Cerebrovascular disease incidence, specifically stroke, increases with advancing age; each passing decade after age 55 doubles the risk for stroke. Moreover, the risk is greater for men than women. An important physiologic risk factor for stroke is the capacity of cerebral vasculature to control and maintain brain blood flow. Two factors determine brain blood flow: cerebrovascular reactivity and cerebral blood flow autoregulation. The latter of these two may most profoundly affect risk for stroke; impairments in cerebral blood flow autoregulation reduce the ability of the cerebral circulation to buffer against rapid and large pressure changes. Age-related impairments in cerebral autoregulation have been described in animals, however there are no comparable data in humans. One factor which may reduce cerebral autoregulation with age is elevated sympathetic outflow. Increased sympathetic activity occurs with aging in humans and also decreases autoregulatory capacity. Therefore, increased stroke risk with age may derive from a shift in cerebral autoregulation due to increased sympathetic activity. Furthermore, in women, this shift may not occur until after menopause. This study will examine gender- and age- related differences in cerebral autoregulation in young, middle-aged, and older healthy men and women. I hypothesize that aging men demonstrate progressively reduced cerebral autoregulation related to increased sympathetic activity and that premenopausal women demonstrate preserved autoregulation with age related to lesser increases in sympathetic activity compared to postmenopausal women. Beat-by-beat relations between pressure and cerebral flow during lower body suction oscillating at 0.03, 0.05, and 0.10 Hz will provide an autoregulation index from differences in spectral gain from higher to lower frequencies. Since both aging and menopause are risk factors for stroke, this data may provide insight into the possible role of impaired cerebral autoregulation as the underlying commonality.
