Sleep Apnea / Sleep Disorder
Definitions & Glossary of Terms
Abdominal Movement - Movement of the abdomen, which
reflects breathing effort and movement of the diaphragm. This is typically
measured by the placement of a sensor band around the chest. Abdominal movement
is recorded in diagnostic sleep studies. This measurement is used in
differentiating the type of sleep apnea.
Advanced Sleep Phase Syndrome - A circadian rhythm disorder in which
phases of the daily sleep/wake cycle are advanced with respect to clock time.
The sleep phase occurs well ahead of conventional bedtime, creating a tendency
to fall asleep or wake up too early.
Airflow Limitation (Flow Limitation) - Partial closure of the upper
airway with reduced airflow.
Alpha Rhythm - An EEG brainwave produced when an individual is in a
relaxed awake condition with their eyes closed. The frequency is 8-13 Hz in
human adults, and is predominately present in the occipital lobe of the brain.
It indicates the awake state in most normal individuals.
Alpha Sleep - Sleep in which alpha activity occurs with sleep EEG
patterns.
Alpha-Delta Sleep - On rare occasions, Delta brainwaves (deep sleep) are
mixed with alpha brainwaves (relaxed wakefulness). Alpha-delta sleep occurs
with conditions such as arthritic pain, stimulant use and thyroid imbalance.
Ambulatory Monitor - Portable system used for the continuous recording
of multiple physiological variables during sleep.
Antidepressant - A class of medications most commonly used in the
treatment of depression. Most antidepressants also reduce REM sleep. In sleep
disorders, they are used to control cataplexy, hypnagogic hallucinations, and
sleep paralysis.
Apnea - Cessation of breathing for 10 or more seconds during sleep.
There are two basic types of sleep apnea: Obstructive Apnea is caused by
a closure of the air passage despite efforts to breathe; Central Apnea
is a lack of effort to breathe. Obstructive Sleep Apnea is by far the most
common type. True apnea during wakefulness is extremely rare.
Apnea/Hypopnea Index - (AHI) (RDI or Respiratory Disturbance Index) The
frequency of abnormal respiratory events per hour of sleep. These events are
classified as Apneas or Hypopneas. Apnea is when breathing (airflow) stops for
10 seconds or more. Hypopnea is a partial blockage of airflow resulting in
arousal and a possible drop in oxygen level. An AHI of 45 would indicate that
the patient is experiencing complete or partial airflow blockage 45 times
per hour.
Apnea Index - The frequency of apneas per hour of sleep.
Arousal - An abrupt change from sleep to wakefulness, or from a
"deeper" stage of non-REM sleep to a "lighter" stage.
Arousal Disorder - A parasomnia disorder presumed to be due to an
abnormal arousal function. The classical arousal disorders are sleepwalking,
sleep terrors, and confusional arousals.
Arousal Threshold - The ease with which a sleeping person is awakened at
a particular time.
Arrhythmia - An absence or irregularity of the heart rhythm caused by
disturbances of the transmission of electrical impulses through the cardiac tissue.
Auto Adjusting Continuous Positive Airway Pressure Device (SmartPAP) - See
CPAP. A type of CPAP machine that monitors changes in the individual's
breathing and compensates automatically by making the appropriate adjustment in
pressure.
Automatism - An automatic action; especially any action performed
without apparent intention or awareness.
Awakening - The return to the polysomnographically defined awake state
from any of the non-REM sleep stages or REM sleep: characterized by alpha and
beta waves, rise in tonic EMG, voluntary eye movements and eye blinks.
Basic Sleep Cycle - See Sleep Cycle.
Benzodiazepines - Class of sedative medication commonly used to treat
anxiety and insomnia.
Beta Activity - Brain waves seen in alert wakefulness which have a
frequency greater than 13 Hz (Hertz).
Bi-Level Positive Airway Pressure (Bi-level or Bi-PAP) - See CPAP.
A CPAP device providing two measured pressure levels of continuous airflow: one
level for inhalation and a lower level for exhalation.
