Forty- versus 20-minute trials of the maintenance of wakefulness test regimen for licensing of drivers.

Study Objectives: Objective assessment of the ability to maintain wakefulness, although very important, is still equivocal. A recent study from our lab has shown that the Maintenance of Wakefulness Test (MWT), when performed with the 20-minute protocol (MWT20), is unreliable in assessing patients who are highly motivated to maintain wakefulness. In this study, we sought to examine whether the 40-minute protocol (MWT40) is a better tool in assessing such individuals.

Methods: One hundred sixty-four consecutive subjects referred to our sleep lab by the Medical Institute for Driving Safety were studied. All subjects underwent a full-night polysomnogram followed by an MWT, 4 trials of 40 minutes each. All subjects knew that if they failed the wakefulness test their driving license would be revoked.

Results: Forty-one subjects out of 164 (25%) fell asleep at least once. Of 39 subjects with severe obstructive sleep apnea, (respiratory disturbance index > 40/h), 19 fell asleep (48.7%). Of 13 subjects with a minimum oxygen saturation level below 65%, 7 fell asleep (53%). In the MWT20, only 7% of patients with severe obstructive sleep apnea fell asleep at least once.

Conclusions: We conclude that the MWT40 is superior to the MWT20 in detecting difficulties maintaining wakefulness in a highly motivated population. However, our results yield a significantly lower detection of difficulties maintaining wakefulness than those reported in healthy subjects, suggesting that the MWT40 is also highly affected by motivation. We believe that, for a highly motivated population (such as for a driver's license validation), different average sleep-latency threshold should be used than in general population.