Circadian Rhythms.Fatigue

Van Dongen HPA, Dinges DF. Circadian rhythms in fatigue, alertness and performance. In Kryger MH, Roth T, Dement WC, eds. Principles and Practice of Sleep Medicine. Philadelphia WB Saunders, Company 2000 391-399. 

Insomnia is characterized as being primary where there is no obvious medical or psychiatric cause. It is a common clinical problan wherein 10-20% of people have chronic insomnia, characterized by trouble sleeping more than three nights a week. It has been directly linked to numerous impacts on individuals such as daytime fatigue, inattention, irritability, poor mood, and reduced energy levels. Consequently, they have reduced productivity, higher woik absenteeism, and an increased risk of depression or substance abuse. There is also a greater risk of traffic and woik-related accidents. Furthermore, studies have shown direct links between circadian rhythm disturbance and an increased risk in health problems, such as diabetes, metabolic disorders and depression. Insomnia is considered secondary if it is caused by external factors such as health conditions, for example, cancer, heart problems, depression, asthma, arthritis, or pain, or as a side effect of medication, or a substance, such as alcohol. 

Some of the physical stressors that influence physical stress are duration of the stress, fatigue, pain or discomfort, hunger or thirst, temperature extremes, atmospheric pressure extremes, oxygen insufficiency, vibration, and disruption of circadian rhythm. 

Twenty-four-hour operations in the field of public and commercial transportation will automatically place operators at risk for sleep loss. This sleep loss mainly stems from a disruption of circadian biological rhythms due to the nature of the service around the clock. While human operator failure cannot be avoided entirely, precautions must be taken to minimize the risk of accidents due to fatigue. 

The increased mental drive necessary to maintain performance was apparent in another study of military recruits kept awake for 3 successive nights (18). An increase in fatigue was accompanied by a decline in rifle-shooting accuracy, both reflecting circadian rhythmicity over which the deteriorating trend was superimposed. There was a clear rhythm in circulating noradrenaline whose peak increased on each of the 3 days of sleep deprivation. 

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