In this issue of the journal, Martinez et al1 examined the relationships between quantitative CT (QCT) parameters of emphysema, airway wall remodelling and airway narrowing and composite clinical and physiological indices of chronic obstructive pulmonary disease (COPD), the BODE index2 and the St George's Respiratory Questionnaire (SGRQ).3 BODE stands for Body mass index (BMI), airflow Obstruction, Dyspnoea and Exercise capacity.

Not surprisingly, these QCT estimates of pathological changes were related to measures of clinical impact. More interestingly, the authors found that there were differences in the strength of the associations between measures of emphysema and airway disease and the composite indices. Measures of emphysema were more closely related with the BODE index while the airway wall abnormalities were better predictors of the SGRQ.

While it has long been recognised that there is a spectrum of changes in the airways and parenchyma in COPD,4 the separation of the airway predominant phenotype from the parenchymal predominant phenotype was largely limited to the autopsy room until the advent of CT. CT has confirmed that some patients have airflow obstruction with little emphysema while others have predominant emphysema with little airway disease. Such individuals form the extremes while the majority of patients have various combinations of airway disease and emphysema.5 In addition, there is evidence that the predominant pattern is to some extent familial6 and is associated with different rates of decline of lung function.7 The presence of airway disease and emphysema on CT can be assessed qualitatively or quantitatively. The power of the quantitative indices, as used in the present study, is that they are completely reproducible provided that similar scanners, imaging parameters and software are used. The hope is that the separate mechanisms that lead to …