BackgroundA congenital diaphragmatic hernia (DH) can result in severe lung hypoplasia that increases the risk of morbidity and mortality after birth; however, little is known about the cardiorespiratory transition at birth.MethodsUsing phase-contrast X-ray imaging and angiography, we examined the cardiorespiratory transition at birth in rabbit kittens with DHs. Surgery was performed on pregnant New Zealand white rabbits (n=18) at 25 days' gestation to induce a left-sided DH. Kittens were delivered at 30 days' gestation, intubated, and ventilated to achieve a tidal volume (V t) of 8 ml/kg in control and 4 ml/kg in DH kittens while they were imaged.ResultsFunctional residual capacity (FRC) recruitment and V t in the hypoplastic left lung were markedly reduced, resulting in a disproportionate distribution of FRC into the right lung. Following lung aeration, relative pulmonary blood flow (PBF) increased equally in both lungs, and the increase in pulmonary venous return was similar in both control and DH kittens.ConclusionThese findings indicate that nonuniform lung hypoplasia caused by DH alters the distribution of ventilation away from hypoplastic and into normally grown lung regions. During transition, the increase in PBF and pulmonary venous return, which is vital for maintaining cardiac output, is not affected by lung hypoplasia.