Non-invasive evaluation of bilateral renal regional blood flow and tubular dynamics during acute unilateral ureteral obstruction.

Background: Global renal haemodynamic responses to acute unilateral ureteral obstruction (AUUO) have been studied extensively in animals, yet little is known about the concurrent changes in haemodynamics and tubular fluid dynamics that occur within the distinct regions of the kidney during AUUO. The advent of electron beam computerized tomography (EBCT) now allows us to evaluate non-invasively intrarenal haemodynamics and tubular fluid dynamics in vivo.

Methods: Using EBCT, we quantified total, cortical and medullary renal blood flow (RBF, C-RBF and M-RBF), and the concurrent intratubular fluid contrast concentration (ITCC) from contrast media dilution curves, prior to, and at 30 and 90 min after the onset of AUUO in five pigs.

Results: At 30 min after AUUO, there was a small 17+/-7% fall in C-RBF that did not quite reach significance (P = 0.076), whereas RBF, M-RBF, glomerular filtration rate (GFR) and ITCC were preserved. At 90 min, both C-RBF and RBF had fallen by 54+/-8 and 45+/-5%, respectively (P<0.05). GFR also tended to decrease (by 49+/-8%, P<0.06), whereas there was preservation of M-RBF. ITCC increased in the proximal and distal tubules, and tended to increase in Henle's loop. In the contralateral kidney, AUUO did not alter the haemodynamics, but transiently decreased ITCC in all tubular segments.

Conclusion: EBCT allows evaluation of AUUO-induced changes in intrarenal haemodynamics and tubular fluid dynamics. AUUO decreased cortical, but not medullary perfusion of the ipsilateral kidney, and increased the ITCC in most tubular segments, suggesting increased tubular reabsorption that may have helped maintain GFR and tubular fluid flow.