1. Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, University of California San Diego, La Jolla, California, USA
2. Department of Psychiatry, University of California San Diego, La Jolla, California, USA
3. Psychology Service, Mental Health Care Line, Veterans Affairs San Diego Healthcare System, La Jolla, California, USA
4. Section of Pulmonary and Critical Care Medicine, Medicine Service, Veterans Affairs San Diego Healthcare System, La Jolla, California, USA