We examined vena cava Doppler flow velocity tracings from 69 fetuses between 22 and 40 weeks' gestation. Twenty-three fetuses had arrhythmias. Fifteen fetuses had absent end-diastolic Doppler velocities in the umbilical artery, a condition associated with intrauterine growth retardation, and 15 normal fetuses with normal umbilical artery Doppler velocity ratios were matched by gestational age. In studies in 16 additional fetuses, inferior vena cava Doppler velocity waveforms were compared with superior vena cava Doppler velocity waveforms. Peak velocities and time-velocity integrals of forward or reverse flow during systole, early diastole, and atrial contraction were measured. In addition, the time-velocity integral during flow coincident with atrial contraction (a wave) was expressed as a percent of the time-velocity integral of total forward flow during both systole and early diastole. Systolic-to-diastolic ratios of inferior vena cava forward time-velocity integrals were not significantly different from systolic-to-diastolic ratios of superior vena cava forward time-velocity integrals (p=0.86), but the percent of blood moving in a reverse direction during atrial contraction in the inferior vena cava was greater than the percent of blood moving in a reverse direction in the superior vena cava (p<0.05). Relative forward flow in early diastole in the group of normal fetuses increased with advancing gestational age (r=0.60, p<0.05). During premature atrial contractions flow in the inferior vena cava was reversed, and the percent of reverse flow during atrial systole increased significantly from 4.5±0.3% to 28.3±3.7% (mean±SEM, p<0.001). During tachyarrhythmias the percent of reverse flow during atrial contraction also increased, with greater increases associated with higher heart rates. During bradycardias the percent of reverse flow during atrial contraction varied with the type of arrhythmia; reverse flow increased with decreasing heart rate in the fetuses with sinus bradycardia. In the group with absent end-diastolic Doppler velocities in the umbilical artery and intrauterine growth retardation, systolic-to-diastolic ratios of the inferior vena cava forward time-velocity integrals increased from 2.76±0.17 to 6.96±0.84 (p<0.001), and the percent of blood moving in a reverse direction during atrial contraction increased from 4.7±0.9% to 13.8±2.3% (p<0.01). These results suggest that fetal vena cava flow velocity patterns are altered in the presence of conditions associated with fetal morbidity and that these alterations can be easily identified by means of Doppler ultrasound techniques.
- Fetuses, human
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine
- Physiology (medical)