Control of heat-induced cutaneous vasodilatation in relation to age

Well matched unacclimatised older (age 55-68, 4 women, 2 men) and younger (age 19-30, 4 women, 2 men) subjects performed 75 min cycle exercise (∼40% {Mathematical expression}) in a hot environment (37°C, 60% rh). Rectal temperature (T_re), mean skin temperature (-T_sk), arm blood flow (ABF, strain gauge plethysmography), and cardiac output (Q, CO₂ rebreathing) were measured to examine age-related differences in heat-induced vasodilatation. T_re and -T_sk rose to the same extent in each group during the exposure. There was no significant intergroup difference in sweat rate (older: 332±43 ml · m^-2 · h^-1, younger: 435±49 ml · m^-2 · h^-1; mean±SEM). However, the older subjects responded to exercise in the heat with a lower ABF response which could be attributed to a lower {Mathematical expression} for the same exercise intensity. The slope of the ABF-T_re relationship was attenuated in the older subjects (9.3±1.3 vs 17.9±3.3 ml · 100 ml^-1 · min^-1 · °C^-1, p <0.05), but the T_re threshold for vasodilatation was about 37.0°C for both groups. These results suggest an altered control of skin vasodilatation during exercise in the heat in older individuals. This attenuated ABF response appears to be unrelated to {Mathematical expression}, and may reflect an age-related change in thermoregulatory cardiovascular function.