PHYSIOLOGICAL VARIATIONS IN THE CARDIAC OUTPUT OF MAN

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Abstract
In 19 experiments on 4 subjects it was found that CO2 did not affect the circulatory system of normal man until it reached a concentration of about 6% in the inspired air. Higher concentrations caused an increase in the pulse rate, blood pressure, and cardiac output. Forced voluntary ventilation of atmospheric air also caused a moderate increase in the circulatory rate. When CO2 was added to the inspired air, to avoid any change in the alveolar tension of this gas, practically similar increases were observed. Since, in the last named experiments, only the mechanical effect of hyperventila-tion was present, the changes observed after natural breathing of CO2-air mixtures or during forced respiration of air are also attributed to the mechanical aid which violent respiratory efforts exert on the circulation.

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