Impact of obstructive sleep apnea on sleep cycles and spindle dynamics: A polysomnographic study

Sleep spindles and the temporal organization of sleep are essential for restorative and cognitive functions, yet their disruption in obstructive sleep apnea (OSA) remains poorly understood. This study examined spindle density and duration across sleep cycles in 30 OSA patients and 22 controls using full-night polysomnography. While total sleep time and stage proportions were similar between groups, sleep efficiency and arousal index worsened with OSA severity. Spindle duration in N2 was significantly reduced in moderate OSA, particularly at frontal sites, with a Group × Cycle interaction indicating altered temporal dynamics, with a significant difference primarily observed in the first sleep cycle. In N3 sleep, spindle density was significantly reduced in severe OSA compared to controls during the fourth sleep cycle. However, no significant group × cycle interaction was observed, indicating limited evidence for progressive spindle density decline with increasing OSA severity. These findings suggest that OSA severity impacts specific temporal aspects of spindle dynamics during the night, yet the alterations are stage-, cycle-, and severity-dependent rather than progressive across severity levels, emphasizing the potential cognitive and clinical relevance of disrupted spindle activity in OSA. Further research is warranted to clarify the mechanisms by which OSA affects sleep spindle modulation.