Emphysema is encountered in 2 to 5 per cent of all necropsies.1 If we exclude the senile type of emphysema and those rare instances of emphysema due primarily to disease of the thorax, it may be said that it is a condition associated with bronchitis and bronchial spasm. These disorders obstruct respiration and bring about persistent pulmonary overdistention. Coughing, which always accompanies them, is thought to exaggerate this distention. Attacks of asthma are nearly always associated with pulmonary emphysema, and hay fever is becoming more important in any study of the disease.
Important in the emphysematous lung is the destruction of many capillaries in thin, atrophic alveolar walls, resulting in an obstructed pulmonary circulation.2 This may lead to a high pulmonary arterial pressure with hypertrophy of the right side of the heart. Statistics compiled from autopsy material by various authors are not in agreement as to the incidence