Metabolic and cardiorespiratory responses to He-O2 breathing during exercise

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Abstract
He is often substituted for N2 as the diluent gas in artificial breathing mixtures. To compare the metabolic and cardiorespiratory responses to helix (79% He-21% O2) breathing during exercise with those to air (79% N2-21% O2) breathing, 2 groups of experiments were conducted. In the first, 4 men performed exercise on the bicycle ergometer at 6 different intensities ranging from mild to severe. Each subject was tested twice at each work rate, once while breathing air and once while breathing He-O2. There were no significant differences between the gases for heart rate or blood lactate concentration. At the 4 lowest work rates neither O2 uptake (.ovrhdot.VO2) nor minute ventilation (.ovrhdot.V) demonstrated a significant difference between the breathing mixtures, but at the 2 highest work rates .ovrhdot.VO2 (P < 0.01) and .ovrhdot.V (P < 0.01) were significantly higher during He-O2 breathing. In the 2nd group of experiments, .ovrhdot.VO2 and .ovrhdot.V were measured in 6 men during exercise that elicited each subject''s maximal O2 uptake (.ovrhdot.VO2 max), once while breathing air and once while breathing He-O2. There were significant differences in .ovrhdot.VO2 max (P < 0.001) and .ovrhdot.V (P < 0.001) between the gases, with He-O2 giving the greater value. Based on the calculated work of breathing, the increase in .ovrhdot.VO2 on He-O2 does not appear to be directly related to the increased .ovrhdot.V. The increased .ovrhdot.V during He-O2 breathing may cause a relative alkalosis, which in turn may be responsible for the increased .ovrhdot.VO2.

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