Update: shortness of breath.

D ifficulty in breathing (also known as shortness of breath, breathless-ness, or dyspnea) is caused by various mechanisms related to different problems in the body. In one's lifetime, one may experience rare episodes of shortness of breath as part of high levels of activity such as exhaustive exertion or during environmental conditions such as high altitude or very warm or cold temperatures. Other than these extreme conditions, shortness of breath is commonly a sign of a medical problem. If the shortness of breath is prolonged and persistent, it is likely to be related to a medical condition. If it is sudden and severe in intensity or even of short duration, however, it may warrant medical evaluation. Other clues of the existence of a medical problem are given in Table 1. Symptom of shortness of breath can be caused by a variety of abnormalities in different organ systems in the body (Figure). • Recent infections such as bronchitis or pneumonia or prolonged (chronic) infections such as tuberculosis or chronic bronchitis. Shortness of breath may be accompanied by dis-colored phlegm or fever. • Asthma, chronic obstructive lung disease, and emphysema: The airways are narrowed with increased resistance to exhaling air from the lung, resulting in air entrapment in the lung. Shortness of breath may be accompanied by wheezing. In asthma , there is usually an allergy history , whereas in chronic obstructive lung disease or emphysema, there is usually a smoking history. • Lung cancer and other tumors: Shortness of breath is commonly accompanied by unintentional appetite and weight loss. There is usually a long and heavy smoking history. • Scarring and damage of lung tissue by toxins (such as asbestosis) or by systemic illnesses (such as rheu-matoid arthritis). There is usually a known history of these systemic illnesses or occupational exposures. • Clot in the lung circulation (pulmonary embolus): Breathlessness is usually sudden, is associated with rapid breathing, and may be accompanied by chest pain. People with blood clots in the legs or pelvis (deep venous thrombosis), debilitating medical conditions, immobility, or inherited tendency to form clots may be prone to this condition. (For more information about pulmonary embo-lism, see the Cardiology Patient Page by Goldhaber and Morrison. 1) • Diseases of the lung sac (pleura): If the pleura thickens, becomes scarred, or is filled with fluid or blood because of infection (pleurisy), cancer, or toxins (asbestosis), or if it becomes …