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The Maintenance of Wakefulness Test and Driving Simulator Home



The Maintenance of Wakefulness Test and Driving Simulator Performance
Siobhan Banks, PhD1,2; Peter Catcheside, PhD1; Leon C. Lack, PhD1,3; Ron R. Grunstein, MD, PhD4; R. Doug McEvoy, MD1,2

Adelaide Institute for Sleep Health, Repatriation General Hospital – Daw Park, Adelaide; 2School of Medicine and 3School of Psychology, Flinders

University of South Australia, Adelaide; 4Woolcock Institute of Medical Research, Sydney, Australia

    Study Objectives: It has been suggested that the Maintenance of Wake-               inversely correlated with braking reaction time. During the partial sleep
    fulness Test (MWT) may be clinically useful to assess fitness to drive, yet          deprivation and alcohol condition, the number of microsleeps during the
    little is known about the actual relationship between sleep latency and             driving task, steering deviation, braking reaction time, and crashes all
    driving performance. This study examined the ability of 2 MWT trials to             negatively correlated with the MWT1 sleep latency. Additionally, construc-
    predict driving-simulator performance in healthy individuals.                       tion of a receiver-operator characteristic curve revealed that MWT1 sleep
    Design: Experimental                                                                latency in the partial sleep deprivation plus alcohol condition significantly
    Setting: NA.                                                                        discriminated subjects who had a crash from those who did not.
    Patients or Participants: Twenty healthy volunteers (mean age 22.8                  Conclusions: These results indicate that sleep latency on the MWT is
    years; 9 men).                                                                      a reasonable predictor of driving simulator performance in sleepy, alco-
    Interventions: NA.                                                                  hol-impaired, normal subjects. Further research is needed to examine the
    Measurements and Results: The MWT and driving-simulator perfor-                     relationship between daytime MWT results and driving simulator perfor-
    mance were examined under 2 conditions—partial sleep deprivation and                mance in sleepy patients (eg, those with obstructive sleep apnea) and in
    a combination of partial sleep deprivation and alcohol consumption. Each            experimentally sleep-deprived normal subjects.
    subject was studied a week apart, with the order randomly assigned. Sub-            Keywords: MWT, Driving, Sleepiness, Alcohol
    jects completed a nighttime 70-minute AusEd driving simulation task and             Citation: Banks S; Catcheside P; Lack LC et al. The maintenance of
    two 40-minute MWT trials, 1 before (MWT1) and 1 after (MWT2) the driv-              wakefulness test and driving simulator performance SLEEP 2005;28(11):
    ing task. In the sleep-deprived condition, the MWT1 sleep latency was               1381-1385.

INTRODUCTION                                                                            tion with other tests, to assess fitness to drive in patients with
                                                                                        sleep disorders (eg, obstructive sleep apnea) who are considered
WHILE ESTIMATES VARY ACCORDING TO COUNTRY                                               at risk of falling asleep while driving. The MWT has also been
AND METHOD OF POLICE REPORTING,1-3 IT IS THOUGHT                                        recommended to assess the alertness of United States Air Force
THAT APPROXIMATELY 20% OF MOTOR VEHICLE crashes                                         pilots suffering from hypersomnia.7
are caused by sleepiness or fatigue. People with obstructive sleep                         Despite the recent recommendations by regulatory authori-
apnea, a disorder characterized by excessive daytime sleepiness,                        ties and the theoretical attraction of the MWT as a test of driv-
are 2- to 7-fold more likely to have a crash than are healthy driv-                     ing safety, little is known about the actual relationship between
ers.4, 5 One of the most important challenges facing the sleep med-                     MWT sleep latency and driving performance. A small prelimi-
icine community is how to accurately measure individuals’ levels                        nary study examining only 5 patients with obstructive sleep apnea
of sleepiness and accident risk. Currently there is no agreed-upon                      found no relationship between the MWT and driving simulator
test or tests of driving safety for sleepy patients. One test that has                  performance.8 A recent study of drivers who had crashed their
been used both in research and clinical settings and that has sub-                      cars demonstrated that the drivers who crashed had significantly
stantial face validity as a measure of sleepiness is the maintenance                    more sleepiness, slower reaction times, and a trend for shorter
of wakefulness test (MWT). The MWT requires subjects to stay                            MWT sleep latencies compared with control subjects.9 A study
awake while in a soporific environment for several periods over a                       that examined the multiple sleep latency test (MSLT), another
day. It can be readily performed in most clinical sleep laboratories                    objective test of sleepiness, and driving simulator performance
and, in fact, is currently recommended in Australia,6 in conjunc-                       found that, while there was a reasonable relationship between the
                                                                                        2 tests, MSLT sleep latency explained little of the error in the
                                                                                        driving task.10
Disclosure Statement                                                                       Today’s society is very demanding on time, both professional-
This was not an industry supported study. Dr. Grunstein has received re-                ly and socially, resulting in a high prevalence of sleep restriction.
