1 Division of Pulmonary and Critical Care Medicine, David Geffen School of Medicine at the University of California at Los Angeles, Los Angeles, California, USA. bkamdar@mednet.ucla.edu.
2 Department of Medicine, David Geffen School of Medicine at the University of California at Los Angeles, Los Angeles, California, USA.
3 Veterans Affairs Greater Los Angeles Healthcare System, Geriatric Research Education and Clinical Center, Los Angeles, California, USA.
4 Outcomes After Critical Illness and Surgery Group, Johns Hopkins University, Baltimore, Maryland, USA.
5 Division of Pulmonary and Critical Care Medicine, Johns Hopkins University, Baltimore, Maryland, USA.
6 Department of Physical Medicine and Rehabilitation, Johns Hopkins University, Baltimore, Maryland, USA.