DETERMINATION OF ERYTHROCYTE VELOCITIES IN THE MAMMALIAN INNER RENAL MEDULLA BY A VIDEO VELOCITY-TRACKING SYSTEM

A video velocity-tracking system was used to measure erythrocyte velocities in vasa recta capillaries of the inner renal medulla in the rat. Two groups of animals prepared with different surgical approaches, ventral or flank, were evaluated. In both groups, instantaneous erythrocyte velocities were predominantly aperiodic and 3-min time-averaged velocities remained within narrow limits (±0.15 mm/sec) over 3 hr. With the ventral approach there was no consistent change in red blood cell velocities, whereas, following the flank approach, erythrocyte velocities increased while urinary osmolality simultaneously decreased. The results from both groups are in agreement with an inverse relationship between medullary blood flow and urinary osmolality. The video velocity-tracking method appears to have several advantages over techniques previously employed to describe quantitatively medullary blood flow. © 1979.