l IntroductionA differential analysis of the cardiotocogram allows conclusions äs to the functional state of the fetus. However, the interpretations of changes in the heart rate depend to a large extent on the experience of the examiner because of the poorly defined deliminations of specific pattems of heart rate changes. New techniques enable the recording of the pre-ejection period (PEP) of the human fetal heart; i.e., the time between ventricular excitation and aortic pressure rise, continuously parallel with the CTG [3,12,16,24,27]. The PEP is a measure of the myocardial contractility. Thus, with adrenergic Stimulation the cardiac contractility increases and the PEP is shortened. On the other hand, an increase in peripheral resistance leads to a lengthening of the PEP äs does a decrease of ventricular filling. Recent experiments in fetal lambs [20,21,37,52,53] showed in acute and chronic experiments [20,29] that in acute hypoxia the PEP falls below the normal ränge, and that with compression the PEP is increased while the relation of the PEP to duration of systole (relative PEP = PEPr) is constant. Furthermore, with umbilical cord complications characteristic PEP changes are seen and chronic and acute hypoxia lead to changes in the baseline level of the PEP. This study de als with the question whether the results of animal experiments from PEP recording together with the CTG apply to the human fetus during birth and whether the characteristics of the PEP and heart rate allow conclusions äs to the pathophysiology of umbilical cord complications. Curriculum vitae THOMAS BÄRTLING was born in 1947 in Material and methodDuring the delivery of 115 fetuses the course of the absolute and relative PEP was recorded for at least 50-90 minutes simultaneously with the CTG. Of the 115 fetuses, 38 had anuchal umbilical cord noted at birth. The CTG and PEP recordings of these 38 fetuses are the subject of the study. During or shortly after PEP recording a blood sample was obtained from the fetal scalp for the analysis of pH, base excess and pC0 2 . Blood gas analysis from umbilical artery blood was performed immediately postpartum. In five fetuses with documented cord complication the transcutaneous oxygen tension was recorded from the presenting part according to the method of HUCH [28,29,30] and recorded together with the PEP and

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Reduced uterine blood flow may be caused by a reduced arterial blood pressure and by an incrcased uterine vascular resistance [2,3, 4], In addition, reduced uterine blood flow seems to occur normally during vigorous uterine contraction in the expulsive stage of labor [1], In pregnant rhesus monkeys and in pregnant guinea pigs uterine O 2 -uptake decreases when uterine blood flow falls below about 80 ml min-1 kg-1 [5,7]. We were interested to know whether similar relations between uterine O 2 -uptake and uterine blood flow occur in sheep, the fetal weight of which is similar to that in human. As the available data do not allow to draw conclusions on this relation we measured uterine O 2 -uptake, uterine blood flow, and uterine vascular resistance in the sheep. The data should give further indications on the effect of reduced uterine blood flow on the fetus. Methods Material11 Merino-sheep near term were used. The maternal weight was 66.6 kg (SD = 7.3 kg). The weight of the uterus was 10.3 kg (SD = 5.0 kg). The mean fetal weight was 4.4 kg (SD = 1.6 kg) and 6 sheep had one and 5 sheep had twp fetuses. AnesthesiaThe sheep were anesthetized with pentobarbital (initial dose 20 mg/kg i. v.; additional infusion at a rate of 5 mg/kg/h). Curriculum vitae

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