Effect of helium on the ventilatory response to hypoxia under normocapnic and hypercapnic conditions

We studied the effect of helium (He) on ventilatory (VI) responses to progressive isocapnic hypoxia. Accordingly, in normal male subjects (age 23-46), we compared hypoxic rebreathes using He as a carrier gas with those utilizing nitrogen (N2) as a carrier gas. When alveolar CO2 tension (PACO2) was maintained at 40 mm Hg, we noted no difference in VI responses to hypoxia between N2 and He trials. In contrast, when PACO2 was maintained at 50 mm Hg, VI responses to hypoxia during the He trials were consistently greater than those noted during the N2 experiments. These results indicate that substitution of He for N2 does not augment VI responses to normocapnic hypoxia; however, this substitution does enhance VI responses to hypercapnic hypoxia.