The 20-min trial of the Maintenance of Wakefulness Test is profoundly affected by motivation.

摘要

Assessment of the ability to maintain wakefulness, although very important both for research and for clinical purposes, is still equivocal. The current gold standard is considered the Maintenance of Wakefulness Test (MWT), although there are two different potential protocols to perform it and the normal reference range has been determined on selected populations. The effect of potential "penalty" on failing the test (i.e., presenting sleepiness) has not been seriously studied. We therefore planned this study to examine the effect of motivation on the MWT results in a potentially sleepy population. We hypothesized that with the knowledge that participants may lose their driving license if they fail the test, the results would indicate significantly less sleepiness than reported for other populations. Fifty-four consecutive subjects at high risk of sleepiness referred to the sleep laboratory for evaluation of their ability to maintain wakefulness were studied. All were referred by the National Council for Driving Safety, knowing that if they failed the test, their driving license would not be renewed. Referral reasons were previously diagnosed: obstructive sleep apnea (OSA; 43%), sleep-related accident (7%), or other causes to suspect sleepiness. All underwent a full-night polysomnography (PSG) followed by MWT, five trials of 20 min each (MWT20). Of the 54 participants, 13 were treated for OSA and 28 had untreated OSA, 21 of them had severe OSA (Respiratory Disturbance Index >30/h). Seventy-four percent of the participants had a BMI >30 kg/m(2). Only 5 of the participants fell asleep in any of the MWT trials (one to five trials), which could not be predicted by severity of OSA, age, BMI, or variables derived from the previous night PSG. Of the 21 patients with severe untreated OSA, only 1 patient fell asleep during the MWT20. We conclude that motivation profoundly affects the MWT results, raising the question what should be considered normal or abnormal when sleepy results may cause penalty or other practical implications. In addition, we believe that these results suggest that for renewal of driving license purposes, the MWT20 is insufficient. We speculate that MWT40, with tighter cutoff threshold, would be a more effective tool.