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Ask the Mental Health Expert Archives 2001-2004

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Sleep Cycles

Q. I have a truck driver who says there are several sleep cycles that occur throughout the day. He claims that this has been well studied and documented. He says because of this, on trips over 3 hours, he runs into a sleep cycle (approximately 3 times a week) and needs to take a nap.

He adheres to all regulations for hour limitations and is limited to 10 hours driving in a day. I would like to study this claim and need some direction of where to look for information. I have never heard of a person who was well rested that needed to actually sleep before they could complete a normal workday. I know everyone is different, but this is a driver that is working less than 45 hours per week and takes a 30 minute lunch break (we don't care if he sleeps or eats during this time).

Can you tell me if this is a fringe study or mainstream?

A. Your driver's claims have a kernel of truth to them, but I suspect there is something else going on with this individual that might merit further investigation. The sleep-wake cycle is complex, and does differ from person to person. In normal individuals, during a typical night's sleep, there is a predictable shift from one stage of sleep to another. These stages are termed non-REM (stages 1-4) and REM, the initials standing for "rapid eye movement".

REM sleep is associated with dreaming, and, along with stages 3 and 4, is a type of deep sleep. These sleep stages produce characteristic wave forms when studied on the electroencephalogram, or EEG. Their wave forms differ from the normal, alert waking state. Normally, people do not cycle into full-blown REM or Non-REM sleep during their usual daytime hours.

However, some people with either (1) sleep deprivation or (2) certain sleep disorders may experience periods of drowsiness or actual sleep during the daytime hours. For example, in the condition called narcolepsy, REM sleep intrudes into wakefulness, causing loss of muscle tone and sleep attacks.

There is also a normal variation in sleepiness that almost all of us experience to some degree. The point of maximal sleepiness occurs at the time of day associated with lowest body temperature-about 4 am-7 am--in persons with a normal daytime activity schedule. Accidents-including truck accidents-tend to peak at this time of day.

However, there is a secondary peak of sleepiness that occurs around 3 pm--and perhaps this is what your driver is referring to. It is probably the basis for the well-known siesta favored by many cultures. In addition, people who are deprived of sleep may experience so-called microsleeps--very brief periods of sleep that may be associated with nodding off and motor vehicle accidents.

Depending on your driver's work schedule, and how regular or irregular it is, he may be experiencing ordinary drowsiness related to sleep deprivation; or, he may be suffering from a sleep disorder or some type, leading to excessive daytime drowsiness.

Besides narcolepsy, some people have sleep breathing disorders, such as obstructive sleep apnea, that leave them un-refreshed and groggy during the day. One option to consider is having your driver undergo an overnight test called a polysomnogram (PSG). This measures brain wave activity, breathing, and other factors, and can detect most sleep disorders. A comprehensive sleep evaluation at an academic medical center sleep lab might be a good way of sorting out the problem.

In short, the question is whether your driver is, in fact, well-rested when he is on the job. For more information, you can log on to the American Sleep Disorder Association site (www.asda.org) for consumer-oriented help.

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September 2002

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