Doppler echocardiography in the human fetus : normal flow velocities and the effect of fetal variables

The objectives of this thesis were as follows. 1. To establish the intra-observer variability in the assessment of fetal atrioventricular flow velocity parameters in the second half of pregnancy. The results are discussed in chapter 3 .2. 2. To assess the distribution of flow velocity waveform parameters at fetal atrioventricular and outflow tract level during the second half of normal pregnancy and to determine whether these parameters are fetal heart rate dependent in the normal fetal heart rate range. Data are presented in chapter 4.1. 3. To determine whether flow velocity waveform parameters at fetal atrioventricular and outflow tract level are changed by fetal breathing movements and, if so, whether this change is gestational-age dependent. To investigate whether time-averaged velocity at fetal atrioventricular and outflow tract level during fetal breathing movements is different from that observed during fetal apnoea. This is discussed in chapter 4.2. 4. To establish the distribution of flow velocity waveform parameters from the fetal ductus arteriosus during the second half of normal gestation and to determi11e whether there is fetal heart rate dependency for these parameters in the normal fetal heart rate range. Results are presented in chapter 5.1. 5. To determine whether flow velocity waveforms in the ductus arteriosus change during fetal breathing movements. If so, to establish (i) whether this change is gestational age-dependent and (ii) whether the presence of normal breathing related ductal blood flow velocity changes is indicative of absent pulmonaty hypoplasia in cases of prolonged severe oligohydramnios following premature rupture of membranes. Data are presented in chapter 5.2. 6. To investigate the relationship between fetal ductal blood flow velocity waveforms and fetal behavioural states. Data are presented in chapter 5.3. 7. To determine the nature of flow velocity waveforms at atrioventricular and outflow tract level during blocked and conducted supraventricular extrasystoles when compared with waveforms obtained from normal sinus beats; to assess the relation between these waveform changes and the preceding beat-to-beat interval. This is discussed in chapter 6.