Lung mechanics in congenital heart disease with increased and decreased pulmonary blood flow

Respiratory rate, tidal volume, dynamic lung compliance, functional residual capacity, and pulmonary resistance were measured within 24 hours of cardiac catheterization in 25 infants, 12 of whom had increased pulmonary blood flow and 13 of whom had decreased PBF. There were no differences in the two groups of patients with respect to V_τ and FRC. Respiratory rate and pulmonary resistance were higher in infants with increased PBF. Lung compliance was significantly lower in infants with increased PBF (4.9 ml/cm H₂O) than in those with decreased PBF (8.9 ml/cm H₂O) (P<0.01). The decrease in C_L in infants with increased PBF significantly correlated with mean pulmonary artery pressure (r=0.798). No correlation was found between C_L and left atrial pressure or magnitude of the left-to-right shunt. Compliance was normal in patients with increased PBF and normal PAP, suggesting that PAP and not PBF is the primary factor that affects C_L in patients with intracardiac left-to-right shunts.