Control of heat-induced cutaneous vasodilatation in relation to age

Summary

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%$\dot V_{{\text{O}}_{{\text{2max}}} }$) 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$\dot Q$ 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 theT _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$\dot V_{{\text{O}}_{{\text{2max}}} }$, and may reflect an age-related change in thermoregulatory cardiovascular function.