Journal of Ultrasound in Medicine, Vol 19, Issue 5 303-314, Copyright © 2000 by American Institute of Ultrasound in Medicine
Understanding the Doppler RI: impact of renal arterial distensibility on the RI in a hydronephrotic ex vivo rabbit kidney model
M. E. Murphy and M. E. Tublin
Department of Pharmacology and Neuroscience, The Albany Medical Center, New York, USA.
The aim of this study was to evaluate the influence of elevated ureteral
pressure on renal arterial distention, and thereby on the Doppler resistive
index. Seven isolated rabbit kidneys were subjected to a pulsatile
perfusion while the renal pelvis was pressurized via the ureter. Renal
vascular pressure, flow, resistance (pressure/flow) and conductance
(flow/pressure) were compared to simultaneous resistive index measurements
using linear regression analysis. Changes in the Conductance Index
(systolic conductance - diastolic conductance/systolic conductance) were
likewise compared to the resistive index. Elevations in ureteral pressure
were significantly correlated with (1) increased resistive index values,
(2) increased mean renal vascular resistance, (3) decreased mean
conductance, and (4) increased conductance index values (for all
correlations P < 0.05). The increases in the resistive index correlated
significantly with increases in the conductance index. This study shows
that elevated ureteral pressure, likely acting via interstitial pressure,
diminishes the conductance of the renal vascular bed. Because this effect
is more dramatic at diastole, the cyclic patterns of flow are altered,
resulting in elevated resistive index values. The results indicate the
importance of the interaction between vascular distensibility and pulsatile
flow, rather than overall mean renal vascular resistance, in determining
resistive index values.