Expiratory Flow Limitation in Obstructive Sleep Apnea and COPD: A Quantitative Method to Detect Pattern Differences...

Area of Science:

• Pulmonary physiology
• Respiratory mechanics
• Diagnostic methods in respiratory diseases

Background:

• Expiratory flow limitation (EFL) presents overlapping patterns in Chronic Obstructive Pulmonary Disease (COPD), Obstructive Sleep Apnea (OSA), and non-OSA obesity.
• The negative expiratory pressure (NEP) technique is used to determine EFL.
• A need exists for quantitative methods to differentiate EFL across these conditions.

Purpose of the Study:

• To assess a quantitative method for evaluating EFL during NEP testing.
• To determine if this method can discriminate between COPD, obese, and OSA patients.
• To compare EFL patterns in seated and supine postures.

Main Methods:

• EFL was quantified using the area under the preceding control tidal breath (Vt) subtended by the NEP curve (%AUC).
• Mean lost flow was calculated as the ratio of %AUC to the percentage of control Vt over which EFL occurred (%EFL) (%AUC/%EFL).
• Comparisons were made in COPD, obese, OSA (mild-moderate and severe), and control subjects in seated and supine positions.

Main Results:

• All patient groups showed significantly higher %EFL than control subjects.
• Supine posture increased %EFL in all groups except COPD.
• %AUC/%EFL was higher in mild-moderate OSA than COPD only when seated; other metrics did not consistently discriminate between groups.

Conclusions:

• The %EFL computation effectively distinguishes EFL in COPD, obese, and OSA patients from controls.
• Computation of %AUC and %AUC/%EFL aids in assessing extrathoracic flow limitation magnitude in obesity and OSA.
• These quantitative measures do not reliably distinguish between COPD, obese, and OSA patient cohorts.