A 55-year-old man is admitted to the hospital with increasing shoness of breath and dry cough for the past few years. He smokes 1.5 packs of cigarettes and drinks about four bottles of beer a day. He is constantly "gasping for air" and now walks with difficulty because he becomes breathless after only a few steps. Prolonged expiration with wheezing is noted. Physical examination shows a barrel chest, hyperresonance on percussion and clubbing of the digits. The patient's face is puffy and red, and he has pitting edema of the legs. A chest X-ray discloses hyperinflation, flattening of the diaphragm and increased retrosternal air space. Which of the following is the appropriate diagnosis?