RESPONSE OF RENAL BLOOD FLOW AND CLEARANCE TO GRADED PARTIAL OBSTRUCTION OF THE RENAL VEIN

Abstract

When renal venous pressure is elevated from 7.5 to 22.4 mm. Hg by partial venous obstruction, direct renal blood flow and renal clearances (PAH and creatinine) decrease by an avg. of 15%. This decrease in blood flow and clearances can be explained almost entirely by the decrease in pressure gradient across the renal vascular circuit resulting from increased venous pressure, since arterial pressure remains essentially constant. Thus, the A-V pressure difference decreases by an avg. of 11.5%. The clearances of PAH and creatinine show parallel reductions, hence there is no alteration in the filtration attributable to venous obstruction. Therefore, no support can be given to the concept that elevated venous pressure increases intraglomerular pressure, at least not in the range studied. The conclusion follows that the increased filtration fraction noted in congestive heart failure is probably attributable to increased efferent arteriolar resistance rather than to high venous pressure. The reduction in glomerular filtration rate resulting from experimentally elevated renal venous pressure is not enough to favor Na retention and, in turn, edema formation. Other mechanisms must be operative in congestive heart failure.