Respiratory Exchange of Oxygen and Carbon Dioxide During Rebreathing from a Rubber Bag

Abstract

During rebreathing from a rubber bag, the nose being compressed with a spring clip so that the lungs and bag form a closed system, O₂ and CO₂ diffuse across the pulmonary epithelium, the direction and rate of diffusion depending on the relative tensions of these gases in the blood and alveolar air. This process has been studied in 18 experiments in 2 normal young men. After the subject had sat in a chair for 10 minutes, the metabolic rate was determined. The subject then expired through a side tube to residual air (an alveolar sample being taken) and then rebreathed from the rubber bag 9 times in 22.2 seconds, being guided by spoken directions from an accurately timed phonograph record. Each inspiration emptied the bag and each expiration was as deep as possible. During the rebreathing alveolar samples were drawn into evacuated tubes at the end of breath No. 3, 6, and 9, dividing each experiment into 3 intervals of 8.0, 7.0, and 7.2 seconds in the order named.

The results of the experiments are presented in tabular form. The contents of the rebreathing bag are noted. The initial volume of the lung-bag system is obtained by adding the gas volume of the bag and the residual lung volume of the subject. In most experiments the initial volume was 2400 + 1570 = 3970 cc. The volume changes in the system were calculated from the changes in percentage of nitrogen which is assumed to take a negligible part in the transepithelial gaseous exchange. The volume changes may also be calculated from the difference of O₂ absorbed and CO₂ discharged. The 2 sets of findings listed side by side are in close agreement with a few exceptions probably due to errors in technique or gas analysis.