372 SPO Abstracts

344 THE EFFECT OF HYPOXIC ACIDEMIA INDUCED BY PLACENTAL EMBOLIZATION OF MYOCARDIAL CONTRACTIUfY AND SYSTOliC TIME INTERVALS IN FETAL SHEEP. RM. Lewinsky", RJ. Morrow", J.W.K. Ritchie. University of Toronto, Toronto, Ontario, Canada.

A study was designed to examine the hypothesis that hypoxic acidemia adversely affects fetal myocardial contractility, thereby causing a prolongation of cardiac systolic time intervals (STI). Fetal sheep (n = 7) at 133 days gestation, were studied in utero under isoflurane anaesthesia. ECG electrodes were applied to the fetal chest and a 2F catheter-tip pressure transducer (Millar) was introduced through a carotid artery into the left ventricle (LV). Hypoxic acidemia was induced by placental embolization with repeated injections of 5'10' 50t'M microspheres every 15 minutes via a catheter placed in the fetal abdominal aorta. The LV pre­ejection period (PEP), isovolumetric contraction time (ICT) and ventricular ejection time were continuously measured from the processed ECG and Dopplercardiogram (DCG) obtained with an HP 8040A monitor. Myocardial contractility was assessed by the maximal value of the first time derivative of the ventricular pressure waveform (dP/dt...J corrected for heart rate and preload. A decrease in fetal arterial pH from 73 to pH 7.0 was associated with a significant decrease in dP/dt.n,. (p=0.003), a prolongation of PEP (p=O.OO4) and ICT (p = 0.002) as well as with a significant increase in the PEP/VET ratio (p = 0.0002). We conclude that hypoxic acidemia decreases fetal myocardial contractility, thereby causing a prolongation of the pre-ejection period and the isovolumetric contraction time.

345 THE EfFECT OF CHANGES IN PRELOAD ANDAFI'ERLOAD ON THE CARDIAC SYSTOUC TIME INTERVALS IN FETAL SHEEP.R.M. Lewinsky". RJ. Morrow, J.W.K. Ritchie. University of Toronto, Toronto, Ontario, Canada.

Systolic time intervals (STI) are potentially useful for the noninvasive assessment of fetal wellbeing. The effect of changes in cardiac loading on these intervals has not been directly examined in an experimental model. Fetal sheep (n=7) at 133 days gestation, were studied in utero under isoflurane anesthesia. ECG electrodes were applied to the fetal chest and a 2F catheter­tip pressure transducer (Millar) was introduced through a carotid artery into the left ventricle (LV). The LV pre-ejection period (PEP), isovulumetric contraction time (lCT) and ventricular ejection time (VET) were continuously measured from the processed ECG and Dopplercardiogram (DCG) obtained with a HP 8040A monitor. Myocardial contractility was assessed by the maximal value of the first time derivative of the ventricular pressure waveform( dP / dt...J corrected for heart rate and preload. Preload was decreased and afterload was increased by brief partial occlusions of the inferior vena cava and the descending aorta respectively, with inflatable balloon catheters in these vessels. Both a decrease in preload and an increase in afterload, caused a significant prolongation of PEP and ICT. ICT is contained within PEP and is the major contributor to its prolongation. VET shortened with both interventions, mostly due to the effect of an increase in heart rate. Myocardial contractility as assessed by dP / dt...,. did not change during these interventions. This study shows that fetal cardiac STIs are directly affected by changes in preload and afterload, changes which are associated with compression of the umbilical cord.

January 1992 Am J Obstet Gynecol

346 FETAL URINE PRODUCTION IN PREMATURE RUPTURE OF THE MEMBRANES. W. L. Donald, University of Illinois at Chicago, Chicago, IL.

The purpose of this study was to determine if fetal urine production is decreased in premature rupture of membranes (PROM). A 3.5 MHz linear transducer was used to perform serial measures every 5 mins. of the longitudinal (A), trans­verse (B), and antero posterior (C) diameters of the fetal bladder in 51 patients with PROM between 30 and 34 weeks, 79 patients with intact membranes between 30 and 34 weeks served as controls. Fetal bladder volume was calculated from the formula for an ovoid sphere: 4/3(pi) . [(A/2)' (B/2)' (C/2) J. Volumes(ml) were plotted against time (mins) and linear regres­sion was used to determine the fetal urinary output (FUO) as m/hr.

RESULTS PROM CONTROLS P

Gestation 30 32 34 30 32 32 Mean FUO 10 12 19 16 19 26 0.05 (SD) (3) (3) (6) (5) (3) (6) Fill Time 29 34 29 23 27 20 0.05 (SD) (7) (6) (9) (8) (7) (5) There was no difference in the maximal bladder volume. CONCLUSION: THERE IS A REDUCTION IN THE FETAL URINARY OUTPUT IN PROM. THE ETIOLOGY REMAINS UNCLEAR.

347 LONGITUDINAL STUDY OF THE AMNIOTIC FlUID INDEX IN POSTDATES PREGNANCY. Ariel D. Marks" M.S., Michael Y. Divon, M.D. Dept. Ob/Gyn, Alben Einstein College of Medicine, Bronx, New York.

Previous invasive studies of the physiology of amniotic fluid levels in postdates pregnancies used dye dilution techniques and documented a weekly decrease of 28% to 61 %. Oligohydramnios was 8 common finding. Recent sonographic studies of the amniotic fluid index (AFI) in postdates patients indicate a mean weekly decrease of 3% - 12%. The incidence of oligohydramnios in recent studies is unclear. These studies were cross-sectional in design and lacked reliable methods to establish gestational age. Purpose: To prospectively and longitudinally evaluate the change in AFI in postdates. Materials and Methods: Serial AFls were obtained semi­weekly in 121 well dated (by cenain LMP consistent with early sonographic exam) pregnancies> 41 weeks' gestation. Poor fetal testing, oligohydramnios (i.e. AFI~6.0cm) or a favorable cervix were used as indications for delivery. Results: The AFI increased in 42 patients (36%). did not change in 3 patients (2%) and decreased in 76 patients (63%). The mean AFI at 41 weeks of gestation was 12.4 ± 4.2 cm (±SD). Overall, there was a significant mean weekly decrease in AFI of 26.2% (p<O.0005). Oligohydramnios was diagnosed in 13% of these patients. The results of this longitudinal study indicate that in postdates patients: 1. There is a 26.2% weekly decrease in AFI. 2. There is a considerable patient variation in AFI as a function of

gestational age. 3. Oligohydramnios is absent in most of these patients with

accurate dating.