search support from Cephalon, ResMed, Sanofi-Synthelabo, GSK, and Neu-                   The associated impact on the ability to perform complex tasks is
rocrine Pharmaceuticals. Dr. McEvoy has received research support and                   potentially devastating. More investigation is needed to ascertain
equipment from ResMed and Massimo. Drs. Banks, Catcheside, and Lack                     the validity of electroencephalogram (EEG)-based sleep labora-
have indicated no financial conflicts of interest.                                        tory tests of sleepiness to predict driving performance. The aim
                                                                                        of this study was to examine the ability of the MWT sleep latency
Submitted for publication April 2005                                                    to predict driving simulator performance in healthy young indi-
Accepted for publication July 2005
                                                                                        viduals who were sleep restricted with and without the presence
Address correspondence to: Siobhan Banks, PhD, Unit for Experimental
                                                                                        of low-dose alcohol. Results from the same experiment showing
Psychiatry, Division of Sleep and Chronobiology, Department of Psychia-
                                                                                        the effects of sleep restriction and low-dose alcohol on driving
try, University of Pennsylvania School of Medicine, 1013 Blockley Hall, 423
Guardian Drive, Philadelphia, PA, USA 19104-6021; Tel: (215) 898-9665;
                                                                                        performance have been reported previously.11
Fax: (215) 573-6410
SLEEP, Vol. 28, No. 11, 2005                                                     1381                           MWT and Driving Simulator Performance—Banks et al
METHODS                                                                       puter program devised to monitor driving impairment from a
                                                                              number of variables, including position on the road, speed de-
   The relationship between MWT sleep latency and driving                     viation over time, reaction time to a braking task (appearance of
simulator performance was examined under 2 conditions—partial                 trucks), and crashes (driving off the road, stoppage events and
sleep deprivation (PSD) and a combination of PSD and alcohol                  crashing into the back of a truck). Early work suggests that this
consumption (PSD-A). Each subject was studied a week apart,                   test is sensitive to varying degrees of sleep deprivation and sleep-
with the order randomly assigned. The MWT and driving simula-                 iness.11,13-15 Subjects were required to “drive” the AusEd simulator
tor performance were examined under 2 conditions. The research                using a steering wheel and pedals. The view, seen from a front-
and ethics committee at the Repatriation General Hospital - Daw               seat perspective, was of a dual-carriage rural road at night, with
Park, Adelaide approved the study, and all subjects gave written              the usual lane divisions and the road edges marked by reflective
informed consent.                                                             posts. A speedometer was displayed in the top left corner of the
                                                                              computer screen. Subjects were asked to maintain their position
Participants                                                                  in the left-hand lane on the road (in accordance with Australian
   Advertisements were posted at the Flinders University of South             driving code), to maintain speed within 60 to 80 kilometers per
Australia campus. Young adults were recruited for this study due              hour, and to react by braking firmly and as quickly as possible to
to the high number of 18- to 30-year olds who have sleep-related              any trucks that appeared ahead in the driving lane. The simulator
car accidents in the early hours of the morning. Subjects were                was programmed to present 4 trucks at approximately 10-minute
excluded if they had a history of sleep disorders (eg, self-reported          intervals during the 70-minute task.
