“Exertional dyspnoea in COPD: the clinical utility of cardiopulmonary exercise testing.” Denis E. O'Donnell, Amany F. Elbehairy, Azmy Faisal, Katherine A. Webb, J. Alberto Neder and Donald A. Mahler. Eur Respir Rev 2016; 25: 333–347.

Exertional dyspnoea intensity is shown relative to a) work rate and b) diaphragm electromyography relative to maximum (EMGdi/EMGdi,max) during incremental cycle exercise in patients with moderate chronic obstructive pulmonary disease (COPD) and age-matched healthy controls. c) Selected qualitative dyspnoea descriptors at the end of incremental cycle exercise in patients with moderate COPD and age-matched healthy controls. d) The relationship between tidal volume (V_T) as a function of predicted vital capacity (VC_pred) and EMGdi/EMGdi,max. Square symbols represent the tidal volume-ventilation inflection points in panels a) and d) and the point at the highest equivalent ventilation (50 L·min⁻¹) in panel b). Data are presented as mean±sem. *: p<0.05 COPD versus healthy controls at rest, at standardised work rates or at peak exercise. Reproduced and modified from [17] with permission.