Shortness of breath—what doctors call dyspnea—is the unpleasant sensation of having difficulty breathing. People experience and describe shortness of breath differently depending on the cause.
The rate and depth of breathing normally increase during exercise and at high altitudes, but the increase seldom causes discomfort. Breathing rate is also increased at rest in people with many disorders, whether of the lungs or 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. People feel as if they cannot breathe fast enough or deeply enough. They may notice that more effort is needed to expand the chest when breathing in or to expel air when breathing out. They may also have the uncomfortable sensation that inhaling (inspiration) is urgently needed before exhaling (expiration) is completed and have various sensations often described as tightness in the chest.
Other symptoms, such as cough or chest pain, may be present depending on the cause of dyspnea.
Dyspnea is usually caused by disorders of the lungs or heart (see Table 3: Some Causes and Features of Shortness of Breath).
The most common causes overall include
Pulmonary embolism (sudden blockage of an artery of the lung, usually by a blood clot) is a less common, but serious cause.
The most common cause in people with a chronic lung or heart disorder is
However, such people may also develop another disorder. For example, people with long-standing asthma may have a heart attack, or people with chronic heart failure may develop pneumonia.
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 speeds up breathing when blood levels of oxygen are low or blood levels of carbon dioxide are high. If the heart or lungs are not functioning normally, even a little exertion can dramatically increase the breathing rate and dyspnea. Dyspnea is so unpleasant that people avoid exertion. As the lung disorder becomes more severe, dyspnea may occur even 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 more effort to expand during inhalation. Severe curvature of the spine (scoliosis) can also restrict breathing because it reduces movement of the rib cage.
In obstructive disorders (such as COPD or asthma), resistance to airflow is increased because the airways are narrowed. Because airways widen during inhalation, air can usually be pulled in. However, because airways narrow during exhalation, air cannot be exhaled from the lungs as fast as normal, and people wheeze and breathing is labored. Dyspnea results when too much air is left in the lungs after exhaling.
People with asthma have dyspnea when they have an attack. Doctors typically advise people to keep an inhaler on hand to use during an attack. The drug in the inhaler helps open the airways.
The heart pumps blood through the lungs. If the heart is pumping inadequately (called heart failure), fluid may accumulate in the lungs—a disorder called pulmonary edema. This disorder causes dyspnea that is often accompanied by a feeling of smothering or heaviness in the chest. The fluid accumulation in the lungs may also narrow the airways and cause wheezing—a disorder called cardiac asthma (see Heart failure).
Some people with heart failure have orthopnea, paroxysmal nocturnal dyspnea, or both. Orthopnea is shortness of breath that occurs when people lie down and is relieved by sitting up. Paroxysmal nocturnal dyspnea is a sudden, often terrifying attack of dyspnea during sleep. People awaken gasping and must sit or stand to catch their breath. This disorder is an extreme form of orthopnea and a sign of severe heart failure (see Symptoms).
When people have anemia or have lost a large amount of blood because of an injury, they have fewer red blood cells. Red blood cells carry oxygen to the tissues, so in these people, the amount of oxygen that blood can deliver is decreased. Most people with anemia are comfortable sitting still. However, they often feel dyspnea during physical activity because the blood cannot deliver the increased oxygen the body requires. Thus, they breathe rapidly and deeply in a reflex effort to try to increase the amount of oxygen in the blood.
If a large amount of acid accumulates in the blood (called metabolic acidosis), people may feel out of breath and begin to pant quickly. Severe kidney failure, sudden worsening of diabetes mellitus, and ingestion of certain drugs or poisons can cause metabolic acidosis. Anemia and heart failure may contribute to dyspnea in people with kidney failure.
In hyperventilation syndrome, people feel that they cannot get enough air, and they breathe heavily and rapidly. This syndrome is commonly caused by anxiety rather than a physical problem. Many people who experience it are frightened, may have chest pain, and may believe they are having a heart attack. They may have a change in consciousness, usually described as feeling that events occurring around them are far away, and they may feel tingling in their hands and feet and around their mouth.
The following information can help people decide whether a doctor's evaluation is needed and help them know what to expect during the evaluation.
In people with dyspnea, the following symptoms are of particular concern:
When to see a doctor:
People who have shortness of breath at rest, chest pain, palpitations, a decreased level of consciousness, agitation, or confusion or have difficulty moving air in or out of their lungs should go to the hospital right away. Such people may need immediate testing, treatment, and sometimes admission to the hospital. Other people should call a doctor. The doctor can determine how rapidly they need to be evaluated based on the nature and severity of their symptoms, their age, and any underlying medical conditions. Typically, they should be evaluated within a few days.
What the doctor does:
Doctors first ask questions about the person's symptoms and medical history. Doctors then do a physical examination. What doctors find during the history and physical examination often suggests a cause and the tests that may need to be done (see Table 3: Some Causes and Features of Shortness of Breath).
Doctors ask questions to determine
The person is also asked questions about past medical history (including any lung or heart disorders), a history of smoking, any family members who have had high blood pressure or high cholesterol levels, and risk factors for pulmonary embolism (such as recent hospitalization, surgery, or long-distance travel).
The physical examination focuses on the heart and lungs. Doctors listen to the lungs for congestion, wheezing, and abnormal sounds called crackles. They listen to the heart for murmurs (suggesting a heart valve disorder). Swelling of both legs suggests heart failure, but swelling of only one leg is more likely to result from a blood clot in the leg. A blood clot in the leg may break off and travel to the blood vessels in the lungs, causing pulmonary embolism.
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To help determine the severity of the problem, doctors measure oxygen levels in the blood with a sensor placed on a finger (pulse oximetry). Typically, they also take a chest x-ray unless the person clearly appears to be having a mild flare-up of an already diagnosed chronic disorder such as asthma or heart failure. The chest x-ray can show evidence of a collapsed lung, pneumonia, and many other lung and heart abnormalities. For most adults, electrocardiography (ECG) is done to check for inadequate blood flow to the heart.
Other tests are done based on results of the examination (see Table 3: Some Causes and Features of Shortness of Breath). Tests to evaluate how well the lungs are functioning (pulmonary function testing—see Pulmonary Function Testing (PFT)) are done when the doctor's examination suggests a lung disorder but the chest x-ray does not provide a diagnosis. Pulmonary function tests 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 restrictive and obstructive abnormalities as well as abnormal oxygen transport.
For people at moderate or high risk of pulmonary embolism, specialized imaging tests, such as computed tomography (CT) angiography or ventilation/perfusion scanning, are done. For people at low risk of pulmonary embolism, a D-dimer test may be done. This blood test helps identify or rule out a blood clot. Other tests may be necessary to diagnose and further evaluate anemia, heart problems, and certain specific lung problems.
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 people cannot breathe deeply or rapidly enough, breathing may be assisted by mechanical ventilation using a breathing tube inserted in the windpipe or a tight-fitting face mask.
Morphine may be given intravenously to reduce anxiety and the discomfort of dyspnea in people with various disorders, including a heart attack, pulmonary embolism, and a terminal illness.
Last full review/revision October 2014 by Noah Lechtzin, MD, MHS