1 Division of Respiratory and Critical Care Medicine, Department of Medicine, National University Hospital, Singapore.
2 Department of Cardiology, National University Heart Centre Singapore, Singapore.
3 Department of Cardiology, National University Heart Centre Singapore; Yong Loo Lin School of Medicine, National University Singapore, Singapore.
4 Division of Respiratory and Critical Care Medicine, Department of Medicine, National University Hospital; Yong Loo Lin School of Medicine, National University Singapore, Singapore.