Forty versus twenty minutes trials maintenance of wakefulness test regimen for driving licensing

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, 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 and sixty four consecutive subjects referred to our sleep lab by the Medical Institute for Driving Safety were studied. All subjects underwent a full night polysomnography (PSG) 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 OSA (RDI>40/h), 19 fell asleep (48.7%). Of 13 subjects with minimal oxygen saturation level below 65%, 7 fell asleep (53%). In the MWT20, only 7% of patients with severe OSA 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 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 driving license validation), different average sleep latency threshold should be used than in general population.