DIRECT OBSERVATION OF INTRAUTERINE RESPIRATORY MOVEMENTS OF THE FETUS AND THE RÔLE OF CARBON DIOXIDE AND OXYGEN IN THEIR REGULATION

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Abstract
The first respiration is not initiated at birth. Fetuses of the rabbit, cat, guinea pig and human show rhythmical resp. movements within the uterus, instead of a state of prolonged apnea. Expt. conditions essential for direct observation of intrauterine breathing for many hrs. involve the hormonal inhibition of labor and the elimination of anesthetics. Regulation of fetal respiration depends upon the O2 and CO3 level of fetal blood, but differs in certain respects from that of the adult: a) O2-want depresses or abolishes fetal resp. movements; b) CO2 deficit results in depression or apnea of the fetus showing that a certain level of CO3 is essential for the maintenance of fetal respiration; c) An excess of CO2 has little or no effect. The depressant action of anox-emia is evidence that carotid body mechanism is not functioning in the rabbit fetus before birth. The rate of respiration of a fetus varies according to the stage of development, being several times more rapid in postmature fetuses than in premature ones. The fetal respiratory system is peculiarly sensitive to narcosis. Resp. movements may be abolished in the fetus at a level of analgesia which does not impair maternal respiration. Prolongation of pregnancy by the inhibition of labor made possible the comparison of the fetus in the intrauterine environment with the newborn of 1, 2 or 3 days, both being at an identical stage of development. The quiescence and relaxation of the uterus under hormonal influence favored continuation of resp. activity without interruption by circulatory disturbance.

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