Relationships between 30% normoxic nitrous oxide breathing, core temperature and exercise ventilation

Hall, Amanda (2003) Relationships between 30% normoxic nitrous oxide breathing, core temperature and exercise ventilation. Masters thesis, Memorial University of Newfoundland.

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Abstract

While working at depth air breathing commercial divers experience nitrogen narcosis and they can become hyperthermic with surface supply heating systems. It is unresolved to what extent narcosis and hyperthermia influence exercise or work ventilation. The 2 studies in this thesis examined the effects of nitrogen narcosis and hyperthermia on phase I and III· of exercise ventilation. The first study examined the effect of 30% normoxic nitrous oxide (N₂O) induced narcosis on both phase III ventilation and on core temperature thresholds for ventilation in 6 male subjects performing an incremental exercise test to exhaustion. The second study examined independent effects of 30% normoxic N₂O induced narcosis and core temperature on phase I exercise ventilation for 6 male subjects exercising in 4 separate 30 s Wingate exercise tests. For 2 Wingate tests subjects remained normothermic for the exercise while for the 2 other Wingate tests prior to exercise they were rendered hyperthermic in a 40°C bath for the test. The first study showed relative to exercise with air breathing that N₂O breathing significantly suppressed exercise ventilation (p<0.05) and the frequency of respiration (p<0.05) while shifting esophageal temperature (Tes) thresholds for ventilation to significantly higher Tes levels (p<0.05). The second study showed a significant (p<0.05) decrease for total ventilation in N₂O normothermic relative to N₂O hyperthermic exercise and this decrease was due to significant decreases in tidal volume (p<0.05). In conclusion, the results support the hypothesis that the control of exercise ventilation includes a neural component as evidenced by nitrogen narcosis suppressing and hyperthermia elevating human ventilation during high intensity exercise.

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