Use of Laplace transform analysis to describe the effect of placental embolisation on umbilical arterial Doppler waveforms in fetal sheep.

This is the first study to investigate changes in umbilical arterial Doppler shift waveforms caused by placental embolisation in fetal lambs described by a Laplace transform analysis method. The complete maximum velocity envelope of the waveform was quantified mathematically by the coefficients of the Laplace transform. The changes in the dominant coefficient were significantly correlated with changes in umbilico-placental vascular resistance. The Doppler shift waveforms reproduced those seen clinically in some growth-retarded pregnancies and were acquired in a clinically realistic manner. Increasing vascular resistance two fold in this experiment appeared to produce more consistent changes in the dominant coefficient of the Laplace transform than in the pulsatility index. Both analysis techniques correlated with umbilico-placental vascular resistance and these correlations were not significantly different from each other.