[Combined B image Doppler sonography--measurements in the in vitro model and in fetal vessels]

With the combination of B-mode real time scanner and a pulsed Doppler unit the blood flow in fetal vessels can be determined. The accuracy and limitations of the method are tested in an in-vitro-model (artificial pulsatile blood circulation in a silicon tube placed in a water bath). Conditions of measurements are constant in the circulation model. For defined pumped flow rates between 350-800 ml/min we found too high Doppler values throughout the range. Depending on the use of high-pass filters and on the higher depth of sample volume the Doppler flow shows an increasing deviation, but there is a good linearity of the Doppler values (r = 0,99). The blood flow in umbilical vein (n = 42) and fetal descending aorta (n = 65) do not differ very much in the last month of normal pregnancy. We found a significant decrease of flow in both vessels after 41 weeks of pregnancy. The clinical validity of quantitative results of Doppler-sonography is limitated by the described problems of high-pass filtering, depth of sample volume and determination of the diameter of the vessel.