Upon enrolling participants, the following will be performed: review of medical history; review of demographic and smoking history; physical examination, blood and sputum collection; six-minute walk test; and questionnaires to assess shortness of breath (MMRC and University of California San Diego SOBQ), sputum production (modified Chronic Bronchitis Symptom Questionnaire), health status (SF-36 and St. George's Respiratory Questionnaire), and psychological traits (Hospital Anxiety/Depression Score, Illness Perception Questionnaire, Coping Index, and an individualized 30-minute clinical interview via telephone).