Yuhao Mao,1,2,* Qi Li,1,* Xueliang Zou,3 Zhijun Zhong,1 Qian Ouyang,1 Chunmei Gan,1 Fang Yi,1 Yaxing Luo,1 Zilin Cheng,1,2 Dongyuan Yao1 

1Neurological Institute of Jiangxi Province and Department of Neurology, Jiangxi Provincial People’s Hospital, The First Affiliated Hospital of Nanchang Medical College, and Xiangya Hospital of Central South University at Jiangxi, Nanchang, Jiangxi, People’s Republic of China; 2Queen Mary College, Nanchang University, Jiangxi, People’s Republic of China; 3Jiangxi Mental Hospital, Nanchang University, Jiangxi, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Dongyuan Yao, Jiangxi Provincial People’s Hospital, 92 Aiguo Road, Nanchang, Jiangxi, 330006, People’s Republic of China, Tel/Fax +86-791-8689-5077, Email yao9000@gmail.com

Background: Obstructive sleep apnea (OSA) is the most common sleep-related breathing disorder characterized by recurrent upper airway collapse and obstruction, leading to reduced or absent breathing during sleep, especially rapid eye movement (REM) sleep, and continuous positive airway pressure treatment (CPAP) is often used for treatment of OSA. Sawtooth waves (STWs) are a characteristic of REM sleep.
Objective: To examine effects of CPAP treatment on STWs during REM sleep in the OSA patients.
Methods: Polysomnographic recordings were performed on 20 moderate-to-severe OSA patients and 16 normal controls, and comparisons of STWs during REM sleep in the OSA patients with and without CPAP treatment (paired t-test or Wilcoxon signed-rank test wherever appropriate), and between OSA patients and normal controls (Student’s t-test or Wilcoxon rank-sum test) were carried out. In addition, linear correlation analyses were used to estimate the relationship of STWs and REM sleep with duration of non-REM (NREM) sleep stage 3 (N3).
Results: The STWs were classified to be apnea/hypopnea associated and not associated (isolated), and the amplitude of the isolated STWs was significantly higher than that of the apnea/hypopnea associated. With CPAP treatment, the percentage of REM sleep with STWs and the amplitude of STWs were significantly increased to the levels, which were not significantly different from those in the normal controls, while the frequency of STWs was not significantly changed. In addition, the total duration of REM sleep and the duration of REM sleep with STWs were both positively correlated with the duration of N3 sleep in the normal controls and the OSA patients with CPAP treatment. Furthermore, CPAP treatment also caused a significant increase in the duration of rapid eye movements in REM sleep.
Conclusion: These findings suggest that there are some interconnections between NREM and REM sleep, and STWs not only represent the quality of REM sleep but also are correlated with N3 sleep.

Keywords: sawtooth wave, obstructive sleep apnea, continuous positive airway pressure, rapid eye movement sleep, non-rapid eye movement sleep