Time-dependent effects of antidepressant drugs on the low dose of apomorphine-induced locomotor hypoactivity in rats

Surfactant deficiency in newborn infants with hyaline membrane disease (HMD) reduces peripheral airway stability, leading to lung atelectasis, inhomogeneity of distribution of ventilation, ventilation/perfusion mismatch, and hypoxemia. The aim of this study was to evaluate the immediate effect of exogenous surfactant treatment on ventilation inhomogeneity (VIH) in infants with HMD. Homogeneity of ventilation was measured repeatedly in ten infants (median gestational age 30 weeks and birthweight 1.50 kg) after Exosurf, and in six infants (median gestational age 30 weeks and birthweight 1.42 kg) after Survanta treatment. Lung function was measured before and 0.5, 2, and 6 hours after administration of a single dose of surfactant. The multiple breath nitrogen washout method was used to measure the time pattern of nitrogen elimination from the lungs. VIH was evaluated by using both a compartmental lung model and a model-independent moment analysis. The two-compartment lung model was found to dominate before surfactant treatment, while a single-compartment model (implying homogeneous ventilation) fitted the washout data best 6 hours after Exosurf treatment (P < 0.01). The same pattern occurred 2 hours after Survanta administration. Moment analysis confirmed the reduction in VIH by both surfactants. This study supports the hypothesis that the improved oxygenation after surfactant treatment in infants with HMD results from a reduction in VIH and an increase in functional residual capacity (FRC).