Night-to-night variability in sleep in cystic fibrosis.

Objectives: The impact of night-to-night variability (NNV) on polysomnography (PSG) has been reported mainly in normal subjects, the elderly and patients with obstructive sleep apnea with focus on changes in the apnea/hypopnea index, rather than measures of nocturnal oxygenation. There is very limited data on NNV in patients with cystic fibrosis (CF). The goal of this study was to assess for first-night effect and reliability of PSG measurements on nocturnal oxygenation and respiratory disturbance in CF.

Methods: A prospective observational study was performed in patients with CF who consented to PSG on two consecutive nights. Paired t-tests and intra-class correlation coefficients (ICCs) were calculated for repeated measures of sleep stage time, sleep efficiency, arousal indices, measures of nocturnal oxygenation, and respiratory events in all sleep stages.

Results: Thirty-one patients with CF were studied, aged 27+/-8 (mean+/-1 SD) years and forced expiratory volume in 1 s (FEV(1)) of 37+/-11% of predicted. Relative to the first-night PSG, on the second PSG, we observed the following: shorter latency to rapid eye movement (REM) sleep (P<0.001), increased sleep efficiency (P<0.01), decreased wake after sleep onset (WASO) time (P<0.01), decreased percentage of non-REM time with oxyhemoglobin saturation by pulse oximetry (SpO(2))< or =90% (P<0.05), decreased number of central apneas per hour (P<0.05) and reduced respiratory rate in stage 2 sleep on night 2 (P<0.05). Despite these changes, the ICCs between night 1 and night 2 showed good repeatability/reliability for measures of nocturnal oxygenation and indices of respiratory disturbance, including the percentage of total sleep time with SpO(2)< or =90% (ICC=0.85) and apnea-hypopnea index (ICC=0.75). Likewise, the ICCs were extremely high for respiratory rate in stage 2 (ICC=0.94), slow wave sleep (ICC=0.97), and REM sleep (ICC=0.96).

Conclusion: Although a first-night effect is seen with sleep efficiency, REM latency, and WASO, a single-night PSG in patients with CF yields reliable information on nocturnal oxygenation and respiratory disturbance.