Subjective sleep assessments are correlated with EEG-related sleep measurements of the first sleep cycle in healthy young adults.

This study examined whether subjective and objective sleep parameters (sleep stage, electroencephalography [EEG] power, heart rate variability) are related to the progression of sleep cycles using differences in the variables between two nights. We hypothesized that the association between night-to-night differences between subjective and objective sleep variables reflect the difference in objective sleep variables in the first sleep cycle. Seventy-seven healthy adults (23.8 ± 2.2 years; 41 females) participated in polysomnographic recordings on two consecutive nights. To extract the variables that represent the difference between the nights, the sleep parameters of Night 1 were subtracted from those of Night 2. Spearman's rho was used to assess correlations between subjective sleep assessments and objective sleep parameters, with false discovery rate correction for multiple comparisons. Subjective sleep assessments were significantly correlated with whole-night sleep architecture and quantitative EEG activity, but not with heart rate variability during the night. Among sleep cycles, subjective sleep parameters were correlated with the objective sleep parameters in the first sleep cycle ("Ease of falling asleep" vs. waking after sleep onset [r = - 0.382], "Depth of sleep" vs. EEG theta power [r = 0.404], "Quality of sleep" vs. the percentage of stage N3 [r = 0.412] and EEG delta power [r = 0.458], all p < 0.05). These results suggest the importance of taking the difference among the nights into account when assessing subjective sleep quality. This study clarified that sleep in the first sleep cycle has a dominant influence on subjective sleep assessments. Supplementary Information: The online version contains supplementary material available at 10.1007/s41105-022-00437-x.

Sleep stage-dependent changes in tonic masseter and cortical activities in young subjects with primary sleep bruxism.

STUDY OBJECTIVES: The present study investigated the hypothesis that subjects with primary sleep bruxism (SB) exhibit masseter and cortical hyperactivities during quiet sleep periods that are associated with a high frequency of rhythmic masticatory muscle activity (RMMA). METHODS: Fifteen SB and ten control participants underwent polysomnographic recordings. The frequencies of oromotor events and arousals and the percentage of arousals with oromotor events were assessed. Masseter muscle tone during sleep was quantified using a cluster analysis. Electroencephalography power and heart rate variability were quantified and then compared between the two groups and among sleep stages. RESULTS: The frequency of RMMA and percentage of arousals with RMMA were significantly higher in SB subjects than in controls in all stages, while these variables for nonrhythmic oromotor events did not significantly differ between the groups. In SB subjects, the frequency of RMMA was the highest in stage N1 and the lowest in stages N3 and R, while the percentage of arousals with RMMA was higher in stage N3 than stages N1 and R. The cluster analysis classified masseter activity during sleep into two clusters for masseter tone and contractions. Masseter muscle tone showed typical stage-dependent changes in both groups but did not significantly differ between the groups. Furthermore, no significant differences were observed in electroencephalography power or heart rate variability between the groups. CONCLUSION: Young SB subjects exhibited sleep stage-dependent increases in the responsiveness of RMMA to transient arousals, but did not show masseter or cortical hyperactivity during sleep.

Discrepancies in the Time Course of Sleep Stage Dynamics, Electroencephalographic Activity and Heart Rate Variability Over Sleep Cycles in the Adaptation Night in Healthy Young Adults.

OBJECTIVE: The aim of the present study was to characterize the cyclic sleep processes of sleep-stage dynamics, cortical activity, and heart rate variability during sleep in the adaptation night in healthy young adults. METHODS: Seventy-four healthy adults participated in polysomnographic recordings on two consecutive nights. Conventional sleep variables were assessed according to standard criteria. Sleep-stage continuity and dynamics were evaluated by sleep runs and transitions, respectively. These variables were compared between the two nights. Electroencephalographic and cardiac activities were subjected to frequency domain analyses. Cycle-by-cycle analysis was performed for the above variables in 34 subjects with four sleep cycles and compared between the two nights. RESULTS: Conventional sleep variables reflected lower sleep quality in the adaptation night than in the experimental night. Bouts of stage N1 and stage N2 were shorter, and bouts of stage Wake were longer in the adaptation night than in the experimental night, but there was no difference in stage N3 or stage REM. The normalized transition probability from stage N2 to stage N1 was higher and that from stage N2 to N3 was lower in the adaptation night, whereas that from stage N3 to other stages did not differ between the nights. Cycle-by-cycle analysis revealed that sleep-stage distribution and cortical beta EEG power differed between the two nights in the first sleep cycle. However, the HF amplitude of the heart rate variability was lower over the four sleep cycles in the adaptation night than in the experimental night. CONCLUSION: The results suggest the distinct vulnerability of the autonomic adaptation processes within the central nervous system in young healthy subjects while sleeping in a sleep laboratory for the first time.