Biological Clock - A term applied to the brain process that regulates
24-hour fluctuations in body temperature, hormone secretion, and a host of
other bodily activities. Its most important function is to foster the daily
alternation of sleep and wakefulness. The biological clock is housed in a pair
of tiny bilateral brain areas called the suprachiasmatic nuclei.
Biological Rhythms (Circadian Rhythms) - An innate daily fluctuation of
physiological or behavioral functions, including sleep-wake states generally
tied to the 24-hour daily dark-light cycle. Sometimes occurs at a measurably
different periodicity (e.g. 23 or 25 hours) when light-dark and other time cues
are removed.
Body Position - In sleep studies, four sleep positions are identified;
back, left side, right side or abdomen. Some tests also indicate if a patient is
sitting up. The amount of time spent sleeping in each position and the
occurrence of respiratory events in a particular position are tabulated. Body
position is recorded in both diagnostic sleep studies and CPAP titration
studies.
Bradycardia - A heart rhythm with a rate below 60 beats per minute in a
human adult.
Brain Waves - Spontaneous electrical activity of the brain studied by
method of electroencephalography (EEG).
Bruxism (Toothgrinding) - Grinding one's teeth while asleep. This occurs
at some time in approximately 70% of people; most have no noticeable side
effects. However, 5% of victims develop symptoms such as tooth wear, jaw pain
and headaches. Episodes of grinding are more severe after stressful days.
Cardiac Arrest - Sudden cessation of heart beat.
Cardiovascular - Pertaining to the heart and blood vessels.
Central Nervous System (CNS) - The brain and spinal cord.
Central Sleep Apnea - A period of at least 10 seconds without airflow,
during which no respiratory effort is evident.
Chronotherapy - Treatment of a circadian rhythm sleep disorder by
systemically changing sleeping and waking times to reset the patient's
biological clock.
Circadian - Any periodicity that is near but not necessarily exactly 24
hours.
Circadian Rhythms - See Biological Rhythms
Claustrophobia - Fear of being confined in any enclosed space, as in a
locked room.
Compliance - Adhering to a regimen of treatment, such as CPAP therapy.
Continuous Positive Airway Pressure (CPAP) Machine - Medical device used
to treat sleep apnea. This apparatus provides a highly effective, non-invasive
therapy that eliminates blockages and prevents collapse of the upper airway by
generating a prescribed level of air pressure that maintains airway patency
during sleep. Air pressure is delivered through a hose to a mask that fits over
the nose, or both nose and mouth. The mask is secured on the face by headgear
that is worn over the head. The appropriate air pressure level is determined
during a "CPAP titration" sleep study. The complete system consists
of a programmable pressure generator, tubing, mask and headgear. Sometimes
referred to as nCPAP (nasal Continuous Positive Airway Pressure).
Confusional Arousals - Also called sleep drunkenness or excessive sleep
inertia, this disorder is an extreme example of the slowness most people feel
upon awakening. People with confusional arousals respond poorly to commands or
questions, and have major memory impairment of things that happened a short time
before.
CPAP Pressure - Amount of pressure needed to maintain an open airway in
a sleep apnea patient being treated with CPAP, expressed in centimeters of
water (cm H20). The positive pressure may range from 5 to 20 cm H20. Different
patients will require different pressures. This value is determined in a CPAP
titration study.
Deep Sleep (Delta Sleep) (Slow Wave Sleep) - In sleep studies, refers
to combined non-REM sleep stages 3 and 4.
Delayed Sleep Phase Syndrome - A circadian rhythm disorder, which in the
daily sleep/wake cycle, is delayed with respect to clock time. Accordingly, the
sleep phase occurs well after the conventional bedtime. Usually associated with
difficulty getting up in the morning.
Delta Sleep (Deep Sleep) (Slow Wave Sleep) - Sleep stages 3 and 4 in
which EEG delta waves are prevalent.
