1 School of Science and Engineering, University of Dundee, Dundee, UK.
2 School of Medicine, University of Dundee, Dundee, UK; Department of Anaesthesia, NHS Tayside, Dundee, UK. Electronic address: g.a.mcleod@dundee.ac.uk.
3 Craigavon Area Hospital, Craigavon, UK.
4 The Newcastle upon Tyne Hospitals NHS Foundation Trust, Newcastle upon Tyne, UK.
5 School of Science and Engineering, University of Dundee, Dundee, UK; School of Medicine, University of Dundee, Dundee, UK.