RESPIRATORY REGULATION DURING EXERCISE IN UNCONDITIONED SUBJECTS 1

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Abstract
Observations were made on ventilation and arterial blood changes in 11 untrained subjects during short periods of moderately severe treadmill exercise. Particular attention was paid to the ventilation changes at the start and conclusion of work, to the course of ventilation in early exercise, to the effect on ventilation of breathing gas mixtures having, respectively, an increased CO2 content, a low oxygen content, and a high oxygen content, and to associated changes in arterial CO2 tension, pH and % oxygen saturation. With untrained subjects there may be large changes during exercise in arterial CO2 tension and pH, and these may begin to develop early in exercise. Exercise did not increase significantly the sensitivity of the respiratory center to arterial CO2 tension, as measured by increase in ventilation per mm. Hg increase in CO2 tension. An attempt is made to estimate in semi-quantitative terms the role played by various respiratory stimuli in regulating ventilation during exercise. These stimuli are a "neurogenic" effect; an oxygen effect, which is provisionally regarded as an increase in sensitivity of the chemoreceptor system to oxygen tension; fall in blood pH; and arterial CO2 tension. There is great variation among untrained subjects in the relative importance of these factors.