Evaluation of slope method for measuring pulmonary blood volume in man

¹ Department of Medicine, Peter Bent Brigham Hospital; and Department of Medicine, Harvard Medical School, Boston, Massachusetts

Knowledge of the pulmonary blood volume is important in several areas of circulatory physiology. However, adequate methods for measuring this volume have not been established. The slope of an indicator-dilution curve across the central circulation has been used in several studies as an indication of this volume. In the present study the blood volume between pulmonary artery and left atrium was measured in 31 human subjects by an application of the well-established mean transit time principle. Slope volumes were also measured. There was poor agreement between the results of the two techniques. Unilateral pulmonary artery occlusion consistently reduced pulmonary blood volume by the mean transit time method, with only minor and less consistent changes in slope volumes. A close correlation between the slopes of curves from simultaneous pulmonary artery and left atrial injections suggested a predominant effect on both curves of factors at or distal to the left side of the heart. It was concluded that the slope method did not measure the pulmonary blood volume in man.