1. Department of Internal Medicine, Section of Pulmonary and Critical Care Medicine, Yale University School of Medicine, New Haven, Connecticut
2. Division of Pulmonary Disease and Critical Care Medicine, Department of Medicine, University of Vermont College of Medicine, Burlington, Vermont
3. Department of Anesthesiology, College of Physicians and Surgeons, Columbia University, New York, New York
4. Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, New York