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Estimates range from 1% to 56% as to the role of fatigue in the motor vehicle accidents which injure 110,000 and kill 5,000 people each year in the United States.This has attracted increasing concern from public health and regulatory authorities. One such authority recently judged fatigue to be the number one problem in commercial transportation. In 1988, Congress directed the Federal Highway Administration to study driver fatigue in commercial truckers; this paper reports data from that study, collected in 1993.
In both the U.S. and Canada, the longest daily time on duty allowed for truckers is 15 hours, the shortest off-duty time is 8 hours, and the longest weekly duty time is 60 hours. But drivers can drive continuously only so long without having 8 hours off: 10 hours in the U.S. and 13 hours in Canada. The study compared truckers under four driving schedules, two types of 10-hour shifts in the U.S. and two types of 13-hour shifts in Canada, one type represented either by a schedule starting at the same time each day or evening, and the other changing departure times by 1-3 hours on each successive day.
Subjects were 80 licensed commercial drivers, 40 in each country and 20 on each schedule. Data were collected during the summer in the U.S. and fall/early winter in Canada. On a preliminary questionnaire, drivers indicated that they needed an average of 7.2 hours (SD=+/-1.2) sleepeach night to be alert the next day.
While driving, subjects were monitored for their or electroencephalograms (EEG) and eye movements or electrooculograms (EOG), while an infrared video recording system kept a record of the driver's face (looking for signs of drowsiness like drooping eyelids and bobbing head) as well as the raod ahead, and a computer recorded the truck's speed and road position.
Drivers slept at times of their own choice in rooms near their travel routes, where sleep polysomnography was conducted on site, including all the usual measures except for plethysmography (measurement of respiratory movements of the chest and abdomen).
Drivers averaged 43 years of age (SD=+/-10) and 28.9 in Body Mass Index (SD=+/-5). During the study, they compiled a total of 400 principal sleep periods, 200 10-hour trips, and 160 13-hour trips. There were 33 intervals between trips (13%) when drivers had less than 8 hours off duty (average=7.4 hrs). Despite the length of time off, the average time spent in bed during principal sleep periods was only 5.2 hrs, slightly longer for younger driver (5.3 hrs) than for older drivers (5.0 hrs). U.S. drivers travelled between St. Louise and Kansas City, Missouri; Canadian drivers betwen Toronto and Montreal. Sleep latency (time taken from going to bed to falling asleep) varied significantly between drivers on different schedules: 19 minutes for drivers on the steady 10-hr day schedule (U.S.), 7 minutes for drivers on a steady (13-hr) night schedule, 15 minutes for drivers on a progressively later (13-hr) evening schedule, and 13 minutes for drivers on a progressively earlier (10-hr) day schedule. Thus, the drivers on the 10-hr regular day schedule seemed the least sleepy, the drivers on the 13-hr regular night schedule the most sleepy.
Drivers slept an average of 4.8 hours, two hours less than they reported needing for optimal alertness. The steady day schedule yielded the longest average duration of sleep (5.4 hours) and the steady night schedule the least (3.8 hours). The younger drivers slept a little more (4.9 hours) than the older drivers (4.6 hours). Sleep efficiency was over 90% for all schedules and number of awakenings indicated sleep was well consolidated.
Drivers took 0 to 3 naps per day, 35 of the 80 drivers taking at least one nap a day. Naps increased the total sleep time per day by an average of 0.45 hours (SD=+/-.31 hours, range=0-1.63 hours). Neither age nor schedule predicted the number of naps.
In two drivers, ages 49 and 55, both on the steady day schedule, pulse oximetry showed repeated desaturations and polysomnography confirmed they had sleep apnea, with 10-30 respiratory events per hour, but otherwise their sleep data did not differ from other drivers.
Monitoring during actual driving revealed two younger drivers at speeds above 45 mph had episodes of drowsiness qualifying as stage 1 sleep. One had five such episodes (over a period of 41 minutes), from 20 secs to 8.7 minutes in duration; the other had two such episodesof 60 and 80 seconds duration at intervals spaced two hours apart. All occurrences of sleep while driving took place between 11 p.m. and 5 a.m.
Of 29,310 six-minute video recordings analyzed, 7% showed the driver to be drowsy. This involved 45 of of the drivers (i.e., 56% on at least one occasion), but the majority of the drowsy segments (1067 or 54%) involved just 8 drivers, five on the steady night schedule. Most (83%) of the drowsy spells occurred between 7 p.m. and 7 a.m.
Night driving was associated with more fatigue, especially night driving after relatively little sleep. The short time periods spent in bed, a matter of driver choice, were disturbing, since they resulted in inadequate sleep. The high sleep efficiency, the short latency to sleep in some drivers, the daytime napping, and the episodes of drowsiness and outright sleep while driving all point to the inadequacy of the sleep obtained by these drivers. In this study, there were insufficient miles driven to expect an accident on a statistical basis, and none occurred.It was presumed that the light stage 1 sleep observed while driving represented a state of partial consciousness of the environment.
Fellow sleep apneics like myself may at first reading feel surprised that there were only two apneics discovered among 80 drivers, a prevalence rate (2.5%) lower than the much-disputed range of 4-10% for men in the general popuation. It would be nice to think that there is some selection bias going on here. That is, one would hope that drivers with diagnosed sleep apnea, or drivers who know themselves to be excessively sleepy, would find other work, such as local runs. Other, less happy alternatives would be that (1) drivers with severe sleep apnea and excess sleepiness are not working because they have been either injured or killed in accidents already; or (2) drivers who know themselves to have such problems would selectively refuse to take part in a study which would highlight a job-threatening condition they were trying to keep secret.
