Simultaneous Measurement of Effective Renal Blood

Unpublished data of Bradley and associates (1) indicate that about 25 to 30 per cent of the cardiac output, as measured by the ballistocardiograph (2), perfuses the kidney of healthy adults at rest. This figure has been reported in a review on renal physiology (3). Levy and Blalock (4) obtained an average value of 18.5 per cent in unanesthetized dogs, using the catheterization technique or heart puncture and the direct Fick principle for the determination of the cardiac output. When normal human values for the resting cardiac output obtained by the direct Fick procedure (5, 6) are divided into the normal human values for effective renal blood flow (7), the resulting effective renal fraction is about 19 to 20 per cent. The present investigation was undertaken to make these measurements simultaneously in a series of normal subjects and in patients with essential hypertension, using the cardiac catheterization technique (8, 9) and the direct Fick principle for the measurements of the cardiac output.