Fetal respiration during the second stage of labor in rabbits and the origin of pulmonary hyaline membrane

Abstract

1.1. Evidence of fetal respiration in rabbits during the period of expulsion, the second stage of labor, is the entrance of the fluid and cells of the birth canal into the air passages.2.2. After labor complicated by perinatal deaths, the lungs or more than 90 per cent of the 117 stillborn and newborn rabbits autopsied were contaminated with blood, epithelial cells, and amorphous debris; large areas of the alveoli and bronchioles of both lungs were involved in 40 per cent of the autopsies.3.3. After normal labor, uncomplicated by deaths, the lungs of 164 newborn rabbits obtained by sacrifice of 30 litters showed only minor quantities of erythrocytes and cellular debris scattered in the air passages; there was no case of massive contamination of the lungs such as characterized 40 per cent of the autopsies of stillborn fetuses and those that died neonatally.4.4. Increase in the duration of labor is linked with increase in foreign matter of the birth canal in the fetal air passages.5.5. The origin of pulmonary hyaline membrane is related to fetal respiration; the entrance of fluid and cellular debris of the birth canal into the fetal air passages during labor accounts for the origin of foreign matter in the lungs of the newborn; the displacement of the eosinophilic matter in a membrane-like layer along the walls of the alveoli and bronchioles results from the expansion of the air passages with the entrance of air.6.6. In littermates expelled through the same birth canal, the foreign cellular debris in the lungs is strikingly similar; however, in the stillborn, its displacement in the form of a film has not occurred.7.7. In the course of parturition of the type characterized by multiple births, the influence of dilatation of the air passages with the entrance of air upon the distribution of the alveolar contents stands out with exceptional detail.8.8. The regular occurrence of atelectasis in areas of the lungs marked by membranelike dispersion of the foreign matter is further evidence of obstruction.9.9. Asphyxia of the newborn involves more than oxygen want; in many instances there is also increase in duration of exposure to a fluid environment containing blcod and bacteria with consequences that extend far beyond the time of birth.