Doppler-Ultrasound measurements in renal allografts depend on the patient's body position

Background: Due to anatomical reasons a position-dependentrenal allograft artery stenosis is being discussed (e.g. only in patient's upright position). The tortuous course of the allograft artery complicates the direct, angle-dependent measurement of maximum systolic flow velocities (vmax). So indirect signs such as intraparenchymal vmax and resistance index might be helpful, but it is unknown how these values change physiologically when patient's body position changes. Patients and methods: We examined renal allografts of 60 patients (38 male, 22 female) with stable graft function using B-Mode-, colour-coded duplex-sonography and pulsed wave-Doppler. We measured vmax and RI-values of three interlobar arteries in the cortex and allograft artery in the hilus in patients standing upright and in horizontal position. Corresponding values were analyzed for significant differences. Results: Intraparenchymal RI-values and vmax were signify cantly reduced in patients upright compared to the horizontal position (16%, MW=0.59 vs. MW=0.70, p < 0.001 resp. 6%, MW=30.18 cm/s vs. MW=32.17 cm/s, p = 0.045). Similar results could be detected in the renal hilus. Conclusions: Patients with stable graft-function show significant, position-dependent differences of the intraparenchymal and hilar RI-values and maximal systolic flow velocities. These changes of Doppler parameters has to be kept in mind for the correct diagnosis of a position dependent allograft artery stenosis.