Two Radiographic Tests for Assessment of Renovascular Hypertension

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Abstract
It is the purpose of this preliminary communication to describe a simple modification of the intravenous pyelogram which demonstrates the characteristically disturbed renal function in hypertensive patients with unilateral renal artery disease and, in addition, to present another physiologic test, namely the recording of pressure measurements in renal artery stenosis. 1. Radiographic Screening Test for Renovascular Hypertension A hemodynamically significant renal artery stenosis results in a diminished pulse pressure downstream to the area of constriction. This usually decreases renal plasma flow and the rate of glomerular filtration. In 1953 Howard et al. (1) demonstrated by bilateral ureteral catheterization that water and sodium excretion by the ischemic kidney is decreased. Classical unilateral renal artery stenosis is characterized by at least 50 per cent reduction in urine flow and 15 per cent decrease in sodium excretion as compared with the uninvolved kidney. The Howard test has been modified and improved in recent years by several investigators (2–5). In unilateral renovascular hypertension an excessive re-absorption of filtered water and sodium in the “ischemic” kidney has been convincingly demonstrated by inulin clearance studies. The classical inulin test is a measure of glomerular filtration, since this agent passes freely through the glomerular membrane without being reabsorbed or excreted by the tubules. Its concentration, therefore, in the urine of both kidneys serves as an indicator for comparing the tubular reabsorption of water. In unilateral renal artery stenosis, a marked hyperconcentration of inulin is found on the involved side, indicating 100 to 600 per cent increased water reabsorption from the tubular apparatus. The total urine flow in the ischemic kidney is at least 50 per cent less than that on the uninvolved side. Mcchesney and Hoppe (6) have shown that the clearance of sodium diatrizoate (Hypaque, Renografin, etc.) is practically identical to that of inulin, which would indicate that modern urographic contrast media are excreted by glomerular filtration only. Inulin and sodium diatrizoate compounds are handled by the kidney in similar manner, and the hyperconcentration invariably present in unilateral renal arterial hypertension should be clearly visible on the intravenous pyelogram. since this is not always so, a simple modification is proposed which may be considered to be a radiographic diatrizoate kidney clearance test. Method The patient is prepared for routine intravenous pyelography with the customary dehydration regime. Following the scout film, 50 ml. of 75 per cent Hypaque or 76 per cent Renografin is injected intravenously as rapidly as possible through a 1-inch, No. 20 needle. The needle is taped in place and connected to an intravenous drip of normal saline solution, which is set at a very slow rate (1 drop every fifteen to thirty seconds).

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