Since Laennec 1 described the clinical and pathological features of pulmonary emphysema, more than a century ago, much has been learned about its pathologic physiology and its progressive clinical course, with cardiac and metabolic complications. However, the initial inciting factors and early pathogenesis still are poorly understood. Because of this hiatus in knowledge, the clinical recognition of emphysema in its early stages is frequently difficult and the results of treatment, once the diagnosis is made, often are disappointing.
Numerous types of emphysema have been described, as have many concepts concerning their relative clinical importance. Thus, an attempt at definition appears advisable before the clinically diagnostic criteria are considered. Pulmonary emphysema is characterized pathologically by large alveolar spaces with attenuated septa, many of which are fragmented; as a result, larger air spaces (blebs or bullae) are formed, thus altering the mechanical (viscoelastic) properties and ventilation of the lungs, as well