[1] Duke Univ, Sch Nursing, Durham, NC 27710 USA
[2] Univ Calif San Francisco, Inst Hlth & Aging, San Francisco, CA 94143 USA
[3] Univ Calif San Francisco, Dept Physiol Nursing, San Francisco, CA 94143 USA
[4] Univ Calif San Francisco, Sect Electrophysiol, Sch Med, San Francisco, CA 94143 USA