Distensibility of the Fetal Lung with Fluid in Sheep

Abstract

ExtractTracheal ligation was performed in 16 fetal lambs at 74-129 days of gestation (normal term, 138-157 days). Operated lambs were subsequently delivered spontaneously at term. Postmortem procedures were performed on the same day and revealed lungs enormously distended with fluid, weighing approximately 10 times more than those found in normal lambs, and displacing the diaphragm to the [joint where it was concave downward, bulging into the abdominal cavity. To measure the rate of lung fluid formation in fetal lambs, catheters were placed in the trachea of three fetuses borne by three ewes near term. Periodic aspiration of fluid following the operation revealed rates of lung fluid formation of 0.015, 0.030, and 0.055 ml/kg/min. The day after surgery pressure measurements of lung fluid made via the catheter in two of these animals revealed an initial pressure of 12 and 19 cm saline. This pressure rose only moderately after injecting 150 ml 0.85% NaCl in 20-ml increments into the fetal lung. The injected fluid was readily recoverable, indicating that it had been accommodated by expansion of the fetal lung and had not passed across lung-lining cells into the fetal circulation. Gestation times were within the normal range. SpeculationFetal lung fluid contains surfactant, which has been biochemically characterized as a phospholipid and as a lecithin. Soya bean phospholipids containing a predominance of lecithins arc capable of sensitizing the rabbit uterus to oxytocin and precipitating premature delivery. The fetus is known to participate in the timing of its own birth, and we speculated whether lung phospholipids formed near term in the fetal lung could reacli the amniotic fluid and precipitate labor. Tracheal occlusion, however, did not alter gestation time in our animals. Other mechanisms of fetal participation in the precipitation of labor must be sought. IntroductionRecent work [5,9, 14, 18] has indicated that fetal lungs secrete fluid. The fluid was thought to flow via the trachea to the oral pharynx, where it was either swallowed or passed via the nose or mouth into the amniotic fluid. Reynolds [17], however, published observations suggesting that with relatively minor pressure changes fluid would move in the reverse direction. He concluded that "it is clear that ... the fetal lung is a

Fetal Pulmonary Surfactant in Amniotic Fluid of Ewes

“…This has been evidenced by the experiment of nature observed by Potter and Bohlender (1941), and by . The author also confirmed this finding by the experiment of tracheal ligation on the fetal lamb in utero (Lanman et al 1971). According to the cineangiographic observation of Adams and his associates, the lung fluid was held in the trachea by the laryngeal sphincter which opened periodically to permit the fluid flow mostly into the esophagus, and to a lesser extent, into the amniotic cavity (Adams et al 1967).…”

“…According to the cineangiographic observation of Adams and his associates, the lung fluid was held in the trachea by the laryngeal sphincter which opened periodically to permit the fluid flow mostly into the esophagus, and to a lesser extent, into the amniotic cavity (Adams et al 1967). Our observation in the previous experiment on the tracheal fluid flow showed the rate of 0.013 to 0.055ml per kg of fetal weight per minute in the fetal lamb (Lanman et al 1971). Reports from other laboratories indicated the similar flow rates (Enhorning andAdams 1965, Ross 1963).…”

Salvage of a Fetus with Congenital High Airway Obstruction Syndrome by ex utero Intrapartum Treatment (EXIT) Procedure

“…In addition, it is uncertain what effect fetal tracheostomy would have on lung development in fetuses with CHAOS. In experimental animal models chronic drainage of tracheal fluid, as would occur with fetal tracheostomy, results in pulmonary hypoplasia [5]. This case suggests that CHAOS diagnosed prior to viability may warrant close observation alone unless there is a pressing indication for fetal intervention.…”

Estimation of Surfactant Lecithin in Amniotic Fluid and Prediction of Respiratory Distress Syndrome

“…This pulmonary secretory func tion, which was first presented in a case report by Potter and Bohlender (7), has been confirmed by the tracheal ligation of fetal lambs in utero which re sulted in normally developed alveoli markedly distended with fluid (8). Several reports including ours describe the flow rate of pulmonary fluid in fetal lambs around 100 ml/kg/day (8)(9)(10)(11).…”

“…This pulmonary secretory func tion, which was first presented in a case report by Potter and Bohlender (7), has been confirmed by the tracheal ligation of fetal lambs in utero which re sulted in normally developed alveoli markedly distended with fluid (8). Several reports including ours describe the flow rate of pulmonary fluid in fetal lambs around 100 ml/kg/day (8)(9)(10)(11). Recently, Dawes (11) observed an outward gush of fluid of the order of 20-40 ml over a period of 3-5 min several times a day with vigorous breathing movements in near-term fetal lambs, and he suggested that pulmonary surfactant was carried out through upper airways to mix with amniotic fluid on those occasions.…”