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COPD Lung Effects

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Updated December 27, 2005

The most important job that the lungs perform is to provide the body with oxygen and to remove carbon dioxide. This process is called gas exchange, and the normal anatomy of the lungs serves this purpose well. The lungs contain 300 million alveoli whose ultrathin walls form the gas exchange surface. Enmeshed in the wall of each of these air sacs is a network of tiny blood vessels, the capillaries, which bring blood to the gas exchange surface. When a person inhales, air flows from the nose and mouth through large and small airways into the alveoli. Oxygen from this air then passes through the thin walls of the inflated alveoli and is taken up by the red blood cells for delivery to the rest of the body. At the same time, carbon dioxide leaves the blood and passes through the alveolar walls into the alveoli. During exhalation, the lung pushes the used air out of the alveoli and through the air passages until it escapes from the nose or mouth.

Gas Exchange

Inhaled air travels through the airways to the alveoli. Blood is pumped out of the heart through the pulmonary arteries to a network of capillaries that surround the alveoli. The oxygen of the inhaled air diffuses out of the alveoli into the blood while carbon dioxide in the blood moves into the alveoli to be exhaled. The oxygen-rich blood is returned to the heart through the pulmonary veins.

When COPD develops, the walls of the small airways and alveoli lose their elasticity. The airway walls thicken, closing off some of the smaller air passages and narrowing larger ones. The passageways also become plugged with mucus. Air continues to get into alveoli when the lung expands during inhalation, but it is often unable to escape during exhalation because the air passages tend to collapse during exhalation, trapping the "stale" air in the lungs. These abnormalities create two serious problems which affect gas exchange:

  • Blood flow and air flow to the walls of the alveoli where gas exchange takes place are uneven or mismatched. In some alveoli there is adequate blood flow but little air, while in others there is a good supply of fresh air but not enough blood flow. When this occurs, fresh air cannot reach areas where there is good blood flow and oxygen cannot enter the bloodstream in normal quantities.

  • Pushing the air through narrowed obstructed airways becomes harder and harder. This tires the respiratory muscles so that they are unable to get enough air to the alveoli. The critical step for removing carbon dioxide from the blood is adequate alveolar airflow. If airflow to the alveoli is insufficient, carbon dioxide builds up in the blood and blood oxygen diminishes. Inadequate supply of fresh air to the alveoli is called hypoventilation. Breathing oxygen can often correct the blood oxygen levels, but this does not help remove carbon dioxide. When carbon dioxide accumulation becomes a severe problem, mechanical breathing machines called respirators, or ventilators, must be used.

Updated 12/27/05

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