Introduction

Subnormal arterial blood pressure.

Baroreflex mechanisms regulate systemic blood pressure by increasing or decreasing heart rate and vascular resistance in response to transient decreases or increases in arterial pressure. With age, the baroreflex response to hypertensive and hypotensive stimuli progressively declines, and the risk of hypotension increases. Baroreflex function is most impaired in elderly patients with hypertension. Signs of impairment include increased blood pressure lability in response to daily activities and hypotension in response to stimuli that lower arterial pressure, particularly drugs.

The diminished baroreflex response may be caused partly by arterial stiffening due to atherosclerosis, which results in dampening of baroreceptor stretch and relaxation during changes in arterial pressure. Reduced adrenergic responsiveness by the aged heart and vasculature may diminish baroreflex-mediated cardioacceleration and vasoconstriction in response to hypotensive stimuli. These changes become clinically significant when common hypotensive stresses, such as postural changes, can no longer be rapidly or completely offset by compensatory increases in heart rate or in vascular resistance.

With age, cerebral blood flow decreases. Cerebral autoregulatory mechanisms usually compensate for acute reductions in blood pressure. Autoregulation of cerebral blood flow is generally maintained with age, except in persons who have symptomatic orthostatic hypotension. However, chronic hypertension raises the lowest blood pressure at which autoregulation can maintain cerebral blood flow. Below this level, blood flow may decrease, increasing the risk of cerebral ischemia. Hypertension, heart disease, diabetes mellitus, and hyperlipidemia further decrease cerebral blood flow. Because of age- and disease-related decreases in cerebral blood flow, elderly patients are vulnerable to cerebral ischemia and syncope if blood pressure decreases.