A Comparison of Each Sleep Stage Autonomic Nervous System Activity in Different Sleep Apnea Severity Levels

Abstract

Sleep apnea has increasingly become a public health issue. To further elucidate the physiological changes in different sleep apnea severity levels, we analyzed the autonomic nervous system (ANS) activity in each sleep stage by heart rate variability (HRV), moreover, we clarified how sleep apnea severity affects hypnogram and sleep quality. Subjects used in this study was obtained from PhysioNet, and the patient data were grouped into mild, moderate, and severe levels of sleep apnea according to apnea–hypopnea index (AHI). The electrocardiogram readings during the period of free apnea were extracted and evaluated by HRV and represented to the sleep stages as follows: Awake, rapid eye movement (REM), and nonrapid eye movement (NREM) in different sleep apnea levels, respectively. The results indicated that the severe group (AHI ≥ 30 events per hour) has higher sympathetic nervous system (SNS) activity and lower parasympathetic nervous system (PNS) activity in NREM. This elevates the ANS tone in NREM similar to Awake, making the ANS activity between NREM and Awake indistinguishable. Furthermore, we evaluated the effects both with (w/) and without (w/o) apnea events in REM and NREM separately. Apnea events that occurred in REM (w/) were not different compared to those in REM (w/o). On the other hand, apnea events occurring in NREM (w/) activated SNS and suppressed PNS activity. This altered the ANS tone, which suggested an early sleep stage transition to REM or Awake. This study indicates how sleep apnea severity correlates to the imbalance of ANS activity and it might disrupt the normal hypnogram. Consequently, from the ANS point of view that patients with severe apnea do not get appropriate rest from sleeping, these patients need some medical interventions or treatment to prevent the development of chronic diseases.