Homeostasis of carbon dioxide during intravenous infusion of carbon dioxide

Abstract

When rats are infused intravenously continuously with blood enriched in an extracorporeal system with 100% CO₂, they are found to excrete the infused CO₂ quantitatively. The excretion is accomplished by increasing ventilation in proportion to the infusion rate. Neither mean arterial pH nor Pco₂ shows a statistically significant change. This constancy of composition is observed at CO₂ infusion rates ranging from zero to an amount equal to six times the resting metabolic CO₂ production. Similarity of this hyperpnea to the chief characteristics of the hyperpnea of exercise is notable. Increased oxygen uptake during this procedure is about 3.5 ml/l. of ventilation, a reasonable value for the oxygen cost of ventilation. Since, during this process the animal is quiescent and shows no other metabolic changes it is suggested that the effective signal for the regulation of arterial Pco₂ is CO₂ itself. The ability of the experimental animal to respond successfully to high rates of loading seems to be limited by failure to make appropriate circulatory adjustments. Removing CO₂ by equilibrating blood with 100% o₂ in the extracorporeal circuit decreases ventilation, but readily leads to an uncontrolled alkalosis. Submitted on April 13, 1960