Evaluation using dogs of a method for estimating mixed venous and arterial PCO2 from a single breath

Estimates of arterial and true mixed venous carbon dioxide tension (PCO2) were made from the continuous records of the changes in carbon dioxide and oxygen tensions in the expired gas during a single prolonged expiration, as described by Kim, Rahn, and Fahri (J. Appl. Physiol. 21: 1338, 1966). The results were compared with the results of direct analyses of systemic arterial and pulmonary arterial blood. There was no systemic error of the arterial estimates over a range of 32-48 Torr or of the venous estimates over a range of 33-59 Torr. The random errors of the arterial and venous estimates were +/- 1.5 and 1.2 Torr (2 SD) respectively. These results are better than those obtained by other noninvasive methods.