P166 Measures of overnight sleep stability in patients with hypersomnolence

INTRODUCTION: Hypersomnolence causes significant impairment of daytime functioning. The multiple sleep latency test (MSLT) measures objective hypersomnolence (OH). Patients with hypersomnolence with a normal MSLT are said to have subjective hypersomnolence (SH). The mechanisms of hypersomnolence in such patients is uncertain. This study describes differences in measures of sleep stability derived from the overnight polysomnography (PSG) in patients with OH and SH. METHODS: A retrospective analysis of 100 patients undergoing PSG/MSLT for investigation of hypersomnolence was performed. Patients were classified as OH (MSLT≤8 min) or SH (MSLT>8min). Sleep stage distribution and PSG-derived markers of sleep stability including cardiopulmonary coupling (CPC), cyclic alternating pattern (CAP) and sleep stage shifts were compared between the two groups. RESULTS: When compared to OH patients (N=50), SH patients (N=50) had significantly more sleep stage shifts, more shifts to stage N1 and longer PSG sleep latency. Small but significantly lower sleep efficiency, higher stage N1 and N3 proportions were also observed in SH patients. OH patients had a small but significantly higher CAP rate and CAP index compared to SH patients. There were no significant differences in CPC metrics between the two groups. CONCLUSION: Several PSG-derived markers of sleep stability indicated that patients with SH experienced more unstable sleep than OH patients. This may provide insight into the underlying pathophysiological mechanisms which differentiate these patient groups and may serve as a future therapeutic target.