snoring or difficulty sleeping), were taking any medication or had
a history of motion sickness. All subjects received an honorarium             Experimental Conditions
of $100.                                                                         The subjects were required to keep a detailed diary of their
                                                                              sleep habits and to wear an activity monitor (Gaehwiler Electronic,
Familiarization Session                                                       Hombrechtikon, Switzerland), which measured their sleep-wake
   During the first visit to the laboratory, which occurred in the            activity for 1 week prior to the experimental conditions. This was
daytime, subjects were introduced to the testing equipment and                done to verify that the subjects had regular sleep habits in the
driving simulator. Subjects underwent three 10-minute practice                week prior to testing, followed the sleep-deprivation protocols,
sessions on the driving simulator and were randomly assigned                  and did not nap during the day of testing. Subjects participated
to condition order. After three 10-minute sessions, the driving               in the 2 experimental conditions in a repeated-measures design,
simulator performance learning effect had become asymptotic                   attending the laboratory twice with a week separating each visit.
(defined as less than a 10% change in performance between the                 In the PSD condition subjects were restricted to 5 hours time in
practice trials). The subjects then completed the Epworth Sleepi-             bed on the night prior to testing (1 AM -6 AM). They were required
ness Scale.12 The subjects took home an activity monitor and a                to telephone a time- and date-stamped answering machine before
sleep diary to be completed in the week prior to testing. Subjects            going to bed and after rising in the morning to ensure compli-
were not required to obtain a specific amount of sleep during the             ance.
testing period (except on the PSD night). They were instructed to                In the PSD-A condition, subjects were required to restrict sleep
keep to their normal sleep-wake pattern.                                      according to the protocol above and to consume alcohol prior to
                                                                              the driving task to produce a blood alcohol concentration (BAC)
Maintenance of Wakefulness Test                                               of approximately 0.04 g/dL, which is just below the legal BAC
                                                                              limit for driving in Australia, 0.05g/dL. To achieve this, subjects
   All MWT trials were performed in a similar setting using a                 consumed 1 mL of 50% alcohol per kg of body weight (in a car-
simplified recording montage (C3/A2, O1/A2, electromyogram,                   bonated, noncaffeinated beverage) at 10:30 PM. At 12:15 AM, they
and electrooculogram). The testing room was sound attenuated,                 consumed another drink with 0.5 mL of 50% alcohol per kg of
insulated from external light, and equipped with dimmer lights                body weight. Blood alcohol levels were estimated immediately
overhead. Ambient temperature in the room was approximately                   before and after the MWT trials and driving test using a calibrated
22oC. Bedroom doors were closed, and all monitoring was per-                  Breathalyzer (Dräger, Alcotest 7410Plus Lübeck, Germany) accu-
formed external to the bedroom to keep noise to a minimum.                    rate to 0.005 g/dL. Subjects were not blinded to alcohol presen-
During each MWT trial, subjects sat semiupright (10o to 30o back              tation, as our aim in this study was to test the subjects in a real-
from vertical) in a comfortable lounge chair that had a high back             world common situation in which the subjects would be aware of
to support the head and neck. Prior to each trial, subjects were              alcohol consumption.
instructed to “keep your eyes open and try not to fall asleep.”
