ABSTRACT
The airow obstruction of COPD can be quantied simply in most individuals as a reduction in the ratio of forced expiratory volume in 1 second (FEV1) to forced vital capacity (FVC; FEV1/FVC) on spirometric testing. Recognition is more difcult when there is accompanying brotic lung disease caused, for example, by pneumoconiosis. The combination of brosis with COPD may lead to
normalisation of FEV1/FVC, albeit with marked impairment of gas transfer and associated disability. FEV1/FVC is unimodally distributed in the population at large, and so the choice of a threshold with which to dene COPD is arbitrary. The Global initiative for Chronic Obstructive Lung Disease (GOLD) criterion of a post-bronchodilator FEV1/FVC of less than 70% is commonly used, but FEV1/ FVC declines with age, and the GOLD criterion leads to relative under-diagnosis of COPD at younger (working) ages and to relative over-diagnosis in the elderly. The lower limit of normal based on population predicted values is more complex to calculate, but is more appropriate for identifying COPD in working populations (Swanney et al., 2008). Tests of small airway function, such as midexpiratory ow rates, are sometimes used, but their clinical signicance is uncertain when they are not accompanied by reductions in FEV1 or FEV1/FVC.
