Obstructive defects are caused by Increased resistance to airflow due to abnormalities within the airway lumen (eg, tumors, secretions, mucosal thickening) Changes in the wall of the airway (eg, contraction of smooth muscle, edema) Decreased elastic recoil (eg, the parenchymal destruction that occurs in emphysema) With decreased airflow, expiratory times are longer than usual, and air may become trapped in the lungs due to incomplete emptying, thereby increasing lung volumes (eg, TLC, RV).