Clinical characteristics of COPD patients with tidal expiratory flow limitation.

We have used impulse oscillometry to identify COPD patients with tidal expiratory flow limitation (EFL), which is a measurement related to small airway disease. We report that 37.4% of COPD patients had EFL; these patients had multiple clinical characteristics of more severe disease including lower forced expiratory volume in 1 second values, greater hyperinflation, reduced exercise performance, and increased small airway impairment. We highlight that EFL can be used to identify a subgroup of COPD patients with distinct characteristics associated with small airway disease.