Physiological Effects at Low Oxygen Tensions of Replacing Oxygen with Carbon dioxide. ∗

Abstract

The following experiments were designed to determine if, on the basis of increased respiratory minute volume, an increased alveolar oxygen tension may be obtained at low-oxygen tensions by replacing some of the oxygen with an equal amount of carbon dioxide. Johnson, Eckman, Ramsay and Barach, 1 in experiments on nembutalized dogs in a low pressure chamber, found that addition of 14.3 mm Hg of CO₂ produced no beneficial effect on the oxygen tension of mixed venous blood. The value of these results is limited by the fact that nembutalized dogs are not normally sensitive to the stimulatory effects of carbon dioxide on respiration. However, in a subsequent study which included 4 human subjects, Himwich, Fazekas, Herrlich, Johnson and Barach 2 found that the oxygen content of the arterial and cerebral venous blood was approximately the same whether a 10% C0₂-90% O₂ mixture or 100% O₂ was breathed at a simulated altitude of about 35,000 feet. Numerous studies have demonstrated that addition of CO₂, without proportionate removal of oxygen alveolar oxygen tension is below that required for normal oxygenation of hemoglobin. However, the problem in the latter case in quite different than when the sum of the oxygen tension plus the carbon dioxide tension is kept constant.

Procedures. Eighteen men between the ages of 23 and 35 were used as subjects. These subjects had no known respiratory or cardiovascular abnormalities. The procedure for performing an experiment was as follows. The subject lay on a cot in the supine position for 10 minutes.