1 Department of Cardiovascular Medicine, Mayo Clinic, Rochester, MN. Electronic address: somers.virend@mayo.edu.
2 Department of Cardiovascular Medicine, Mayo Clinic, Rochester, MN; Department of Internal Medicine, Brno Municipal Hospital of Merciful Brothers, Brno and Faculty of Medicine and Dentistry, Palacky University, Olomouc, Czech Republic.
3 Department of Respiratory and Critical Medicine of Beijing Anzhen Hospital, Capital Medical University, Beijing, China.