Spirometry and flow-volume curve in patients with obstructive sleep apnea

OBJECTIVE: To assess the prevalence of spirometric abnormalities in obstructive sleep apnea (OSA) patients and its clinical utility in diagnosing OSA.

METHODS: We conducted an observational study between March 2006 and March 2007 at King Khalid University Hospital on consecutive patients presenting with suspected OSA. Spirometric indices of forced expiratory volume in 1 second (FEV1)/forced expiratory volume (FVC), maximum mid-expiratory flow (MMEF)75/25, peak expiratory flow (PEF), forced expiratory flow (FEF)50, and forced inspiratory flow (FIF)50 were analyzed for 138 patients with OSA. Expiratory and inspiratory flow volume curves were examined for the presence of fluttering of the upper airway (saw-tooth sign) and signs of upper airway obstruction defined as a FEF50/FIF50 >1. Patients with flow-volume curve abnormalities were compared with patients who did not show any abnormalities.

RESULTS: Saw-tooth sign was present in 12.3% and the ratio of FEF50/FIF50 >1 was found in 26.1% of OSA patients. Obstructive sleep apnea patients who had these abnormalities did not differ from patients who did not have them with regard to age, body mass index, apnea-hypopnea index (AHI), desaturation index and other spirometric indices. The presence of saw-tooth sign and FEF50/FIF50 >1 was not related to the severity of AHI

CONCLUSION: Spirometric abnormalities are not common in OSA patients not known to have underlying chronic lung diseases. Saw-tooth sign and FEF50/FIF50 >1 are not useful in predicting OSA.