Tough at the top: must end-expiratory lung volume make way for end-inspiratory lung volume?

A reduced exercise capacity, which limits the performance of activities of daily living and social participation, is a cardinal feature of chronic obstructive pulmonary disease (COPD). Breathlessness is the main limiting symptom, although, depending on the task undertaken [1], leg discomfort is prominent in a substantial minority of patients. Dyspnoea arises through the interplay of pulmonary manifestations of COPD (airflow obstruction, emphysema and destruction of the pulmonary vascular bed) [2], systemic effects of the disease [3] and neural mechanisms [4, 5]. These complex relationships remain incompletely understood. Traditionally, both the severity of COPD and the efficacy of treatment interventions have been assessed using resting lung function measures, particularly forced expiratory volume in 1 s (FEV1). However, health status is more closely associated with lung volume measurements [6] than FEV1, and bronchodilator-based therapies can improve lung volumes at rest [7] and during exercise [8] without change in FEV1, prompting interest in the study of dynamic lung volumes and dyspnoea arising during exercise.