Delta Waves - Delta waves have a frequency of 2 cycles per second (cps)
or slower and amplitudes greater than 75 microvolts peak to peak (the
difference between the most negative and positive points of the wave). Also
known as Delta Activity.
Diagnostic Sleep Study - Continuous monitoring of several physiological
activities in a sleeping individual. Usually carried out to determine the
absence or presence of a specific sleep disorder. A diagnostic sleep study can
be performed in a sleep disorders center or in a patient's home with portable
recording equipment.
Diaphragm - The large, concave muscle attached to the rib cage at bottom
of the chest (top of the abdomen). Inhalation occurs when the diaphragm
contracts. Exhalation is usually passive as the muscle relaxes.
Diurnal - Active and wakeful in the daytime, as opposed to active in the
nighttime.
DME - (Durable Medical Equipment) - Devices such as wheelchairs and
walkers, which are prescribed on the order of a physician. This includes CPAP
and Bi-Level machines.
Drowsiness, Drowsy - A state of quiet wakefulness that typically occurs
prior to sleep onset. If the eyes are closed, diffuse and slowed alpha activity
usually is present, which then gives way to early features of stage 1 sleep.
Dyssomnias - A class of sleep disorders that produce either insomnia or
excessive sleepiness.
Electrocardiography (EKG) (ECG) - Method of measuring the
electrical activity of the heart. EKG is continuously recorded in both
diagnostic sleep studies and CPAP titration sleep studies.
Electrodes - Small devices that transmit brain waves or other biological
electrical signals from a patient to a polysomnograph machine, where the signal
is amplified and displayed.
Electroencephalogram (EEG) - A recording of the electrical activity generated
by the brain. Brain wave frequencies are expressed in hertz (Hz) or cycles per
second (cps), and amplitude is expressed in microvolts. Characteristic
frequency and amplitude patterns of the activity define which stage of sleep
the patient is experiencing. Brain waves are recorded in both diagnostic and
CPAP titration sleep studies.
Electromyogram (EMG) - A recording of the electrical activity of the
muscles. The absence of very low level of EMG activity indicates the presence
of REM sleep. Very high levels can help identify periods of wakefulness.
Non-invasive EMG is recorded in both diagnostic and CPAP titration sleep
studies.
Electrooculogram (EOG) - A recording of the movements of the eyes. If
rapid eye movements are detected during sleep, the subject is in REM sleep,
which is the state in which vivid dreaming takes place. EOG is recorded in both
diagnostic and CPAP titration sleep studies.
EPAP - (Expiratory Positive Airway Pressure) - The pressure prescribed
for the expiratory (breathing out) phase of an individual on Bi-level CPAP
therapy for OSA (obstructive sleep apnea).
Epidemiology - The scientific discipline that studies the incidence,
distribution, and control of disease in a population. Includes the study of
factors that affect the progress of an illness, and, in the case of many
chronic diseases, their natural history.
Epoch - A standard 30-second page of the sleep recording that is
assigned a sleep stage designation; occasionally, for special purposes, longer
or shorter epochs are scored.
Epworth Sleepiness Scale - An index of sleep propensity during the day
as perceived by patients, and derived from the answers to 8 questions.
Esophageal Pressure - A measurement used to determine respiratory effort
and by inference, airway resistance. Considered an invasive measure, it is
sometimes used in polysomnographic testing that is conducted in sleep disorders
centers.
Excessive Daytime Sleepiness (EDS, Somnolence, Hypersomnia) - A
subjective report of difficulty in maintaining the awake state, accompanied by
a ready entrance into sleep when the individual is sedentary; may be
quantitatively measured by use of subjectively defined rating scales of
sleepiness.
Expiratory Phase - The phase of the breathing cycle in which air is
expelled.
Fatigue - A feeling of tiredness or weariness usually associated
with performance decrements.
Fiberoptic Nasopharyngoscope - A flexible fiberoptic scope used to
examine the nasal passages, pharynx, hypopharynx and larynx.
