Inhibition by carotid baroreflex of exercise-induced increases in arterial pressure

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.