Chronic obstructive pulmonary disease, or COPD, is a life-threatening condition commonly caused by years of smoking. Doctors say that over time the damage interferes with the natural exchange of oxygen and carbon dioxide in the lungs. COPD is not curable but treatment can extend a patient's life. Doctors often treat it with steroids. Now, a study shows that low doses of the medicine given by mouth are equal to, or better than, a heavy dose administered into the blood.