Breathing of Amniotic Fluid as a Normal Function of Fetal Respiration

Abstract

The demonstration of rhythmical respiratory movements of the fetus long before term raises the question whether or not amniotic fluid normally enters the lungs before birth as a result of these movements. 1 , 2 , 3 In order to determine the existence of a tidal flow of amniotic fluid in the respiratory tract, India ink was added to the amniotic fluid. In a typical experiment the uterus of a rabbit at term, i. e., 32 days, was exposed by laparotomy carried out beneath the surface of a bath of Ringer solution at 37°. General anesthesia was avoided by section of the spinal cord in the lumbar region, and inhibition of uterine contractions was obtained by injection of one cc. (100 rat units) of Antuitrin S (Parke, Davis & Co.) on the 25th day of pregnancy. The head of a fetus was distinguished readily through the transparent uterine wall. One cc. of 50% India ink was injected within the amniotic sac in the dorsal neck region between the ears. After intervals ranging from one to 60 minutes the trachea was closed by clamping the neck of the fetus. The lungs were examined and fixed in formalin before removal of the clamp.

Comparison was made of the lungs of fetuses which had been showing respiratory movements with those of litter-mates in which breathing had been suppressed by injection of pentobarbital sodium. In breathing fetuses, the lungs were blackened, while in contrast in apneic fetuses the lungs were normal. Microscopical examination showed carbon particles in the alveoli of the lungs of the former but not the latter.

In litter-mates which were breathing at different rates, it was found that the lungs were darker in those which showed the greater respiratory activity.