Pulmonary function and effects of body position in patients with obstructive sleep apnea

Objective: Obstructive sleep apnea (OSA) is known to be associated with upper airway collapse during sleep. However, OSA has also been suggested to have effects on the lower airway. This study examined the association between pulmonary function test (PFT) results during daytime and OSA according to the severity of OSA and presence of obesity. Changes in PFT results with body position (sitting vs. supine) were also analyzed. Methods: A total of 46 patients who were diagnosed with OSA were included in this study. Patients were grouped according to the severity of OSA and presence of obesity. Results: Obese, severe OSA patients tended to show poorer pulmonary function than non-obese, mild-to-moderate OSA patients. Forced expiratory volume in 1 second/forced vital capacity (FEV1/FVC; sitting), peak expiratory flow (PEF; sitting), and forced expiratory flow during the middle half of the FVC (FEF25-75; supine) were significantly lower in the severe OSA group than the mild-to-moderate OSA group (p=0.020, p=0.044, and p=0.042, respectively). Positional change from sitting to the supine position significantly reduced pulmonary function in the total OSA patient population. The effect of body position on PFT results was greater in non-obese, mild-to-moderate OSA patients. FEF25-75 in the sitting position was still significantly related to the apnea-hypopnea index in OSA patients after adjusting for other factors (p=0.048). Conclusion: This study indicated that relationships exist between lower airway function, body position, and OSA. The PFT is a simple test that can provide useful information about the upper and lower airways in OSA patients.