Sleep stage dynamics in young patients with sleep bruxism.

STUDY OBJECTIVES: We hypothesized that sleep stage dynamics are different in patients with sleep bruxism (SB) and that these changes are associated with the occurrence of rhythmic masticatory muscle activity (RMMA). METHODS: Fifteen healthy controls and 15 patients with SB underwent overnight polysomnography. Sleep variables and survival curves of continuous runs of each sleep stage were compared between the groups. Stage transition dynamics and the probability of stage fragmentation were analyzed for three epochs before and after the epoch with RMMA. Survival curves of continuous runs of each sleep stage, terminated with or without RMMA, were also compared. RESULTS: There were no significant differences in sleep variables between the groups, except for shorter sleep latency, shorter rapid eye movement (REM) latency, and longer total N1 duration in SB patients than in controls. REM sleep and N2 were significantly less continuous in SB patients than in controls. In the SB group, stage fragmentation probability was significantly increased for the epoch with RMMA compared with the baseline for all stages. Meanwhile, the occurrence of RMMA did not affect the continuity of N2 or REM; however, the occurrence of RMMA was preceded by more continuous N3 runs. CONCLUSIONS: Sleep stage dynamics differed between SB patients and controls. RMMA does not result in sleep disruption but is likely associated with dissipation of sleep pressure. Less continuity of REM sleep in SB may provide insights into the underlying pathophysiological mechanisms of SB, which may be related to REM sleep processes such as cortical desynchronized states or brainstem activation.

Sleep Quality, Psychologic Profiles, Cardiac Activity, and Salivary Biomarkers in Young Subjects with Different Degrees of Rhythmic Masticatory Muscle Activity: A Polysomnography Study.

AIMS: To investigate the objective and subjective characteristics of sleep and psychosomatic and physiologic variables in young subjects with different frequencies of rhythmic masticatory muscle activity (RMMA) during sleep. METHODS: A total of 54 young (mean age 23.8 ± 2.1 years), healthy subjects underwent polysomnographic (PSG) recordings for 2 nights. Sleep and psychosomatic states were assessed prior to PSG using validated questionnaires, and the following PSG variables were assessed before and after sleep: subjective sleep quality, physical symptoms, anxiety level, and salivary biomarkers. Second-night sleep and oromotor variables were scored according to standard criteria as well as the quantitative autonomic activity during the night. These variables were compared among the high- (H-RMMA, n = 21, mean RMMA index: 5.7 times/hour) and low- (L-RMMA, n = 13, 2.6 times/hour) frequency RMMA and control (CTL, n = 20 subjects, 1.0 time/hour) groups. RESULTS: Sleep and psychosomatic states did not differ among the three groups. No group differences were noted for nonrhythmic oromotor events. Sleep architecture did not differ among the three groups except for sleep latency being shorter (P = .008) and microarousal index being higher (P = .013) in the H-RMMA group. Mean heart rate during sleep was lower (Stage N2, P = .008; Stage N3, P = .036; Stage R, P = .045) in the H-RMMA group, but the heart rate variability did not differ among the three groups. Sleep quality and anxiety level before and after sleep did not differ among the three groups. Cortisol did not differ among the three groups, while chromogranin A in the morning was slightly lower in the L-RMMA group (median: 9.1 pmol/mg) than in the H-RMMA group (12.3 pmol/mg) (P = .049). CONCLUSION: In otherwise healthy subjects presenting normal physiologic variables, neither significant nor consistent differences in sleep architecture, psychologic states, heart rate variability, or salivary biomarkers in relation to the frequency of RMMA were found.