Abstract

The linear relationship bteween minute ventilation (VE) and C02 output (Vc02) was steeper in 9 of 10 healthy subjects, when treadmill walking was carried out breathing 14 oxygen than when breathing air. This confirmed that the ventilatory response to modest exercise was usually potentiated by mild hypoxia. Arterial oxygen saturation did not significantly correlate with VE inseven healthy subjects, walking, breathing air or 14 oxygen, whereas there was a significant correlation between VE and calculated mixed venous saturation in five of these subjects. Transient relief of hypoxia, when breathing 14 oxygen, by five breaths of 30 oxygen both at rest and during walking, reduced ventilation more at higher levels of exercise. This indicated that the peripheral chemoreceptor response to a given level of arterial desaturation was enhanced by exercise. Directly measured femoral venous saturation was correlated with VE in another three subjects, and there was also a close, but curvilinear, relationship between VE and femoral venous lactate concentrations during similar exercise, when breathing 21 or 14 oxygen. We suggest that receptors in working muscle could be sensitized by muscular hypoxia during exercise when breathing 14 oxygen, and thus contribute to the potentiation of the peripheral chemoreceptor stimulation of exercise ventilation by hypoxia. Verf.-Referat