450 Disturbances of Respiration. 



the abdominal viscera into the thoracic cavity) usually rapidly 

 cause death because of the resulting impossibility of breathing. 

 Difficulty of respiration is similarly occasioned by embarrassment 

 of and pressure upon the diaphragm by meteorism of the abdom- 

 inal organs, tumors, etc., where the alteration of contracting 

 movements and resting stages is lost in consequence of tetanic 

 spasm of the thoracic muscles and diaphragm. When air gains 

 entrance to one of the pleural spaces because of a wound of the 

 thoracic wall or rupture of the lung (perforating wounds, rupture 

 of suppurating foci), the lung afifected contracts from the action 

 of its elastic tissue and, because being no longer impervious to 

 air, it must adapt itself to the intrathoracic conditions (the me- 

 diastinum is pressed toward the opposite side by the entering air 

 and may even be ruptured) ; expansion of the lung is, therefore, 

 no longer possible, as the organ cannot follow the movements of 

 the chest wall and lies loosely (that is. fixed only at its root) in 

 the chest cavity. The thorax and lungs cannot properly expand 

 and collapse if the chest cavities are occupied by fluid exudates 

 (dropsy, pleurisy), or if the respiratory surfaces of the lungs are 

 lessened, if a greater or less portion of the pulmonary alveoli are 

 filled up or solidified by pressure of collections of exuded material, 

 tumors or parasites and thus deprived of their air. However, 

 even on the contrary if the lungs are excessively inflated, over- 

 distended, a condition known as emphysema, aeration of the or- 

 gans and interchange of gases with the blood are impaired ; the 

 lung not collapsing properly in this condition, the air escaping 

 with difficulty ( the carbonic acid is unable to pass out by dif- 

 fusion to a sufficient degree), f.nd the capillaries narrowed by 

 being stretched and not permitting the blood to flow readily through 

 their lumina. Under any such condition breathing becomes 

 labored and air hunger becomes apparent. In addition circula- 

 torv disturbances are induced, sometimes due to pressure upon 

 the thin walled veins bv accumulations of fluid in the chest cavity 

 and bv the uninterrupted enlargement of volume of the lungs, 

 this causing congestion in practically all of the veins (v. dropsy), 

 the factor of aspiration of venous blood fails ; and as terminal 

 features difficulties of discharge of the blood from the right heart 

 grow apace (resistance in pulmonary arterial area), if the vas- 

 cular distribution in the lungs be embarrassed by pressure or 

 obstructive influences ( secondary cardiac hypertrophy and dila- 

 tation). 



