Peripheral vascular tone during heat load is modified by exercise intensity

Abstract

Nonevaporative heat loss [ radiation (R) and convection (C) ] and evaporative heat loss [ evaporation (E) ] from the hand (Rh + Ch) and (Eh) were measured in four healthy men exercised on a bicycle ergometer at 20, 35, and 45% of VO2max at an ambient temperature (Ta) of 20 degrees C with a gradient layer type direct hand calorimeter. Esophageal (Tes) and mean skin temperatures (Tsk) were continuously measured. Leg exercise at these intensities produced initially a fall followed by an increase in (Rh + Ch). Tes was positively correlated to % VO2max during exercise. Thermal conductance in the hand (k) was computed by dividing the total heat loss from the hand (Rh + Ch + Eh) by the difference between Tes and mean hand temperature. All subjects had significantly lower (Rh + Ch) and k at a given Tes during exercise with a higher intensity. The slope indicating the relation between (Rh + Ch) and Tes was 9.18, 6.25, and 5.04 W per degree C at 20, 35, and 45% VO2max, respectively. The slope of k vs. Tes was 28.64, 20.82, and 16.61 W/m2 X degree C degree C at 20, 35, and 45% VO2max, respectively. These results indicated that thermoregulatory vasodilation was reduced by the increasing reflex vasoconstrictor tone caused by increasing intensity of exercise as a non-thermal factor.