Abstract 340 Poster Session IV, Tuesday, 5/4 (poster 247)

Introduction: Emergence of states is a significant aspect of brain maturation. In all species, active sleep state occupies the major proportion of time in early brain development and decreases after birth. Hence state has been used as an index of brain development. There is controversy with regard to the acceleration or retardation of the brain development in the growth restricted (GR) fetus. There are no data available about the developmental pattern of sleep state in these fetuses.

Hypothesis: The GR fetus will demonstrate patterns of EEG-derived sleep states that are divergent from those compared to normally grown lambs.

Methods: Nineteen experiments were carried out in 5 chronically catheterized pregnant sheep between 117-144 days of gestation (GA) where term is 148d. Maternal catheters were placed at 92-94 days GA. To induce GR, three mothers were bled about 20cc/day and the other 2 ewes served as controls. Prior research has demonstrated that this is a reliable and reproducible method for inducing fetal growth restriction. At 112-114 days GA, fetal catheters and bioelectric leads were placed. Ten studies were performed before 130 days (early development) and 9 after 130 days (late development). The fetal EEG was analyzed using spectral analysis. The sleep states were characterized by EEG spectral edge with <8 Hz as quite sleep (QS) and ≥8Hz as active sleep (AS).

Results: Control and GR fetus had comparable amounts of active sleep in early development (22±11% vs 22±9%, p=ns) and in late development (49±12% vs 36±5%, p=ns). The following table shows the power (µv) present in the various frequency bands of the EEG during late development

Table 1 No caption available
Full size table

In comparison between control and GR fetus during EEG-defined quiet sleep, a decrease (p<0.05) in total and 1-4 Hz power, while in active sleep a decrease (p<0.05) in 12-24 Hz and 1-4 Hz power was observed. These are frequency bands which most reliably discriminate quiet and active sleep.

Conclusions: Even though the amount of time GR fetus spends in active sleep is not different from control fetus, the power in the predominant bands of active and quite sleep is significantly less. This may represent either a decrease in the size of neural network underlying the production this activity or reduction of synchronous firing.