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 possi bly 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, ul trasound was performed in 10 fetal sheep during acute experiments under gen eral anaesthesia to ensure good recording control and optimal insonation, B ased on 33 Doppler measurements at the ductus venosus inlet, the ratio V-me an/V-max was determined to be 0.69 (SD +/- 0.07) regardless of V-max pulsat ility index, vessel diameter, or angle of insonation, These results confirm the previous prediction based on a computational model that the velocity p rofile is partially blunted, The equation V-mean = 0.7V(max) is recommended for determining V-mean in the ductus venosus. (C) 1998 World Federation fo r Ultrasound in Medicine & Biology.