Inhibiting regional sweat evaporation modifies the ventilatory response to exercise: interactions between core and skin temperature.

In humans, elevated body temperatures can markedly increase the ventilatory response to exercise. However, the impact of changing the effective body surface area (BSA) for sweat evaporation (BSA) on such responses is unclear. Ten healthy adults (9 males, 1 female) performed eight exercise trials cycling at 6 W/kg of metabolic heat production for 60 min. Four conditions were used where BSA corresponded to 100%, 80%, 60%, and 40% of BSA using vapor-impermeable material. Four trials (one at each BSA) were performed at 25°C air temperature, and four trials (one at each BSA) at 40°C air temperature, each with 20% humidity. The slope of the relation between minute ventilation and carbon dioxide elimination (V̇/V̇co slope) assessed the ventilatory response. At 25°C, the V̇/V̇co slope was elevated by 1.9 and 2.6 units when decreasing BSA from 100 to 80 and to 40% ( = 0.033 and 0.004, respectively). At 40°C, V̇/V̇co slope was elevated by 3.3 and 4.7 units, when decreasing BSA from 100 to 60 and to 40% ( = 0.016 and < 0.001, respectively). Linear regression analyses using group average data from each condition demonstrated that end-exercise mean body temperature (integration of core and mean skin temperature) was better associated with the end-exercise ventilatory response, compared with core temperature alone. Overall, we show that impeding regional sweat evaporation increases the ventilatory response to exercise in temperate and hot environmental conditions, and the effect is mediated primarily by increases in mean body temperature. Exercise in the heat increases the slope of the relation between minute ventilation and carbon dioxide elimination (V̇/V̇co slope) in young healthy adults. An indispensable role for skin temperature in modulating the ventilatory response to exercise is noted, contradicting common belief that internal/core temperature acts independently as a controller of ventilation during hyperthermia.