The relationship between fetal inferior vena cava diameter pulse and flow velocity waveforms in normal and compromised pregnancies.

摘要

BACKGROUND: The circulation is characteristically assessed by pressure and flow. OBJECTIVE: To evaluate the hemodynamic significance of fetal inferior vena cava (IVC) flow velocity waveform (FVW) indices in relation to the diameter pulse waveform (DPW). STUDY DESIGN: Doppler ultrasound and a phase locked loop echo tracking system were used to measure the FVW and the DPW in the fetal IVC, respectively. SUBJECTS: We studied 98 normal fetuses (20 to 40 weeks) and 65 compromised fetuses with increased umbilical placental resistance. RESULTS: The DPW consisted of four waves (A, X, V, and Y waves). Three components (systolic flow; S, diastolic flow; D, reverse flow; R during atrial contraction) were identified in the FVW. The FVW indices were examined in relation to the X descent {(A - X) / A%} of the DPW. The compromised group was divided into three subgroups by the X descent. In 15 fetuses the waveform was normal. In 32 there was a high pulsatile pattern with deep descent form the A crest to X trough. In 18 the X descent was shallow and the pulsatility appeared reduced. The high and low pulsatile patterns were associated with an increase in the S/D ratio and the R/S ratio, respectively. CONCLUSION: In fetal compromise the high pulsatility DPW may result from increased end-diastolic pressure in response to the increase in ventricular afterload caused by the placental vessel obliteration. The S/D ratio of the FVW may reflect the increasing cardiac afterload. The low pulsatility DPW may indicate depressed myocardial function and output. In the FVW, the R/S ratio may be associated with this.