What Goes Wrong With the Lungs and Other Organs in Chronic Obstructive Pulmonary Disease?

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.

Age-related change in the lung function and effect of
smoking and smoking cessation

Adapted from 1984 Surgeon General's Report

Pulmonary function studies of large groups of people show that lung function--the ability to move air into and out of the lungs--declines slowly with age even in healthy nonsmokers. Because healthy nonsmokers have excess lung capacity, this gradual loss of function does not lead to any symptoms. In smokers, however, lung function tends to worsen much more rapidly. If a smoker stops smoking before serious COPD develops, the rate at which lung function declines returns to almost normal. Unfortunately, because some lung damage cannot be reversed, pulmonary function is unlikely to return completely to normal.

In smokers, lung function tends to worsen much more rapidly than in nonsmokers.

COPD also makes the heart work much harder, especially the main chamber on the right side (right ventricle) which is responsible for pumping blood into the lungs. As COPD progresses, the amount of oxygen in the blood decreases which causes blood vessels in the lung to constrict. At the same time many of the small blood vessels in the lung have been damaged or destroyed as a result of the disease process. More and more work is required from the right ventricle to force blood through the remaining narrowed vessels. To perform this task, the right ventricle enlarges and thickens. When this occurs the normal rhythm of the heart may be disturbed by abnormal beats. This condition, in which the heart is enlarged because of lung problems, is called cor pulmonale. Patients with cor pulmonale tire easily and have chest pains and palpitations. If an additional strain is placed on the lungs and heart by a normally minor illness such as a cold, the heart may be unable to pump enough blood to meet the needs of other organs. This results in the inability of the liver and kidneys to carry out their normal functions which leads to swelling of the abdomen, legs, and ankles.

Another adjustment the body makes to inadequate blood oxygen is called secondary polycythemia, an increased production of oxygen-carrying red blood cells. The larger than normal number of red blood cells is helpful up to a point; however, a large overpopulation of red cells thickens the blood so much that it clogs small blood vessels causing a new set of problems. People who have poor supply of oxygen usually have a bluish tinge to their skin, lips, and nailbeds, a condition called cyanosis.

Too little oxygen and too much carbon dioxide in the blood also affect the nervous system, especially the brain, and can cause a variety of problems including headache, inability to sleep, impaired mental ability, and irritability.