[1] Fdn S Maugeri, Ist Sci Pavia, Resp Unit, Turin, Italy
[2] Ist Sci Montescano, Resp Unit, Turin, Italy
[3] CTO Hosp, IRCCS, Resp Unit, Turin, Italy
[4] S Luigi Gonzaga Hosp, Resp Unit, Orbassano, Italy
[5] Osped S Maria Misericordia, Resp Unit, Udine, Italy
[6] Univ Pavia, Dept Hlth Sci, Sect Med Stat & Epidemiol, Resp Unit, I-27100 Pavia, Italy