1. Divison of Pulmonary and Critical Care, Department of Medicine, Denver Health Medical Center, Denver, Colorado, USA
2. Department of Medicine, University of Colorado School of Medicine, Anschutz Medical Campus, Aurora, Colorado, USA
3. Division of General Internal Medicine, Department of Medicine, University of Colorado School of Medicine, Anschutz Medical Campus, Aurora, Colorado, USA
4. Department of Medicine, Department of Veterans Affairs, Eastern Colorado Health Care System, Aurora, Colorado, USA