Chest
Volume 101, Issue 4, April 1992, Pages 893-897
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Clinical Investigations
Maintenance of Wakefulness Test in Obstructive Sleep Apnea Syndrome

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The usefulness of a 40-min per trial version of the maintenance of wakefulness test was assessed in 322 patients with obstructive sleep apnea. This test is a variant of the multiple sleep latency test in which patients are asked to remain awake in a quiet darkened room, and then monitored for electroencephalographic sleep onset. The four trials of the test are each stopped after 40 min. The mean sleep latency for all patients was 26.0 ± 11.8 (SD) min. In a group of 24 patients who underwent treatment with nasal continuous positive airway pressure, the mean sleep latency increased from 18.0±12.3 to 31.9±10.4. The strongest nocturnal correlates of the MWT sleep latency were respiratory arousal index (r= — .35), mean oxygen saturation (r = .30), and weight/height ratio (r = — .25). These correlations were comparable to other studies using the MSLT. There were strong intercorrelations among the variables. In the more severe groups, measures of hypoxemia were more strongly correlated with MWT sleep latency. A two-factor analysis of variance using respiratory arousal index and several measures of oxyhemoglobin saturation indicated that both arousals from sleep and degree of hypoxemia contribute interactively to daytime dysfunction in patients with sleep apnea. The MWT appears useful in evaluating disability from daytime sleepiness.

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METHODS

A total of 322 consecutive obstructive sleep apnea patients were administered the MWT. We excluded from our series all patients who were in frank organ failure such as uncompensated congestive heart failure or chronic obstructive airways disease. Furthermore, we always attempted to evaluate patients after their systems were cleared of medications known to affect the central nervous system, in general, or sleep in particular. However, withdrawal of such drugs was not always possible due to the

RESULTS

Characteristics of the sleep apnea patients are shown in Table 1. Figure 1 shows the means and standard errors of the four MWT trials. The four-trial average MWT sleep latency was 26.0 min ±11.8 (SD).

Individual correlations between clinical data and MWT sleep latency are shown in Table 2. Note that respiratory events and subsequent arousals are the most highly correlated factors. Figure 2 shows the progressively lower MWT sleep latencies as the RAI increases. Many of the parameters, in

DISCUSSION

We have summarized our experiences with the MWT in obstructive sleep apnea. In clinically interpreting this test, mean sleep latencies above 33 appear to be normal in patients with no clinical sleep disorders. However, we have studied only a small number of control subjects at this time.9

The range of daytime alertness is quite broad at all levels of sleep apnea. We observed patients with normal MWTs whose RAI was in the 40 to 60 range, and some MWTs were markedly abnormal (less than 20 min) in

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    Quantification of several types of EEG contamination may be important for evaluation of human subjects in different clinical conditions, and research studies. As an example, we can use this quantification to accompany routine Maintenance of Wakefulness Test (MWT) that is used clinically in disorders connected with excessive somnolence such as narcolepsy and sleep apnea syndrome [25,26]. MWT has also been used to examine treatment efficacy [26,27], by performing multiple tests and comparing results over a period of time, to determine if treatment is helping a patient to overcome sleepiness.

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Supported by PHS grants. R01 NS20459 and R03 AA08235 to Dr. Mitler, by Clinical Research Center grant RR00833 to Scripps Clinic and Research Foundation, by a grant from the American Narcolepsy Association, and by a grant from Seoul National University to Dr. Jeong (Teuk-jin-yeon-gu-bi, 1991). This is publication number 6549-NP from the Research Institute of Scripps Clinic.

Manuscript received May 17; revision accepted July 24.

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