Circadian Rhythms

 

 

What are Circadian Rhythms?

Our bodies have a natural inbuilt clock which controls how sleepy we feel throughout the 24 hour cycle. Many more aspects of our physiology, for example secretion of hormones, body temperature and lung function, are also influenced by this daily rhythm. Important signals, in particular external light, fine tune our so called ‘biological’ clock. This system is responsive to change and allows us to adapt to seasonal variations in light-dark cycles. However we are not yet evolutionarily attuned to rapid changes in time zones and suffer ‘jet lag’ when we travel around the world. The lack of synchrony of the day-night cycle with our body’s natural rhythms means that we feel cold or hungry at odd times of the day and find it difficult to sleep at appropriate times even if we are tired.

Circadian Rhythm Disorders
These disorders occur when the natural inclination to sleep occurs at an inappropriate time. Sleep itself, once initiated, is normal but the timing of the sleep phase invariably causes problems for the sufferer.

Delayed sleep phase syndrome: This condition causes the sleep pattern to shift forwards through the 24 hour cycle so that instead of falling asleep in the late evening, the sufferer cannot fall asleep until the early hours of the morning. Sleep is cut short in order to wake for work or school and as a consequence the sufferer becomes chronically sleep deprived, tired and moody in the day. When allowed to lie in bed the person with delayed sleep phase will sleep through to lunchtime or early afternoon. It is quite natural for adolescents to delay their sleep phase to some extent but if unchecked and bedtimes drift past midnight they may develop true delayed sleep phase syndrome which will impact on their ability to function in school and college. This condition needs to be distinguished from other causes of difficulty falling asleep such as restless legs and anxiety. It is amenable to treatment with good sleep hygiene, chronotherapy (resetting the biological clock), light therapy and sometimes melatonin.

Advanced sleep phase syndrome: This is a rarer condition where the sleep phase is advanced so that the sufferer falls asleep early in the evening and wakes in the early hours of the morning. It tends to cause less disruption to daily life than delayed sleep phase syndrome as generally an adequate period of sleep is achieved. Nonetheless it is also amenable to treatment.

 

 

REM behaviour disorder

 

 

REM behaviour disorder is a rare and unusual condition which most commonly affects men over the age of 50. REM sleep (or dream sleep) is associated with relaxation of the muscles - this prevents the dreamer from acting out their dreams. In REM sleep behaviour disorder this switching off mechanism fails so that the sufferer is able to move during their dreams. Characteristically people with this condition will recall vivid, often violent dreams and may act these out talking, shouting, fighting off imagined assailants and even jumping through window to escape an imagined attacker. Commonly the sufferer may hurt themselves during these episodes and can also hurt their bed partner. Around 40% of cases have no obvious cause for this condition but it can also be associated with diseases of the nervous system such as Parkinson's disease and dementia. Diagnosis can only be accurately made by a sleep study and treatments can be offered to improve symptoms.