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According to a survey made by the TNS Sofres (a French survey enterprise) in 2006 for the Institute for Sleep and Vigilance, "27% of the French people are disturbed by a problem of sleepiness.

One adult in ten, one teenager in five has a chronic sleep lack."



The first cause of excessive daytime sleepiness (EDS) is often the least investigated in accidentology studies [1]: it is the chronic lack of sleep.
The subject, who has though a good quality of sleep, cannot adapt to the social, familial and professional demands which are imposed on him/her.

Here, it is truly a matter of a chronicadaptation disorder because an occasional lack of sleep is easily compensated thanks to the power of rebound sleep the following night or during a nap. Here, the subject suffers all the time from a need to sleep which he/she often fights with a constant behavioural agitation.
All studies show that sleep deprivation leads to a fall of intellectual, emotional and physical performances.
The endocannabinoid system (cf.) allows to understand better the consequences of sleep deprivation on appetite, immunity, pain and mood.
The first consequence of sleep lack is the risk of accidents linked to excessive sleepiness.

  • Voluntary sleep deprivation
  • It has been measured that the average duration of sleep has fallen of more than one hour in the last century. Our grandparents have grown up in a world where people went to sleep much earlier than now.

    Average sleep duration has thus gone from 9 to 7 hours a day.

    More and more individuals take on their sleep time because the choice of activities which can be made at night becomes larger all the time.

    Television, video games, Internet and work at home are the main reasons to delay bedtime.
    It appears clearly that children and teenagers are amongst the population which is most exposed to a lack of sleep.

    Studies agree to demonstrate the very negative impact of sleep deprivation on memory and, as it was discovered more recently, on social behaviour or food intake balance.
    A perfect control of one’s sleep seems to be one of modern life’s challenges...

    The other causes of sleep deprivation mostly concern night and shift workers who do not have the ability to compensate their sleep debts by a good quality diurnal sleep. It is particularly the case of the « morning subjects » who are more vulnerable regarding night work.
    On the opposite, « evening subjects » are hindered by the actual work schedules and stand very badly, for example, the advice to go to work early from « Bison futé » (a French traffic radio station).
    With night workers, the rest conditions (noise, temperature, lighting, environment quality) must be taken into account to estimate and prevent the risk of excessive daytime sleepiness.
    Special chromotherapy glasses (which limit the arousing effect of the morning light), enhance night workers’ diurnal sleep.

  • Phase shift syndromes.
  • The subject would benefit of a satisfying sleep if he/she only could dissociate his sleep/wake rhythm from the social rhythms. He/she suffers from difficulties to sleep at the « right moment ».

    • The most frequent is the delayed phase syndrome. The subject suffers from sleep onset insomnia in the evenings, at « normal » hours, but will be able to fall asleep deeply in the end of the night.
      For that type of person, the alarm clock is a true « instrument of torture » because the sleep debt is very important when he/she has to get up after a few hours of sleep.
      The untimely practice of the nap (cf.) or of sleeping over often has an aggravating effect on evening insomnia.

      Sleep typology studies highlight the « extreme evening » characteristics of these sleepers (who are often rather long sleepers).
      The interview of (voluntary) night workers puts forward similar characteristics with a good adaptation to diurnal sleep.

      JPEG - 55.7 kb
      Adapted from : http://sommeil.univ-lyon1.fr/

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    • Less frequent but well described in medical publications :the advanced phase syndrome.
      As a mirror image of the previous, the subject suffers from EDS from the first hours of the evening and goes to sleep « with the birds» around 7 or 8 PM and wakes up much too early.
      The mutation of a part of the gene which programs the biological clock has been shown in the « familial advanced phase syndrome » (FAPS).
      JPEG - 12.6 kb
      Une mutation génétique (autosomiale dominante) dans le "syndrome d’avance de phase familial"


      "FAPS" is a dominant autosomic disturbance of the circadian rhythm. The concerned subjects are "very early risers" with a phase advance of 4 hours of sleep rhythm, body temperature, and melatonin secretion. (...) Some circadian rhythm disturbances can thus be imputed to a genetic mutation (affecting gene hPer2, very close to that known in Drosophila)."

      A behavioural phase advance (too early bedtime because of boredom +++) can be encountered in the interview of subjects who suffer from maintaining sleep insomnia.
      Too many old subjects are thus treated erroneously for insomnia because they are awake from the middle of the night.

    • The hyper-nycthemeral syndrome is described as being the ability to sleep on a rhythm longer than 24 hours (nycthemeron).
      Isolation experiments sheltered from external « time givers » have shown that the sleep rhythm of one third of the people gets shifted compared to their internal clocks (which continue to run on a 24 hours basis).
      When the subject has slept enough one night, he/she does not feel the need to go to sleep the following evening and delays his/her bedtime.
      If he/she has to wake up « normally » at 7 AM the next morning, he/she will have to « shorten his/her night » and build up a sleep debt. A sleep « rebound » will occur during a too long nap.
      That type of compensation sleep is very powerful and risks to be the starting point of a true vicious circle. The subject is no longer sleepy in the evening because of his/her too long nap and gets up again the next morning with a sleep debt.

      That vicious circle leads gradually to a chronobiological disturbance of the sleep pendulums (cf). Decompensation occurs at the occasion of an additional tiredness, with the shape of a complaint of insomnia.
      The sleeping pills have here, too, a concealing action which considerably worsens the situation if the subject does not understand that he/she has to get up early to reverse the process.

      Multiple functional disorders appear at an earlier stage of desynchronization.


Conclusions

  • Sleepiness is much more dangerous than tiredness...
    (Read the opinion of road security specialists)(in French)
    "The tired driver has to make a break every two hours, stretch out his/her legs, talk, and he/she can go on again... But for the sleepy driver, there is only one way to get rest: sleep. » (Dr Pierre Phillips)

      The respective role of individual genetic predispositions (the ground), on one hand, and of atypical schedules and life habits, on the other hand, is often badly defined in the problematic of sleepiness caused by sleep deprivation.
    • Teenagers find pleasure and have a feeling of freedom when they stay up alone during the night...
    • The case of a writer from New-York has been reported who was said to live on a period of 30 hours instead of 24 with no troubles...
    • Some night workers enjoy to work in atmospheres which are calmer than during the day...
  • It is thought that each subject adapts his/her choice of living more or less consciously to his/her somnological performances (and not the opposite).
    In other words, it is possible to choose to work with an atypical schedule, but it is not possible to choose to be ableto adapt to it.
    (It is thus imperative to know the mechanisms of the chronobiological regulation of sleep).
    The tolerance of the subject will depend on the performances of his/her recovery sleep. It seems that there exist, in some people, true chronobiological contraindications to night work.
  • "Sleep is individual and deserves individual information".

    A good sleeper goes to sleep trustfully, wakes up fit... and must not be sleepy during the day.

Footnotes

[1The BAAC file, bulletin of analysis of traffic accidents with body injuries, does not mention the notion of sleepiness before or during the accident




Auteur | Contact | Copyleft | Traductions | derniere modif 21 October 2007.