Audio spectrum analysis of umbilical artery Doppler ultrasound signals

Sammanfattning: The aim of this thesis was to develop an objective method for evaluation of umbilical artery circulation based on auditory perception of the Doppler sound signals. Study I. The operator listened to synthetically produced sound signals from continuous flow. The human ear was most sensitive to sound frequencies in the lower range from this type of flow. Study II. Doppler signals were recorded from the umbilical artery of sheep fetuses. An objective sound measure, MAXpeak-15dB (the frequency band where the energy level had decreased by 15 dB from its maximum level) was identified and found to correlate well with the sonographer’s subjective grading and with the traditional waveform analysis. Studies III and IV. Fetoplacental and uteroplacental circulation was investigated before and after treatment with corticosteroids of women at risk for preterm birth. A transient decrease in pulsatility index (PI) in the umbilical artery and ductus venosus occurred after steroid treatment. MAXpeak-15dB increased significantly after corticosteroids parallel with a decrease in PI and was more sensitive to the changes in flow. Study V. MAXpeak-15dB was applied on umbilical artery Doppler signals in high-risk pregnancies and was found to show similar results as the traditional PI in predicting the probability of composite adverse pregnancy outcome. Receiver operating characteristic curves were used with an area under curve (AUC) of 0.842 for MAXpeak-15dB and 0.836 for PI. When the two parameters were combined the predictive performance was improved (AUC 0.894). MAXpeak-15dB might thus provide additional clinically useful information on the hemodynamics of fetoplacental circulation.