URINARY OXYGEN TENSION RATIO AND SODIUM REABSORPTION RATIO IN DIAGNOSING RENOVASCULAR HYPERTENSION

Abstract

Split renal function studies including examinations on urinary oxygen tension and reabsorption of sodium were carried out on 13 cases of unilateral renovascular hypertension, 4 cases of bilateral renovascular hypertension, 5 cases of essential hypertension and on 5 cases with unilateral renal disorders not relating to hypertension.
Anaerobically collected renal pelvic urine was examined by the gas analyzer with Clark type oxygen electrode. The urinary oxygen tension ratio (% increase) was calculated as
ischemic side-contralateral side/contralateral side×100 (%)
and the sodium reabsorption ratio (% reduction) was calculated as
contralateral side-ischemic side/contralateral side×100 (%)
where reabsorption of sodium of the each kidney was calculated as (GFR×serum sodium content-urine volume×urinary sodium content).
As for urinary oxygen tension ratio, 10 out of 13 unilateral renovascular hypertensives showed 30% or more increases, whereas one case showed only a 10% increase and the other 2 showed no increase.
Every operated unilateral renovascular hypertensive patients showing 30% or more increases in urinary oxygen tension ratio gained normotension after surgery, whereas 2 cases without significant elevation of urinary oxygen tension ratio did not show any improvement in their hypertensive state postoperatively.
Urinary oxygen tension ratio of bilateral renovascular hypertensive patients ranged between 0-30% and that of the control gorup without renal disease ranged between 3--6%.
The control group with unilateral renal diseases showed decreased urinary oxygen tension on the diseased side except in one case.
Unilateral renovascular hypertensive patients had 25% or more reduction in sodium reabsorption ratio. Bilateral renovascular hypertensive patients showed no more reduction than 25% whereas the control group showed various distribution in reduction percentages.
Urinary oxygen tension ratio showed correlationship with the Howard test and with the RVRR (renal vein renin ratio).
Elevated urinary oxygen tension in the ischemic kidney can be attributed to reduced urinary sodium reabsorption and hence reduced oxygen consumption in the renal medulla.
The urinary oxygen tension ratio (% increase) coupled with the sodium reabsorption ratio (% decrease) can be one of the indicators of renal ischemia in diagnosing unilateral renovascular hypertension.