Association of the forced oscillation technique with negative expiratory pressure in COPD

• Expiratory flow limitation (EFL) is common in patients with severe COPD.
• The negative expiratory pressure (NEP) technique is the gold standard for detecting EFL.
• We assessed the association of the forced oscillation technique (FOT) with NEP.
• Respiratory system reactance at 5 Hz was identified as an independent predictor.

Expiratory flow limitation (EFL) during tidal breathing is common in patients with severe COPD, and a major determinant of dynamic hyperinflation and exercise limitation. The negative expiratory pressure (NEP) technique has been the gold standard to detect EFL, while the forced oscillation technique (FOT) has also been reported to detect it. However, the association of FOT with NEP is not fully understood. We assessed whether broadband frequency FOT would predict the presence of EFL measured by NEP. FOT, NEP, and spirometry were performed in 51 patients with COPD. The extent of emphysema was measured by high-resolution computed tomography and scored. Fifteen patients were classified into the EFL-positive group and 36 into the EFL-negative group. In multivariate logistic regression analysis, EFL was independently predicted by emphysema score, forced vital capacity, and whole-breath respiratory system reactance at 5 Hz (X5). The receiver operator characteristic curve analysis revealed that inspiratory X5 best predicted EFL-positivity. X5-related forced oscillatory parameters are useful for detecting EFL in the management of COPD.