[1] Natl Heart & Lung Inst, Imperial Coll London, London, England
[2] Royal Brompton & Harefield Hosp, Resp Med, London, England
[3] Hywel Dda Univ Hlth Board, Carmarthen, England
[4] Brunel Univ London, Dept Hlth Sci, Uxbridge, England
[5] Umm Al Qura Univ Coll Appl Med Sci, Fac Appl Med Sci, Clin Technol Dept, Mecca, Saudi Arabia
[6] Taibah Univ, Coll Med Sci & Rehabil, Dept Resp Therapy, Al Madinah Almunawarah, Saudi Arabia
[7] Jazan Univ, Fac Appl Med Sci, Resp Therapy Dept, Jazan, Saudi Arabia
[8] Imperial Coll, Patient Experience Res Ctr, London, England
[9] Imperial Coll Healthcare NHS Trust, Resp Med, London, England
[10] UCL, Dept Behav Sci & Hlth, London, England