Normal sleep consists of cycles of non-rapid eye movement (NREM) sleep alternating with rapid eye movement (REM) sleep. NREM sleep consists of light sleep and deep sleep. REM sleep is also known as “dream” sleep. The function of sleep is believed to be restorative, a time of rest and repair for the body.
Adults need an average of 8 hours of sleep (Range of 6 - 10 hours). It is normal to fall asleep within 10 to 20 minutes of going to bed, to wake up spontaneously once or twice in the night then fall back to sleep readily, and wake up feeling refreshed. Children need more sleep and tend to have more deep sleep, while the elderly have more frequent awakenings and less deep sleep.
The serious short and long term consequences of sleep deprivation reflect the important restorative functions of sleep. When we do not get enough sleep, our thinking, memory, concentration, alertness and mood are affected. Daytime sleepiness leads to poor school or work performance and can result in serious accidents. Left untreated, long term sleep disturbances decrease quality of life and can lead to increased morbidity and mortality.
Sleep disorders are sleep-related disturbances due to underlying medical problems, lifestyle and environmental factors which usually cause sleep disruption, leading to insufficient or poor quality sleep.
People with excessive daytime sleepiness severe enough to cause social or occupational disruption should undergo formal evaluation by a physician. Those with suspected sleep apnoea or narcolepsy usually need to undergo sleep studies.
Insomnia refers to difficulty falling or staying asleep, or a perception of unrefreshing sleep. Insomnia is often related to more than one cause, including psychological and lifestyle factors:
Patients with persistent insomnia should be evaluated by a physician to rule out underlying depression, which often presents with early morning waking. Patients who are unable to sleep without sleeping pills may need to be referred to a sleep disorders clinic. Most patients with insomnia can be managed with lifestyle modifications and medication, and do not usually need a sleep study.
Abnormal behaviour in sleep often does not require specific treatment unless there is risk of injury, or if the abnormal movements disrupt sleep. Examples of sleep disorders associated with abnormal movements are restless legs syndrome and periodic limb movement disorder, in which excessive leg jerking before or during sleep causes insomnia or excessive daytime sleepiness.
The parasomnias are abnormal behaviours during sleep which can occur in children or adults:
A sleep study is frequently required to evaluate these conditions. They must be distinguished from seizures occurring during sleep, which can appear very similar.
Some sleep disorders such as restless legs syndrome, obstructive sleep apnoea, narcolepsy and the parasomnias have a genetic component and may run in families.
People who have irregular sleep schedules, including shift workers and those who travel across multiple time zones frequently, are also at increased risk of developing sleep related problems.
Lifestyle factors such as excessive caffeine consumption, lack of regular exercise, poor stress management and smoking all contribute to sleep disturbances.
In general, the quality of sleep declines with age. As a result of this, as well as degenerative changes and weight gain which increase with age, sleep related disorders tend to become more frequent as we grow older.
Most sleep disorders can be diagnosed with a good sleep history, including questions about the patient’s sleep habits, lifestyle, medications and a physical examination. A sleep study may be required in some patients.
Most sleep disorders can be managed conservatively with a combination of good sleep education, medication and behavioural modification. In certain conditions like obstructive sleep apnoea, specific therapy may include positive airway pressure therapy (pressurised air delivered via a mask) or upper airway surgery.
Difficult cases are referred to physicians trained in the management of sleep disorders. Many sleep disorder clinics are staffed by health professionals in multiple disciplines, such as neurologists, respiratory physicians, ENT surgeons, psychologists and psychiatrists.
Most sleep disorder clinics have sleep laboratory facilities for sleep studies. PSG and MSLT recordings are performed by qualified PSG technologists. For patients with obstructive sleep apnoea, respiratory therapists assist in special sleep studies in which positive airway pressure is applied at various settings so that optimal therapeutic pressure settings can be determined.
Sleep patterns can be studied in the laboratory using machines which record brainwave activity, breathing, heart rate and limb movements during sleep. The most common types of sleep studies are:
PSG involves staying overnight in the sleep laboratory and being hooked up to a machine which is monitored by sleep technologists. At least 6 hours of sleep are recorded using electrodes attached to the scalp and limbs, special belts across the chest and abdomen, airflow monitors and ECG leads. PSG is usually indicated in patients in whom sleep related breathing disorders and abnormal movements in sleep are suspected.
The MSLT follows the overnight PSG, comprising four 20-minute naps at two-hour intervals throughout the day. It is indicated for the diagnosis of narcolepsy and also to assess the severity of sleepiness in patients who complain of excessive daytime sleepiness.