A 52 year old woman presents to your clinic with a 6 month history of productive cough and wheeze on exertion. In the past 2 months the patient describes finding it difficult to keep up with their grandchildren. The patient is a current smoker, smoking two packs per day for the past 18 years. On exam, the patient is slightly barrel-chested, has fair air entry bilaterally with a prolonged expiratory phase. You suspect this patient has COPD.