Defining chronic obstructive pulmonary disease... and the elephant in the room.

So what constitutes disease in COPD? Combinations of the forced expiratory volume in one second (FEV1), forced vital capacity (FVC) and the slow vital capacity (SVC) are used to help classify lung disease. What is normal? What reference equations does one use? Is the lower limit of normal (LLN) for the FEV1/FVC more accurate than the fixed ratio of 0.70? Does lung function have to be measured after bronchodilation? All of the factors mentioned contribute to the determination of COPD prevalence in populations, as is seen in the article by SHIRTCLIFFE et al. [3] in the current issue of the European Respiratory Journal.