Pressure/Flow Relations in the Kidney

Abstract

A system for perfusing a dog''s kidney in situ with independently variable mean and pulse pressures and for measuring the rates of arterial inflow over prolonged periods is described. The results failed to reveal that changes in arterial pulse pressure per se have any effect on renal blood flow. The renal vessels (kidney in situ) show prolonged and significant autonomous variations in resistance following abrupt changes in arterial pressure which are not due to pulse pressure changes. Such adjustments in vascular resistance must be taken into consideration in establishing pressure/flow relations by exptl. methods. When pressure/flow curves are plotted after pressure stabilization they usually resemble those previously reported in that they are concave to the pressure axis in ranges of pressure above 80 mm. Hg. Linear curves were usually obtained when resistance to flow was high, but occasionally also when it was low. The renal resistance calculated with allowance for so-called yield pressure decreased markedly when arterial pressure was lowered to approx. 80 mm. Hg, reached a minimum at approx. 65 mm. Hg and thereafter remained fairly constant. The arterial pressure existing at the point at which all flow ceases does not seem to be a practical indicator of vascular resistance in the kidney. An evaluation of data from this investigation led to the conclusion that the changes in renal resistance represent active adjustments in caliber of the afferent glomerular vessels.