Preliminary observations on the maintenance of wakefulness test in mild obstructive sleep apnea patients [P171]

The Maintenance of Wakefulness Test (MWT) tests an individual's ability to stay awake in an environment of decreased sensory stimulation. The definition of sleep during an MWT, and thus cessation of the test, is the appearance of 3 epochs of Stage 1 sleep or 1 epoch of any other sleep stage. This procedure may be an insensitive measure of excessive sleepiness in mildly affected individuals. Methods: MWT was performed in 18 patients (age 47.4 ± 7 yrs, 2 female) entering a RCT of treatment for mild OSA (RDI 5-30/hr; mean 17.4 ±6.8) and MWT scores compared with other tests of vigilance and subjective sleepiness (Psychomotor Vigilance Task (mean of the 10% slowest responses; PVT10), ESS, Visual Analogue Score of Sleepiness; VASS). In a subset of patients recruited at Daw Park (n=8) a novel method which sums all micro-sleeps (appearance of thêta EEG activity >2.5 seconds) during the MWT (MicrSIp; sleep (sec)/ test time (mins)) was compared with the traditional MWT score and with the other measures of sleepiness. Results: Mean MWT sleep latency for the mild OSA patients was 34.7 ±6.9 mins (cf normal mean sleep latency 35.2 ±7.9'). MWT scores were not significantly correlated with PVT10 (r -.29, p = 0.14), ESS (r = - .31, p = 0.16) orVASS (r -.06, p = 0.45). In the subset analysis (n=8) MicrSIp showed expected diurnal variability (max sleep occurring in the 1340 hr test (p=0.002)). MicrSIp was correlated with PVT10 (r .79, p = 0.03) and VASS (r .63, p = 0.04) but not with ESS (p = 0.42). Total MicrSIp was weakly correlated with the MWT score (r -.49, p = .12). Conclusions: MWT results in mild OSA patients were similar to those recorded in normal subjects and correlated only weakly with other measures of daytime sleepiness. Measuring all sleep episodes (MicrSIp) during the MWT may prove to be a more sensitive and accurate measure of impaired vigilance and excessive sleepiness.