What do you make of the fact that the two previously undiagnosed, untreated sleep apneics didn't stand out from the other truckers as to the various measures of sleepiness on the job? The authors, whose primary interest isn't sleep apnea, don't address the question at all, but I think anyone can make a good guess: all the drivers were severely sleep-deprivedon a chronic basis by reason of what is often termed "voluntary sleep restriction,"so it would be unlikely for them to function much better than sleep apneics with mild to moderate disorder. It bears some thinking about when we consider those of us, not truck but car drivers, who voluntarily restrict sleep in order to stay up late doing work around the house, watching TV, going out, studying, etc., despite having to get up early the next day for work or school or other obligations. It is a truism that none of us has enough time for all the things in our lives--even a disabled, unemployed sleep apneic like myself. We therefore try to "steal" the time from our sleep, but the physiological accountant who checks the books of our sleep time neither errs nor has mercy.
This is one point where I think we sleep apneics need to pay attention. Our apneas and hypopneas may be adequately suppressed by CPAP, our periodic leg movements of sleep by medications, our arousals may have ceased, but we may continue symptomatic for excessive sleepiness for the very reason that most people are--not allowing ourselves enough time for sleep.
To use myself as an example once again, I have no job to wake up for, but I have made it a habit to get up a little before my wife, whose work starts at 7:45 a.m., in order to make her coffee, breakfast in bed, and lunch, then drive her to work. In the evening, we repeatedly tell each other that we will go to bed earlier than our usual 12 midnight, but things keep coming up--things we finally get to talk about in bed, projects we get started on too late in the evening and want to finish rather than stop in the middle, etc.--which delay our bedtime or at least our sleep time just about every night. Therefore I suppose I get an average of 6 hours of sleep each night, far less than the 9 hours I guess I need.
How do I deal with this? Sometimes, after taking my wife to work, I go right back to bed for another couple of hours, catching up on a lot of my missed sleep. But that means the three dogs' lengthy morning walk is delayed and I may wake up to a nasty surprise on the floor. It is also impossible if I have morning appointments. Or it may be impossible once I have had my usual 2 or 3 giant cups of coffee and morning medication. Anyway, almost always I will take another nap around noon for an hour or two, which you would think to be enough total sleep time. But my wife comes home late in the afternoon exhausted and I often join her in bed, partly to encourage her to get the extra rest she needs, and fall asleep myself for another hour, probably one reason neither of us feel like going to bed for the night "earlier" as we keep promising ourselves. In other words, much of my current daytime sleeping may be explainable on the basis of habits derived from environmental factors (quite unlike the case when I was living alone, free to sleep and wake when I wanted, and still sleeping on the floor under my office desk at work). So, do I still have apneic excessive drowsiness, or not? It is hard for me to tell, except that every now and then I spent most of an entire day or two in bed.
Yet even that may be a phenomenon learned long ago from the days of my severest sleep apnea, when I learned that the easiest, cheapest way to escape stress, worry, disappointment, and so on was to go to bed. It isn't as dangerous as alcohol or drugs, as expensive as vacations, as fattening as sweets--and so on! Sleep--the ideal defense against the world's woes? But carry it too far, and it becomes something like coma, waking for only a half hour or an hour at a time to go to the bathroom before retiring again. It can remove you from real life almost as effectively as death.
To conclude with a return from my own autobiography to the paper at hand--did it alarm you to learn that a truck driver was found to be asleep for 8 continuous minutes while driving? Is it possible for someone to drive while asleep, even in light stage 1 sleep?The authors suggest the sleep was light enough to allow some perception of the environment in this instance, but it is surprising that they report nothing on eye movements or even-related EEG potentials to indicate that the driver actually was attending to the road. I am guessing that a driver on cruise control, on a very straight road, with virtually no curves, banks, or traffic, and perfect tracking, could let his truck "drive itself" like a plane on autopilot. In my own experiencing driving while terribly drowsy and quite possibly in stage 1 sleep, it feels like driving while intoxicated. The perception of the vehicle drifting out of the lane is enough to evoke a brief arousal and course correction. But this is precisely the kind of event that may cause other drivers to veer away and get into an accident where the sleepy driver isn't even directly involved, as recently occurred to a sleep apneic who nevertheless got sentenced to 15 years in prison for his causal role in an accident which left him and his own car undamaged but was fatal to others!
So, we sleep apneics are not alone in suffering drowsiness which increases risk of accidents. We may take some consolation from the fact that, at least, our drowsiness is not usually a result of "voluntary" sleep restriction or other "volitional" bad behavior like drinking or drugging and driving. Alas, as a psychiatrist, I don't know if I really believe in the concepts underlying the dichotomy of "voluntary" or "involuntary" behavior. Certainly I would view the sleep apneic who knows he has it and what he can do about it but refuses to take measures recommended by doctors, as more culpable in an accident than the one that doesn't realize he has anything wrong with him, or that takes treatment for his apnea with incomplete results. What to do about such people? To make it less personal, what do you want to see done about truck drivers who repeatedly use their sleep time to run errands, etc., so are constantly sleep deprived and drowsy when they drive? Do we consider it a matter of individual freedom to make that kind of choice? The drunken driver is deplorable for many reasons besides his driving and nobody minds taking stringent action against him. But he is far from being the only one who endangers all of us on the road. Remember that some estimates attribute more than half of all vehicle accidents to drowsiness!
For more material on this fascinating topic so critically relevant to sleep apneics, check out ARTICLE #1, ARTICLE #7, ARTICLE #25, or ARTICLE #38.
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ARTICLE AND MY COMMENTS ON IT? CAN YOU RELATE IT TO ANY PERSONAL EXPERIENCES?
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