AHI Apnoea
Hypopnoea Index = average number of apnoeas and
hypopnoeas per hour.
AI Arousal index =
the total number of arousals scored per hour of sleep.
These arousals are then classified as beingcaused by a
respiratory event, leg movement or just spontaneously.
Apnoea complete
absence of breathing for more than 10 seconds. It can be
of three types:
Central where no effort is made to breathe,
Obstructive where no breathing occurs despite repeated efforts due to a limitation of flow through the upper airway.
Mixed where there is a combination of effort to breathe and no effort to breathe.
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.
BiPAP Method of ventilation with an inspiratory
pressure (IPAP) and expiratory pressure (EPAP). This is
usedif CPAP is not sufficient, as in patients with
neuromuscular weakness or scoliosis.
Bruxism Teeth grinding.
Cataplexy A symptom of narcolepsy, where without
warning there is sudden paralysis of the muscles (atonia)
usuallycausing the person to fall to the ground. This
often occurs at a time of high emotion.
Central Apnoea This is an apnoea (cessation of
airflow) in which there is no respiratory effort.
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 a small portable
electrically driven air pump, and connected by tubing to
a nasal mask that is worn during sleep.
Dysomnia Sleep disorder causing sleepiness. Such
conditions are OSA and PLMS.
EEG Electro encephalo gram, a test of electrical
function of the brain. Can be used to subdivide or
stage the level of sleep from wake, to light (stage
1), moderate (stage 2), deep (stages 3 and 4) or
dreaming (REM) sleep.
EMG Electro myelo gram, a test of 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 ribcage to detect the contraction of
the breathing muscles and on the legs to detect leg
movements. They are also aid the staging of sleep, and
are useful in the diagnosis of excessive leg movements
at night.
ESS Epworth Sleepiness Scale. Asks a series of 18
questions about how likely a patient is to doze off or
fall asleep in a variety of situations, according to
recent times, and sleepiness must not be confused with
tiredness. The maximum score is 24. Each situation
(sitting, reading, watching TV, driving, lying down,
after lunch) is assessed on a scale of 0 (no chance of
dozing) to 3 (high chance of dozing). A score of greater
than 8 indicates sleepiness. Higher scores indicate
greatersleepiness.
Hypopnoea Occurs when there is a partial or incomplete
absence of breathing. Like apnoeas, these may be central
orobstructive. Paradoxical breathing is likely to be
present if obstructive, whilst in phase respiration
would be present ifcentral. Central hypopnoeas may be
associated with cardiac problems, in which case they
would appear at regular intervals.
Hypoventilation Occurs when a patient breathes too
slowly or too shallow to maintain normal respiration.
This isaccompanied by an elevated CO2 level whilst
awake, which rises further when asleep. This in turn,
affects the oxygen level.
This may be seen throughout the night and not be as a
result of apnoeas and hypopnoeas.
Insomnia Inability to obtain enough sleep. This may be
perceived (sleep state misperception) or real. Insomnia
may be classified as either difficulty initiating sleep
insomnia (DISI), difficulty maintaining sleep insomnia (DMSI)
or waking too early.
Mixed Apnoea This is an apnoea (cessation of airflow),
in which there are features of both central (no effort)
and obstructive (effort to breathe) apnoeas.
MSLT Multiple Sleep Latency Test. Used to assess how
long it takes to fall asleep. Usually repeated 4 or 5
times in one day. Abnormally short sleep latencies are
common in instances of sleep deprivation, such as
insufficient sleep period time and severe sleep apnoea.
A diagnosis of narcolepsy occurs if there is a short
mean sleep latency and the presence of two or more
sleep-onset REMs.
MWT Maintenance of Wakefulness test. Similar protocol
to the MSLT, occurring 4 times a day at 2 hr intervals,
but the patient is asked to stay awake, sitting still in
a dimly lit room.
Nadir The lowest point. SaO 2 nadir means the lowest
saturation at the time specified eg. REM nadir compared
to NREM nadir.
Nasal Pressure Measures the airflow at the nares
(nostrils) and monitors the change in pressure.
Narcolepsy A condition of unknown aetiology
characterised by sudden attacks of sleep or muscle
weakness (cataplexy), hallucinations and sleep
paralysis.
