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Carotid sinus reflex control of coronary blood flow in human subjects
Insights
Hypertension impairs baroreflex control of coronary circulation. In normal individuals, reduced carotid pressure constricts coronary vessels, but this reflex is blunted in hypertensive patients, affecting blood flow regulation.
Area of Science:
- Cardiovascular Physiology
- Baroreceptor Reflexes
- Hypertension Research
Background:
- Baroreflex sensitivity is often reduced in hypertensive patients.
- The carotid sinus plays a key role in regulating systemic and coronary hemodynamics via the baroreflex.
- Understanding how baroreflex dysfunction impacts coronary circulation in hypertension is crucial.
Purpose of the Study:
- To compare the effects of carotid sinus hypotension on systemic and coronary hemodynamics in normal subjects and hypertensive patients.
- To investigate the baroreflex-mediated coronary vascular response to reduced carotid transmural pressure.
- To assess baroreflex responsiveness in hypertensive patients versus normal controls.
Main Methods:
- Systemic and coronary hemodynamics were measured before and during carotid transmural pressure reduction using a pneumatic neck chamber.
- Baroreflex responsiveness was evaluated via phenylephrine-induced bradycardia and carotid sinus hypotension.
- Coronary blood flow was assessed using continuous thermodilution in 15 normal subjects and 15 hypertensive patients.
Main Results:
- Hypertensive patients exhibited reduced baroreflex responsiveness compared to normal subjects.
- In normal subjects, carotid sinus hypotension increased blood pressure, cardiac output, and coronary blood flow, with coronary vasoconstriction.
- In hypertensive patients, the stimulus increased blood pressure and coronary blood flow but did not significantly alter coronary vascular resistance or myocardial oxygen consumption, indicating a blunted coronary vasoconstrictive response.
Conclusions:
- Carotid sinus hypotension elicits reflex coronary vasoconstriction in normal individuals.
- This reflex coronary vasoconstriction is significantly blunted in hypertensive patients with reduced baroreflex sensitivity.
- Baroreflex dysfunction in hypertension may impair the normal regulation of coronary blood flow.
Abstract:
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.