Acclimatization of older men to work in heat

Four men, ages 44—60, repeated daily work experiments in the heat by which they had demonstrated on themselves rapid acclimatization to work in a hot climate 21 years earlier. The work, heat stress, and duration of exposure were those originally found to cause marked hyperpyrexia and circulatory strain in unacclimatized men (mean age 31 years) on the 1st day in the heat. Under these conditions, the subjects sweated at 1.3— 1.5 kg/hr. Tolerance of the men on the 1st day of exposure was no less than when they were younger. Body temperatures and heart rates of the older men were lowered in successive days of exposure and the work was judged progressively easier. Final values of body temperature reached after 5—7 days of exposure were about the same as observed originally after the same number of exposures. Thus, these older men exhibited about the same degree of strain during work in the heat as they did 21 years earlier and acclimatized about as well.

aging; hyperthermia

Submitted on October 1, 1964

Relations between sweating, cutaneous blood flow, and body temperature in work

Men worked on a treadmill for periods of 5, 5, 10, 10, 10 and 10 min, stopping for 2 min between work periods to be weighed. Finger and mean skin temperatures decreased at the beginning of work (10 mets). When room temperature was 25 C vasodilation occurred in the finger in the third work period as gastrocnemius muscle and femoral vein temperatures reached maximal values. Temperatures of skin and saphenous vein blood rose rapidly as the men reclined during the rest periods and decreased when work was resumed, coinciding with changes of femoral temperature in the opposite directions. These rapid shifts in temperature indicate that during the rest periods the proportion of blood coming from the skin into the trunk of the femoral was greater than during the work periods. The onset of sweating, the rate of its increase in the early stages of these work experiments, and its decline in recovery more nearly paralleled corresponding changes in femoral temperature than any of the other temperatures measured.

exercise; femoral vein temperature; temperature regulation; saphenous vein temperature; skin temperature

Submitted on October 5, 1964

Preacclimatization of men to heat by training

During April 1963, five distance runners from the Indiana University track team and one champion swimmer performed 85-min walks on a treadmill at 5.6 km/hr up a 5.6% grade in a hot environment (40 C DB, 25% relative humidity). Although none had been exposed to the heat since the preceding summer, the runners made responses typical of heat-acclimatized men. Untrained subjects exposed to the same stresses and the swimmer failed to regulate body temperature effectively. Although sweat rate was less in the runners than in the untrained men, it was 2.4 times greater per degree rise of rectal temperature for the runners. The runners produced 8% less metabolic heat per square meter of body surface than did the untrained men, and they also had much higher tissue heat conductance values. The swimmer's difficulty in adjusting to the heat stress was largely due to his relatively high metabolic cost in walking on the treadmill. It is thought that the preacclimatized state of the trained men probably resulted from the daily elevations of central temperature in their strenuous workouts during the preceding months.

acclimatization to heat; heat stress; hyperthermia; sweat rate; metabolic rate; tissue heat conductance; temperature regulation

Submitted on June 11, 1964

Artificial Pneumothorax as a Treatment of Pulmonary Tuberculosis

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