[1] Univ Glasgow, Sch Med, Glasgow G12 8QQ, Lanark, Scotland
[2] Univ Glasgow, Sch Med, Acad Unit Anaesthesia Pain & Crit Care Med, Glasgow G12 8QQ, Lanark, Scotland
[3] Univ Glasgow, Sch Med, Nursing & Healthcare Sch, Glasgow G12 8QQ, Lanark, Scotland
[4] Univ Glasgow, Coll Sci & Engn, Sch Math & Stat, Glasgow G12 8QQ, Lanark, Scotland
[5] Glasgow Royal Infirm, Glasgow G4 0SF, Lanark, Scotland
[6] Univ Glasgow, Dept Clin Phys, Glasgow G12 8QQ, Lanark, Scotland