Parental Attention IELTS Reading Answers

Sleep medicine is a relatively young field in the UK, with only a couple of centers until the 1980s. In the last decade a number of centers have sprouted, often led by chest physicians and ENT (Ear, Nose and Throat) surgeons with an interest in obstructive sleep apnea, forcing neurologists and neurophysiologists to wake up and contribute to the non-respiratory aspect of this neglected subject.

Within sleep, two states are recognized - non rapid eye movement (NREM and rapid eye movement (REM). These alternate cyclically through the night with cycle time of 90 minutes (50 ~ 60 minutes in the newborn). NREM sleep evolved with the homeothermic state and is divided into four stages: stage 1 and 2 which are considered light sleep, and stages 3 and 4 which are considered deep sleep with high arousal threshold.

REM is ontogenetically primitive with EEG (electroencephalo-graph) activity closer to wake state, intermittent bursts of REMs and muscle atonia interrupted by phasic burst producing asynchronous twitching. The atonia of REM sleep prevents acting out of dreams and is lost in REM behavior disorder when dreams content becomes violent and patients act out their dream, often resulting in injury.

REM behavior disorder can be a precursor of neurodegenerative disease including Parkinsons. Dream content - pleasant or unpleasant -will be remembered on waking from REM sleep but there is often little or no memory of the preceding mental activity on arousals from REM sleep, even when associated with complex behaviors and autonomic disturbance as occurs in night terrors or sleep walking.

In the newborn, 50 percent of total sleep time is occupied by REM sleep, progressively shrinking to 25 percent in the adult, the first block of REM sleep occurring about 90 minutes after sleep onset. Abrupt withdrawal of alcohol and many centrally acting recreational and non-recreational drugs can cause REM sleep to occur at sleep onset.

This can also increase total REM sleep, leading to intense vivid often frightening dreams, similar to that experienced by patients with narcolepsy.

The NREM/REM sleep states are interrupted by brief arousals and transient awakenings. The frequency of the arousals may increase with emotional disturbance or environmental discomfort but also in many intrinsic sleep disorders such as periodic leg movements in sleep, obstructive sleep apnea and narcolepsy.

7 The NREM/REM sleep states are interrupted by brief arousals and transient awakenings. The frequency of the arousals may increase with emotional disturbance or environmental discomfort but also in many intrinsic sleep disorders such

as periodic leg movements in sleep, obstructive sleep apnea and narcolepsy.

A basic rest/activity cycle originates in fetal life. The newborn sleeps an equal amount during the day and night, the sleep/wake cycle organized around three to four hourly feeds. By the second month favoring of sleep towards night time occurs and by six months the baby will have about 12 hour of sleep at night in addition to a couple of daytime naps.

In general, children born prematurely have a tendency to be awake more at night in the first year and breast-fed babies wake more frequently, but the difference disappears by the second year. Persistent night awakenings in infants and toddlers usually reflect the child's inability to self-soothe back to sleep without parental attention and will respond to a well supported behavioral programme.

The establishment of a consolidated night sleep pattern in children reflects brain maturation and may be disrupted in children with developmental problems. Even in this group success is possible by persisting with behavioral work, though many pediatricians prescribe melatonin for these children with some success. But as the long-term safety of

melatonin remains unknown it should be used as a last resort.

There are now good studies looking at short term use of melatonin in sleep wake cycle disorders such as delayed sleep phase syndrome. Its use as a hypnotic should be discouraged, especially in the developing child as there is uncertainty on other cycles, such as menstrual. 

In addition to the NREM/REM cycles, there is a circadian sleep/wake cycle entrained by intrinsic rhythms -melatonin and body temperature and extrinsic factors - light and social cues such as mealtimes, work times.

The pineal hormone melatonin plays a role in entraining the sleep/wake cycle to the light/dark cycle. Melatonin secretion is high in darkness and low in daylight hours, the process beginning in the retina with the supra chiasmatic nucleus playing a major role as a sleep regulator via melatonin. Blind people may lose this entrainment and develop a free running sleep/wake cycle with progressive advancement of sleep onset time.

Polymorphism of the circadian clock gene has now been identified with the population divided between morning types (larks) and evening types (owls). Those predisposed to later sleep onset time are susceptible to developing delayed sleep phase syndrome especially during adolescence when sleep requirement increases and there is a tendency towards later time for sleeping and waking.

In delayed sleep phase syndrome, sleep onset is delayed to the early hours of the morning with consequent difficulty in waking in time for school/work. Once established advancing sleep onset time is difficult and requires treatment with appropriately timed melatonin or bright light therapy, or chronotherapy -advancing sleep onset progressively forwards until the desired sleep time is reached.

In contrast the elderly who are more susceptible to perturbation in their sleep/wake schedule can develop advanced sleep phase syndrome with sleep onset occurring early in the evening. Shift workers often struggle to cope with shift patterns as they grow older due to difficulty in re-adjusting their circadian clock. In general, morning bright light

exposure is a more powerful synchronizer of the circadian rhythm than melatonin.