Natural history

There is increasing interest in developing a better understanding of the natural history of the two most frequent chronic lower respiratory diseases, asthma and chronic obstructive pulmonary disease (COPD). Asthma is a heterogeneous condition, and one of the main obstacles in understanding its natural history has been the lack of well-defined markers for the different disease phenotypes grouped under this common label. In the case of COPD, it is apparent that, although smoking is the main demonstrated cause of this condition, a simple strategy of discouraging tobacco consumption has proven insufficient to prevent the enormous impact of nicotine addiction on public health. When discussing the natural history of asthma and COPD, an important issue is the overlap between these two conditions. It has been conclusively shown that, at the population level, adults who report asthma are more likely to also report chronic bronchitis and/or emphysema as compared with subjects with no asthma and recent epidemiological evidence shows that active asthma is a strong risk factor for acquiring a subsequent diagnosis of COPD. The overlap may be explained by the fact that asthma and COPD share common risk factors or, alternatively, by the possible progression of persistent asthma into chronic airflow limitation, the clinical hallmark of COPD.