Paul Reading. ABC of Sleep Medicine (ABC Series). BMJ Books (2013)
Newborns typically spend over half of the 24-hour period in a state resembling REM sleep. They have wakeful episodes lasting two or three hours interspersed with similar relatively short sleep periods across the day–night period. In the ﬁrst two years, a prolonged nocturnal sleep usually becomes established, invariably encouraged by parental input, with afternoon naps remaining the norm until around ﬁve years of age.
The commonest pattern through teenage life is for sleep onset to become progressively later. Although lifestyle factors and habits may fuel this tendency, there is also evidence that most teenagers have internal clock mechanisms predisposing them to become ‘night owls’. The most obvious practical consequence of this pattern is extreme difﬁculty arising at a conventional hour for educational purposes.
Beyond adolescence, however, the brain’s internal clock tends to ‘advance’. With each subsequent decade, the natural desire to sleep typically occurs around 30 minutes earlier.
Figure 1.5. The suprachiasmatic nucleus in the hypothalamus is circled with magniﬁcation of the cellular component. This small area of the brain contains around 25 000 neurons but is the ‘master’ timekeeper of all circadian rhythms in the body.
Таблица 1.2. Вопросы для оценки повышенной сонливости.
|Question or probe||Implications for positive answer|
|Are you waking up from naps without realising you had been sleep?||Indicates ‘sleep attacks’; can be seen in any cause of severe excessive sleepiness such as narcolepsy|
|Given the chance, could you nap more than once a day?||Implies excessive sleepiness rather than, for example, simple fatigue|
|Have you fallen asleep in unusual situations, such as in public (e.g. on buses, in shops)?||Implies signiﬁcantly excessive sleepiness|
|Do you regularly fall asleep within a few minutes when a passenger in a car?||May indicate signiﬁcant sleepiness|
|Do you routinely fall asleep when watching ﬁlms on television?||May indicate signiﬁcant sleepiness|
|Have friends or family commented on you dropping off to sleep inappropriately?||Usually implies excessive sleepiness, particularly in some situations where it may not be appreciated by the subject (e.g. Parkinson’s disease or dementia)|
|Are you prone to frequent lapses or ‘automatic’ behaviours (e.g. placing objects in inappropriate places or losing items around the house)?||May imply ‘microsleeps’ or brief periods of inattention as an indication of signiﬁcant sleepiness|
|At times do you ﬁnd it very hard to concentrate or take in new information?||Particularly in those who ﬁght the urge to sleep, it might not be appreciated that impaired vigilance and concentration are early markers of signiﬁcant sleepiness|
|Do you feel hyperactive at times and unable to focus or attend to a simple task?||Distractibility resembling attention deﬁcit and hyperactivity disorder (ADHD) may reﬂect underlying sleepiness, particularly in children|
The most striking age-related change in sleep patterns relates to a progressive deterioration in sleep consolidation. Several minor arousals, usually later in the night, might be considered normal in early middle-age. In the healthy elderly, frank sleep fragmentation is extremely common. The depth of slow wave sleep (non-REM stages 3 and 4) also reduces dramatically with age, with the earliest changes evident in males as young as 25.
The increased depth of non-REM sleep in younger subjects accounts for the extreme difﬁculty often encountered if children need to be woken from deep sleep in the ﬁrst third of the night. Forced arousals frequently produce apparent confusion or ‘sleep drunkenness’, a phenomenon also frequently observed in sleepdeprived adults.