Shortness of breath on exertion has many possible causes. Most commonly it is due to problems with the lungs, airways or heart. Other problems may cause shortness of breath on exertion as well. Examples of lung problems causing shortness of breath include chronic obstructive pulmonary disease, a disease of lung tissue often associated with smoking. Asthma can affect the airways and cause shortness of breath. Congestive heart failure also leads to shortness of breath.
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Chronic Obstructive Pulmonary Disease
Chronic obstructive pulmonary disease is considered a single disease with two variants: emphysema and chronic bronchitis. A person with COPD typically has elements of both. Emphysema is the loss of normal lung tissue. Gases such as oxygen and carbon dioxide are not exchanged with the environment as efficiently due to the loss of tissue, causing it to be more difficult to compensate for the increased demand for oxygen during exertion. Bronchitis narrows the airways making it more difficult to transfer air between the lungs and atmosphere, and plugging narrow airways with mucus.
Asthma is similar to chronic bronchitis in that it causes narrowing of the airways and excessive mucus production. However, chronic bronchitis is always present while asthma is triggered by sensitive airways. Common triggers of asthma include animals, dust, weather changes, smoke and even exercise. Once triggered, the constricted airways cause shortness of breath.
Congestive Heart Failure
Congestive heart failure occurs as the heart is weakened, for example by a heart attack, coronary artery disease or infection. As a result the kidneys do not get enough blood and respond by retaining fluid in the body, making even more work for the heart. Fluid backs up in the tissues and lungs. The fluid in the lungs, plus the extra work a weak heart is performing leads to shortness of breath with exertion.
Many other problems may also cause shortness of breath with exertion. Some examples include the following. Blood clots in the lungs, called pulmonary emboli typically cause shortness of breath. Heart attacks and angina also may lead to shortness of breath and are usually caused by narrowed arteries in the heart. At high altitude, less oxygen is available to the lungs. Anxiety, a lack of exercise and obesity are other contributing factors.