Expiratory Flow Limitation in Obstructive Sleep Apnea and COPD: A Quantitative Method to Detect Pattern Differences Using the Negative Expiratory Pressure Technique

Ahmet Baydur*, 1, Cheryl Vigen2, Zhanghua Chen3
1 Division of Pulmonary and Critical Care Medicine, Keck School of Medicine, University of Southern California (USC), USA
2 Department of Occupational Therapy, Herman Ostrow School of Dentistry of USC, Los Angeles CA, 90033, USA
3 Department of Preventive Medicine, Keck School of Medicine, USC, Los Angeles CA, 90033, USA

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© Baydur et al.; Licensee Bentham Open.

open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

* Address correspondence to this author at the Division of Pulmonary and Critical Care Medicine, Keck School of Medicine, University of Southern California, IRD 723, 2020 Zonal Avenue, Los Angeles, CA 90033, USA; Tel: 323-226-7923; Fax: 323-226-7238; E-mail:



Expiratory flow limitation (EFL), determined by the negative expiratory pressure (NEP) technique, can exhibit overlapping patterns in COPD, obstructive sleep apnea (OSA) and non-OSA obesity. We assessed the ability of a quantitative method to assess EFL to discriminate COPD from obese and OSA patients during NEP (-2 to -3 cm H2O) testing.


EFL was quantified by measuring the area under the preceding control tidal breath (Vt) subtended by the NEP curve (%AUC). To quantify mean lost flow, the ratio of %AUC to percentage of control Vt over which EFL occurred (%EFL) (= %AUC/%EFL) was computed. Percent EFL, %AUC, and %AUC/%EFL was compared in 42 patients with COPD, 28 obese subjects without OSA, 50 with OSA (26 mild-moderate, 24 severe) and 19 control subjects, in seated and supine postures.


All patients exhibited %EFL values significantly higher than control subjects, corrected for age and gender (ANOVA). All but the COPD group exhibited higher %EFL while supine, but not %AUC or %AUC/%EFL. Amongst seated subjects, %EFL was highest in COPD, and amongst supine groups, it was greatest in OSA and COPD. %AUC/%EFL was significantly higher in mild-moderate OSA than in COPD only while seated. %AUC or %AUC/%EFL did not discriminate amongst other cohorts in either posture.


Computation of %EFL helps distinguish EFL in COPD, obese and OSA patients from those of control subjects. Computation of %AUC and %AUC/%EFL is useful in determining the magnitude of extrathoracic FL in individuals with obesity and OSA, but does not distinguish between cohorts.

Keywords: : Negative expiratory pressure, sleep apnea, COPD..