COPD: Overview of Definitions, Epidemiology, and Factors Influencing Its Development: Conclusion
In this regard, it is reasonable to consider the process of emphysema. As noted above, current concepts suggest that damage of the alveolar structures results in destruction of alveolar walls, and hence, emphysema. Excess of proteases, for example elastase released by neutrophils in excess of antipro-teolytic protective mechanisms such as ar-protease inhibitor, can lead to this process. Other proteases, produced by neutrophils as well as other cells, likely can also contribute to this process. Other toxic species, moreover, including oxidants and toxic peptides such as defensins, may also play important roles. Thus, it is likely that the development of emphysema reflects a complex series of mechanisms that can damage alveolar structures.
This damage of alveolar structures, however, likely takes place even in normal individuals. Emphysema likely only results when the extent of damage exceeds mechanisms for repair. In this regard, cigarette smoke has been reported to inhibit elastin synthesis, to inhibit the enzyme responsible for crosslinking of newly synthesized elastin, and to inhibit fibroblast recruitment and proliferation. It is possible that cigarette smoke could lead to the development of emphysema not only by increasing tissue destruction, but also by impairing tissue repair. Finally, other factors likely also contribute to impaired tissue repair. In this respect, Sahebjami and Domino have reported that starvation can accelerate the development of elastase-induced emphysema in an animal model. Consistent with this, the same group has reported that emphysema is more severe in underweight individuals with the same degree of airflow limitation than in overweight or normal-weight individuals. While this cross-sectional observation cannot establish cause and effect, it certainly supports the concept that nutritional status may affect lung repair, which could in turn predispose to the development of emphysema. sildenafil citrate pink
In summary, COPD is a heterogeneous collection of conditions that can affect various structures within the lung in a number of different ways. These various processes can all result in limitation of expiratory airflow. If severe enough, this physiologic abnormality defines COPD. The various conditions that can lead to this syndrome are prevalent and often relentlessly progressive. In aggregate, they represent an important public health problem. The presentations in this supplement outline diagnostic and therapeutic strategies by which the practitioner can assist patients suffering from this condition.