Dr. Celli discussed the pathology and physiology of COPD, highlighting the characteristics that offer targets for specific therapies. He pointed out differences between previous practices and the new guidelines. Currently, for example, a vital capacity measurement must be taken and an obstruction must be documented before a diagnosis of COPD can be made. An asthmatic who has a reversible obstruction that does return to normal does not have COPD under the new guidelines. The obstruction can be caused either by airway disease, as is illustrated classically with chronic bronchitis, or parenchymal destruction, as is seen in emphysema.
Obstruction also is seen in small airway or inflammatory airway disease.
The lung parenchyma serve to hold the airways open and supply the elasticity that allows the lung to respond to changes in pressure. Once this elasticity is gone, the lung becomes very compliant and will no longer return to its original volume upon exhalation. Dr. Celli illustrated the deleterious effects of this increased compliance by contrasting the normal breathing cycle with the breathing cycle in COPD patients. People with normal lungs have a large capacity to generate high flow rates, during both inspiration and expiration. On the other hand, a patient who develops COPD will have a depression in exhalatory flow which sometimes may reach limitation even during normal tidal breathing.