COPD: Overview of Definitions, Epidemiology, and Factors Influencing Its Development: Risk Factors for COPD
Whatever the causes for limitation of expiratory airflow, its presence has serious prognostic significance. In this regard, lung function, measured as the FEV1? increases into young adulthood, then decreases. In normal nonsmokers, the rate of decline in FEVX is about 20 mL/yr or about 1 L over a 50-year adult life span. Smokers have a more rapid decline which, on average, is twice that of normal nonsmokers. While this is often asymptomatic, this limitation of expiratory airflow is strongly associated with all-cause mortality. In about 15% of smokers, lung function declines at a rate more rapid than that in the average smoker. As a result, lung function can decline below 2 L, at which point the individual often develops symptoms, usually dyspnea on exertion. Symptoms related to airflow limitation are generally progressive with further loss of lung function. Individuals often experience severe limitation in physical performance when the FEV1 declines below 1 L. mycanadianpharmacy
Risk Factors for COPD
The natural history of COPD, therefore, is strongly influenced by the rate of decline in FEVr One major factor influencing this rate of decline is cigarette smoking. The rate of decline shows a very strong relationship with smoking and with the amount smoked. For individuals smoking a given amount, however, the rate of decline can be quite variable. The factors influencing this variability are generally undetermined. Exposures other than cigarette smoke likely play a role as certain occupational exposures also have been associated with an accelerated rate of decline. Not all of the determinants of rate of decline of FEVX are external, however. Importantly, individuals who have limitation of airflow, that is they presumably have experienced an accelerated rate of decline in the past, are likely to experience an accelerated rate of decline in the future. This observation has been termed the “horse racing effect” and implies that the features which lead to an accelerated rate of decline in FEV1 are likely present throughout the lifetime of the individual. While a number of such factors likely exist, the only factor well established at the present time is deficiency of arprotease inhibitor. Lack of this serum protein, which can be inherited as an autosomal recessive trait, can be associated with accelerated rate of development of emphysema in nonsmokers and a markedly accelerated rate in smokers. Description of this condition has led to the concept that proteolytic activity in excess of antiprotease-protective mechanisms can lead to the damage and destruction of the alveolar walls that characterize emphysema.