From the Guidelines
Non-REM (NREM) sleep is the stage with decreased airway resistance. During NREM sleep, particularly in stages 3 and 4 (deep sleep), there is maintained muscle tone in the upper airway muscles, which helps keep the airway open and reduces resistance to airflow. This is important because during sleep, there is a natural decrease in muscle tone throughout the body. In contrast, during REM sleep, there is significant muscle atonia (loss of muscle tone) that affects most skeletal muscles, including those that maintain airway patency. This reduction in muscle tone during REM sleep can lead to increased airway collapsibility, narrowing of the airway, and consequently higher airway resistance. The study on non-CPAP therapies in obstructive sleep apnea 1 highlights the importance of changes in respiratory drive, airway tone, or surface forces that cause airway closure during sleep, which is relevant to understanding the differences in airway resistance between NREM and REM sleep. Key points to consider include:
- Maintained muscle tone in the upper airway muscles during NREM sleep
- Significant muscle atonia during REM sleep
- Increased airway collapsibility and resistance during REM sleep
- Relevance to sleep-related breathing disorders, such as obstructive sleep apnea, which tend to be more severe during REM sleep.
From the Research
Sleep Stages and Airway Resistance
- The relationship between sleep stages and airway resistance is complex, with various studies investigating this phenomenon 2, 3, 4, 5.
- One study found that upper airway muscle activity is elevated during slow-wave sleep (SWS) compared to lighter sleep stages, which may help preserve upper airway patency during this stage 2.
- Another study discovered that phasic electromyographic activity of the genioglossus increases in normals during slow-wave sleep, suggesting a potential mechanism for maintaining upper airway patency 4.
- However, the study also found that upper airway resistance was not different between SWS and Stage 2 sleep, indicating that other factors may influence airway resistance 4.
Decreased Airway Resistance
- Decreased airway resistance is not explicitly mentioned in the provided studies as a characteristic of a specific sleep stage.
- However, one study found that the arousal index was higher in stage 2 compared to slow wave sleep and REM, suggesting that sleep stage may have an impact on airway resistance 5.
- Another study discovered that bilevel positive airway pressure (PAP) therapy can reduce expiratory PAP and improve sleep quality in patients with obstructive sleep apnea, but this is not directly related to the sleep stage 6.
Sleep Stage and Airway Resistance
- The available evidence suggests that sleep stage may have an impact on airway resistance, with slow-wave sleep potentially having increased upper airway muscle activity to preserve patency 2, 4.
- However, the relationship between sleep stage and airway resistance is complex and influenced by various factors, including sleep position and nasal dilation 5.