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

Abstract

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...

Arterial baroreflex alters strength and mechanisms of muscle metaboreflex during dynamic exercise

“…It is generally accepted that the baroreflex is reset to a higher pressure during exercise with little change in sensitivity, and this allows the arterial pressure to increase with exercise (5,17,26,28). Several investigators have shown that arterial baroreceptors act as an inhibitory signal during exercise to oppose sympathoexcitation (25,37,38). Sheriff et al (32) examined the extent to which arterial baroreflexes attenuate the increase in the pressor response evoked by the muscle metaboreflex during mild exercise in conscious dogs.…”

“…Previous investigators showed that the pressor reflexes to static muscle contraction in anesthetized animals as well as metaboreflex activation during mild exercise in conscious animals were greater after denervation of the arterial baroreceptors and concluded that arterial baroreflexes attenuate the pressor response initiated by activation of skeletal muscle afferents (32, 37). Together, these findings suggest that afferent input of the arterial baroreceptors acts as an inhibitory signal during dynamic exercise to oppose sympathoexcitation induced by activation of skeletal muscle afferents (25,26,32,38). However, the extent to which the arterial baroreflex modifies the mechanisms mediating muscle metaboreflex pressor responses is unknown.…”

Additional Physical Activity During Cardiac Rehabilitation Leads to an Improved Heart Rate Recovery in Male Patients After Coronary Artery Bypass Grafting

“…Evidence for a central mechanism, considered to be a release of inhibitory commands from the motor cortex to the parasympathetic center, 16 or afferent stimulation from baroreflex or chemoreflex functions, 17 has typically utilized the initial R-R interval changes during the post-exercise recovery periods. Imai et al demonstrated that a release of inhibitory central command rather than baro-or chemoreceptor stimulation may play an important role in postexercise vagal reactivation, because the HR during the first 30 s of recovery minimally depends on the exercise intensity.…”

Factors influencing blood pressure and heart rate variability in hypertensive humans.

“…49 This latter point remains controversial; arterial baroreceptor reflexes of conscious dogs appear to continue to operate effectively during treadmill exercise. 50 " 52 The strong association we observed between BRS and blood pressure variability could be explained if the reflex regulation of blood pressure was preserved during physical activity but was less potent in hypertensive than in normal subjects.…”