EVALUATION OF RENAL RESISTANCES, WITH SPECIAL REFERENCE TO CHANGES IN ESSENTIAL HYPERTENSION 1

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Abstract
Equations are developed for calculation of the total renal resistance, R, the afferent arteriolar resistance, RA, the pure efferent, Re, and the net efferent arteriolar resistance Re (a term that includes the diversion of the glomerular filtrate around the efferent arteriole), and the venular resistance, RV. The calculations are based upon the clinically determinable variables of mean arterial blood pressure, renal blood flow and plasma flow, filtration rate, protein concn. of the blood and renal venous (or femoral) pressure. Assumptions with respect to renal intersitial pressure and other matters pertinent to the validity of the working equations are stated. Some of the limiting clinical conditions under which the working equations are applicable are defined. Calculations are presented for the above resistances in 22 normal subjects who had been examined under standard conditions. A hitherto unrecorded datum is the relatively large magnitude of the renal venular resistance, which in the avg. equals the resistance of either the efferent or afferent arterioles. Data on 51 subjects with essential hypertension reveal that the predominant change in the renal circulation in this disease is an increase in afferent arteriolar resistance. This increase is relatively greater than the increase in the resistance of the systemic arterioles.