Changes in oxygen and carbon dioxide in the genesis of sleep bruxism: a mechanism study

Abstract

Purpose: Rhythmic masticatory muscle activity (RMMA), a biomarker of sleep bruxism (SB), has been associated with mild hypoxia and/or big breaths in some adults with non-sleep-disordered breathing. The purpose of this study was to investigate that concurrent oxygen and carbon dioxide fluctuations are among the physiological variables that contribute to RMMA onset.

Methods: Twelve subjects (5 female, 7 male, mean age: 43 ± 11) underwent polysomnography recording in a sleep laboratory. RMMA index and apnea-hypopnea index were calculated. Oxygen saturation (SpO₂) was estimated by finger pulse oximeter and end-tidal CO₂ (ETCO₂) by nasal airflow cannula before and after RMMA onset. Given the expected response time delay between actual arterial hypoxemia and fingertip pulse detection, we adjusted the SpO₂ desaturation onset to the onset of masseter muscle activity using a 17 s criterion based on ETCO₂ shifts.

Results: SpO₂ was slightly but significantly lower than at baseline (max: -0.6%) in the 6–4 s before RMMA onset and significantly higher in the 6–18 s after onset (0.9%; p < 0.05). Although ETCO₂ before RMMA onset did not differ from baseline, it decreased at 8–10 s after onset (-1.7 mmHg: p < 0.05). No changes in SpO₂ or ETCO₂ in relation to RMMA onset reached a critical clinical threshold.

Conclusions: The mild transient hypoxia observed before RMMA onset was not associated with a change in ETCO₂. The mild and brief oxygen fluctuations before RMMA onset may reflect a physiological response that seems to have little influence on SB genesis.