1. Department of Medicine, University of Alberta, Edmonton, Alberta T6G2B7, Canada.
2. Department of Medicine, Imperial College London, London W12 0NN, UK.
3. National Pulmonary Hypertension Service, Imperial College Healthcare National Health Service Trust, Hammersmith Hospital, Du Cane Road, London W12 0NN, UK.
4. Department of Biomedical Engineering, University of Alberta, Edmonton, Alberta T6G2B7, Canada.
5. Medical Research Council, London Institute of Medical Sciences, Hammersmith Hospital Campus, Imperial College London, London W12 0NN, UK.
6. Sheffield Pulmonary Vascular Disease Unit, Royal Hallamshire Hospital, Sheffield S10 2JF, UK.
7. Department of Surgery, University of Alberta, Edmonton, Alberta T6G2B7, Canada.
8. National Heart and Lung Institute, Imperial College London, Dovehouse Street, London SW3 6LY, UK.