Nightcap: laboratory and home-based evaluation of a portable sleep monitor

In this paper, we describe the first field tests of a home-based sleep monitoring system, the Nightcap, which uses eyelid and body movement sensors to discriminate wake, NREM, and REM sleep automatically. Ten normal young adults were studied in the sleep laboratory and at home to allow comparison of Nightcap-derived measures with those obtained by traditional polysomnography. The agreement between the two techniques was 87% based on 1-min epochs--93% for NREM, 80% for REM, and 72% for wake. When the values for sleep latency, REM latency, wake time, NREM time, and REM time calculated from polysomnograph records were compared with the values calculated from Nightcap data, no significant differences were seen. In cases of extremely poor sleep, objective sleep efficiency estimates correlated well with subjective reports, suggesting that the Nightcap is sensitive to clinically relevant changes in the quality of sleep. This new device should prove useful to researchers wishing to study the psychophysiology and pathophysiology of sleep in more naturalistic and cost-effective paradigms than possible in the traditional sleep laboratory.