BREATHING MOVEMENTS TRANSIENTLY INCREASE LUNG VOLUMES 1N FETAL SHEEP

Abstract

Recent studies indicate that fetal breathing movements (FBM) stimulate fetal lung growth. We chronically studied 18 fetal sheep to determine if FBM affect lung growth by transiently increasing the total volume of fluid (TVF) in the potential airways and air spaces. In 14 fetuses, the trachea was ligated; a catheter with an exteriorized loop diverted all tracheal fluid into a soft intrauterine bag. In 4 fetuses, the trachea was patent; we aspirated tracheal fluid through a small catheter after occluding the glottis with an inflated balloon tipped catheter. On alternate days, we aspirated fluid from the lungs after ≥9 minutes of either FBM or no FBM. The order of collection varied. Using inulin dilution, 64.8±9.6% of the TVF was aspirated through the tracheal catheters (mean ±SD; similar after FBM or no FBM). In every fetus, the volume aspirated after FBM was greater than that aspirated after no FBM. These volumes, in fetuses with the ligated trachea, were 20.5±7.9 ml/kg after no FBM and 28.9±9.8 ml/kg after FBM (p<0.01). In fetuses with the patent trachea, these volumes were 20.7±2.5 after no FBM and 24.5±2.4 ml/kg after FBM (p<0.05). The daily incidence of FBM (both groups) and the tracheal fluid production rate (ligated group) were similar on both study days for each fetus. We conclude: FBM intermittently increase the volume of fluid that can be aspirated from the fetal lungs. This suggests that the TVF in the potential airways and air spaces also increases; this increase in volume may stimulate lung growth. (USPHS HL-27356)