Many insults expose the entire lung to damage either because the inciting agent is airborne or because the inciting agent is bloodborne. However, it is readily apparent from radiographs that although the insult may be diffuse, the pathologic response rarely is. Asbestosis, worse in the lower lobes, or silicosis, worse in the upper lobes, are only two examples of this phenomenon. The immediate question is: if the insult affects the entire lung, why is the distribution nonuniform? The answer most likely resides in the physiologic "environment" of the lung.

We've long known that gravity profoundly affects the physiology of the lung, such that ventilation and perfusion are nonuniform. These physiologic variables give rise to environments in the lung which differ, and in turn affect the distribution of pathologic processes.

Further Information
Ventilation and Perfusion Matching in the Lung:
A computer model for teaching pulmonary physiology (Requires Shockwave)
Martin E. Doerfler, MD
Associate Professor of Clinical Medicine
Director, Critical Care Medicine
Division of Pulmonary / Critical Care Medicine
New York University Medical Center