The oxygen saturation of blood in the venae cavae, right-heart chambers, and pulmonary vessels of healthy subjects.

Abstract Twenty-six healthy ambulatory subjects with cardiovascular respiratory systems normal in all clinical and laboratory aspects were investigated by cardiac catheterization. Multiple determinations of blood oxygen saturations were made in rapid succession by cuvette oximeter at various sites in the right side of the heart. With the subject breathing air, the mean and range of the percentage oxygen saturation of radial arterial blood equalled 97.3 (95 to 99) per cent and of the venous blood withdrawn from the inferior vena cava, superior vena cava, right atrium, right ventricle, and pulmonary artery, 83.0 (76 to 88) per cent, 76.8 (66 to 84) per cent, 79.5 (72 to 86) per cent, 78.5 (64 to 84) per cent, and 78.4 (73 to 85) per cent, respectively, while that from the pulmonary artery wedge position equalled 98.2 (90 to 100) per cent. The factors responsible for the variation in the oxygen saturation of venous blood were analyzed and methods suggested for reducing this variation. The mean of the average differences in oxygen saturation between multiple paired samples of blood withdrawn in rapid succession from the right atrium and inferior vena cava, right atrium and superior vena cava, right atrium and lower part of the right ventricle, and upper part of the right ventricle and pulmonary artery equaled −2.2, + 3.2, + 0.1, and + 0.1 per cent, respectively. With this method there is a 95 per cent likelihood that an abnormal source of arterialized blood (left-to-right shunt) is present within the right atrium when saturation of blood from it uniformly exceeds that in the inferior vena cava by more than 4 per cent, that in the superior vena cava by more than 8 per cent, or an average of the inferior and superior caval samples by more than 3 per cent. In the absence of an atrial septal defect, arterialization in the right ventricle at the 95 per cent likelihood level can be considered to be demonstrated when its saturation exceeds that in the right atrium by more than 3 per cent and, in the absence of a ventricular septal defect, arterialization in the pulmonary artery is indicated when oxygen saturation of blood from it exceeds that from high in the right ventricle by more than 2 per cent. Comparison of the average oxygen saturation of blood withdrawn from all positions within the right ventricle with those obtained from the right atrium and pulmonary artery was suggestive of a slight but significant reduction in the oxygen saturation of the venous blood during its passage through the ventricle. Streamline flow of blood from the coronary sinus and thebesian veins draining into the right ventricle was considered a likely explanation of this finding, although transient increases in cardiac output engendered by anxiety consequent to ectopic beats during manipulation of the catheter may be involved. Variations in the oxygen saturation of multiple samples of mixed venous blood from the pulmonary artery from the same individual were consistent with the interpretation that the average maximal intra-individual variation in cardiac output, in these healthy subjects under conditions of supine rest, was ±17 per cent.