[1] Churchill Hosp, Dept Resp Med, Oxford OX3 7LJ, England
[2] Royal United Hosp, Dept Anaesthet, Bath BA1 3NG, Avon, England
[3] Cheltenham Gen Hosp, Dept Colorectal Surg, Cheltenham, Glos, England
[4] Cheltenham Gen Hosp, Dept Gastroenterol, Cheltenham, Glos, England