Flattening Index - A number that indicates the amount of airflow
limitation caused by partial closure of the upper airway. 0.3 indicates an open
airway, 0.15 is mildly obstructed, 0.1 is severely limited airflow, and 0.0
reflects a totally closed airway. Flattening Index is used to identify a
condition known as Upper Airway Resistance Syndrome (UARS), and is continuously
recorded in some diagnostic sleep studies and CPAP titration studies.
Flow Limitation - Partial closure of the upper airway, which impedes the
flow of air into the lungs.
Forbidden Zone - Period of strongest clock-dependent alerting, usually
in the evening. Prevents falling asleep.
Fragmentation (pertaining to Sleep Architecture) - The interruption of a
sleep stage due to the transition to a lighter stage, or to wakefulness,
leading to disrupted sleep cycles.
GABA (Gamma-Amniobutyric Acid) - A major inhibiting
compound (neurotransmitter) in the brain, which is considered to be involved in
muscle relaxation, sleep, diminished emotional reaction and sedation. GABA is
released in the greatest amount from the cerebral cortex during slow wave
sleep.
Gastroesphageal Reflux Disease (GERD) - The flow of stomach acid upwards
into the esophagus, which can cause arousals and disrupt sleep.
Genioglossus tongue advancement - Surgical treatment sometimes used for
sleep apnea or snoring. This is designed to improve the airway behind the base
of the tongue. The genioglossus, which is the main tongue muscle, relaxes
during sleep, often allowing the tongue to fall into the airway. This muscle
attaches to the middle of the lower jaw. If a segment of bone containing this
muscle is pulled forward and stabilized, it can open the airway space behind
the tongue. This procedure does not move the teeth or jaw. It is performed
under local intravenous sedation or general anesthesia and requires a one or
two day hospital stay
Habitual Snorers - Individuals who snore nearly every night.
Heart Rate or beats per minute (bpm) - Pace or speed of the heart
measured in beats per minute; 60-80 is generally considered normal. Heart rate
is continuously monitored in both diagnostic sleep studies and CPAP titration
studies.
Hertz (Hz) - A unit of frequency measuring cycles per second (cps). A
measurement used in describing sleep EEG brain waves.
Histogram - A graph showing frequency distributions.
Humidification - Adding moisture to the airflow as an adjunct to CPAP
(Continuous Positive Airway Pressure) therapy in the treatment of obstructive
sleep apnea (OSA). Humidification is added to the CPAP device by diverting the
airflow over a cool or heated water reservoir (humidifier) to prevent the upper
airway from drying out.
Hyoid Suspension - Surgical procedure sometimes used in the treatment of
sleep apnea or snoring. It is designed to improve the airway behind the base of
the tongue. The hyoid bone is located in the neck where some tongue muscles
attach. If the hyoid bone containing these muscles is pulled forward in front
of the voice box, it can open the airway space behind the tongue. This is
performed under local intravenous sedation or general anesthesia, and requires
a one or two day hospital stay.
Hypercapnia - An excess of carbon dioxide in the blood.
Hyperirritability - Extreme irritability; often seen in sleep deprived
subjects.
Hypersomnia - Sleeping for uncharacteristically long periods of time.
Hypersomnolence - Excessive daytime sleepiness.
Hypertension - High blood pressure.
Hypnic Jerk - Sensation of falling, and then "jerking" awake
just as one drifts to sleep. It is a normal sensation experienced by many
people.
Hypnophobia - Morbid fear of falling asleep.
Hypnotics - Sleep-inducing medications; sleeping pills.
Hypopharynx - The lowermost portion of the pharynx leading to the larynx
and esophagus.
Hypopnea - An episode of diminished breathing during sleep, caused by a
partial airway obstruction, and resulting in arousal. Usually accompanied by
oxygen desaturation. Hypopneas may be just as serious as apneas and have the
same troublesome effects.
Hypoventilation - Reduced rate and depth of breathing.
Hypoxemia - Lack of an adequate amount of oxygen in the blood.
