1 King's College London, Cicely Saunders Institute, London, UK.
2 NIHR Respiratory Biomedical Research Unit, Royal Brompton and Harefield NHS Foundation Trust and Imperial College London, London, UK.
3 Harefield Pulmonary Rehabilitation Unit, Harefield Hospital, Harefield, UK.
4 NIHR Respiratory Biomedical Research Unit, Royal Brompton and Harefield NHS Foundation Trust and Imperial College London, London, UK [email protected].