A.Yogev, A. Hall, O. Jay, & M.D. White.

Simon Fraser University, Burnaby, BC, Canada

Together nitrogen narcosis and hyperthermia appear to suppress pulmonary ventilation (VE) during submaximal exercise. It is unresolved how VE is influenced by nitrogen narcosis and hyperthermia at the onset of intense exercise. PURPOSE/HYPOTHESIS: To assess influences of nitrogen narcosis, that was simulated with normoxic 30% nitrous oxide (N2O), and hyperthermia on VE responses short duration, high intensity exercise. It was hypothesized normoxic 30% N2O and hyperthermia would suppress ventilation. METHODS: Ten college age males volunteered for the study that was approved by the SFU Office of Research Ethics. Temperatures on 4 body surface sites (chest, thigh, forehead, lower back) and esophageal temperatures (TES) were recorded with calibrated thermocouples. The total VE, mean of tidal volume (VT) and frequency of breathing (FB) were measured with a calibrated, breath-by-breath metabolic cart. In 2 normothermic and 2 hyperthermic WINGATE exercise trials, volunteers cycled on a seated ergometer when breathing either air or normoxic 30% N2O. Before each hyperthermic trial, TES was increased in a 40oC water tank until it was 1.5oC above its resting value. Each trial included a 15 min rest, 30 s warm up and 30 s Wingate test. A repeated measure ANOVA was employed for the analysis with factors of Core Temperature (Normothermic, Hyperthermic) and Gas Type (Air, normoxic 30% N2O). The significance level was set at 0.05. RESULTS: There was a trend (p=0.10) for a main effect of Core Temperature on mean VT. The VT of 1.7 ± 0.5 L (mean ±SD) during the normothermic WINGATE test with air breathing showed a trend (p=0.07) to be lower than that of 2.1 ± 0.5 L during the hyperthermic WINGATE test with normoxic 30% N2O breathing. There were no main effects for Core Temperature or Gas Type on either FB nor total VE. CONCLUSION: This preliminary evidence suggests during high intensity exercise, when breathing normoxic N2O with a hyperthermic core temperature, that there is a trend for an elevation of exercise ventilation relative to the same exercise with a normothermic core temperature and air breathing.

Supported by NSERC and CFI

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