Carotid sinus reflex control of coronary blood flow in human subjects

Systemic and coronary hemodynamics were assessed before and during a reduction in carotid transmural pressure. This reduction was induced by means of a pneumatic neck chamber in 15 normal subjects and 15 hypertensive patients with a normal coronary arteriogram. A reduced baroreflex responsiveness was demonstrated in hypertensive patients as compared with normal subjects by evaluating both the reflex bradycardia evoked by intravenous administration of phenylephrine and the reflex increase in blood pressure during carotid sinus hypotension. In normal subjects, the reduction in carotid transmural pressure induced a significant increase in mean blood pressure, total peripheral resistance, cardiac output, heart rate, coronary vascular resistance, coronary blood flow assessed by the continuous thermodilution method and myocardial oxygen consumption. In hypertensive patients, the same stimulus significantly increased mean blood pressure, cardiac output, heart rate and coronary blood flow while no significant change was detected in coronary vascular resistance and myocardial oxygen consumption. The increase in mean blood pressure, total peripheral resistance and cardiac output was significantly higher in normal subjects than in hypertensive patients. These results suggest that in normal subjects carotid sinus hypotension evokes reflex coronary vasoconstriction, whereas this response is blunted in hypertensive patients with reduced baroreflex sensitivity.