Circulatory control during acute physical stress in healthy young and older men.

Abstract

Aging has been associated with alterations in the physiological responses to physical stressors. This study investigated the regional and systemic hemodynamic responses and venous plasma catecholamine responses to three commonly encountered physical stressors (dynamic exercise, isometric exercise, and orthostasis) in groups of young (25.9 ± 0.7 yr, mean ± SE, range 21 to 29) and older (65.0 ± 0.8 yr, mean ± SE, range 60 to 72) healthy males. In separate experimental sessions, subjects performed supine leg cycling at three submaximal levels (∼45%, ∼65%, and ∼85% of peak oxygen uptake), isometric handgrip to exhaustion (30% of maximal force), and two types of orthostatic stress (lower body negative pressure (LBNP) and standing). In general, there were no differences between the young and older subjects in any baseline hemodynamic variable or baseline plasma catecholamine concentrations. In response to all levels of leg cycling, the young and older subjects had similar arterial blood pressure responses. However, the older subjects did demonstrate an augmented forearm vasoconstriction, mediated at least in part, by greater sympathetic vasoconstriction in the skeletal muscle circulation, perhaps necessary to help offset a lower cardiac output response. In response to isometric handgrip, there was a lesser heart rate response in the older subjects, but there were no age-related differences in the selected regional hemodynamic responses, arterial blood pressure response or the plasma norepinephrine responses. Likewise, in response to both types of orthostatic stress, the older subjects demonstrated a lesser tachycardic response, but there was no decline in their ability to maintain arterial pressure. Therefore, the main conclusion of these studies is that, although aging may alter the regulatory scheme, the arterial pressure response to these forms of acute physical stress is not impaired in older humans.