The contribution of intrapleural pressures to the pathogenesis of emphysema

Abstract

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.