Reflex control of heart rate in the unanesthetized dog.

TLDR: Installing aortic cuffs permitted us to raise or lower arterial pressure sinusoidally over a frequency range from .05 to .20 cycles/set in awake dogs, and vagal and sympathetic heart rate responses could be separated by drugs and by the speed of response.

Abstract: SCHER, ALLEN M., AND ALLAN C. YOUNG. Reflex control of heart rate in the unanestheticed dog. Am. J. Physiol. 218(3) : 780-789. 1970.-Implanted aortic cuffs permitted us to raise or lower arterial pressure sinusoidally over a frequency range from .05 to .20 cycles/set in awake dogs. Vagal and sympathetic heart rate responses could be separated by drugs and by the speed of response. Responses to increased pressure were vagal. Vagal changes in the cardiac interval depended only on the systolic pressure on that beat. There is negligible phase angle between the pressure change and the resulting interval at any frequency and a constant amplification (a change in pressure produces the same change in interval). Sympathetic and vagal effects were combined when pressure was lowered up to 30 mm Hg below normal. Sympathetic changes are characterized by an increasing phase lag (interval lagging pressure) and a decreasing amplification as the frequency of the pressure change increases. Sympathetic effects are strongest under atropine and Nembutal. The resting dog does not change his total peripheral resistance when the arterial pressure is raised. Regulation in the resting, intact dog is mainly via vagal changes in heart rate. There is a strong respiratory effect on heart rate in many animals. Equations are presented to describe the responses.