As COPD progresses, many changes occur in your lungs. You may have excessive mucus or sputum produced in your airways that can result in narrowing, or even closing of the airways. Lung tissue is often destroyed by cigarette smoke. Both the narrowing of the airways and damage to the lung tissue contribute to poor gas exchange in the lung. Narrowed airways make it hard for you to breathe oxygen into the areas where it can reach the blood. Areas of destroyed lung tissue reduce the area for gas exchange to occur. When these processes become severe enough, the lungs are not able to provide enough oxygen for the body's needs. Since this occurs very gradually, you may not realize if your blood oxygen level is lower, however you may notice decreased exercise tolerance because your muscles are not receiving enough oxygen. Your body responds in many ways to oxygen deficiency.
Pressure in the lungs and heart: The arteries that carry blood from the right side of the heart into the lungs sense low oxygen levels and constrict in an effort to direct that blood to more normal areas of the lung. This causes pressure in the pulmonary arteries to rise and this pressure, in turn, is transmitted back to the right side of the heart. The right side of the heart cannot handle increased pressure very well. In response, it dilates and contracts ineffectively and eventually the heart will fail. One of the most common signs of this circumstance is swelling or edema of the legs. Additionally, less blood will be delivered to the left side of the heart, and it will have less blood to pump to the rest of the body.
Raised levels of hemoglobin: Over time, other changes can occur. Hemoglobin, which carries oxygen in the blood, may increase to compensate for a chronically low supply of oxygen. This response, called secondary polycythemia can make the blood thick, and impair its ability to flow easily. If this happens, intellectual functioning may suffer or, rarely, you could suffer a stroke. To prevent these problems, your doctor will monitor your hemoglobin levels and, if the levels become dangerously elevated, your doctor will arrange for you to have blood removed just as if you were donating blood.
