Forty- Versus 20-Minute Trials of the Maintenance of Wakefulness Test Regimen for Licensing of Drivers

Prevention of motor vehicle crashes is a challenge for authorities worldwide. Many motor vehicle crashes, in particular fatal ones, are caused by drivers who suffer from excessive daytime sleepiness (EDS) and fall asleep while driving. EDS may result from various sleep disorders, such as obstructive sleep apnea (OSA), insomnia, jet lag, sleep deprivation, narcolepsy, and others. EDS impairs the individual’s daytime performance and may lead to motor vehicle crashes and work-related accidents.1–5 A case-control study by Teran-Santos et al6 of groups of drivers who were involved in motor vehicle crashes, determined that drivers who suffer from OSA (more than 10 apneas or hypopneas per hour of sleep) have a higher likelihood of being involved in motor vehicle crashes. Treatment of OSA with continuous positive airway pressure) can reduce the likelihood of these crashes.7–9 Therefore, diagnosing OSA and treating these patients is an important public health issue. It is difficult to objectively and accurately assess daytime sleepiness and maintenance of wakefulness.10,11 Although the quality of sleep and the severity of sleep disorders can be objectively quantified, there is no clear correlation between any of these variables and the degree of daytime sleepiness, as assessed by the currently available tests.12–15 These tests consist of subjective questionnaires such as the Epworth Sleepiness Scale (ESS)16–18 and objective methods such as Multiple Sleep Latency Test (MSLT),19,20 the Maintenance of Wakefulness Test (MWT),19,21 and the more recently introduced Psychomotor Vigilance Test.22,23 During the MSLT, the patient is instructed to try to fall asleep during five 20-minute daytime trials. During the MWT, the subject is instructed to stay awake in soporific circumstances during four 20- or 40-minute trials. Thus, the MSLT quantifies the drive to sleep whereas the MWT evaluates the ability to maintain wakefulness. It is quite common for people who fall asleep during the MSLT to manage to maintain wakefulness during the MWT.24 Hence, logically, the MWT is the preferred test for examining the ability of drivers to remain alert, in cases of suspected EDS.25–28 The diagnostic criteria for the MWT were determined in 1997 by Doghramji et al.29 In research conducted on 64 healthy subjects, a score of less than 2 standard deviations from the average was considered diagnostic of a severe problem in the ability to maintain wakefulness. The threshold value for the MWT20 protocol was lower than 10.9 minutes and, for the MWT40, was lower than 19.4 minutes. In a similar trial by Banks et al,30 the threshold value for the MWT40 was 26.1 minutes. However, these tests were performed in experimental settings with no potential real-life factors that may affect the results.31,32 The clinical use of the MSLT and MWT have recently been thoroughly reviewed by Arand et al.19 Among other conclusions, they suggest that the MWT is affected by many factors besides daytime sleepiness and that it doesn’t discriminate well between normal populations and patients with sleep disorders.19 In a recent study from our lab, we reported that, under conditions of high motivation (i.e., when failing the MWT may lead to losing one’s license to drive), only 5 out of 54 potentially sleepy drivers fell asleep in any of the 5 trials of the MWT20.33 The calculated average MWT scores were higher than in any of the previously published papers. Some of the patients in that study had severe untreated OSA, and others had been involved in a previous sleep-related crash. From the subgroup of 32 subjects with severe untreated OSA, only 1 fell asleep. We, therefore, concluded that motivation had a significant effect on the MWT20 and that the test is not reliable in the evaluation of sleepiness in highly motivated subjects. Thus, in the current study, we sought to assess whether the MWT40 regimen is a more reliable tool to quantify difficulties maintaining wakefulness in a motivated population. A study by Bonnet et al34 reported that financial reward could not motivate 12 healthy volunteers to increase their sleep latency during the MWT40 protocol, suggesting that the ability to stay awake during the MWT40 is less likely to be affected by motivation and is a better measure of alertness than the MSLT. In the current study, we utilized a different motivator (the threat of losing a license to drive) and sought to compare the MWT40 (tested on a new dataset of patients) with the MWT20 regimen (using previously reported data), in a population of potentially sleepy patients.