Tissue pressure and critical closing pressure in the dog kidney

Abstract

The study was undertaken to investigate a possible relationship between renal tissue pressure and the arteriovenous pressure difference at zero flow in the dog kidney. Experiments were performed on the isolated blood perfused kidney and on the kidney in situ in the eviscerated dog. Continuous strain gauge recordings of the arterial pressure, tissue pressure and rates of weight loss (venous outflow) were obtained after cessation of the renal arterial inflow. Results indicate a positive arterial pressure intercept at zero flow, but provide evidence for the absence of a general critical closing pressure in the dog kidney. After arrest of the renal arterial inflow the arteriovenous pressure difference fell to a mean value of 1.7 mm Hg as tissue pressure declined to a mean of 2.9 mm Hg and the venous outflow approached zero. It is suggested that the existing renal tissue pressure acts as a collapsing force on renal blood vessels producing a positive arteriovenous pressure difference at zero flow. A general ‘critical closing pressure’ need not be postulated to account for these findings.