1. Division of Pulmonary Rehabilitation, Istituti Clinici Scientifici Maugeri, IRCCS, 21049 Tradate, Italy
2. Department of Medicine and Surgery, University of Insubria, 2100 Varese, Italy
3. Clinical Epidemiology of Respiratory Diseases Service, Istituti Clinici Scientifici Maugeri, IRCCS, 21049 Tradate, Italy
4. Allergy and Immunology Unit, Istituti Clinici Scientifici Maugeri, IRCCS, 27100 Pavia, Italy