[1] Univ London Imperial Coll Sci Technol & Med, Sch Med, Natl Heart & Lung Inst, London SW3 6LY, England
[2] Charing Cross Hosp, Natl Heart & Lung Inst, Imperial Coll, Sch Med, London, England
[3] Hammersmith Hosp, Imperial Coll, Sch Med, Dept Med Stat & Evaluat, London, England