Calverley PM.
Breathlessness during exercise in COPD: how do the drugs work?
Thorax 2004 Jun; 59 (6): 455-7.
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The inability to exercise because of distressing breathlessness is one of the most frequent problems experienced by patients with chronic obstructive pulmonary disease (COPD)1 and is a major determinant of impaired quality of life.2 Our understanding of why this occurs and how best to treat it has improved significantly in the last decade. At one level the problem appears relatively straightforward. Exercise invariably involves an increase in whole body oxygen consumption and carbon dioxide production, which requires an appropriate rise in alveolar ventilation if arterial carbon dioxide tension is to remain constant. In patients with COPD the ability to increase minute ventilation is restricted as is the capacity to empty their lungs quickly, hence exercise limitation occurs at a lower workload than in age matched healthy subjects. Although there is much truth in this simple scheme, it does not do justice to the many complex adaptive responses that patients use to cope with their chronic airflow obstruction, nor does it explain the variability seen in both the duration of exercise and the intensity of breathlessness in patients with apparently similar levels of airflow obstruction.

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