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Category: Aeromedical Aeromedical
Content source: SKYbrary About SKYbrary
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A circadian rhythm is any biological process that displays a built in, self sustained, oscillation of about 24 hours. These 24-hour rhythms have been widely observed in plants, animals, fungi, and cyanobacteria. They are adjusted (entrained) to the local environment by external cues, which include light, temperature and redox cycles.

Disruption of the Biological Clock

An individual's circadian rhythm can be best described as an internal biological clock that regulates our body functions, based on our wake/sleep cycle. Circadian rhythms are not only important in determining sleep cycles but also in feeding patterns. There are clear patterns of brain wave activity, hormone production, cell regeneration, and other biological activities linked to these daily cycles. Possibly because days were longer in the distant past, the circadian cycle is a 25 hour cycle. Any time that our normal circadian rhythm is altered or interrupted, it will have physiological and behavioural impacts. This is better known as circadian rhythm disruption, or CRD.

Effects of Circadian Rhythm Disruption

Shift work almost always causes CRD because the internal body clock is at odds with the shift pattern impacting on performance and increasing the risk of accidents and health problems. Shift workers suffering from CRD may experience difficulty falling and staying asleep, increased daytime sleepiness, a general lack of energy in the morning, an increase in energy in the evening or late at night, difficulty concentrating, oversleeping and trouble getting up and increased negative moods. The most debilitating symptom of CRD is Fatigue but people experiencing CRD may also experience insomnia, headaches and digestive problems.

Impact of Circadian Rhythm Disruption on Pilots

CRD-induced fatigue can have physiological and psychological ramifications including increased reaction time, decreased attention, impaired memory, distraction, irritability and indifference.

Jet Lag

Rapid time zone changes, common amongst flight and cabin crews operating long haul causes CRD. See the separate article on Jet Lag for more information on how to manage CRD and reset the biological clock.

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