Impact of age on critical closing pressure of the cerebral circulation during dynamic exercise in humans.

Limited information is available regarding cerebral vascular responses to dynamic exercise in older adults. We examined the influence of age on exercise-induced changes in the critical closing pressure (CCP) of the cerebral vasculature. Twelve young and twelve older subjects performed two bouts of steady-state cycling at low and moderate intensities (30 and 50% heart rate reserve). Mean arterial pressure (MAP), middle cerebral artery blood velocity (MCA V) and partial pressure of end-tidal carbon dioxide ( ) were measured. The CCP was estimated by linear extrapolation of pairs of systolic and diastolic blood pressure and MCA V waveforms. Exercise-induced increases in MAP were greater in older subjects (P < 0.01), while mean MCA V (MCA V(mean)) responses to exercise were similar between groups (P = 0.59). The CCP was elevated from rest during low- and moderate-intensity exercise in both groups (moderate exercise: young, +13 ± 2 mmHg and older, +22 ± 2 mmHg; P < 0.01), with the older subjects exhibiting greater increases in CCP during both exercise intensities (moderate exercise: young, +43 ± 9% rest versus older, +153 ± 45% rest; P = 0.04). In contrast, cerebral vascular conductance index (MCA V(mean)/MAP; CVCi) was only decreased during moderate exercise in older subjects (P < 0.01) and CVCi was not altered from rest in young subjects during low- or moderate-intensity cycling. No age-group differences were observed in at rest or during two intensities of exercise (P = 0.40). These data demonstrate that older subjects exhibit larger exercise-induced increases in CCP and decreases in CVCi. Thus, ageing is associated with greater increases in cerebral vascular tone during low- and moderate-intensity dynamic exercise.