Hypoxia - A deficiency of oxygen reaching the tissues of the body.
Imidazopyridines - Newest class of medications that induce
sleepiness. They are short acting and few side effects have been found with
this class of hypnotics. (Zolpidem, trade name Ambien, is in this class).
Inappropriate Sleep Episodes - Periods of sleep that are not planned and
often occur in an unsafe situation (i.e., while driving). These episodes are
always due to sleep deprivation.
Insomnia - Difficulty with falling asleep or staying asleep.
Inspiratory Phase - Part of the breathing cycle during which air is
inhaled.
"Intermediary" Sleep Stage - A term sometimes used for non-REM
stage 2 sleep. See Deep Sleep, Light Sleep.
Invasive - Refers to a medical procedure in which a bodily orifice or
the skin must be penetrated for the purpose of collecting data, or for
diagnosing or treating a disorder.
IPAP - Inspiratory Positive Airway Pressure. The pressure prescribed by
a physician for the inspiratory phase on a Bi-level CPAP device, used in the
treatment of OSA.
Jet Lag - A disturbance induced by a major rapid shift in
environmental time during travel to a new time zone. Symptoms include fatigue,
sleep and impaired alertness.
K-Alpha - A type of micro-arousal where a K complex is followed by
several seconds of alpha rhythm.
K Complex - An EEG waveform most commonly found in stage 2 sleep. It has
a well-delineated negative sharp wave that is immediately followed by a slower
positive component.
Laser Assisted Uvuloplasty (LAUP) - Surgical treatment
usually used for simple snoring or mild obstructive sleep apnea. This procedure
is designed to open the airway behind the palate. It requires multiple
procedures where the laser reduces tissue of the palate and the area heals by
scarring. It is an outpatient procedure performed under local anesthesia.
Leg Movement - Leg movements are recorded in diagnostic sleep studies to
test for Periodic Limb Movement Disorder.
Letter of Medical Necessity (LMN) - Special document that is a certification
by a physician that the prescribed item(s) is medically indicated, reasonable
and necessary with reference to the standards of medical practice and treatment
of the patient's condition.
Light-Dark Cycle - The periodic pattern of light (artificial or natural)
alternating with darkness.
Light Sleep - A common term used to describe non-REM sleep stage 1, and
sometimes, stage 2.
Light Therapy - Used to treat SAD (Seasonal Affective Disorder) and
other conditions. Exposing the eyes to light of appropriate intensity and
duration at the appropriate time of day to affect the timing, duration and
quality of sleep.
Limit-Setting Sleep Disorder - Occurs when a child stalls or refuses to
go to bed, and subsequently does not receive enough sleep.
Linear Sleepiness Rating Scale - A measure of subjective sleepiness. The
scale consists of a horizontal line, 100 mm in length on which the right
extreme is labeled "Very Sleepy" and the left extreme is labeled
"Very Wide Awake."
Macroglossia - Large tongue; usually a congenital disorder (present at
birth). May result from other medical conditions such as acromegaly.
Marijuana - Parts or extracts of the hemp plant, which contain an active
ingredient called tetrahydrocanabinol (THC) that is euphorogenic. Some people
use marijuana at bedtime as an aid to falling asleep.
Maxillofacial - Pertains to the jaws and face.
Maxillomandibular advancement - This surgical procedure opens the airway
behind the palate as well as behind the base of the tongue. The operation cuts
the bone of the upper and lower jaw and pulls these structures forward. This is
performed under general anesthesia and requires a two-day hospital stay. This
type of treatment is usually done if previous procedures have not completely
improved the obstructive breathing episodes and the patient has persistent
symptoms of daytime sleepiness and fatigue.
Melatonin - A hormone secreted by the pineal gland in the brain.
Melatonin has been reported to have hypnotic properties, leading some to
suggest that melatonin, which is released at night, may be an endogenous sleep
inducer.
MESAM 4 - Type of portable recording device used in diagnostic sleep
studies.
