Dysfunction of the respiratory system, which supplies the body with the oxygen needed for metabolic activities in the cells and removes carbon dioxide, a product of cellular metabolism. The respiratory system includes the nose, mouth, throat, larynx, trachea, bronchi, lungs, and the muscles of respiration such as the intercostal muscles and the diaphragm. See also Respiration.
The lung has a great reserve capacity, and therefore a significant amount of disease usually must be present to produce clinical signs and symptoms. Shortness of breath (dyspnea) on exertion is the most common symptom of a respiratory disorder. Shortness of breath while at rest is indicative of severe respiratory disease and usually implies a severe abnormality of the lung tissue. If the respiratory system is so diseased that normal oxygenation of the blood cannot occur, blood remains dark, and a bluish color can be seen in the lips or under the fingernails; this condition is referred to as cyanosis. Other signs and symptoms of respiratory disorder can include fever, chest pain, coughing, excess sputum production, and hemoptysis (coughing up blood). Most of these signs and symptoms are nonspecific. See also Hypoxia.
Most diseases of the airways increase the resistance against which air is sucked in and pushed out of the lungs. Diseases of the nose usually have little influence since collateral respiration through the mouth compensates easily. Diseases of the throat, larynx, and trachea can significantly inhibit the flow of air into the lungs. Infections in the back of the throat, such as in diphtheria, can cause marked swelling of mucous membranes, resulting in air obstruction. Edema (swelling) of the mucosal lining of the larynx can also cause a reduction in air flow. Likewise, air flow can be inhibited in asthma, in which the smooth muscle in the trachea and bronchi episodically constricts. Chronic bronchitis results in inflammation of and excess mucus production by the bronchi and this also can lead to a reduction in air flow. Bronchiolitis, a condition that usually occurs in children and is often caused by a respiratory virus, results in narrowing and inflammation of small airways and a decrease in air flow.
Pneumonia, cancer, and emphysema are the most common lung diseases and are a major cause of morbidity and mortality in the United States. Of the four major types of lung cancer, approximately 90% can be attributed to the carcinogens present in cigarette smoke. Lung cancer may be detected in asymptomatic persons with a routine chest x-ray, or it may be discovered because of pain, excess coughing, or hemoptysis. See also Cancer (medicine); Emphysema; Pneumonia.
Among the diseases of pulmonary circulation, congenital malformations of the heart and pulmonary artery account for many cases of respiratory insufficiency in newborn and younger children. In adults, acquired heart diseases can cause backup of blood into the lung and an increased pressure in the pulmonary circulatory system. Also, blood clots, which usually develop first in the deep veins of the legs, can break free and flow to the heart. There they enter the pulmonary arteries and wedge in their small branches, where the clots are referred to as pulmonary thromboemboli, and can cause areas of death in the lung tissue (pulmonary infarcts). Persons who develop thromboemboli usually have chest pain and shortness of breath, and some have hemoptysis. See also Cardiovascular system; Circulation disorders.
Some neuromuscular diseases, such as poliomyelitis and amyotrophic lateral sclerosis (Lou Gehrig's disease), can cause dysfunction of the muscles of respiration. The resulting inability of these muscles to move air into the lungs can cause severe shortness of breath and predispose the patient to pneumonia. See also Muscular system disorders; Poliomyelitis; Respiratory system.
