Volume 167 Number 2

glycolysis and energy metabolism in preeclampsia. AM] OBSTET GYNECOL 1987;157:97-101. 14. Sostman HD, Armitage 1M, Fischer ]J. NMR in cancer. 1. High resolution spectroscopy of tumors. Mag Resonance Imaging 1984;2:265-78. 15. Noyszewski EA, Raman], Trupin SR, McFarlin BL, Dawson MJ. Phosphorus 31 nuclear magnetic resonance examination of female reproductive tissues. AM ] OBSTET GYNECOL 1989;161:282-8. 16. lies RA, Stevens AN, Griffiths]R, Morris PG. Phosphorylation status of liver by 3!P NMR spectroscopy, and its implications for metabolic control. Biochem] 1985;229: 141-51.

NMR spectroscopy of normal and growth-retarded placentas

17. Fox H. Effect of hypoxia on trophoblast in organ culture. AM] OBSTET GYNECOL 1970; 107: 1058-64. 18. MacLennan AH, Sharp F, Shaw-Dunn J. The ultrastructure of human trophoblast in spontaneous and induced hypoxia using a system of organ culture. ] Obstet Gynaecol Br Commonw 1972;79:113-21. 19. Trudinger B], Cook CM, Thompson RS, Giles WB, Connelly A. Low-dose aspirin therapy improves fetal weight in umbilical placental insufficiency. AM] OBSTET GYNECOL 1988;159:681-5.

Electrocortical activity, electroocular activity, and breathing movements in fetal sheep with prolonged and graded hypoxemia Bryan S. Richardson, MD, Lesley Carmichael, BSc, Jacobus Homan, BSc, and John E. Patrick, MD London, Ontario, Canada OBJECTIVE: Our objective was to determine the effect of a prolonged and graded reduction in fetal arterial oxygen saturation on electrocortical activity and associated biophysical variables. STUDY DESIGN: Fourteen unanesthetized fetal sheep were studied between 126 and 135 days' gestation with continuous monitoring of electrocortical and electroocular activity and breathing movements, during a 24-hour control period, and subsequently during 4 days of prolonged and graded hypoxemia induced by progressively lowering the maternal inspired oxygen concentration. RESULTS: Graded reduction in fetal arterial oxygen saturation resulted in little change in arterial pH until close to 30% when metabolic acidemia was apparent. The incidence of low-voltage electrocortical activity, electroocular activity, and breathing movements were marginally decreased with hypoxemia alone; however, a significant decrease was not apparent until associated with the onset of fetal acidemia. CONCLUSION: Hypoxemia of a chronic nature must approach the level at which acidemia becomes apparent before a marked change in fetal behavioral activity is noted. (AM J OSSTET GVNECOL 1992;167:553-8.)

Key words: Fetal behavior state, breathing movements, hypoxemia It is well recognized that the human fetus near term displays a periodicity in behavioral and biophysical parameters with coincidence of such into well-defined behavioral states similar to those described for the human newborn.' Cyclic changes in fetal behavioral state and From the Department of Obstetrics and Gynaecology and Physiology, St. Joseph's Health Centre, Lawson Research Institute, The University of Western Ontario. Supported by grants from the Canadian Medical Research Council. Received for publication October 28,1991; revised March 13,1992; accepted March 31,1992. Reprint requests:Bryan S. Richardson, MD, Department ofObstetrics and Gynaecology, Lawson Research Institute, St. Joseph's Hospital, 268 Grosvenor St., London, Ontario, Canada N6A 4V2.


state-related parameters are thus characteristic of the healthy fetus and provide a basis for the biophysical assessment of fetal health." However, although biophysical parameters appear to reflect fetal health at the time of study; their time course for alteration when fetal oxygenation becomes restricted is unknown, which may limit their usefulness in predicting fetal compromise. Studies with the chronically catheterized fetal lamb with short-term, induced hypoxemia show the incidence of low-voltage electrocortical activity, electroocular activity, and breathing movements to be variably reduced.v" Although further supporting the role ofbiophysical parameters in the assessment of fetal health,


554 Richardson at al.

August 1992


these studies do not predict the response to a slow and progressive decrease in fetal oxygenation, as might be encountered in the high-risk human pregnancy. To determine the effect of a progressive decrease in fetal oxygenation on behavioral activity, we have therefore studied fetal electrocortical activity as a measure of behavioral state and associated biophysical parameters, including e1ectroocular activity and breathing movements in the chronically catheterized sheep fetus with prolonged and graded reductions in fetal arterial oxygen saturation. Material and methods