Microsleep - Very brief episode of sleep that occurs in the midst of
ongoing wakeful activity. Microsleeps are associated with sleep deprivation,
drowsiness and automatic behavior.
Mixed Sleep Apnea - Combination of central and obstructive apnea.
Monocyclic - Having a single major sleep period and a single major wake
period in one 24-hour day.
Motor Activity in Sleep - Any muscular movement during sleep.
Movement Arousal - A body movement associated with an EEG pattern of
arousal or a full awakening.
Motor Atonia - Absence of muscle activity during sleep, a normal
phenomenon during REM sleep.
Multiple Sleep Latency Test (MSLT) - The standard test used to quantify
the overall daytime sleep tendency by measuring the speed of falling asleep
(sleep latency) usually in 5 tests carried out at two-hour intervals. This test
also helps in the diagnosis of narcolepsy. Patients with narcolepsy often go
directly from wakefulness to REM, which can be evaluated with the MSLT.
Muscle Tone - The amount of tension in a muscle.
Myoclonus - Muscle contractions in the form of abrupt "jerks"
or twitches generally lasting less than 100 milliseconds. The term should not
be confused with the periodic limb movements of sleep that characteristically
have a duration of 0.5-5 seconds.
Nap - A short period of sleep generally obtained at a time
separate from the daily major sleep period.
Narcolepsy - A sleep disorder characterized by excessive sleepiness,
cataplexy, sleep paralysis, hypnagogic hallucinations, and an abnormal tendency
to pass directly into REM sleep from wakefulness. It was recently found to be
caused by an abnormal gene in the brain.
Nasal Airflow/Nasal Ventilation - A recording of the respiratory cycle
by measuring inspiratory and expiratory airflow. In diagnostic sleep studies it
is referred to as nasal ventilation or respiratory airflow. It is measured
through heat or pressure changes at the nares. This value is usually recorded
in both diagnostic sleep studies and CPAP titration sleep studies.
National Commission on Sleep Disorders Research - Created by the U.S.
Congress in 1990, the commission conducted a comprehensive study of the social
and economic impact of sleep disorders in America, and made recommendations
based on its findings to Congress in January of 1993.
Neurology - A specialized branch of medicine that deals specifically
with the nervous system and its diseases.
Neurotransmitters - Endogenous chemical components that are released
from axon terminals of one neuron and transmit the signal to the next neuron by
combining with its receptor molecules. Examples of neurotransmitters that
appear to be important in the control of sleep and wakefulness include:
norepinephrine, serotonin, acetylcholine, dopamine, adrenaline and histamine.
The process of neurotransmission may be inhibited, modulated, or
enhanced by other chemical mediators within the brain, or by exogenous
pharmaceuticals.
Nightmare - An unpleasant and/or frightening dream that usually awakens
a person from REM sleep. Occasionally called a dream anxiety attack, it is not
synonymous with a night (sleep) terror.
Night Terrors - Also known as sleep terrors, or pavor nocturnus. Usually
a disorder of childhood, characterized by a piercing scream, signs of intense
fear, and unresponsiveness to other people. It is not a REM stage nightmare,
but an incomplete arousal from slow wave sleep. If awakened during a night
terror, the individual is usually confused and does not remember details of the
event. Night terrors are different from nightmares in that if an individual is
awakened during a nightmare, he or she functions well and may have some recall
of the nightmare.
Nyctophobia - Morbid fear of the night and darkness.
Nocturia - Excessive, and often frequent, urination during the night.
Nocturnal - "Of the night;" pertains to events that happen
during sleep or the hours of darkness.
Nocturnal Confusion - Episodes of delirium and/or disorientation close
to or during nighttime sleep; often seen in victims of Alzheimer's disease and
more common in the elderly.
Nocturnal Enuresis (Bedwetting) - The release of urine while asleep.
Non-Invasive - Medical procedure that does not penetrate the skin or a
body cavity.
