The pathobiology and epidemiology of human emphysema

Clinical-Radiologic-Pathologic Correlation of Smoking-Related Diffuse Parenchymal Lung Disease

The direct toxicity of cigarette smoke and the body's subsequent response to this lung injury leads to a wide array of pathologic manifestations and disease states that lead to both reversible and irreversible injury to the large airways, small airways, alveolar walls, and alveolar spaces. These include emphysema, bronchitis, bronchiolitis, acute eosinophilic pneumonia, pulmonary Langerhans cell histiocytosis, respiratory bronchiolitis, desquamative interstitial pneumonia, and pulmonary fibrosis. Although these various forms of injury have different pathologic and imaging manifestations, they are all part of the spectrum of smoking-related diffuse parenchymal lung disease.

Imaging of small airways and emphysema

High-resolution chest computed tomography (CT) is one of the most useful techniques available for imaging bronchiolitis because it shows highly specific direct and indirect imaging signs. The distribution and combination of these various signs can further classify bronchiolitis as either cellular/inflammatory or fibrotic/constrictive. Emphysema is characterized by destruction of the airspaces, and a brief discussion of imaging findings of this class of disease is also included. Typical CT findings include destruction of airspace, attenuated vasculatures, and hyperlucent as well as hyperinflated lungs.

Gene therapy for chronic obstructive pulmonary disease: twilight or triumph?

Chronic obstructive pulmonary disease (COPD) is a clinical syndrome presenting as progressive airflow limitation that is poorly reversible as a result of bronchitis and emphysema. The prevalence of COPD is alarming and even more so its current and projected impact on morbidity and mortality. To date, there are no effective treatments for emphysema, nor are there efficient clinical management strategies. Existing and prospective therapies, although promising, have yet to demonstrate their efficacy to slow, halt or reverse the disease. Novel approaches using gene therapy and stem cell technologies may offer new opportunities. However, this will remain almost entirely dependent on a more thorough understanding of the pathogenesis of COPD. This review is not aimed at highlighting the vast effort of studying COPD, but rather describing the state of the field in an abstract fashion to expose the focus of research efforts to date, which has primarily been limited to predisposing factors and inflammation. We would like to draw attention to other elements of the disease, such as the alveolar remodelling that characterises emphysema. Although the main cause may prove to be elusive, carefully designed clinical treatment and management may deliver the required therapeutic outcome.

The contribution of intrapleural pressures to the pathogenesis of emphysema

This paper maintains that negative intrapleural pressure is a prerequisite for the appearance of emphysema, either simply by the enlargement of the air space in combination with elastolytic enzymatic factors, or, frequently, by its contribution to the breakdown of collagen and elastin fibers through the increase in intrapulmonary pressures. Hence the factors that make the intrapleural pressure more negative play an indirect part in causing emphysema. Thus the development of collagen fibers, whatever its cause, gives rise to a reduction in the lung compliance which may produce more negative intrapleural pressure and, in consequence, an increase in the intrapulmonary pressures. The development of collagen fibers also contributes to the unequal distribution of these pressures in various regions, including the microenvironment of the lung, resulting in the breakdown of fibers in some areas due to the powerful forces that develop in them. It is by this mechanism that the development of collagen fibers contributes to the development of emphysema in areas that have suffered damage, in combination with enzymatic factors or even without them. Moreover, the intensified functioning of the respiratory muscles which may result from a reduction in the functional capacity of the lung parenchyma may also contribute indirectly to the pathogenesis of emphysema through the more negative intrapleural pressure. A chest radiogram cannot distinguish what is occurring in the microenvironment of the lung; it can, however, follow from a distance the overall changes throughout the subjects' lives. The present work is the product of such a follow-up. Chest radiograms show that very often the pulmonary fibrosis may be combined with emphysema or may precede the emphysema. The more negative the intrapleural pressure becomes, the greater its role in the production of emphysema. It is claimed that the form of the emphysema depends on the conditions created in the lung microenvironment and that negative intrapleural pressure plays a greater or lesser role in all forms of emphysema, including panacinar emphysema.

Emphysema and metalloelastase expression in mouse lung induced by cigarette smoke

Cigarette smoke (CS) causes pulmonary emphysema in humans and elastin degradation plays a key role in its pathogenesis. Previous studies on CS-exposed animals have been equivocal and have not clearly demonstrated the progression of the disease. In this study, morphometry was used to assess lung modifications to alveolar septa, airspaces, elastic and collagen fibers, and alveolar macrophages. Male (n = 40) C57/BL6 mice were exposed 3 times/day, whole body, to CS from three cigarettes for 10, 20, 30, or 60 days. Control groups (n = 10) were sham-smoked or received no exposure (day 0, n = 10). Morphometry included measurements of volume fraction of alveolar septa and airspaces, elastic and collagen fibers, and surface fraction of elastic fibers and alveolar septa. Morphometrical differences in mice after 60 days of exposure were greater than those after 10, 20, or 30 days, suggesting a progression of the disease. Inflammatory lesions in the lungs of mice contained significantly more metalloelastase (MMP-12) in macrophages at 10, 20, and 30 days than in controls of mice exposed for 60 days. These results suggest that elastin degradation took place during development of pulmonary changes in mice exposed to CS, and activation of MMPs specific for elastin may be a determining factor for susceptibility to emphysema.

Emphysema: the challenge of the remodelled lung

Emphysema is recognized as the component of chronic obstructive airways disease that is responsible for airways obstruction. Different patterns of emphysema are, however, recognized, suggesting possible different pathogenetic processes within the lung. This, coupled with the associated idea of susceptibility factors to the development of emphysema, has led to studies of genes that may be involved in the defence of the lung from proteolytic and oxidative damage. These studies have been driven by the goal of finding a treatment for emphysema, but appear to have lost sight of the fundamental remodelling of the lung that has occurred in patients with emphysema and the fact that it is not a single morphological entity.