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

Chronic obstructive pulmonary disease (COPD) is one of the leading causes of disability and death in both the developed and developing world 1. We are starting to understand about pathogenesis, progression and prognosis in COPD, but the understanding of any disease starts with defining what one is actually talking about 2. 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 . What is “normal”? An online dictionary lists the following definitions: “Conforming with, adhering to, or constituting a norm, standard, pattern, level, or type; typical. Functioning or occurring in a natural way; lacking observable abnormalities or deficiencies. Occurring naturally and not because of disease, inoculation, or any experimental treatment” 4. A related question is: what constitutes “disease”? In discussing COPD, Snider 2 defined disease as: “a condition or state in a group of persons who have specified characteristics by …