NREM Sleep (Non-Rapid Eye Movement, Non-Rem) - All sleep stages other
than REM sleep; made up of sleep stages 1 through 4. Characterized by a slowing
of brain waves and some physiological functions. A state that lacks the visible
motility of rapid eye movements and twitches. See Sleep Stages.
NREM-REM Sleep Cycle (synonymous with Sleep Cycle) - A period during
sleep composed of a NREM sleep episode followed by a REM sleep episode. Each
NREM-REM sleep couplet is equal to one cycle; with the average duration in
adults being 90 minutes. An adult sleep period of 6.5-8.5 hours generally
consists of four to six cycles.
NREM Sleep Intrusion - A brief period of NREM sleep patterns appearing
in REM sleep, outside of its usual sleep cycle position.
NREM Sleep Period - The NREM sleep portion of NREM-REM sleep cycle. See
Sleep Cycle, Sleep Stages.
NREM Sleep - Consists of sleep stages 1 through 4, and characterized by
a decrease of mental activity. A state that lacks the visible motility of rapid
eye movements and twitches, and exhibits a different EEG pattern than REM
sleep. See Sleep Stages.
Obesity-Hypoventilation Syndrome - A term applied to obese
individuals who have abnormally slow and shallow respiration (hypoventilation)
during wakefulness, resulting in an increased level of carbon dioxide in the
blood.
Obstructive Hypopnea - Periodic, partial closure of the throat during
sleep resulting in reduced air exchange. The medical consequences of this
partial closure can be as severe as sleep apnea (full closure of throat)
Usually characterized by snoring, excessive daytime sleepiness, and other
symptoms of fatigue
Obstructive Sleep Apnea - Repetitive cessation of breathing during sleep
for 10 seconds or more due to complete closure (collapse) of the throat.
Usually characterized by snoring, excessive daytime sleepiness, and other
symptoms of fatigue.
Ondine's Curse - Condition in which the respiratory center in the brain
is unable to stimulate breathing in response to an increased amount of carbon
dioxide in the blood. Ondine's Curse is synonymous with central alveolar
hypoventilation and typically worsens during sleep.
Optimum Sleep - The average amount of sleep needed every night by any
given individual. Most adults require about 7 to 8.5 hours per night, although
this number is subjective, and may vary from person to person.
Oscillograph - A device that displays ongoing physiological patterns
(EEG) or other variables usually tracing on moving paper or a CRT screen.
Oxygen Desaturation - Less than normal amount of oxygen carried by
hemoglobin in the blood. A value below 90% is considered abnormal.
Oxygen Saturation - A measure of oxygen carried by hemoglobin in the
blood. Normal values range from 90% to 100%. An important indicator of sleep
disordered breathingthat is directly affected by the degree of throat closure
(partial vs. complete) and its duration. Oxygen saturation is recorded in both
diagnostic sleep studies and titration studies.
Oximeter - Medical device used to provide estimates of arterial oxygen
saturation (SaO2) by utilizing selected wavelengths of light to noninvasively
determine the saturation of oxyhemoglobin (SpO2).
Oximetry - Test used to continuously monitor the oxygen saturation of
arterial blood from a pulse oximeter sensor attached to the finger.
Quiet Sleep - The term frequently used instead of NREM sleep in
describing the sleep of infants. Quiet/NREM sleep comprises 50% of a newborns'
total sleep time.
Radiofrequency - Electromagnetic radiation in the frequency range 3
kilohertz (kHz) to 300 gigahertz (GHz). It is generally considered to include
microwaves and radio waves. Microwaves occupy the spectral region between 300
GHz and 300 MHz, while RF or radio waves include 300 MHz to 3 kHz. The primary
health effects of radiofrequency energy are considered to be thermal. The
absorption of radiofrequency energy varies with frequency.
Radiofrequency (RF) Procedure (Somnoplasty) - A procedure for treating
nasal obstruction, snoring and in some cases, sleep apnea. This procedure uses
radio wave energy to reduce snoring and the size of a redundant soft palate.
These techniques are performed under local anesthesia as an out-patient
procedure.
