Evaluation of Methods for Estimating Renal Medullary Blood Flow

Abstract

Although only 10-15% of renal blood flow enters the medulla, renal medullary hemodynamics have been implicated as a key factor for the ability of the kidney to excrete concentrated or diluted urine and to be involved in sodium homeostasis. Due to the obvious importance of medullary hemodynamics, several methods have been developed or modified for estimating regional renal blood flow. The aim of the present paper is to evaluate critically the most commonly used methods available today. Those which are considered in this paper are: (1) albumin accumulation (Lilienfield), (2) rubidium-86 uptake, (3) transit time-indicator dilution, (4) red cell velocity tracking, (5) red cell flux (fluorescently labeled red cells) and (6) laser-Doppler flowmetry. Depending on the method of choice, the reported control values for renal medullary blood flow differ up to tenfold. Overall, it appears that the discrepancies in values obtained from the different methods will not be resolved until the methods are compared directly in the same animal and during different experimental conditions. Furthermore, one needs to understand and describe accurately the involved errors so that proper corrections can be made. It seems likely, however, that the majority of the techniques can be used to study relative changes, but attempts should not be made to draw conclusions about the absolute flow value. In this regard the laser-Doppler method seems to be superior in its simplicity of use and its large advantage of continuous and relatively noninvasive measurement.

Regional responsiveness of renal perfusion to activation of the renal nerves

“…These studies suggested variously that MBF is more sensitive than CBF to neural activation (12) or that renal nerve stimulation can increase MBF (24). Regardless, these studies should be interpreted with great care, because the validity of their methodology has been questioned (11,23).…”

Reactive oxygen species cause diabetes-induced decrease in renal oxygen tension

“…Renal medullary blood flow is normally low in order to preserve osmotic gradients and enhance urinary concentration [12,13]. At the same time, medullary oxygen consumption is high, since the medullary thick ascending limb is responsible for the generation of an osmotic gradient by active reabsorption of sodium.…”

Influence of acute selective endothelin-receptor-A blockade on renal hemodynamics in a rat model of chronic allograft rejection

“…lc). The variability in flow measurements was within expected ranges, as described previously [9,20,321. The calculated vascular resistances did not indicate a decreasing vascular tone in macrovasculature or micro-vasculature (Table 1) tective effect of ET-A receptor blockade to its known anti-proliferative properties or to a concomitant improvement of renal hemodynamics.…”

“…The signals of the two probes were transmitted to a laser flow meter (MBF 3D, Moor Instruments). Validation of transit time and laser Doppler methods are given elsewhere [17,20,321. The experimental setting was established and has been used in several projects in our laboratory.…”