1 Centre for Human and Applied Physiological Sciences, King's College London, London WC2R 2LS, UK.
2 Department of Respiratory Medicine, King's College Hospital NHS Foundation Trust, London, UK.
3 Centre for Human and Applied Physiological Sciences, King's College London, London WC2R 2LS, UK; Department of Respiratory Medicine, King's College Hospital NHS Foundation Trust, London, UK.
4 Centre for Human and Applied Physiological Sciences, King's College London, London WC2R 2LS, UK; Department of Respiratory Medicine, King's College Hospital NHS Foundation Trust, London, UK. Electronic address: m.waller@nhs.net.