1. VA San Diego Healthcare System Sleep Medicine Section, Department of Medicine, , San Diego, CA , USA
2. Critical Care, Sleep Medicine and Physiology, University of California at San Diego Department of Medicine, Division of Pulmonary, , La Jolla, CA , USA
3. Health Services Research & Development Unit, VA San Diego Healthcare System , San Diego, CA , USA
4. VA San Francisco Healthcare System Sleep Medicine Section, Department of Medicine, , San Francisco, CA , USA
5. University of California at San Diego Department of Medicine, , La Jolla, CA , USA