RESEARCH ARTICLE
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
Article Information
Identifiers and Pagination:
Year: 2012Volume: 6
First Page: 111
Last Page: 120
Publisher ID: TORMJ-6-111
DOI: 10.2174/1874306401206010111
Article History:
Received Date: 1/6/2012Revision Received Date: 29/6/2012
Acceptance Date: 13/8/2012
Electronic publication date: 31/10/2012
Collection year: 2012
open-access license: This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.
Abstract
Background:
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.
Methods:
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.
Results:
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.
Conclusions:
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.
