The Clinical Significance of Expiratory Flow Limitation in Chronic Obstructive Pulmonary Disease

Abstract

Background

Expiratory flow limitation (EFL) is a key pathological feature of COPD, occurring when expiratory flow cannot increase despite rising alveolar pressure. It contributes to hyperinflation and intrinsic positive end-expiratory pressure (iPEEP). The influence of supine posture on these abnormalities and their relationship with orthopnoea, dyspnoea and sleep disturbance is poorly understood. Improved physiological characterization may support personalised treatment.

Aim

To examine relationships between EFL, hyperinflation and iPEEP in COPD, focusing on the effects of supine posture and their associations with exercise limitation, dyspnoea and sleep disturbance.

Methods

Participants with stable COPD contributed to up to four studies. Assessments included questionnaires, lung function testing, respiratory mechanics measured by forced oscillation in seated and supine positions, incremental shuttle walk test (ISWT), in-laboratory polysomnography, and oscillometry via a bespoke CPAP circuit to estimate the pressure required to abolish EFL as a surrogate of iPEEP.

Results

In the postural study (n=42), COPD participants showed persistent supine hyperinflation with no increase in inspiratory capacity (IC), unlike healthy controls (n=14). Variability in IC responses correlated with EFL (rs=−0.41 p=0.007). In the sleep cohort (n=28), impaired supine mechanics and hyperinflation were associated with respiratory arousals, poorer gas exchange and hypoventilation. In the exercise cohort (n=25), resting hyperinflation, but not EFL, correlated with reduced ISWT distance (rs=0.59 p=0.02). Non-invasive iPEEP measurement was feasible (n=8) but technically complex.

Conclusion

Supine posture worsens EFL and contributes to persistent hyperinflation in COPD. These abnormalities are associated with sleep disturbance, impaired nocturnal gas exchange and reduced exercise capacity. Non-invasive iPEEP measurement may improve disease phenotyping but requires further technical development.