lung and airway disorders
Atelectasis
Introduction
Atelectasis is a condition in which all or part of a lung becomes airless and collapses. Blockage of the bronchial tubes is a common cause of atelectasis. Shortness of breath can develop if oxygen levels are low or pneumonia occurs. Chest x-ray is used to confirm the diagnosis. Treatment may involve making sure deep breathing occurs, relieving airway blockages, or both. The main function of the lungs is to absorb oxygen into the bloodstream from the atmosphere and to expel carbon dioxide from the blood into the exhaled breath (gas exchange—see figure). For gas exchange to occur, the small air sacs within the lungs (alveoli) must remain open and filled with air. Alveoli are kept open by the elastic structure of the lung and by a liquid lining called surfactant. Surfactant counters the natural tendency of the alveoli to close (collapse). Periodic deep breaths, which people take unconsciously, and coughing also help keep alveoli open. Coughing expels any mucus or other secretions that could block the airways leading to the alveoli. If the alveoli are closed for any reason, they cannot participate in gas exchange. The more alveoli that are closed, the less gas exchange occurs. Accordingly, atelectasis can decrease the level of oxygen in the blood. The body compensates for a small amount of atelectasis by closing off (constricting) the blood vessels in the affected area. This constriction redirects blood flow to alveoli that are open so that gas exchange can continue. 