Baroreflex

The baroreflex, or baroreceptor reflex, is a rapid negative feedback mechanism that helps maintain stable arterial blood pressure. It detects changes in arterial wall stretch via baroreceptors located mainly in the carotid sinus and the aortic arch. Afferent signals travel to the brainstem through the glossopharyngeal nerve (IX) from the carotid sinus and the vagus nerve (X) from the aortic arch, reaching the nucleus tractus solitarius in the medulla.

The medullary baroreflex center integrates these signals and modulates autonomic output to the heart and vasculature. An increase in arterial pressure raises baroreceptor firing, which enhances parasympathetic (vagal) activity and inhibits sympathetic outflow, lowering heart rate, contractility, and vascular tone. A fall in pressure reduces baroreceptor firing, leading to increased sympathetic activity and decreased parasympathetic activity, which raise heart rate, contractility, and peripheral resistance. The result is rapid, beat-to-beat regulation of mean arterial pressure.

Over longer periods, the baroreflex can reset its set point in response to sustained blood pressure changes, such as in chronic hypertension, to maintain a new baseline. This resetting can reduce reflex sensitivity to further blood pressure fluctuations. Baroreflex sensitivity also tends to decline with aging or autonomic dysfunction, affecting short-term stability of blood pressure.

Clinically, the baroreflex arc can be evaluated by maneuvers such as carotid sinus massage or pharmacologic testing that assess reflex integrity and sensitivity. Impairment of baroreflex function is linked to labile blood pressures, orthostatic hypotension, and various cardiovascular disorders.