The Neonatal Transitional Circulation: A Combined Noninvasive Assessment

Dramatic changes occur in the circulation of the newborn during the transition from fetal to neonatal life. Closure of the foramen ovale and ductus arteriosus, decrease in pulmonary vascular resistance, and improvement in right ventricular compliance are among these changes. These physiologicalanatomical events were characterized by means of two‐dimensional, Doppler and color flow echocardiography. Forty‐five full‐term infants (22 male, 23 female) were studied at a mean age of 4.2 hours (T1), 25.5 hours (T2), 49.8 hours (T3), and 73.8 hours (T4) by two‐dimensional, Doppler and color flow echocardiography. At T1, T2, T3, and T4, the ductus arteriosus was patent by color flow echocardiography in 100%, 34%, 22%, and 11%, respectively. Conversely, patency of the ductus by Doppler alone was detected in 100% (T1), 13% (T2, T3), and 11% (T4). Reversal of flow in the descending aorta, reflective of diastolic ductal filling, was not sensitive in detecting ductal patency (T1 50%, T2 3%, T3 and T4 O%). The patency of the foramen ovale was noted to decrease over the course of the study. Right ventricular compliance was quantitatively assessed by pulsed‐Doppler diastolic properties (E‐to‐A ratio). This changed significantly from T1 to T4 (0.90 to 0.97) reflecting improving compliance of the right ventricle. The ratio of acceleration to ejection time, a Doppler estimation measure of pulmonary vascular resistance, increased from 0.28 to 0.33 (T1 to T4) reflecting a decrease in pulmonary vascular resistance. The incidence of tricuspid regurgitation detected by color flow mapping was 100% throughout the course of the study in multiple views. In comparison, tricuspid regurgitation detected by Doppler interrogation without color flow guidance was only present in 94% (T1), 53% (T2), 52% (T3), and 33% (T4) of infants studied. Timing of foramen ovale and ductus arteriosus closure can be determined noninvasively with great sensitivity. Changes in right ventricular compliance and pulmonary vascular resistance can also be assessed noninvasively. The presence of tricuspid regurgitation was appreciated best by use of color flow mapping. Echocardiography is a useful tool in assessing the neonatal transitional circulation.