Effects of elevated core temperature and normoxic 30% nitrous oxide on human ventilation during short duration, high intensity exercise.

It was hypothesized that normoxic 30% nitrous oxide (N 2 O) would suppress and hyperthermia would increase exercise ventilation during short duration, high intensity exercise. Thirteen males (24.2 ± 0.8 y; mean ± SE), of normal physique (BMI, 23.8 ± 1.0 kg m −2 ), performed 4 separate 30 s Wingate tests on a cycle ergometer. Exercise ventilation and its components, as well as mean skin and esophageal temperature ( T ES ), were assessed in 2 way experimental design with factors of Thermal State (Normothermia or Hyperthermia) and Gas Type (Air or 30% Normomoxic N 2 O). In the 2 hyperthermic tests T ES was elevated to ∼38.5 °C in a 40 °C bath. The main results indicated a significant interaction ( F = 7.14, P = 0.02) between Gas Type and Thermal state for the exercise-induced increase in ventilation (Δ V ˙ E ). During both the normothermia and hyperthermia conditions with AIR breathing, the exercise Δ V ˙ E was ∼80 L min −1 and it was significantly decreased to 73.1 ± 24.1 L min −1 in the normothermia condition with N 2 O breathing relative to that of 92.0 ± 25.0 L min −1 in the hyperthermia condition with N 2 O breathing. In conclusion, normoxic N 2 O breathing suppressed high intensity exercise ventilation during normothermia relative to that during hyperthermia on account of decreases in the tidal volume and this led CO 2 retention. [ABSTRACT FROM AUTHOR]