Comparison of the Oxford sleep resistance test and the multiple sleep latency test.

OBJECTIVE The Oxford Sleep Resistance Test (OSLER) consists of four tests over 40 minutes conducted in a dark and quiet room. If a dim light flashes the patient has to briefly depress a button and then press it again immediately which indicates that the patient resists sleep. The Multiple Wakefullness test (MWT) is another test to assess the ability to maintain wakefulness. Previous studies found a good correlation between the sleep latencies measured with the Osler and the MWT. The most widely used Multiple Sleep Latency Test (MSLT) measures the propensity to fall asleep and not the inability to stay awake. Up to date there are no studies comparing the Osler and the MSLT, which is the aim of the study presented here. APPROACH After a night of polysomnography we investigated the sleep latencies the following day with the Osler and the MSLT in 43 patients suffering from moderate or severe obstructive sleep apnea (OSA) (33 men and 10 women; median age 59 years; median apnea hypopnea index 30.5 per hour sleep). We analysed the correlation between these two tests and between values in the Epworth Sleepiness Scale (ESS) and the Karolinska Sleepiness Scale (KSS) and these two tests. MAIN RESULTS We did not find a correlation between the Osler and the MSLT nor between these two tests and the questionnaires (ESS, KSS). The only significant correlation was found between the mean MSLT latency and the sleep onset latency in the polysomnography the night before. Seven patients stayed awake during the Osler and showed a decreased mean sleep latency in the MSLT. SIGNIFICANCE The Osler, the MSLT and the questionnaires are measuring different objective and subjective aspects of sleepiness. In untreated OSA patients an increased propensity to fall asleep was not automatically associated with the inability to stay awake.