Maturational changes and effects of chronic hypoxemia on electrocortical activity in the ovine fetus.

We have studied the maturation of electrocortical (ECoG) activity in fetal sheep and the impact of chronic hypoxemia using a growth restriction model with placental embolizations. Twenty chronically catheterized fetal sheep (control, n=9; hypoxemic, n=11) were monitored at 116-119, 121-126 and 128-134 days gestational age (term=145 days), with ECoG activity scored using automated analysis of amplitude and frequency components to distinguish low-voltage/high frequency (LV/HF) and high-voltage/low frequency (HV/LF) state epochs, along with indeterminate voltage/frequency (IV/F) and transition period activities. We have shown that multiple aspects of ECoG state activity in the ovine fetus undergo maturational change as electrophysiologic measures of brain development. With chronic fetal hypoxemia, some maturational changes continue to occur, i.e. ECoG activity amplitude and 95% SEF, indicating the resiliency of these parameters to adverse conditioning. However, some maturational changes were altered, i.e. LV/HF and HV/LF incidence and duration, and likely regulated and adaptive with a decrease in the brain's nonessential energy needs, while some were altered, i.e. IV/F incidence and duration, and state transition times, and likely indicating a degree of aberrant development in associated control circuitries. This may then have consequences for disturbed sleep-wake patterns during later life and for adverse neurologic sequelae known to be increased in humans born with growth restriction.