulus. When one vagal stimulus was delivered per cardiac cycle, the pacemaker response curve (curve of the P-P interval as a function of the P-St interval) was sinusoidal in configuration, with a maximum at a P-St interval of 135 msec and a minimum at 349 msec. The mean P-P interval was 568 msec, and the mean amplitude of the pacemaker response curve was 58 msec.In any given experiment, the range of P-P intervals encompassed by the pacemaker response curve defined a range of frequencies over which S-A nodal rhythm became synchronized with the activity in the vagus nerves. Over such a range, increases in the frequency of vagal stimulation evoked paradoxical increases in heart rate. On either side of this range of synchronization, vagal stimulation elicited pronounced rhythmic oscillations of P-P and P-R intervals. The frequency of such oscillations was equal to the difference between the vagal stimulation frequency and the mean heart rate. The oscillations in P-R interval were approximately 180° out of phase with the oscillations in P-P interval.