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

This 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 alpha-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 analyzed. 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.