Respiratory and Circulatory Response to Added Air Flow Resistance during Exercise

Abstract

The effects of external air flow resistance (gas mask) on the respiratory and circulatory response to submaximal and maximal exercise were studied in 10 healthy subjects. The results of the experiments with the mask are compared with the results of experiments in which a conventional respiratory valve was used. The mask had an inspiratory resistance 9 cm H₂O per litre per sec and expiratory resistance 26 cm H₂O per litre per sec. The inspiratory and expiratory resistance of the respiratory valve was 1-7 cm H₂O per litre per sec. Oxygen uptake was the same for a given work load in both series of experiments up to 1200 kpm/min, i.e. to approximately 75 per cent of the maximal work capacity of the subjects, but a significant decrease in oxygen uptake during maximal work was observed when the mask was used. Pulmonary ventilation wa3 always lower with the mask than with the valve and the difference increased with increased work load. The inspiratory resistance of the mask caused a lowering of respiratory rate which was partly compensated for by the increase in tidal volume. This compensation failed at maximal exertion resulting in a marked pulmonary hypoventilation. The same maximal heart rate was observed in both series although at submaximal work loads the heart rate was higher with the mask than with the valve.