Pulse pressure assessment in the human fetal descending aorta.

Pulsatile vessel diameter recordings were obtained at two different levels of the fetal descending aorta in ten third-trimester human fetuses using an echo-tracking system. A derivation of the Moens-Korteweg equation was used to estimate the pulse pressure amplitude in this vessel. The positive phase of the first derivative of the diameter curves was cross correlated to assess the propagation time of the pulse wave. It is postulated that this method minimises the measuring errors resulting from diameter pulse wave changes during propagation along the longitudinal axis of the descending aorta. It was estimated from repeated measurements that approximately 13 recordings of 5.2 s each are required to assess the mean pulse pressure amplitude for an individual fetus with an estimated random error of 10%.