Relationship Between Expiratory Muscle Dysfunction and Dynamic Hyperinflation in Advanced Chronic Obstructive Pulmonary Disease

Abstract

Background and objectives Dynamic hyperinflation and expiratory flow limitation, which are physiologically linked phenomena, play a role in the pathophysiology of dyspnea and have a negative impact on quality of life in patients with chronic obstructive pulmonary disease (COPD). The expiratory muscle dysfunction associated with advanced COPD may be involved in the genesis of dynamic hyperinflation. Our objective was to study the relationship between expiratory muscle dysfunction and dynamic hyperinflation and to analyze their association with dyspnea and quality of life in patients with advanced COPD. Patients and methods In 25 patients we measured lung function, exercise capacity (measured by incremental ergometry and the 6-minute walk test), expiratory flow limitation and end-expiratory lung volume (EELV) during exercise, respiratory muscle function, dyspnea, and quality of life (using the St George's Respiratory Questionnaire [SGRQ]). Results The patients, whose mean forced expiratory volume in 1 second (FEV1) was 31% of predicted, exhibited a moderate decrease in respiratory muscle strength and resistance to fatigue. Expiratory flow limitation was observed in 19 patients at rest and in 24 patients at 70% of maximal workload (W max). EELV increased from rest to 70% of W max (9% of predicted forced vital capacity). At 70% of W max, EELV correlated inversely with expiratory flow limitation (ρ=−0.42), inspiratory (ρ=−0.43) and expiratory (ρ=−0.42) muscle endurance, and maximal oxygen uptake (ρ=−0.52). The increase in EELV from resting to 70% of W max correlated with dyspnea (ρ=0.53), and expiratory flow limitation at 70% of W max correlated with the activity score on the SGRQ (ρ=−0.56). FEV1, expiratory muscle endurance and expiratory flow limitation were independent predictors of EELV at 70% W max. Conclusion In advanced COPD, decreased resistance to fatigue in expiratory muscles is associated with an increase in dynamic hyperinflation (and less expiratory flow limitation) during exercise, a pattern that in turn correlates with more severe dyspnea and reduced quality of life.