Original articleAn automatic ambulatory device for detection of AASM defined arousals from sleep: the WP100
Introduction
Sleep fragmentation in patients with sleep apnea syndrome can result in non-restorative sleep and consequent daytime sleepiness and impairment of cognitive and psychomotor performance [1], [2], [3]. Even normal subjects become sleepier and their mood is impaired during the day following experimental sleep fragmentation by brief arousals [4]. Thus, the number of arousals is a useful marker of sleep quality, independent of traditional sleep quality markers such as sleep latency, wake after sleep onset and sleep efficiency. The currently recommended criteria for scoring arousals consist of a notable EEG shift for at least 3 s but no more than 15 s during all NREM stages of sleep, assuming sleep is recorded prior to and following the event for at least 10 s. Since EEG alpha waves or mixed frequency waves are common during REM sleep, the definition of arousal during REM sleep relies on a combination of EEG defined arousal and increased EMG or body movements [5]. These criteria are rather difficult to determine, and a relatively large inter-scorer variability has been reported in scoring arousals from sleep [6], [7]. Thus, an automatic and reliable method to detect arousals has been sought [8]. We have recently reported that an automatic analysis of peripheral arterial tone (PAT) signal recording – a simple, reproducible and time saving procedure – can accurately detect arousals from sleep [9]. In this previous study, PAT signal has been recorded as an additional channel in a standard polysomnography (PSG) set-up, with sleep/wake scoring derived from the PSG. The fact that standard PSG is a relatively cumbersome and expensive procedure drives researchers to develop ambulatory methods and devices. For the diagnosis of obstructive sleep apnea (OSA), several devices have been produced [10], [11], [12], [13], yet none have gained enough popularity to be widely used for clinical purposes. For the detection of sleep fragmentation, the pulse transit time (PTT) method has been introduced. Pitson et al. reported a good correlation between PTT and EEG frequency shifts in response to external stimuli in normal subjects [14]. PTT could also, to some extent, detect sleep disordered breathing events [15]. Argod et al. found a reasonable agreement between standard scoring of PTT in detecting non-apneic obstructive respiratory events, but reported a very high inter-observer variability in the scoring of both (30–37%) [16]. In the current study, we sought to examine and validate the accuracy of the recently developed ambulatory WP100 device (Watch_PAT100) in the detection of arousals from sleep, as defined by the American Academy of Sleep Medicine (AASM) [5].
Section snippets
Subjects
The study group consisted of 61 consecutive adult patients referred to the Technion Sleep Disorders Center for evaluation of presumed obstructive sleep apnea syndrome (OSAS) and an additional seven young healthy volunteers, recruited via advertisements in the Faculty of Medicine, with no complaints of sleep disruption, daytime sleepiness or snoring. The healthy volunteers were free of disease and medications. The exclusion criteria for the suspected OSAS patients were: permanent pacemaker,
Results
Characteristics of the study population are presented in Table 1. The average age and BMI were 46±14 years and 28±6 kg/m2, respectively. The average RDI for the whole group was 34±26 events/h. As can be seen, there were similar numbers of subjects in the various apnea severity ranges. The average ESS score for the whole group was 9.5±6, with the score tending to be higher as the severity of apnea increased.
Fig. 1 displays a scatter graph of the PSG-ARI (gold standard) vs. the PAT-AAI values for
Discussion
This study shows that the standard AASM-based ‘EEG arousals’ can be accurately assessed by measuring ‘autonomic arousals’ using the WP100 ambulatory device. This is consistent with the observation that arousals are associated with sympathetic activation, and can be accurately measured by an in-lab PAT channel added to a standard PSG [9].
Until now, ambulatory sleep monitoring equipment has been focused on measuring only the sleep/wake state (actigraphy) [22], sleep apnea indices (primarily
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Amir Bar, Michal Betito, Robert Schnall and Jacob Sheffy are employees of Itamar Medical and Giora Pillar and Peretz Lavie are consultants for Itamar Medical Ltd.