Circulating plasma volume and renal function.

The relationships of circulating plasma volume (PV) to effective renal plasma flow and glomerular filtration rate (GFR) were investigated in reference to their interrelated changes induced by upright posture in normal subjects and patients with chronic glomerulonephritis. The following relation was obtained: (percentage change in GFR) = k(percentage change in PV). The values of k were 3.4 for the normal and 3.1 for the patients. There was no statistically significant difference between the two. On account of the above relation the recumbent level of glomerular filtration rate (GFR)r was derived from the recumbent level of circulating plasma volume (PV)r as follows: (GFR)r = Kp [(PV)r]k, where Kp is a constant. On the other hand, the decreases (percentage) in effective renal plasma flow were biphasically related to those in PV. Mean arterial pressure rose in upright posture in many cases, but its changes (percentage) showed no correlation with the changes (percentage) in GFR. These results suggest that in a small decrease in PV, GFR does not decrease with the fall in mean arterial pressure, but with the power function of PV. The possible mechanisms of these changes in renal function are examined with special reference to the structure of renal arterial system.