Pulmonary arterial resistance and compliance in preterm infants

Background Preterm birth is known to be associated with an increased risk of pulmonary arterial hypertension, although how preterm birth influences pulmonary hemodynamics has not been fully understood. Pulmonary arterial resistance (Rp) and compliance (Cp) are important factors to assess the pulmonary circulation. The purpose of this study is to clarify the relationship between Rp and Cp in preterm infants. Methods We performed cardiac catheterization in 96 infants (50 males) with ventricular septal defect, and compared pulmonary hemodynamic parameters including Rp and Cp between preterm and full-term infants. Results Thirteen infants were preterm. There were no significant differences in sex, age, preoperative pulmonary arterial pressure, preoperative pulmonary-to-systemic flow ratio, and preoperative Rp between the 2 groups. However, preoperative Cp and resistor-capacitor (RC) time in preterm infants were significantly lower than those in full-term infants (2.1 vs 2.8 mL/mmHg/m² and 0.31 vs 0.36 s, respectively; p < 0.05 and p < 0.01, respectively). Postoperative systolic and mean pulmonary arterial pressures were higher in preterm infants than those in full-term infants (29 vs 25 mm Hg and 18 vs 14 mm Hg, respectively; both p < 0.01). It was also observed that postoperative Cp was lower in preterm infants, although postoperative Rp remained unchanged. Conclusions We demonstrated that preterm infants with pulmonary arterial hypertension had lower Cp than full-term infants, causing a modest increase in pulmonary arterial pressure. It is important to consider the unique pulmonary vasculature characterized by lower Cp, when managing preterm infants with congenital heart disease.