Outcome measures in chronic obstructive pulmonary disease (COPD)

Lung density determined by CT scanning may be a useful outcome measure in COPD Forced expiratory volume in 1 second (FEV1) is by far the most well established outcome variable in obstructive pulmonary disease. Numerous studies have documented the correlation of this parameter with clinical variables such as severity of disease and mortality,1 and spirometric measurements have been standardised by international recommendations on lung function testing.2 Nevertheless, in real life the relevance of a maximal blow through a narrow tube is not always self-evident, and the intuitive clinical meaningfulness of this surrogate parameter is therefore perhaps less obvious. FEV1 has further limitations in chronic obstructive pulmonary disease (COPD). In general, dynamic lung volumes such as FEV1 and forced vital capacity (FVC) are highly effort dependent. However, in emphysematous subjects an abnormally low FEV1 is partly caused by the dynamic collapse of the airways which is also effort dependent. Therefore, in COPD the result of a more moderated manoeuvre is usually superior to the result of a maximal effort. This phenomenon adds to the variability of repeated measurements and, in COPD, the standard deviation of repeated measurements of FEV1 is larger than the annual decline, even in heavy smokers.3 For these reasons there is an increasing interest in other measures such as number of exacerbations or disease specific questionnaire scores as alternative outcome measures for monitoring the progress of emphysema in randomised clinical trials. Another new outcome measure is lung density …