1 Foundation Year Two Doctor Aintree University Hospital, Lower Lane, Fazakerley, Liverpool, L9 7AL.
2 Respiratory Consultant and Senior Clinical Lecturer Liverpool Centre for Cardiovascular Science, University of Liverpool, Brownlow Hill, Liverpool, L69 7TX.
3 Professor of Cardiovascular Medicine Liverpool Centre for Cardiovascular Science, University of Liverpool, Brownlow Hill, Liverpool, L69 7TX.
4 Respiratory Consultant and Sleep Physician, and Sleep and Ventilation Lead Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield Teaching Hospital, Herries Road, Sheffield, S5 7AU.