Blood velocity profile in the ductus venosus inlet expressed by the mean/maximum velocity ratio

Mean blood velocity (V(mean)) is needed for calculating blood flow and possibly the;pressure. gradient across the ductus venosus. Interference from low velocities from neighbouring vessels makes the direct Doppler measurement of V(mean) unreliable. Therefore, it is suggested that V(mean) can be derived more reliably from the maximum velocity (V(max)) once the velocity profile, expressed as the ratio V(mean)/V(max), is known. To determine this ratio, ultrasound was performed in 10 fetal sheep during acute experiments under general anaesthesia to ensure good recording control and optimal insonation, Based on 33 Doppler measurements at the ductus venosus inlet, the ratio V(mean)/V(max) was determined to be 0.69 (SD +/- 0.07) regardless of V(max) pulsatility index, vessel diameter, or angle of insonation, These results confirm the previous prediction based on a computational model that the velocity profile is partially blunted, The equation V(mean) = 0.7V(max) is recommended for determining V(mean) in the ductus venosus. (C) 1998 World Federation for Ultrasound in Medicine & Biology.