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Cardiovascular and Metabolic Responses to Intermittent Umbilical Cord Occlusion in the Preterm Ovine Fetus

Department of Obstetrics and Gynaecology, Royal Free and University College Medical School, University College London, Gower Street Campus, 86-96 Chenies Mews, London WC1E 6HX, United Kingdom rmjblgr{at}ucl.ac.uk

Jacobus Homan, BSc

Susan E. White, BSc

Bryan S. Richardson, MD

MRC Group in Fetal and Neonatal Health and Development; Departments of Obstetrics and Gynecology and Physiology, Lawson Research Institute, University of Western Ontario, London, Canada

Objective: To determine the cardiovascular and metabolic responses to umbilical cord occlusion in the preterm ovine fetus and the impact of repetitive intermittent insults over a 4-day period.

Methods: Repetitive umbilical cord occlusions (experimental group, n = 7; control group, n = 7) were performed daily 112-115 days' gestation, term = 147 days). Mean arterial pressure (MAP), fetal heart rate (FHR), and FHR variation were monitored, and arterial blood was sampled at predetermined intervals.

Results: During umbilical cord occlusions, arterial oxygen pressure (Pao₂) (approximately 17 mmHg) and glucose (approximately 0.3) millimoles per liter (mmol/L) fell and arterial carbon dioxide pressure (approximately 8 mmHg) rose (P < .01) to a similar extent on days 1 and 4. Umbilical cord occlusion produced a rise in lactate over the course of successive umbilical cord occlusions each day, the magnitude of which tended to be reduced by day 4 (0.3 ± 0.1 versus 0.6 ± 0.1 mmol/L). Control hour FHR and MAP were unaltered over the 4 days, but the delta () FHR to Pao₂ ratio during umbilical cord occlusions was less on day 4 than on day 1 (6.0 ± 0.4 versus 10.9 ± 1.5 beats per minute/mmHg; P < .01). During occlusion hours, high FHR variation episodes, as a measure of fetal activity, were reduced (14.6 ± 1.5 versus 4.2 ± 1.3 min/h; P < .01), whereas the reduction in short-term (7.4 ± .07 to 5.8 ± 0.6 milliseconds; P < .05) and long-term (34.9 ± 2.7 to 30.0 ± 0.6 milliseconds; P < .05) FHR variation reached significance only on day 4.

Conclusion: The increase in lactate and reduced high-FHR variation episodes over successive umbilical cord occlusions may affect fetal growth and development. Furthermore, repeated umbilical cord occlusions over several days alter the preterm FHR response to subsequent stresses, suggesting an altered chemoreflex response.

Key Words: Umbilical cord • fetus • cardiovascular • heart rate variation

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