Sleep Irregularity in the Previous Week Influences the First-Night Effect in Polysomnographic Studies

OBJECTIVE: The first-night effect is a well-known phenomenon resulting from an individual's maladaptation to the unfamiliar environment of a sleep laboratory. However, there have been no direct reports of the effect of previous sleep patterns on the first-night effect. We aimed to investigate the effect the previous week's sleep pattern on the first-night effect. METHODS: Twenty-four young, healthy, male participants completed the study procedure. During one week prior to study, the participants kept sleep diaries and wore actigraphs to identify sleep-wake pattern. Two consecutive nights of polysomnography were conducted after that. Wilcoxon signed-rank tests were applied to compare sleep variables of the two nights. Variance (standard deviation) of sleep onset time during the previous week was used as an index of irregularity. A Kendall's ranked correlation analysis and a linear regression test were applied to detect correlation between sleep irregularity and the first-night effect measured by polysomnography. RESULTS: There were significant differences in the values of sleep efficiency (p=0.011) and wake after sleep onset (WASO) (p=0.006) between the two nights. Sleep efficiency was lower and WASO was higher on the first night as compared to the second night. Sleep irregularity in the previous week was negatively correlated with sleep efficiency (p<0.001) of the first night, but was not significantly correlated with any other sleep parameters. CONCLUSION: We replicated the existence of the first-night effect commonly observed in sleep studies. Sleep irregularity in the previous week may influence the first-night effect in polysomnographic studies.

Changes in Multiple Sleep Latency Test Results according to Different Criteria of Sleep Onset / 수면정신생리

OBJECTIVES: The multiple sleep latency test (MSLT) is commonly used as a valid objective measure of sleepiness. The procedure of MSLT is well standardized but the sleep onset criterion is somewhat variable. One epoch of stage 1 sleep is the most commonly used criterion, and the criterion of three epochs of stage 1 sleep is also used. The purpose of this study was to compare the two criteria used to determine sleep onset. METHODS: We retrospectively analyzed 60 consecutive MSLT that were performed according to a standaridized protocol. We scored each test using the two different criteria for sleep onset and then statistically analyed the results. RESULTS: Using the different criteria, 20 patients among 60 showed changes in mean sleep latency (33.3%). The extent of change ranged from 1.3% to 38.5% (mean 15.9%). Non-narcoleptic patients showed a significantly higher incidence of change than other sleep disorder patients. CONCLUSION: Changes in mean sleep latency occurred according to the different criteria of sleep onset. But the difference arising from different criteria was statistically not significant in patients with moderate to severe sleepiness. Considering that 1 epoch criterion for sleep onset is more sensitive in detecting clinically significant sleepiness, the authors suggest that the 1 epoch criterion is more reliable than the 3 epochs criterion.