SUMMARY. Mean arterial blood pressure, heart rate, and cardiac output were measured during continuous graded exercise (5.5 km/hr; 0, 7, 14, and 21% grades) in conscious dogs, under each of the following four conditions: (1) baroreceptors intact, (2) chronic aortic arch denervation, (3) chronic aortic arch denervation and surgical preparation of the carotid sinuses for later reversible vascular isolation, and (4) chronic aortic arch denervation and carotid sinuses vascularly isolated at a fixed pressure. Arterial blood pressure increased with increasing work load to a maximum of 12 ± 3, 18 ± 5, and 14 + 5 mm Hg above control in conditions 1, 2, and 3, respectively. In condition 4, the maximum increase in pressure during graded exercise was 51 ± 7 mm Hg above control. Upon cessation of graded exercise, the increase in arterial pressure persisted through the 5-minute recovery period. Heart rate and cardiac output increased similarly in proportion to work load under all four conditions. In contrast to dogs in condition 4, three dogs with chronic sinoaortic denervation showed no work load-related increase in arterial pressure during exercise. Thus, during exercise, the carotid baroreflex acts to balance finely the opposing effects of sympathetic vasoconstriction and metabolic vasodilation. (Circ Res 52: 253-262, 1983) THE QUESTION of regulation of arterial blood pressure by carotid and aortic baroreceptors during exercise is controversial (Bevegard and Shepherd, 1966;Vatner et al., 1970; Krasney et al v 1974; McRitchie et al., 1976;Melcher and Donald, 1981). Studies in dogs have utilized chronic denervation of aortic and of carotid baroreceptors, singly or in combination. Using these techniques, Krasney et al. (1974) and McRitchie et al. (1976) have concluded that arterial baroreflexes are not involved in the regulation of arterial pressure during exercise. The development of a technique to produce reversible vascular isolation of the carotid sinuses (Stephenson and Donald, 1980a) has permitted evaluation of the role of the carotid baroreflex in the regulation of arterial pressure by examining the cardiovascular responses when the carotid sinuses are acutely prevented from responding to arterial pressure. Melcher and Donald (1981) used this preparation in conscious exercising dogs and found that the response of arterial blood pressure to light and to severe exercise was normal when only the carotid baroreceptors or only the aortic and vagal cardiopulmonary receptors were able to respond to the stress. When all three systems were inoperative, arterial pressure fell with the start of light exercise and remained depressed throughout the run. They concluded that the carotid baroreflex had a significant, although not indispensable, role in the complex interaction of the several mechanisms that act to maintain arterial pressure during exercise.This study examines the ability of carotid baroreceptors to regulate arterial pressure during graded exercise in the chronic absence of the aortic baroreflex. Two preparations wer...

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Mean arterial blood pressure, heart rate, and cardiac output were monitored at rest and during exercise of two grades of severity in conscious dogs under control conditions and after progressive interruption of the baroreflexes. Aortic arch denervation and vascular isolation and pressurization of the carotid sinuses were used to interrupt arterial baroreflexes. Subsequent interruption of cardiopulmonary afferents was produced by acute bilateral cervical vagotomy. The results indicate that 1) with the cardiopulmonary receptors alone operative, the arterial blood pressure response to exercise is abnormal, 2) cardiopulmonary receptors do not contribute to the moment-to-moment modulation of arterial pressure, and 3) the carotid sinuses, aortic arch, and cardiopulmonary receptors are all involved in determining the mean level of arterial blood pressure. It is concluded that vagally innervated cardiopulmonary receptors do not have a significant role in regulating arterial blood pressure during exercise but are involved in establishing the general level of arterial blood pressure.

To examine the role of cardiopulmonary receptors in arterial blood pressure regulation during and after exercise, conscious dogs with chronic sinoaortic denervation were subjected to 12 min of light exercise and 12 min of exercise that increased in severity every 3 min. Hemodynamic measurements were made before and after interruption of cardiopulmonary afferents by bilateral cervical vagotomy. During both exercise protocols, after an initial transient decrease, the arterial blood pressure remained close to resting values before and after vagotomy. On cessation of the graded exercise, the arterial blood pressure did not change before, but a rapid and sustained increase in pressure occurred after vagotomy. At the time of this increase the cardiac output and heart rate were returning rapidly to the resting level. The study demonstrates that in the chronic absence of arterial baroreflexes, vagal afferents prevent a rise in arterial blood pressure after vigorous exercise presumably by the action of cardiopulmonary receptors causing a rapid dilatation of systemic resistance vessels.

In 12 conscious dogs, the mean increase of 26 mmHg in arterial pressure during carotid occlusion was augmented by 52 mmHg after section of the left cervical vagus nerve and 6 mmHg after right vagal section. In 18 anesthetized dogs, in which the cervical vagal nerves were reversibly cold blocked, corresponding values were 33, 28, and 6 mmHg, respectively. In nine of these dogs, this left-sided dominance was present after bilateral section of the vagal cardiopulmonary afferents; it was absent after bilateral section of the aortic nerves in the other nine dogs. In five dogs on cardiopulmonary bypass with heart and lungs excluded, pressure within the isolated aorta and major intrathoracic arteries was raised from 120 to 220 mmHg. The resultant hypotension reflexly induced by activation of aortic baroreceptors was reduced by left but not by right vagal cold block. It was concluded that, in the dog, the left aortic nerve provided the major inhibition of the increase in arterial pressure after carotid occlusion.