NREM Sleep Non Rapid Eye Movement Sleep. Consists of 4
stages NREM1 and NREM2 are light sleep, whilst NREM3
and NREM4 are deep sleep. Patients are easier to arouse
from light sleep than deep sleep. NREM sleep is termed
quiet sleep in infants.
OSA/OSAS Obstructive Sleep Apnoea / Obstructive Sleep
Apnoea Syndrome. Obstructive sleep apnoea (OSA) is a
serious, potentially life-threatening condition
characterised by:
repetitive pauses in breathing during sleep due to collapse of the upper airway,
which is usually accompanied by a reduction in oxygen levels in the blood, and
followed by an awakening to breathe.
Oximetry The measurement of oxygen saturation levels
in the body, expressed as a percentage. This may be
measured by a finger/ear probe (SpO2) or blood gas
analysis (SaO2). The baseline measurement relates to the
awake resting level.
Parasomnia
Sleep disorder that generally does not
cause tiredness, such as bruxism (tooth grinding), sleep
walking (somnambulism), sleep talking (somniliquy) and
enuiresis (bed wetting). Parasomnias tend to run in
families and are more common in childhood. They usually
do not require medical attention but may be a source of
embarrassment for the child and family. Tiredness can
occur if significant sleep fragmentation occurs as a
result of the parasomnia.
PLMD Periodic limb movement disorder. Defined as 4 or
more movements (of 0.5 5 seconds duration) within 5-90
second period. A diagnosis of PLMD requires an index (PLMI)
of at least 5.
Polysomnogram A sleep study consisting of measurements
of electrical activity in the brain, eyes, muscles and
heart, in addition to measurements of breathing and
oxygen.
Primary snoring Snoring during sleep with no apnoea/hypoventilation,
and no changes to blood gasses.
RDI Respiratory Disturbance Index. The total
respiratory disturbance (all scored respiratory events)
per study, expressed as average number per hour. In our
lab, Respiratory events are scored using the Chicago
criteria. These events are greater than ten seconds in
adults and more than two respiratory cycles in children
(usually about 8 seconds).
REM sleep Rapid Eye Movement sleep. REMs are a normal
characteristic of the level of sleep during which
dreaming occurs., and are ssociated with extremes of
muscles relaxation (atonia), which can bring on sleep
apnoea if it were to occurat all. Also seen at sleep
onset, and in excess quantities in narcolepsy.
RLS Restless Leg Syndrome. Thought to affect 5% of the
population whereby sufferers have uncomfortable (cramp,
burning, weakness, itchy) sensations in their legs.
These sensations may also be felt in the feet, thighs,
trunk and arms.
Sensations can be alleviated by movement, reduction in
temperature or treated with medication. More common in
women(particularly during pregnancy), and can occur in
children. Often runs in families. Sufferers may avoid
social situations.
Sleep Architecture Refers to the distribution of sleep
stages throughout the sleep study. This changes with age
and is affected by conditions disrupting sleep, such as
sleep apnoea. Cycling between REM and NREM normally
occurs every 90 minutes in adults and there are
percentages of each sleep state that are normal for age
groups.
Sleep Efficiency - Expressed as a percentage of total
sleep time (TST) of time in bed (TIB). This is reduced
by awakenings after sleep onset but does not consider
sleep architecture.
Slow-wave Sleep This is the deepest state of sleep, in
which big, slow delta waves are present on EEG. Also
known as NREM3 and NREM4 or deep sleep.
Upper Airway Resistance Syndrome (UARS) Occurs when
there are no discrete apnoeas or changes to airflow.
Ventilatory responses are normal but increased work of
breathing during sleep causes frequent arousals,
affecting sleep quality. This can be associated with
snoring and daytime symptoms such as sleepiness and
reduced alertness.
UPPP Uvulo Palato Pharyngo Plasty, surgery involving
the removal of the uvula and the soft part of the palate
or roof of the mouth, in addition to any redundant
tissue at the back of the mouth.
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 in. Alternatively, it can be provided
by a machine, a ventilator, used in people with Central
Sleep Apnoea.