Heat-exercise performance of pyridostigmine-treated subjects wearing chemical protective clothing

Pyridostigmine bromide is currently the pretreatment of choice for operation in a chemical warfare (CW) environment. Under CW conditions, subjects are exposed to thermal stress caused by CW protective clothing. This investigation was conducted to determine if pyridostigmine affects various physiological and biophysical parameters of human temperature regulation in subjects wearing CW protective clothing. Pyridostigmine was administered orally in a randomized double-blind crossover study in four doses of 30 mg every 8 h. An average of 33% whole blood cholinesterase inhibition was induced in the pyridostigmine treated group 4 h after ingestion of last tablet. The subjects were exposed to 170 min exercise-heat stress (Tdb = 33°C; rh = 60%) consisting of 60 min in a sitting position and two 50-min walks (1.39 m.s^-1, 5% grade) separated by 10 min of rest. Non-evaporative heat exchange was significantly higher, -14.0 and -10.6 W.m^-2 (p < 0.03), for the pyridostigmine-treated subjects. No additional differences were found between treatments in the physiological responses and heat balance parameters at the end of exposure: heart rate (HR) was (mean ± S.D.) 154 ± 16 and 151 ± 24 bpm, rectal temperature (Tre) was 39.0 ± 0.4 and 38.9 ± 0.2°C, heat storage over the 2 h of exercise was 62 ± 15 and 70 ± 15 W.m^-2, and sweat rate was 832 ± 185 and 748 ± 52 g.h^-1, in the pyridostigmine and placebo treatments, respectively. We conclude that pyridostigmine, in the dosage used in this study, does not increase the physiological strain resulting from CW protective garments worn during exercise in hot conditions.