Objectives: Sleep states and physiological changes during sleep may be useful in assessing brain function. We hypothesized that infants with transposition of great vessels (TGV) exhibit recognizable states of sleep under conditions of isocapnic hypoxemia. Also, we speculated that early correction of hypoxemia may result in significant changes in the physiological characteristics of quiet and active sleep.
Methods: Six-hour continuous cardiorespiratory and electrocortical recordings were performed in five term infants with TGV, pre- and postoperatively along with simultaneous minute by minute behavioral sleep state assignment. Data were sorted for sleep states and percent sleep time for each state was computed. Measurements of state-dependent variables, i.e., heart rate (HR), heart rate variability (HRSD), respiratory frequency (f), variability in respiratory frequency (fSD), and spectral properties of the EEG during quiet and active sleep were compared for both pre- and postoperative periods.
Results: All infants showed significant differences in state-dependent variables between quiet and active sleep, both during preoperative (mean O2 saturation = 80.9 +/- 2.8) and postoperative (mean O2 saturation = 92.8 +/- 0.5) periods. As compared to preoperative period, postoperatively during quiet sleep, HR and HRSD were lower, and EEG power was greater; and during active sleep, HR, HRSD, and fSD decreased and EEG power increased. Also, in the postoperative period % quiet sleep increased and % active sleep decreased.
Conclusions: Under conditions of isocapnic hypoxemia infants with TGV vessels exhibit clearly recognizable states of sleep. Correction of hypoxemia is associated with significant changes in state-dependent variables both during quiet and active sleep.