[Ultrasonic Doppler method for noninvasive determination of fetal blood flow volumes]

Fetal blood flow volume and unteroplacental flow profiles can be measured with a linear real time scanner in conjunction with a pulsed Doppler system. It was the aim of this study to simulate the blood flow volume under varying experimental conditions by using an in-vitro model, and to examine and compare pulsed Doppler equipments. Defined flow rates between 200 and 1200 ml/min were pumped via a tygon tube placed in a liquid bath. The sample volume was kept constant, the depths of the tube were varied. Processing of the Doppler signals was done by spectrum analysis. There was a good correlation between true and ultrasonically measured flow rates (r = 0.96-1). However, particularly low flow rates resulted in an overestimation of blood flow when using high-pass filtering for avoiding Doppler signals arising from the vessel wall. These errors probably not only depend on the flow profiles, but also on the measuring techniques involved with the individual instruments. The effect of high-pass filtering must be taken into account when interpreting the results, particularly in the case of low-flow rates.