COPD
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Dyspnea and activity limitation are the primary symptoms of chronic obstructive pulmonary disease and progress relentlessly as the disease advances. In COPD, dyspnea is multifactorial but abnormal dynamic ventilatory mechanics are believed to be important. Dynamic lung hyperinflation occurs during exercise in the majority of flow-limited patients with chronic obstructive pulmonary disease and may have serious sensory and mechanical consequences. ⋯ The mechanisms by which dynamic lung hyperinflation give rise to exertional dyspnea and exercise intolerance are complex. However, recent mechanistic studies suggest that dynamic lung hyperinflation-induced volume restriction and consequent neuromechanical uncoupling of the respiratory system are key mechanisms. This review examines, in some detail, the derangements of ventilatory mechanics that are peculiar to chronic obstructive pulmonary disease and attempts to provide a mechanistic rationale for the attendant respiratory discomfort and activity limitation.
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Interpreting changes in outcomes of clinical trials in chronic obstructive pulmonary disease should be viewed from a broader perspective than only the statistical significance of the findings. The minimal clinical difference in outcome measures provides a conceptual framework to assist in clinical trial interpretation and a methodology to assess the clinical relevance of study results. ⋯ Although the minimal clinically important difference has been suggested for a wide range of outcomes of importance in chronic obstructive pulmonary disease, many have not been subjected to rigorous analysis. For newer tools such as activity monitors and questionnaires and measures not widely employed such as laboratory-based exercise tests, minimal clinically important differences remain to be determined.