They encompass a wide variety of disorders due to the multitude of structures that make up the respiratory system and the diversity of their functions. In general, respiratory disorders fall into one of the major categories described below. As their name suggests, these disorders involve obstruction or narrowing of the airways, which limits air flow through the bronchi and results in shortness of breath, wheezing, or coughing. The most common of these disorders are asthma, chronic bronchitis, and emphysema. While asthma generally is reversible, chronic bronchitis and emphysema are usually persistent.
Cigarette smoking is a risk factor for the development of chronic bronchitis and emphysema.
Diseases in this group cause the lungs to be smaller than normal. Some disorders, such as sarcoidosis and pulmonary fibrosis, are characterized by shrinking of the lung as its connective fibers turn into scar tissue. Lung size may be restricted by an abnormal shape of the chest, such as that caused by severe curvature of the spine or deformities of the ribs. Proper expansion of the lungs may be restricted by diseases of the nerves or muscles that control expansion or by diseases of the pleura. Finally, tumors or large amounts of fluids in or around the lung may interfere with its movement and reduce the volume of lung available for breathing.