Radionuclide constant pressure perfusion study on measurement of exit urine flow: experimental and preliminary clinical investigations.

To calculate exit urine flow from the renal pelvis to the bladder in hydronephrosis, a simple method, radionuclide constant pressure perfusion study, was used. The mathematical model proposed for calculation of the exit flow (F) was simple: F = (initial slope)/Do'/exp(-0.148d), where F is expressed as flow rate (ml. per minute) of infused radioactive solution into the bladder. The value of the initial slope is expressed as a count rate per minute of time-activity curve of the bladder. Do' is a count rate per ml. of infused radioactive solution, which was measured by a gamma camera in air, and d is depth (cm.) of the bladder from the body surface to the vesical mucosa. The number -0.148 indicates the effective linear attenuation coefficient of 99mtechnetium, which was determined by a phantom study. In the experimental studies calculated flow correlated well with real pump flow. In preliminary clinical studies in 16 patients (20 kidneys) who underwent nephrostomy, measurement of flow rate at steady intrapelvic pressure with no subtraction of intra-abdominal pressure in 12 of 14 nonobstructed cases demonstrated a pressure-dependent pattern in which flow increased linearly in response to the pressure increase. In 2 nonobstructed children radionuclide constant pressure perfusion study failed: 1 due to crying and 1 to unknown causes. In 2 cases of complete or equivocal obstruction by constant perfusion (Whitaker test) only minimal or no flow rate was found at the maximum intrapelvic pressure increase of 24 cm. water. The urine flow was observed only in the repeated study in 3 patients. These phenomena were assumed to be due to immature expertise in the new technique. This new technique can provide physiological measurement of the urine flow at variable levels of constant intrapelvic pressure in hydronephrotic patients, although the pressure-flow relationship for identifying partial obstruction from nonobstruction still remains to be clarified in further clinical studies.