Intrapelvic Pressure and Urinary Flow Rate in Obstructed and Nonobstructed Human Kidneys

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Abstract
The intrapelvic pressure and urinary flow rate were measured during rest and diuresis induced by intravenous infusion of mannitol solution or furosemide in 18 adult patients with unilateral hydronephrosis and in a control series of 4 patients without outflow obstruction. The findings were related to the renal parenchymal function of the kidney, evaluated by isotope renography, and the distal tubular function as shown by the maximum urine concentration ability. The resting pelvic pressure during normal hydration varied from 1.3 to 10 cm. water in obstructed and nonobstructed kidneys. During osmotic diuresis the pressure gradually increased to an average maximum value of 34.5 cm. water (range 15.0 to 137.0 cm. water) in the hydronephrotic kidneys and 17.5 cm. water (range 7.5 to 25.0 cm. water) in the control kidneys, the difference being statistically significant. A statistically significant difference in maximum pressure during osmotic diuresis was found between hydronephrotic kidneys without (range 33.0 to 137.0 cm. water) and with (range 15.0 to 24.0 cm. water) previous episodes of upper urinary tract infections. In patients with hydronephrosis the maximum urinary flow rate was lower from the affected than from the nonobstructed contralateral kidney. In the control series the maximum flow rate during induced diuresis was never < 7 ml. per minute, which probably is the highest inflow rate that could be used to demonstrate the presence of obstruction by measuring the intrapelvic pressure. The demonstration of intrapelvic pressures within normal limits in obstructed hydronephrotic kidneys with reduced maximum concentration ability after episodes of infection indicates that pressure measurements cannot be used to detect the presence of obstruction in complicated hydronephrosis.

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