What can impulse oscillometry and pulmonary function testing tell us about obstructive sleep apnea: a case-control...

Area of Science:

• Pulmonary Medicine
• Sleep Medicine
• Respiratory Physiology

Background:

• Obesity is a significant risk factor for obstructive sleep apnea (OSA).
• Altered lung mechanics, including chest wall loading and lung recoil, are suspected in obese individuals with OSA.
• Functional residual capacity (FRC) changes in this population require further investigation.

Purpose of the Study:

• To investigate if functional residual capacity (FRC) is reduced in obese patients with obstructive sleep apnea (OSA) compared to obese patients without OSA.
• To explore the potential roles of decreased chest wall recoil and increased lung recoil in FRC reduction.
• To assess the relationship between respiratory mechanical properties and OSA severity.

Main Methods:

• Overnight polysomnography was used to diagnose OSA in overweight and obese subjects.
• Lung volumes and respiratory mechanics were measured using plethysmography and impulse oscillometry.
• Subjects were categorized into OSA (cases) and non-OSA (controls) groups.

Main Results:

• Obese patients with OSA showed significantly lower expiratory reserve volume and FRC compared to controls.
• Higher respiratory impedance and resistance at 5 Hz, and lower reactance at low frequencies were observed in OSA cases.
• Reactance at 5 Hz (Xrs5) strongly correlated with OSA severity (Apnea-Hypopnea Index) and FRC.

Conclusions:

• FRC is significantly reduced in obese patients with OSA, potentially due to increased lung elastic recoil.
• The correlation between Xrs5 and OSA severity suggests possible upper airway stenosis.
• Increased lung elastic recoil may be a contributing factor to the development of OSA in obese individuals.