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Prolonged Mild Hypoxia Alters Fetal Sheep Electrocorticogram Activity

Jie Zhang, MD

G. Angela Massmann, MD, MS

Perinatal Research Laboratory, Department of Obstetrics and Gynecology, Center for Research in Obstetrics and Gynecology, Wake Forest University School of Medicine, Winston-Salem, North Carolina

Jorge P. Figueroa, MD, PhD

Department of Obstetrics and Gynecology, Wake Forest University School of Medicine, Medical Center Boulevard, Winston-Salem, NC 27157 figureoa{at}wfubmc.edu

Objective: To assess the effects of prolonged mild hypoxemia on fetal brain electrocorticogram (ECoG) in late gestation.

Study Design: Fetal and maternal catheters were placed under general anesthesia and animals allocated at random to receive intratracheal maternal administration of either nitrogen (n = 8) or compressed air (n = 8). Five days after surgery (125 days' gestational age), nitrogen infusion was adjusted to reduce fetal brachial artery PO₂ by 25%. The targeted decrease in fetal oxygenation was maintained for 5 days while fetal ECoG activity and fetal and maternal cardiovascular variables were continuously recorded. Data are presented as mean ± SEM and were analyzed by two-way analysis of variance (ANOVA) or two-sample t test.

Results: Nitrogen infusion decreased fetal PO₂ by 26% (20.5 ± 1.7 versus 14.3 ± 0.8) without changing fetal PCO₂ or pH. Mild fetal hypoxemia was associated with fetal tachycardia and increased fetal blood pressure (P <.05). Fetal ECoG in hypoxic fetuses showed a significant decrease in the time spent in high voltage (HV) (P <.05) and an increase in the time spent in low voltage (LV) and in the number of low voltage events (P <.05). Also, a significant decrease in the proportion of 1-4 Hz and an increase in the proportion of 13-20 Hz frequencies was observed in LV events without a significant change in the frequency profile of HV events (P <.05).

Conclusion: Prolonged mild hypoxemia significantly altered fetal homeostasis as reflected by the sustained tachycardia and increased blood pressure. Fetal ECoG activity was affected significantly in a qualitatively and quantitative manner by mild prolonged hypoxema.

Key Words: Mild hypoxemia • electrocorticogram • fetal sheep • heart rate • power spectrum

Journal of the Society for Gynecologic Investigation, Vol. 13, No. 6, 404-411 (2006)
DOI: 10.1016/j.jsgi.2006.05.007


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