Shortness of breath (dyspnea) is the sensation of difficult or labored breathing (see Symptoms of Lung Disorders: Shortness of Breath).
Any disorder that upsets the normal, delicate balance between the body's oxygen supply and oxygen requirement can cause shortness of breath. It is a common symptom of lung disorders, including infections, asthma, and allergies. Shortness of breath can also occur in people who have a disorder of the respiratory muscles, a disorder of the nervous system that interferes with breathing, or too few red blood cells to carry oxygen to tissues (anemia).
Shortness of breath is also a common symptom of heart disorders, mainly heart failure (Heart Failure) and coronary artery disease (Coronary Artery Disease).
In heart failure, shortness of breath results from fluid seeping into the air spaces of the lungs—a condition called pulmonary congestion or pulmonary edema. Ultimately, this process is similar to drowning. In the early stages of heart failure, shortness of breath may occur only during physical activity. As heart failure worsens, shortness of breath occurs with less and less activity and eventually occurs at rest. Shortness of breath at rest occurs mostly when people lie down because fluid seeps throughout the lung tissue. This symptom often occurs at night and is then called nocturnal dyspnea. When people sit up and dangle their legs, gravity causes fluid to collect at the base of the lungs, reducing symptoms. Consequently, people with nocturnal dyspnea usually sleep propped up by pillows to avoid lying flat.
In coronary artery disease, shortness of breath usually occurs during physical activity, but in people with severe disease, it may occur during minimal activity or during rest.
Sometimes the symptoms suggest a cause to the doctor. Nocturnal dyspnea that is relieved by sitting up and dangling the legs suggests heart failure. Shortness of breath that occurs during physical activity and is accompanied by chest pain suggests coronary artery disease. Shortness of breath with cough and fever suggests a lung infection. Shortness of breath that seems to be triggered by exposure to something in the environment, such as smoke or animal hair, suggests asthma or an allergic disorder.
If the cause is not obvious, tests are usually done. The tests are chosen based on the person's particular symptoms, physical examination, and other factors suggesting a specific disorder. But most often, a chest x-ray and measurement of oxygen levels with a small sensor placed over a finger (pulse oximetry) are done. Electrocardiography (ECG) is commonly performed in adults, particularly if they have risk factors for heart disorders.
Last full review/revision April 2006 by Paul H. Tanser, MD