Comparison of the oxygen cost of breathing and lactatemia during exercise between nitrogen-oxygen breathing and helium-oxygen breathing

The purpose of this study was to compare the oxygen cost of breathing during exercise when inspiring mixtures of either 80% nitrogen/20% oxygen (N₂-O_{2) or 80% helium/20% oxygen (He-02). Four male subjects exercised on a bicycle ergometer for 20 minutes at a rate of approximately 60% of their VO2 max. During the final 10 minutes of exercise, they hyperventilated voluntarily at a breathing rate of 60 breaths per minute. The minute ventilation achieved during hyperventilation with He-02 was significantly higher than that with N2-O2 (p < 0.05), but there was no significant difference in the oxygen cost of breathing between the two gases (p > .5). The average cost of breathing for He-02 was 3.9 ml/1 at an average ventilation of 81.8 1/min; the average cost of breathing for N2-O2 was 3.5 ml/1 at an average ventilation of 56.1 1/min. Lactate concentration was measured to determine if voluntary isocapnic hyperventi1ation caused increased blood lactate levels. No significant difference was found in lactate concentration between the two gases and between the two exercise periods of normal ventilation and voluntary hyperventilation. This study suggests that one can sustain a higher ventilation with He-02 without increasing the O2 cost of that ventilation.}