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Circadian Rhythm Room

Circadian rhythm is an internal body rhythm that cycles approximately every 24 hours.
Thus the name circa = about
                         dia = a day.

There are many indicators of this rhythm but the most evident of these is the core body temperature.
[shiftworker online]
It's important to note that as your core body temperature changes so does your behaviour.

This diagram shows a typical core body temperature curve.
[Body Temperature Changes in a 24 hr Period]
 

You can see body temperature drops significantly around 23:00 - 24:00 (11 p.m. - midnight). This trend continues until it reaches its trough at about 04:30 am. Night shift workers can relate to this as one tends to feel colder even though the ambient temperature remains the same.
 
 
 

When shift workers reach this trough they tend to have the following 3 behaviours:
1. uncontrollable urge to go to sleep.
2. "peripheral hallucinations" - the shift worker experiences seeing things out of the corner of their eye's that are not really there.(click here for an interesting night shift story.)
3. "shift paralysis" a) individual knows they must move but can't.
b) individual knows they must move but give themselves every excuse in the book not to.

From approximately 06:00 - 06:30 (am) the body temperature begins to rise. At this point the shift worker sometimes experiences a surge of energy. But this energy is short lived, as the desire to sleep and fatigue associated with night work begins to catch up. I have witnessed this myself many times. When I have started my drive home in the morning I feel fairly alert. Before long I find it hard to finish the drive due to fatigue.

Most , (not all) , night shift workers go straight to bed when they get home. While they are asleep their body temperatures keep rising and reach a peak around 12:00 (noon) to 13:00 (1 p.m.).
This peak in temperature, coupled with a need to go to the wash room, typically wakes the person up. (This seems to get me every time).
After getting up, sleep tends to become very difficult if not impossible.
This is known as "sleep maintenance insomnia"
This is one of the most frequent complaints of shift workers. (It sure is mine).

At around 14:00 (2 p.m.) to 17:00 (5 p.m.) the body temperature dips slightly. This is often called the "post lunch dip," but you do not need to eat to get it, it is a natural body rhythm. Since the body temperature drops here this can be a good time for the shift worker to try to sleep. We have all felt this tiredness regardless of how well we have slept.

At approximately 20:00 (8 p.m.) the body temperature starts to go back up and peaks at around 22:00 (10 p.m.). After this the body temperature begins to decline again and the cycle repeats itself.

A person can change the timing of their body temperate rhythm, but for a shift worker it is rare if even possible because of the constant change.
If a person was working straight nights and stayed on the same sleep/wake cycle even on their time off, they could change this rhythm, but it is unlikely one would do this because of social aspects.
Travellers experience this same temperature rhythm problem. It's known as "Jet Lag". It can be solved if the person stays in the new time zone for a while. It has been shown to take two weeks for a person to change their body temperature rhythm in this situation.

Take a trip without leaving home:
[shiftworker online]
Our circadian system is only able to adjust to a change of an hour or two a day at most. When a person works a night shift it results in a sudden 8 hour change which is like flying from Chicago to Europe. This is why it gets the name "blue-collar jet lag." When a person works a rotating shift schedule of a week of days, nights and then evenings it is comparable to taking a tour around the world in three weeks, without the pleasures of visiting England, Japan or Spain.


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