• Pierantonio Laveneziana, Katherine A Webb, Josuel Ora, Karin Wadell, and Denis E O'Donnell.
• Respiratory Investigation Unit, Department of Medicine, Queen’s University, Kingston, Ontario, Canada.
• Am. J. Respir. Crit. Care Med.. 2011 Dec 15;184(12):1367-73.

RationalePatients with chronic obstructive pulmonary disease (COPD) primarily describe their exertional dyspnea using descriptors alluding to increased effort or work of breathing and unsatisfied inspiration or inspiratory difficulty.ObjectivesThe purpose of this study was to examine the impact of changes in dynamic respiratory mechanics during incremental (INCR) and high-intensity constant work-rate (CWR) cycle exercise on the evolution of dyspnea intensity and its major qualitative dimensions in patients with moderate-to-severe COPD.MethodsSixteen subjects with COPD performed symptom-limited INCR and CWR cycle exercise tests. Measurements included dyspnea intensity and qualitative descriptors, breathing pattern, operating lung volumes, and esophageal pressure (Pes).Measurements And Main ResultsDuring both exercise tests, there was an inflection in the relation between tidal volume (Vt) and ventilation. This inflection occurred significantly earlier in time during CWR versus INCR exercise but at a similar ventilation, Vt, and tidal Pes swing. Beyond this inflection, there was no further change in Vt despite a continued increase in ventilation and tidal Pes. During both tests, "work and effort" was the dominant dyspnea descriptor selected up to the inflection point, whereas after this point dyspnea intensity and the selection frequency of "unsatisfied inspiration" rose sharply.ConclusionsRegardless of the exercise test protocol, the inflection (or plateau) in the Vt response marked the point where dyspnea intensity rose abruptly and there was a transition in the dominant qualitative descriptor choice from "work and effort" to "unsatisfied inspiration." Intensity and quality of dyspnea evolve separately and are strongly influenced by mechanical constraints on Vt expansion during exercise in COPD.

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