The abnormalities in lung structure and function in senile and emphysematous lung were studied, and the cardinal factors of the development from the senile lung to chronic obstructive emphysema were speculated to be as follows. First, chronic bronchitis which is a common disorder in senile lung, is apt to develop into bronchiolitis, with acinar inflammation in the acute exacerbation and causes the damage of the wall of respiratory bronchioli and alveolar ducts. Secondly, as a result, there is a pressure inbalance between the intrapulmonary pressure which tends to collapse the airway, the elasticity which tends to distend the airway and the intrabronchial pressure. Those agents which disturb the pressure balance were studied theoretically and measured practically. Thirdly, the check valve phenomenon develops by the pressure inbalance. The vicious circle of repeated check valve phenomenon accelerates the progression of the chronic pulmonary emphysema. The other agents; obstructive change, cough, exercise and hyperventilation also accelerate the development and progression of the chronic pulmonary emphysema. A new index of check valve index (C.V.I.) was proposed in differentiating chronic pulmonary emphysema from bronchial asthma. Application of check valve index in conjunction with one second vital capacity per vital capacity (1"VC/VC) is available for diagnosis of chronic pulmonary emphysema.