Subjects were asked not to use any extraordinary mental or physi-             Experimental Procedure
cal measures (eg face slapping to avoid sleep). The recordings
were then started, and the lights dimmed to an illumination of 1                 Subjects arrived at the laboratory at 9:00 PM. Their BAC was
lux. Each trial was terminated at the first occurrence of sustained           ascertained with the Breathalyzer, a urine sample was taken to
sleep (3 consecutive 30-second epochs of stage 1 sleep or 1 epoch             test for habitual drugs of abuse (eg, opioids, cannabinoids, and
of any other stage) or after 40 minutes if there was no sleep.                amphetamine—all tested negative), and activity monitors were
                                                                              downloaded to ensure that the subjects had complied with the
AusEd Driving Simulator                                                       study protocol requirements. The subjects’ timepieces were re-
                                                                              moved so that they had no external time cues. Standard surface
  The AusEd driving simulation task used in this study is a com-              electrodes were applied for monitoring: EEG (C3/A2, C4/A1),
SLEEP, Vol. 28, No. 11, 2005                                           1382                        MWT and Driving Simulator Performance—Banks et al
submental electromyogram, left and right eye movements, and                  did not. A ROC curve is a plot of the true positive rate against
electrocardiogram. All parameters were recorded using the Sleep-             the false positive rate for all possible cut points of a diagnostic
watch (Compumedics, Melbourne, Australia) data-acquisition                   test. An area of 0.84 under the curve, for example, means that a
system. Subjects then completed the Stanford Sleepiness Scale.16             randomly selected individual from the positive group has a test
Subjects were allowed a short practice run on the driving simu-              value larger than that of a randomly chosen individual from the
lator and given a standardized snack (150 calories; dry biscuits             negative group 84% of the time. The closer the curve follows the
and cheese) and alcohol or an equivalent volume of the carbon-               left-hand and the top border of ROC curve space, the more ac-
ated noncaffeinated beverage at 10:30 PM and at 12:15 AM. The                curate the test. The closer the curve is to the 45-degree diagonal
protocol of this study had to allow for the consumption of alco-             of ROC curve space, the less accurate the test. The area under a
hol (10 minutes to consume and 30 minutes to stabilize for BAC               ROC curve therefore provides a measure of the performance of
readings) and other tests (eg, the Psychomotor Vigilance Task, the           the test, in this case the utility of MWT sleep latency to predict
results of which have been reported previously).17                           driving simulator crashes. Mann-Whitney U tests were used to
   The first MWT (MWT1) commenced at 11:30 PM. Subjects                      determine if the area under the ROC curves differed from 0.5 (ie,
started the 70-minute driving simulation at 1:00 AM and were                 a test that discriminates no better than pure chance).
prompted every 4.5 minutes during the driving task to answer
simple questions about their perception of level of driving perfor-          RESULTS
mance and crash risk (results reported elsewhere).11 Subjects were
                                                                                Twenty healthy subjects (11 women, mean age 21.9±2.2; 9
told that the probes would sound at random intervals. The driving
                                                                             men, mean age 23.8±4.8) participated. All subjects had normal
task took place in a private, semidark (10 lux), and sound-attenu-
                                                                             body mass index (23.3±3.1). All participants were university stu-
ated room. The second MWT (MWT2) commenced at 02:15 AM.
                                                                             dents, who consumed 2 or fewer servings of caffeine (2 small
The experiment concluded at approximately 3 AM, and subjects
                                                                             cups of regular coffee or tea, 2 chocolate bars [50 grams each],
were driven home by taxi cab.
                                                                             2 cans of cola, etc) per week and 6 or fewer standard alcoholic
DATA ANALYSIS                                                                beverages a week (eg weekend social drinkers). In addition, all
                                                                             subjects had current driver’s licenses, and all were experienced
Maintenance of Wakefulness Test                                              at computer game controls and formats. The mean Epworth
                                                                             Sleepiness Scale score at familiarization for the whole group was
   Sleep latency was defined as the first appearance of 3 epochs of          6.4±3.9. All subjects had a regular sleep-wake cycle in the week
stage 1 sleep or 1 epoch of any other sleep stage. Subjects with no          prior to testing, with activity-monitor data showing subjects were
sleep onset were assigned a value of 40 minutes. Both the individ-           inactive for an average of 411±37 minutes per night. They sub-
ual trial sleep latencies and the mean sleep latency were recorded           jectively reported (sleep diary kept for 7 days) that they obtained
for each condition.                                                          an average of 423.6±45.8 minutes of sleep per night. No subjects
                                                                             were excluded on the basis of the amount of sleep obtained in the
AusEd Driving Simulator                                                      week before testing. All subjects had zero BAC and a negative
   This study examined mean steering deviation (subject’s me-                urine drug test on arrival at the laboratory on experimental nights.
