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Physiology and Pharmacology of Temperature Regulation

The effects of hyperthermia and hypoxia on ventilation during low-intensity steady-state exercise

School of Kinesiology, Simon Fraser University, Burnaby, British Columbia, Canada

Submitted 31 December 2005 ; accepted in final form 15 August 2006

This study assessed whether the elevated sensitivity of ventilation to hypoxia during exercise is accounted for by an elevation of esophageal temperature (T_es). Eleven males volunteered for two exercise sessions on an underwater, head-out cycle ergometer at a steady-state rate of oxygen consumption (O₂) of 0.87 l/min (SD 0.07). In one exercise session, 31.5°C (SD 1.4) water held T_es at a normothermic level of 37.1°C, and in the other exercise session, water at 38.2°C (SD 0.1) maintained a hyperthermic T_es of 38.5°C. After a 30-min rest and 20-min warm-up, exercising participants inhaled air for 10 min [Euoxia 1 (E1)], an isocapnic hypoxic gas mixture with 12% O₂ in N₂ (H1) for the next 10 min and air again [Euoxia 2 (E2)] for the last 10 min. A significant increase in _E during all hyperthermia conditions (0.01< P < 0.048) was evident; however, during hyperthermic hypoxia, there was a disproportionate and significant (P = 0.017) increase in _E relative to normothermic hypoxia. This was the main explanation for a significant esophageal temperature and gas type interaction (P = 0.012) for _E. Significant effects of hyperthermia, isocapnic hypoxia, and their positive interaction remained evident after removing the influence of O₂ on _E. Serum lactate and potassium concentrations, as well as hemoglobin oxygen saturation, were each not significantly different between normothermic and hyperthermic-hypoxic conditions. In conclusion, the elevated sensitivity of exercise ventilation to hypoxia during exertion appears to be modulated by elevations in esophageal temperature, potentially because of a temperature-mediated stimulation of the peripheral chemoreceptors.

oxygen consumption; isocapnia; hyperpnea; chemosensitivity; immersion

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