A subpopulation of young SB subjects can show concomitant respiratory events. Further large sample studies are needed to demonstrate that the occurrence of subclinical respiratory events represents a clinical subtype of SB.

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Purpose: The aims of the present study were to investigate the temporal relationships between jaw and bodily movements and clarify motor processes in the genesis of rhythmic masticatory muscle activity (RMMA) in sleep bruxism (SB). Methods: Video-polysomnography recordings were obtained from ten subjects with SB (mean age: 23.4 ± 1.6 years) and ten matched normal controls (CTL) (mean age: 24.4 ± 3.2 years). RMMA and nonspecific masseter activity (NSMA) were scored in association with bodily movements in the leg, arm, head, and trunk using electromyography and video recordings. The relationship between oromotor episodes and bodily movements was assessed in terms of sleep stage distributions and temporal relationships. Cardiac changes preceding oromotor episodes in stage N2 were assessed. Results: Approximately 80% of RMMA and NSMA were associated with movements in one or more body sites. RMMA and NSMA were more frequently associated with movements of the leg (70-75%) and arm (40-55%) than movements of the head (17-22%) and trunk (5-25%). The relationship between oromotor episodes and bodily movements did not significantly differ among sleep stages. Oromotor episodes and bodily movements did not show a consistent temporal pattern in the SB and CTL groups. Regardless of the temporal relationship between oromotor episodes and bodily movements, the mean heart rate significantly increased by 5 beats before the onset of oromotor episodes. Conclusions: No specific temporal motor patterns were found between RMMA and bodily movements. RMMA and NSMA represent a repertoire of arousalrelated autonomic motor responses during sleep.

Study Objectives: The present study aimed to investigate the occurrence and characteristics of apnea-hypopnea events in young nonobese healthy Japanese participants. Methods: One hundred and three young adult participants without sleep complaints (men: 56; women: 47; age: 24.5 ± 3.0 years; body mass index: 20.9 ± 1.8 kg/m 2 ) underwent 2-night polysomnography. Data on the 2nd night were scored according to American Academy of Sleep Medicine criteria version 2.1. The apneahypopnea index (AHI) was estimated. The arousal threshold was calculated in participants with AHI ≥ 5 events/h. Apnea-hypopnea events were rescored by 3 other criteria issued by the American Academy of Sleep Medicine (AASM): Chicago criteria in 1999 and recommended and alternative criteria in 2007. Results: Participants had good sleep characterized by high sleep efficiency (93.2%). Mean AHI of AASM 2.1 recommended criteria was 4.0 ± 5.3 events/h. AHI was significantly higher in men (median [range] = 4.0 [.3-35.8] events/h) than in women (1.6 [.1-18.1] events/h). The prevalence rates of AHI ≥ 5 events/h and ≥ 15 events/h were 25.2 and 3.9%, respectively. The arousal threshold was estimated as −7.7 ± 2.6 cm H 2 O. AHI was lower for AASM 2007 recommended criteria (.8 [.0-18.2 events/h]) and AASM 2007 alternative (2.0 [.1-32.2] events/h) than for AASM version 2.1 recommended criteria (2.4 [.1-32.9] events/h) and AASM ] events/h). The percentage of participants with AHI ≥ 5 events/h was approximately 2-fold higher with AASM Chicago (44.6%) than with AASM version 2.1 recommended criteria. Conclusions: The present study demonstrated that 25% of young nonobese Japanese participants had subclinical obstructive sleep apnea. The presence of frequent airflow limitations may be a risk factor for the development of obstructive sleep apnea in Japanese individuals.