dian position on the road, excluding crashes), reaction time (in             Data from the activity monitors showed that subjects complied
response to trucks on the road ahead), and number of driving sim-            with the sleep-restriction protocol. They were inactive for 270±20
ulator crashes (off-road, truck collision, or stoppage events). The          minutes on the night before testing. Subjects rated themselves as
mean number of crashes was determined for each 4.5-minute bin                moderately sleepy according to the Stanford Sleepiness Scale on
and for the whole task.                                                      both experimental nights (PSD mean 4.0±1.2 and PSD-A mean
EEG Microsleep Analysis                                                         MWT mean sleep latency was significantly lower at the 2:15
                                                                             am trial than at 11:30 PM trial in both the experimental conditions
   The EEG (C3-A2) during the driving simulation task was as-                (P<.001). There was a trend for a reduction in the mean sleep
sessed for the appearance of microsleeps. A microsleep was de-               latency with the consumption of alcohol, but the difference was
fined as a burst of EEG theta activity greater than 3 seconds in             not statistically significant (P=.07; See Table 1). Forty percent
duration.18,19 The cumulative theta time (seconds) was determined            and 80% of subjects achieved sleep onset in the PSD and PSD-A
for each subject.                                                            conditions, respectively.
                                                                                The subjects’ mean BACs on the alcohol night at the start and
Correlations                                                                 end of the 70-minutes driving simulation were 0.037±0.011g/dL
   Pearson correlations were conducted between the driving sim-              and 0.021±0.009g/dL. Before and after MWT1, subjects’ mean
ulator parameters (mean steering deviation, reaction time, and
crashes), mean cumulative microsleep, and MWT sleep latency                   Table 1—Sleep Latency on the Maintenance of Wakefulness Test
for both conditions.
                                                                                    Sleep Deprivation        Sleep Deprivation and Alcohol
                                                                              MWT1       MWT2       Mean     MWT1      MWT2        Mean
ROC Curve Analysis                                                            31.7±11.9 25.2±16.2 28.9±13.2 25.4±16.1 19.3±14.6 22.3±14.8
   Receiver operating characteristic (ROC) curves were con-
                                                                              Sleep latency is presented in minutes, mean + SD; Maintenance of
structed to assess the ability of MWT to distinguish those sub-
                                                                              Wakefulness Test 1 (MWT1) occurred at 11:30 PM and MWT2 oc-
jects who had a crash during the simulation task from those who               curred at 2:15 AM.

SLEEP, Vol. 28, No. 11, 2005                                          1383                        MWT and Driving Simulator Performance—Banks et al
 Table 2—Correlations Between Driving Simulator Parameters and
                                                                                                  Area under
 Sleep Latency on the Maintenance of Wakefulness Test                                             curve= 0.81
                          Sleep Deprivation    Sleep Deprivation
                                                   and Alcohol
                        MWT1     MWT2         MWT1        MWT2

                                                                               (True +ve rate)
 Microsleeps             -0.02     0.00        -0.45*      -0.43

 Reaction time          -0.52*    -0.47        -0.51*      -0.15
 Mean steering deviation -0.24    -0.27       -0.59**      -0.25
 Number of crashes       -0.19    -0.14        -0.54*      -0.27
 Maintenance of Wakefulness Test 1 (MWT1) occurred at 11:30     PM
 and (MWT2) occurred at 2:15 AM.
BACs were 0.031±0.01g/dL and 0.026±0.012g/dL, and, before
and after MWT2, subjects’ mean BACs were 0.021±0.009g/dL                                                               1-Specificity
and 0.012±0.008g/dL.                                                                                                 (False +ve rate)
   In the PSD condition only driving simulator reaction time to                     Figure 1—The true positive rate (short Maintenance of Wakefulness
the appearance of trucks correlated with MWT1 (see Table 2).                        Test [MWT] sleep latency and presence of a driving simulator crash)
In the combined PSD-A condition, however, the driving simu-                         versus false positive rate (short MWT sleep latency without subjects
lator parameters and the duration of microsleeps correlated with                    having crashed) of the MWT directly before the driving task during
MWT sleep latency but only at the 11:30 PM trial, with the MWT1                     the combined sleep restriction and alcohol condition.
explaining between 20% to 35% of the variance of the driving                   but the difference was not statistically significant, consistent with
simulator parameters (see Table 2).                                            increased variance in sleep-latency after alcohol consumption.
