Surgical pneumothorax exerts its deleterious effects largely through disturbances which it produces in the normal pressure relations within the thorax. On the same side as the opening in the chest wall, the normal negative pressure becomes obliterated, the lung becomes markedly collapsed and the alteration of the pressure relations is transmitted to the opposite side to a degree depending on the condition of the mediastinum. Thus, widespread disturbances are produced in the cardiorespiratory physiology which may be divided, according to their genesis, into four groups:
1. Those produced by the collapse of the lung on the side which is open.
2. Those due to the effects of the changed pressure relations on the lung of the opposite side.
3. Those due to the mechanical interference with efficient inspiration and expiration of the opening in the chest wall.
4. Those due to the changed pressure relations about the heart and great