THE RELATIONSHIP BETWEEN ABDOMINAL, UTERINE AND ARTERIAL PRESSURES DURING LABOR

Abstract

By means of a set of differential manometers simultaneous records were taken during normal human labor pains of 1, the systemic arterial pressure; 2, the effective head of maternal blood pressure to the placenta; 3, the total intra-uterine pressure; 4, the contribution of the uterine wall to the intra-uterine pressure. Human uterine contractions result in smooth symmetrical pressure rises which vary in height from 25 to 95 mm. Hg and subject the uterine wall to an average maximal tension of 500 gms. per square cm. of uterine wall cross area. During delivery of the head, the average maximal expulsive force was 15 kgm. The frequency and duration of uterine contractions were unaffected by morphine, nitrous oxide-oxygen, the barbiturates, cyclopropane, ether and chloroform. The strength of the uterine contractions, markedly reduced by ether and chloroform, was unaffected by the other anesthetics. All of the above drugs reduced the contribution of the abdominal muscles to the intra-uterine pressure. During labor pains the systemic blood pressure increases and the pulse pressure widens. The effective maternal arterial pressure to the placenta diminishes[long dash]sometimes to zero. The pressure which irrigates the placenta is increased by obstetrical anesthetics and by epinephrine.