Validation study on sleep parameters by actigraphy for normal subjects

Abstract

Dear Editor: O’Hare et al. reported the performance of three sleep monitoring devices for measuring sleep parameters in 20 normal subjects against sleep polysomnography (PSG) [1]. The authors used two non-contact radio-frequency biomot ion sensors , named SleepMinder® and S leepDes ign® , and an acce l e rome te r , named Actiwatch®. Compared with sleep PSG, all three devices overestimated total sleep time and underestimated wake after sleep onset and sleep onset latency. I appreciate that the authors checked the validity of three sleep monitoring devices, including Actiwatch®, against sleep PSG. Although the agreement of sleep/wake judgment by sleep monitoring devices is satisfactory for normal subjects, the authors recognized the limitation when these devices were applied for patients with insomnia. I have a query on their study with special emphasis on Actiwatch®. O’Hare et al. quoted a paper on selecting appropriate cutoff point for sleep-wake judgment [2], but there is no definite way to determine the best sensitivity of sleepwake judgment for every subject. Kushida et al. found the best overall accuracy and ability to detect wakefulness using Actiwatch® and PSG, when the “high-sensitivity” setting (20 counts per minute) was used [3]. Peterson et al. adopted the default sensitivity setting (40 counts per minute), and they described the overestimation of total sleep time and underestimation of wake after sleep onset by Actiwatch® [4], which was the same study outcome by O’Hare et al. There is a difference between brain activity and physical movement during sleep, and the discrepancy of sleep parameters between sleep PSG and sleep monitoring devices would be obvious for insomniacs [5]. Validation study of sleep parameters by SleepMinder®, SleepDesign®, and Actiwatch® as a tool for sleep/wake judgment should also be conducted in patients with sleep apnea syndrome and other sleep disorders.