Heat exchange through cutaneous vasodilation after atropine treatment in a cool environment.

This report summarizes a tightly controlled laboratory study in which the thermoregulatory effects of an intramuscular injection of atropine sulfate (2 mg) were compared with a placebo injection of sterile saline during exposure to a cool environment. Four subjects were tested during seated cycle exercise at a moderate exercise intensity (55% Vo2 peak) at an ambient temperature of 22 degrees C (37% relative humidity; ambient water vapor pressure 1.0 kPa). Esophageal temperature (Tes), mean weighted skin temperature (Tsk), and forearm sweating rate (ms) were continuously measured during 30 min of rest and 35 min of exercise. Skin blood flow (FBF) from the forearm was measured twice each minute by venous occlusion plethysmography. Whole-body sweating was calculated from weight changes pre- and post-exercise. The expected decrease in whole-body and local sweating rate (-57% and -68%, respectively) occurred in the atropine-treated subjects. By 10-15 min of exercise, dry heat loss (R + C, radiative and convective heat exchange) was significantly elevated from the head, chest, back, arm, forearm, and thigh in the atropine experiments. Core temperature actually decreased 0.2 degrees C (p less than 0.05) in the atropine-treated subjects during exercise as a result of enhanced dry heat exchange. By 25 min of exercise. FBF was 98% (p less than 0.05) greater after atropine treatment. These results show that the peripheral modification of cutaneous blood flow which occurs in atropine-treated subjects is sufficient to markedly alter heat exchange in a cool environment.