Surgical procedures. Guidelines for the care and use of animals were followed as established by the Canadian Council on Animal Care and approved by the university. Studies were performed on 14 fetal sheep of mixed breed between 126 and 135 days' gestation (term 147 days). Fetuses were prepared for study at least 3 days before initiation of all experiments. The ewes were anesthetized with 1.0% to 1.5% halothane and 50% ox ygen /50% nitrous oxide, and the uterus was exposed and opened through a lower abdominal midline incision. Polyvinyl catheters were placed in the brachiocephalic trunk, the inferior vena cava, and the sagittal sinus, as previously reported.' Tracheal and amniotic fluid catheters were also placed as previously described.' Electrodes of Teflon-coated stainless steel wire (Cooner, Chatsworth, Calif.) were implanted biparietally on the dura for fetal electroencephalographic recordings and through the lateral orbital ridge of the zygomatic bone of each eye for c1ectroocular recordings. A reference electrode was placed in the loose connective tissue overlying the occipital bone of the skull. The catheters, containing heparinized saline solution, and wires were exteriorized through the flank of the ewe, and the abdomen was closed in layers. Polyvinyl catheters were then placed in the maternal femoral artery and vein. At the time of surgery, 1 gm of dihydrostreptomycin and 800 ,000 U of penicillin G were injected intramuscularly into the 'ewe, and after the uterus was closed l ,OOO ,OOO U of penicillin G was injected into both the fetal hind-limb vein and the amniotic cavity. This antibiotic coverage was continued daily for 2 to 3 days. Postoperatively the animals were maintained in individual cages suitable for continuous monitoring, with food and water available. Physiologic measurements. Each fetal lamb was studied during a 24-hour normoxic control period and subsequently during 4 days of prolonged and graded hypoxemia. Strain gauge manometers (Statham model P-23 ID, Gould, Oxnard, Calif.) and a strip-chart recorder (model 78D, Grass , Quincy, Mass.) were used to record pressures in the trachea, amniotic fluid, and brachiocephalic artery. Mean arterial blood pressure referenced to amniotic fluid pressure was calculated as diastolic plus 0.4 of pulse pressure. Electrical signals

J Obstet Gynecol

were. processed with a common mode rejection preamplifier (model 7 PSll], Grass). Fetal heart rate was measured by a cardiotachometer (model 7P44B) triggered from the arterial pulse pressure wave. Fetal electrocortical and electroocular potentials were displayed directl y on the chart recorder passing through a passive band-pass filter , 0.3 to 30 Hz on the preamplifier. Continuous recordings of electrocortical, electroocular potentials, tracheal pressure, amniotic fluid pressure, fetal arterial blood pressure, and fetal heart rate were obtained throughout the normoxic control period and the 4 days of induced hypoxemia. During this time the ewe's head was placed in a perspex chamber (volume 4.6 cubic feet) secured within the animals' cage, yet allowing for free access to food and water. Prolonged and graded hypoxemia was induced by progressively lowering the oxygen concentration within the perspex chamber with 1% to 2% carbon dioxide added as monitored by periodic measurement of oxygen and carbon dioxide gas tensions ; on day 1 to 18%, da y 2 to 16%, day 3 to 12% to 14%, and on da y 4 to 10% to 12% with the change in maternal inspired oxygen concentration occurring at approximately 10 AM each da y. Total gas flow to the perspex chamber was 40 L/min. Fetal arterial blood was sampled three times each da y at - 8 Mi, 12 noon, and 3 PM during both the 24-hour control period and the 4 da ys of induced hypoxia. At 12 noon each da y a paired sagittal vein blood sample was also obtained and radionuclide-labeled microspheres were injected into the inferior vena cava for determination of regional organ blood flows. All blood samples were analyzed for oxygen saturation, hemoglobin, oxygen content, pH, Po 2 , and Pco.. Brachiocephalic artery blood samples at 12 noon each day were also analyzed for corticotropin and cortisol. Fetal blood loss per day was -4 ml from blood sampling and 4 ml for reference sampling for blood flow determinations. On completion of each daily microsphere injection and subsequent blood sam pling, the fetus was transfused with 8 ml maternal blood . Arterial oxygen saturation and hemoglobin were measured in duplicate by an OSM2 (Radiometer, Copenhagen) hemoximeter, and ox ygen content was then calculated with an oxygen capacity of 1.36 ml oxygen /gm hemoglobin". Blood pH , Paz, and Pco, were anal yzed on an ABL-3 (Radiometer) blood gas analyzer with temperature corrected to 39.5° C. Oxygen and carbon dioxide concentrations within the perspex chamber were also analyzed on an ABL-3 blood gas anal yzer. Data analysis. Although all animals showed a progressive decrease in oxygenation, fetal arterial oxygen saturation values were nonetheless variable, averaging 57.0% ± 2.3% (SEM) on the control day (range 70.4 to 44 .2) and with induced hypoxia decreasing to 46.2 % ± 3.1 % on day 1 (range 63.3 to 27.0), 36.4 % ± 3.3% on day 2 (range 55.6 to 18.8),

Fetal behavioral activity with prolonged hypoxemia 555

Volu me 167 Number 2

Table I. Brachiocephalic arterial blood measurements Arterial oxygen satu ration

Art erial oxygen saturation (%) Arte rial oxygen conten t (mm ol / L)

I'aoz (to rr)

Pac o , (to r r)

pH (arterial) Base excess (mmoIL) Hem oglobin (gmllOO ml)

>6 0%


50 %-40%

40 %-30%

Electrocortical activity, electroocular activity, and breathing movements in fetal sheep with prolonged and graded hypoxemia.

Our objective was to determine the effect of a prolonged and graded reduction in fetal arterial oxygen saturation on electrocortical activity and asso...
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