• chronic obstructive pulmonary disease
• computed tomography
• lung densitometry
• outcome measures

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 …