1 Division of Pulmonary, Allergy, Critical Care and Sleep Medicine, Department of Medicine, Atlanta Veterans Affairs Health Care System, Decatur, GA, 30033, USA; Emory University, Atlanta, GA, 30322, USA.
2 Pulmonary Critical Care, Sleep & Allergy Division, Department of Internal Medicine, University of Nebraska Medical Center, 985910 Nebraska Medical Center, Omaha, NE, 68198-5910, USA; Research Service, Veterans Affairs Nebraska-Western Iowa Health Care System, Omaha, NE, 68105, USA; Department of Environmental, Agricultural and Occupational Health, College of Public Health, University of Nebraska Medical Center, 985910 Nebraska Medical Center, Omaha, NE, 68198-5910, USA. Electronic address: twyatt@unmc.edu.