Fetal Respiratory Movements in the Cat

FETAL FETAL respiratory movements have been described in several mammals, including the rat (Corey, 1932), rabbit (Snyder and Rosenfeld, 1937), sheep (Barcroft and Barron, 1936 and i937), and man (Ahlfeld, 1905; Windle, Dragstedt, Murray, and Green, 1938). The present study in the cat was undertaken to compare the movements of respiration at various stages in fetal life and under conditions as nearly normal as possible, as well as in states of experimental fetal anoxemia and carbon dioxide excess. We wished to learn whether or not the fetus responds to conditions which serve as respiratory stimuli in the adult. Cats in various stages of pregnancy were anesthetized with ether before ligating the carotid arteries high in the neck and the basilar artery at the rostral one-third of the pons (Pollock and Davis, 1924) an hour or more (usually 2 or 3 hours) before experiments were begun. With this procedure the animals entered a state of partial decerebration. Conscious voluntary activity was lost; but respiration, although temporarily impaired by the procedure, was usually restored within an hour or two to about normal and, in several instances, was considerably increased in rate and depth; body temperature and blood pressure were usually not affected significantly. The explanation for the maintenance of rapid breathing and normal temperature seems to be that enough blood reached the midbrain and diencephalon by collaterial circulation around the ligature on the basilar artery to support the integrity of centers there even though the cerebral hemispheres were quite lacking in blood flow. After the vessels had been ligated, ether was discontinued; later on, the cat's abdomen could be opened under physiological saline or Locke's solution in a constant-temperature bath with no further anesthesia. All the fetuses exposed were delivered through small openings in the uterus at the ends of the zonary placentas and were examined with placental circulation intact. Various experimental procedures were used during the course of the study of fetal reactions.