Abnormal inspiratory flow-volume curves in patients with sleep-disordered breathing

Although flow-volume curves are valuable in detecting extrathoracic airway obstruction, their role in testing patients with sleep-disordered breathing is undefined. To determine whether patients with sleep-disordered breathing have abnormal flow-volume curves consistent with variable extrathoracic obstruction, 60 subjects referred with suspected with suspected sleep disorders prospectively underwent spirometry and assessment of flow-volume curves. These tests were interpreted independent of the outcome of polysomnography. Fourteen of 35 subjects (40%) with sleep-disordered breathing had abnormal flow-volume curves consistent with variable extrathoracic airway obstruction, and 2 of 25 (8%) with no breathing disorder had extrathoracic obstruction (p<0.02). The presence of extrathoracic airway obstruction in subjects with mixed or obstructive sleep apnea did not correlate with age, the presence of snoring, excessive daytime hypersomnolence, obesity, or the severity of sleep apnea. Abnormal flow-volume curves were found more frequently in women who had no obvious structural upper airway abnormality. Because of the high specificity (92%) of the flow-volume curve, the finding of extrathoracic obstruction in patients with a history consistent with sleep-disordered breathing substantially increases the likelihood that sleep apnea is present.