Vascular responses to stimulation of carotid, aortic and coronary artery baroreceptors with pulsatile and non‐pulsatile pressures in anaesthetized dogs

Abstract

SUMMARYThis research was designed to compare coronary, carotid and aortic arch baroreceptors in terms of the ranges of pressures required to elicit reflex vascular responses and the possible differences between the responses to pulsatile and non-pulsatile stimuli. Dogs were anaesthetized with a-chloralose, artificially ventilated and the chests opened wide. A perfusion circuit allowed independent control of pressures distending the three baroreceptor regions. A cardiopulmonary bypass and ventricular fibrillation prevented cardiac pulsations from influencing coronary baroreceptor pressure. The caudal region of the animal was perfused at constant flow and vascular resistance responses were assessed from changes in perfusion pressure. Only tests in which the overall response exceeded 3 kPa (22.5 mmHg) were analysed. Reflex responses were obtained to significantly lower coronary pressures than were required to induce responses from other regions. The inflexion points of the stimulus-response curves for pulsatile coronary, carotid and aortic pressures were 10.5 + 0 6, 15 5 + 1 8 and 16 4 + 1 7 kPa (79 + 5, 116 + 14 and 123 + 13 mmHg, respectively; values are means + S.E.M.). When the responses to pulsatile stimuli were compared with those to non-pulsatile stimuli, it was noted that for the carotid receptors, lower pressures were required to induce responses (inflexion pressure less) and the slope of the stimulus-response curve was less. Pulsatile aortic pressures induced a parallel (downward) displacement of the curve but no change in inflexion point or slope. The coronary baroreceptor stimulus-response relationship was unaffected by pulsatility. These results show differences between the characteristics of the three baroreceptors with coronary receptors being unaffected by pressure pulsatility but likely to be of importance in hypotensive situations.

Effects of simulated obstructive sleep apnoea on the human carotid baroreceptor–vascular resistance reflex

“…The reflex effects of these are very complex due to their diversity (Hainsworth, 1991). Stimulation of aortic (Hainsworth et al 1970) and coronary (McMahon et al 1996) baroreceptors would be expected to decrease blood pressure and vascular resistance. Effects may also result from low pressure receptors in the atria and pulmonary arteries.…”

Cardiovascular control from cardiac and pulmonary vascular receptors

“…Note the lower operating range of the coronary baroreceptors. From McMahon et al (1996). they differ from the other baroreceptors in that, at least in the dog, they do not result in changes in heart rate. They also have a number of other characteristics marking them as distinct.…”

“…They also have a number of other characteristics marking them as distinct. They have a much lower threshold for activation and saturate at lower pressures (McMahon et al ). Also, unlike other baroreceptors, they do not show signs of resetting over the short term (McMahon et al ), and stimulation of the coronary baroreceptors results in a much more prolonged central inhibition of efferent sympathetic nerve activity (Drinkhill et al ; Fig.…”

Autonomic Nervous System

“…Very low frequency fl uctuations are thought to represent long-term regulatory mechanisms related to thermoregulation or to humoral factors [ 17 ]. The powers of the different components and the total power of the entire spectrum are expressed in absolute units (ms 2 ). LF and HF components can also be expressed as normalised units.…”

“…Different receptors show different characteristics so that increasing pressure recruits more receptors. Also, different baroreceptors groups operate over different ranges: coronary baroreceptors have a lower pressure range than those in the aorta and carotid arteries [ 2 ].Baroreceptors "reset" when subjected to sustained changes in pressure. This starts to occur in less than 30 min.…”