   A ROC curve (see figure 1) revealed that the MWT trial di-                  We postulate that increased variance in subjects’ sleepiness after
rectly before the driving task in the PSD-A condition was able to              alcohol consumption allowed the relationship between MWT and
discriminate between subjects who crashed and those who did not                driving simulator performance to become evident. The increased
(Mann-Whitney U test, P=.006). The area under the curve was                    variance in sleepiness after alcohol consumption was most like-
0.81±0.10. Neither the MWT before or after the driving task in                 ly due to more subjects falling asleep and less truncation of the
the PSD condition (P=.22 and P=.32, respectively) nor the MWT                  sample to 40 minutes. This relationship needs further examina-
after the driving task in the PSD-A condition (P=.23) significantly            tion in patient populations (eg, those with obstructive sleep apnea
discriminated between the 2 conditions (crash, no-crash).                      and narcolepsy) who have existing trait sleepiness rather than ex-
                                                                               perimentally induced sleepiness in normal subjects with alcohol.
DISCUSSION                                                                     Alcohol may have also affected MWT sleep latency by reduc-
                                                                               ing subject compliance and motivation to follow instructions and
   This study found that MWT1 correlated with reaction time in
                                                                               remain vigilant. There is some literature to suggest that alcohol
both conditions, with a slightly greater magnitude of relationship
                                                                               reduces subjects’ general motivation to perform.21
in the PSD-A condition. Other parameters such as microsleeps,
                                                                                  The MWT and driving simulator reaction-time results corre-
steering deviation, and crashes, only correlated with MWT1 in
                                                                               lated well in both conditions, with MWT sleep latency accounting
the PSD-A condition. The MWT was found to explain a fifth to a
                                                                               for just under one third of the variance in reaction time. Reaction
third of the variance in the driving-performance measures in the
                                                                               time has been found to be very sensitive to sleep loss and alcohol
PSD-A condition when the subjects were more sleepy and im-
                                                                               consumption20,22 and is recognized as a good measure of perfor-
paired due to the alcohol consumption. The MWT trial prior to the
                                                                               mance.23-29 Reaction time is a vital component of driving perfor-
driving task in the PSD-A condition was able to discern subjects
                                                                               mance. The correlation between MWT sleep latency and reaction
who had a crash during the driving task from those who did not.
                                                                               time increases the validity of the MWT as an indicator of driving
These results suggest that there is validity in using the MWT to
predict driving performance.
                                                                                  A limitation of this study was that polysomnography was not
   The subjects’ BACs during the first MWT on the PSD-A night
                                                                               conducted in the subjects to completely rule out the presence of a
were close to those during the driving task (0.031±0.010g/dL be-
                                                                               sleep disorder. However, every effort was made to ensure that the
fore MWT1 and 0.037±0.011g/dL before the driving simulation
                                                                               results of all screening tools used (eg, the Pittsburg Sleep Qual-
task). However, during the second MWT, the average BACs were
                                                                               ity Inventory and Epworth Sleepiness Scale) were within normal
much lower (0.021±0.009g/dL before MWT2). The higher BACs
                                                                               limits. Additionally, the subjects were young, had normal body
likely contributed to the increased degree of relationship between
                                                                               mass indexes, and wore actigraphy for several weeks, confirming
the first MWT and the subjects’ performance during the driving
                                                                               that all subjects had normal sleep-wake times. It remains pos-
simulation task.
                                                                               sible, however, that a subject may have had a sleep disorder that
   The consumption of alcohol was an important factor in this
                                                                               effected their MWT results and driving simulation performance.
study. Low doses of alcohol have been found to increase sleepi-
                                                                                  In conclusion, these results indicate that MWT sleep latency
ness and performance impairment in the already sleep-restricted
                                                                               is a reasonable predictor of driving simulator performance in
individual.11,20 In the current study, there was a trend for a reduc-
                                                                               sleepy, alcohol-impaired, normal subjects. This study represents
tion in the mean sleep latency with the consumption of alcohol,
                                                                               a first step in examining the relationship between MWT and driv-

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SLEEP, Vol. 28, No. 11, 2005                                                  1385                         MWT and Driving Simulator Performance—Banks et al

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