Effects of environmental factors on heat tolerance and mechanism underlining hyperthemic hyperventilation.

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We aimed to investigate the effects of environmental factors on heat tolerance and to elucidate the mechanisms underlining the hyperthermic hyperventilation in humans.1. We tested the hypothesis that, in humans, hyperthermic hyperpnea elicited in resting subjects differs from that elicited during submaximal, moderate intensity exercise. It was suggested that hyperthermic hyperpnea does indeed differ depending upon whether one is at rest or exercising at submaximal, moderate intensity.2. We tested the hypothesis that, in humans, exercise-heat acclimation (6-days) changes the hyperthermic hyperpnea during exercise in the heat. It was suggested that heat acclimation does not affect the hyperthermic hyperpnea, although it markedly enhances the cutaneous vasodilatory response during exercise.3. We tested the hypothesis that hyperthermic hyperventilation in part reflects enhanced chemoreceptor ventilatory 0_2 drive, and that the resultant hypocapnia attenuates ventilatory responses and/or mi … More ddle cerebral artery mean blood velocity in resting humans. It was suggested that, in resting humans, although hyperthermia increases chemoreceptor ventilatory 0_2 drive, the relative contribution of the chemoreceptor ventilatory 0_2 drive to hyperthemic hyperventilation is small (〜20%) and unchanged with increasing core temperature, and hypocapnia induced by hyperthermic hyperventilation reduces cerebral blood flow but not ventilatory responses.4. We investigated whether the environmental factors affect the heat tolerance during exercise. Fourteen students exercised in the heat and the relationships among those physiological parameters, the climate conditions of their home towns and the usage of air-conditioner. The relationships between their heat tolerance index such as the sweat rate, increase rate of skin blood flow in the forearm, the increase rate of minute ventilation and the climate data were not significant, suggesting that the recent life style including air conditioning and exercise experience could override the effects of climate of the home town on the heat tolerance in the students. Less