Upper airway closing pressures in obstructive sleep apnea.

Area of Science:

• Respiratory Medicine
• Sleep Medicine
• Physiology

Background:

• Obstructive sleep apnea (OSA) is characterized by upper airway collapse during sleep.
• Understanding the collapsibility of the upper airway and the body's response to airway pressure is crucial for effective treatment.

Purpose of the Study:

• To investigate the effects of continuous positive airway pressure (CPAP) on upper airway stability in patients with OSA.
• To determine the upper airway closing pressure (UACP) during different sleep stages and its response to CPAP and nasal occlusion.

Main Methods:

• 18 patients with OSA underwent polysomnography with a specialized breathing circuit.
• Nasal occlusion and varying levels of CPAP were applied to assess upper airway collapsibility and closing pressure.
• Nasal pressure was monitored and compared to tracheal or esophageal pressure to detect airway closure.

Main Results:

• Low levels of CPAP (2.5-15.0 cmH2O) prevented OSA and improved sleep quality, including stable stage III/IV and REM sleep.
• The upper airway was more collapsible during stage I/II NREM and REM sleep compared to stage III/IV NREM sleep.
• Upper airway closing pressure (UACP) was lowest during REM sleep (2.4 cmH2O) and highest during stage III/IV NREM sleep (4.2 cmH2O).
• CPAP did not alter UACP in stage I/II NREM and REM sleep but stabilized the upper airway in stage III/IV NREM sleep, suggesting a reflex response.

Conclusions:

• CPAP is effective in preventing OSA and improving sleep architecture.
• Upper airway collapsibility varies significantly across different sleep stages.
• The upper airway dilator muscles may not respond to asphyxia during sleep, but a reflex response to CPAP may enhance muscle tone during deeper sleep stages.