Glossary

A glossary of commonly used sleep terminology:

APNOEA: a word used to describe complete absence of breathing for more than 10 seconds which usually occurs during sleep. It can be of two types: CENTRAL - where no effort is made to breathe, and OBSTRUCTIVE - where no breathing occurs despite repeated efforts to suck air into the lungs against a blocked upper airway. The word is derived from two Greek words "A" for absence of, and "PNOEA" meaning "to breathe". Hypopnea occurs when there is partial or incomplete absence of breathing.

AROUSAL: the stimulation of the brain, causing the subject to go from deep to a lighter level of sleep. This can be easily detected during a sleep study as a change in sleep stage. Arousal can be due to low blood oxygen, high blood carbon dioxide, jerky leg movements, or environmental factors such as loud noises.

CARBON DIOXIDE: one of many waste products of the body. This waste product is removed from the tissues and blood by the lungs into the atmosphere.

CATAPLEXY: a symptom of narcolepsy, where without warning there is sudden paralysis of the muscles, usually causing the person to fall to the ground.This often occurs at a time of high emotion.

CIRCADIAN RHYTHM: the normal sleep - wake cycle that allows the cyclical release of hormones and restoration of energy, and allows optimal body functions during the day.

CPAP: Continuous Positive Airway Pressure, a method of preventing throat or pharyngeal collapse. Positive pressure is delivered to the throat via the nose by a small portable electrically driven, connected by tubing to a nasal mask, worn whilst asleep.

ECG: Electro cardio gram, a test of the electrical function of the heart.

EEG: Electro encephalo gram, a test of the electrical function of the brain. Can be used to subdivide or "stage" the level of sleep into wake, light (stage 1) moderate (stage 2), deep sleep (slow wave or stages 3 and 4) or dreaming (REM) sleep.

EOG: Electro oculo gram, a test of the electrical activity of the eyes, performed by placing wires on skin beside eyes. Helpful aid to staging sleep as it detects the rapid eye movement (REM) of dreaming sleep.

EMG: Electro myelo gram, a test of the electrical activity of the muscles. Sensing electrodes can be placed over any muscle, but are usually placed on the skin over the muscles under the jaw to detect upper airway muscle activity, on the rib cage to detect the contraction of the breathing muscles and on the legs of detect leg movements. They are also a helpful aid to the staging of sleep, and are useful in the diagnosis of excessive leg movements at night.

ENURESIS: bed wetting. Common finding in children with sleep apnoea.

INSOMNIA: inability to obtain enough sleep.

MSLT: Multiple Sleep Latency Test. Test of how long it takes to fall asleep. Usually repeacted 4 or 5 times in one day. Abnormally short time before you fall sleep is seen is sleep deprivation, severe sleep apnoea and narcolepsy.

NARCOLEPSY: a condition of unknown cause characterised by sudden attacks of sleep or muscle weakness, hallucinations and sleep paralysis.

PALATE: the roof of the mouth. Consists of bone (hard plate) and tissue (soft palate) from which hangs the uvula.

PHARYNX: the area of the upper airway or throat at the back of the tongue. This is the soft or collapsible part of the throat.

POLYSOMNOGRAM: a sleep study consisting of measurements of electrical activity in the brain, eyes, muscles, heart in addition to measurements of breathing and oxygen.

REM SLEEP: Rapid Eye Movement Sleep. Rapid eye movements are a normal characteristic of the level of sleep during which dreaming occurs. It is associated with extremes of muscle relaxation, which could bring on sleep apnoea, if it were to occur at all. Also seen in excess quantities in narcolepsy.

SIDS: Sudden Infant Death Syndrome - another term for cot death.

"SIMPLE" SNORING: a noise generated by the partial collapse of the throat, particularly at the level of the pharynx, without a significant reduction in airflow (breathing).

SLEEP APNOEA: cessation of breathing during sleep, of longer than 10 seconds.

THROAT: the air passage between the nose and mouth, and the lungs. Usually a stiff rigid pipe, except in the region of the back of the tongue, called the pharynx, which is floppy and liable to collapse during sleep.

TRACHEOSTOMY: a hole made by an operation in the rigid part of the throat (near the Adam's apple) which bypasses the nasopharynx region. Once the main treatment of sleep apnoea, now superseded by nasal CPAP. Sometimes used in central sleep apnoea when day and night ventilation is required.

UPPER AIRWAY: consists of the nose, mouth, pharynx, larynx, throat.

UPPP: Uvulo Palato Pharyngo Plasty. An operation in which the uvula and the soft part of the palate or roof of the mouth is removed, in addition to the removal of any redundant tissue at the back of the mouth.

UVULA: the normal piece of fleshy tissue attached to the back of the roof of the mouth. Responsible in part for the noise of snoring.

VENTILATION: the rhythmical entry and exit of air into the lungs. It requires a trigger from the brain and muscles to keep the throat open and muscles to expand the chest, sucking air in. Alternatively, it can be provided by a machine, a ventilator, used in people with central sleep apnoea.