Baroreflex Sensitivity (BRS)

Pressure-sensing receptors in the aortic arch and carotid sinuses, the major arteries near the heart, continuously monitor blood pressure. When pressure rises above normal, these receptors fire rapidly and send signals through the nervous system to the brain’s cardiovascular control centers. The response is immediate: the parasympathetic branch slows the heart and reduces output, bringing pressure back down. When pressure falls, sympathetic activity increases heart rate and constricts blood vessels to restore it. This closed-loop correction system is the baroreflex.

Baroreflex sensitivity is expressed as the change in heart rate interval (in milliseconds) per millimeter of mercury of blood pressure change. A sensitivity of 15 to 20 ms/mmHg means the heart interval shifts by 15 to 20 milliseconds for every 1 mmHg swing in blood pressure, a robust and responsive system. As this value declines, blood pressure corrections become slower and less accurate, leaving the cardiovascular system less stable under exercise, stress, and postural changes.

Baroreflex sensitivity declines naturally with age, hypertension, and metabolic dysfunction, and is independently associated with cardiovascular mortality risk. Aerobic training is the most potent intervention: Kingwell et al. showed aerobic exercise training significantly raises BRS in both healthy and hypertensive adults by increasing vagal tone and improving arterial compliance. The mechanism overlaps substantially with HRV: both reflect parasympathetic tone, but BRS specifically captures how the system responds under dynamic blood pressure challenge rather than at rest.