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Dyspnea (shortness of breath) is the unpleasant sensation of difficulty in breathing.
An increase in the rate and depth of breathing occurs normally during exercise and at high altitudes, but the increase seldom causes discomfort. Breathing is also increased at rest in people with many illnesses, whether of the lungs or of other parts of the body. For example, people with a fever generally breathe faster.
With dyspnea, faster breathing is accompanied by the sensation of running out of air. The person feels a sensation of not being able to breathe fast enough or deeply enough. Other sensations include an awareness of increased muscular effort to expand the chest when breathing in or to expel air when breathing out, the uncomfortable sensation that inhaling (inspiration) is urgently needed before exhaling (expiration) is completed, and various sensations often described as tightness in the chest.
Causes
Lung Disorders:
People who have lung disorders often experience dyspnea when they physically exert themselves. During exercise, the body makes more carbon dioxide and uses more oxygen. The respiratory center in the brain accelerates breathing when blood levels of oxygen are low or blood levels of carbon dioxide are high. If the heart or lungs are not functioning properly, even a little exertion can lead to dramatic increases in breathing rates and dyspnea. Dyspnea is so unpleasant that the person avoids exertion. As the lung disorder becomes more severe, dyspnea may even occur at rest.
Dyspnea may result from restrictive or obstructive lung disorders. In restrictive lung disorders (such as idiopathic pulmonary fibrosis), lungs become stiff and require increased effort to expand during inhalation. Severe curvature of the spine (scoliosis) also restricts breathing by reducing the movement of the rib cage. In obstructive disorders (such as chronic obstructive pulmonary disease or asthma), resistance to airflow is increased because the airways are narrowed. Because airways widen on inhalation, air can usually be pulled in. However, because airways narrow on exhalation, air cannot be exhaled from the lungs as fast as normal, and breathing becomes labored.
Heart Failure:
The heart pumps blood through the lungs. The heart must function properly for the lungs to function normally. If the heart is pumping inadequately (heart failure), fluid may accumulate in the lungs, a condition called pulmonary edema. This condition causes dyspnea that is often accompanied by a feeling of smothering or heaviness in the chest. The fluid accumulation in the lungs may also lead to airway narrowing and wheezing—a condition called cardiac asthma.
Some people with heart failure experience orthopnea, paroxysmal nocturnal dyspnea, or both. Orthopnea is shortness of breath when a person lies down that is relieved by sitting up. Paroxysmal nocturnal dyspnea is a sudden, often terrifying, attack of shortness of breath during sleep. The person awakens gasping and must sit or stand to take a breath. This condition is an extreme form of orthopnea and a sign of severe heart failure (see Heart Failure: Symptoms).
Anemia:
Dyspnea can also occur in people who have anemia or blood loss because of a decreased number of red blood cells, which carry oxygen to the tissues. The person breathes rapidly and deeply, in a reflex effort to try to increase the amount of oxygen in the blood.
Other Causes:
Someone with severe kidney failure or sudden worsening of diabetes mellitus or someone who has taken certain drugs or poisons feels out of breath and may begin to pant quickly because of an accumulation of a large amount of acids in the blood (a condition called metabolic acidosis). Anemia and heart failure may also contribute to dyspnea in people with kidney failure.
Hyperventilation syndrome causes people to feel that they cannot get enough air, and they breathe heavily and rapidly. This condition is commonly caused by anxiety rather than a physical problem. Many people who experience this syndrome are frightened, may have chest pain, and may believe they are having a heart attack. People may experience a change in consciousness usually described as a feeling that events occurring around them are far away, and they may experience tingling in the hands and feet and around the mouth.
Evaluation and Treatment
Doctors can usually get an idea of what is causing dyspnea from the person's symptoms and the results of a physical examination. A chest x-ray and measurement of levels of oxygen in the blood with arterial blood gas testing or pulse oximetry help determine the cause. The chest x-ray can show evidence of pneumonia and many other lung abnormalities and can often show evidence of heart failure. A low blood oxygen level usually indicates a heart or lung problem. Pulmonary function testing (see Diagnosis of Lung Disorders: Pulmonary Function Testing (PFT)) can measure the degree of restriction or obstruction and the ability of the lungs to transport oxygen from the air to the blood. A lung problem may include both restrictive and obstructive defects as well as abnormal oxygen transport. Other tests may be necessary to diagnose and further evaluate anemia, heart problems, certain specific lung problems, and kidney failure.
Treatment of dyspnea is directed at the cause. People with a low blood oxygen level are given supplemental oxygen using plastic nasal prongs or a plastic mask worn over the face. In severe cases, particularly if a person cannot breathe deeply or rapidly enough, doctors may assist breathing by mechanical ventilation administered through a breathing tube inserted into the trachea or through a tight-fitting face mask.
Last full review/revision November 2006 by James H. Fisher, MD
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