V/Q mismatch: emphysema

Emphysema is defined by destruction of airways distal to the terminal bronchioloe.

Physiology of emphysema involves gradual destruction of alveolar septae and of the pulmonary capillary bed, leading to decreased ability to oxygenate blood. The body compensates with lowered cardiac output and hyperventilation. Thus, V/Q mismatch results in relatively limited blood flow through a fairly well oxygenated lung with normal blood gases and pressures in the lung, in contrast to the situation in bronchitis patients who are referred to as “blue bloaters.” Because of low cardiac output, however, the rest of the body suffers from tissue hypoxia and pulmonary cachexia. Eventually, these patients develop muscle wasting and weight loss and are identified as “pink puffers.”

(In bronchitis, the reverse situation is the case. The body compensates to mucus clogged airways and a relatively intact alveolar bed with a decrease in ventilation and an increase in cardiac output, which worsens baseline oxygenation.)