Reciprocal Oxygen Changes on Both Sides of Placenta During Uterine Contraction and Relaxation

Abstract

Attention has been directed to the intermittent character of intrauterine fetal respiratory movements and it has been suggested that prelabor uterine contractions may be related to this phenomenon. 1 Other motor activities of unanesthetized fetuses delivered with the placental circulation intact varied with contraction and relaxation of the uterus. With each contraction, reddening of umbilical veins and corresponding improvement of fetal color was observed. Uterine relaxation led to darkening of the blood. It was evident that alteration of respiratory gas content of the fetal blood was related to the fluctuations in fetal activities. The umbilical vein blood was richer in oxygen during uterine contraction than during relaxation. 2 Do these changes occur normally in utero or are they, perhaps, the result of operative interference with the placental exchange mechanism? The present experiments were planned to help determine the answer.

Large superficial tributaries of the uterine veins carry blood from the maternal side of the placentæ of the cat. It was possible to obtain 0.2 cc samples of blood principally from the placenta from these vessels for analysis by the Van Slyke and Neill 3 micro-manometric method for combined carbon dioxide and oxygen determinations. The cats were not anesthetized but had been decerebrated by tying the carotid and basilar arteries an hour or more before. The uteri were exposed after immersing the animals in a constant temperature bath of Locke's solution.

If the undisturbed fetuses are removing more oxygen from the maternal blood during uterine contraction than during relaxation, the blood leaving the placenta on the maternal side should be lower in oxygen in the period of contraction. Estimations of the blood oxygen are presented in the Table I.

The placental samples were taken as close to one another as possible but the maternal femoral arterial and the umbilical blood samples were drawn earlier and later; often 30 minutes or more elapsed between them.