Rapid Eye Movement Sleep (REM Sleep) - See REM Sleep, Sleep Stages.
REM Density - The frequency of eye movements per unit of time during REM
sleep.
REM-Associated Disorders - Sleep disturbances that occur in REM sleep.
REM Motor Atonia - The suppression, or paralysis, of voluntary muscles
during REM sleep. These muscles become completely flaccid and limp.
REM Sleep (Rapid Eye Movement Sleep) - The sleep stage in which vivid
dreaming occurs; identified by the occurrence of rapid eye movements under
closed eyelids, motor atonia and low voltage EEG patterns. Also associated with
bursts of muscular twitching, irregular breathing, irregular heart rate, and
increased autonomic activity.
REM Sleep Behavior Disorder - A disorder in which REM motor atonia is
partially or completely absent. People with this disorder are able to move
their muscles and act out their dreams. The behaviors may include punching,
kicking, leaping and running from the bed.
REM Sleep Episode - The REM sleep portion of a NREM-REM sleep cycle.
There are typically 4-6 REM sleep episodes during an entire sleep period. Early
episodes may be only several minutes in duration. Later REM episodes are
usually longer, lasting 20 to 60 minutes.
REM Sleep Intrusion - A brief interval of REM sleep appearing out of its
usual positioning in the NREM sleep cycle.
REM Sleep Latency - The interval from sleep onset to the first
appearance of REM sleep.
REM Sleep Onset - The designation for the first epoch of a REM sleep
episode.
REM Sleep Percent - The proportion of total sleep time occupied by REM
sleep.
REM Sleep Rebound - A compensatory increase in REM sleep following a
reduction of REM Sleep Percent. An increase in time, frequency and density of
REM sleep episodes.
Respiratory Care Practitioner (RCP) - A licensed health care
professional specifically trained in cardiopulmonary assessment, diagnostics,
therapy administration, and patient education, including the identification and
treatment of sleep disorders.
Respiratory Disturbance Index (RDI)(Apnea/Hypopnea Index) - The
frequency of abnormal respiratory events per hour of sleep. These events are
classified as Apneas or Hypopneas. Apnea is when breathing (airflow) stops for
10 seconds or more. Hypopnea is a partial blockage of airflow resulting in
arousal and a possible drop in oxygen level. An RDI of 45 would indicate that
the patient is experiencing complete or partial airflow blockage 45 times
per hour.
Restless Legs Syndrome - The sleep disorder characterized by tingling,
creeping, crawling, or aching sensation in the legs that tends to occur when an
individual is not moving. There is an almost irresistible urge to move the legs
that relieve the sensations. Inability to remain at rest can result in severe
sleep disturbance.
Restlessness (Referring to Quality of Sleep) - Persistent or recurrent
body movements, arousals, or brief awakenings in the course of sleep.
Seasonal Affective Disorder (SAD) - A mood disorder
occurring in the winter months characterized by diminished energy, hypersomnia,
overeating and depressed mood. Exposure to bright light in the morning hours
may be effective in alleviating or decreasing symptoms.
Sedatives - Drugs that tend to calm, reduce nervousness or excitement,
and foster sleep onset.
Sedentary Situation - Does not require physical activity, e.g. working
at a desk, sitting in a meeting or in a theater, watching television.
Septoplasty - Surgery on the nasal septum (the partition that divides
the nasal passage).
Serotonin - A neurotransmitter in the brain that modulates mood,
appetite, sexual activity, aggression, body temperature and sleep.
Shiftwork - Working during times other than the conventional daytime
hours of 9:00 a.m. to 5:00 p.m.
Siesta - A custom in many cultures of napping in the afternoon, usually
after the noon meal. This allows people in tropical climates to avoid the
hottest part of the day; it also takes advantage of the body's normal
post-lunch (postprandial) dip in alertness.
Sleep - Overall state in which an individual rests quiescently in a
recumbent position, disengages from the environment, and become unresponsive to
stimuli.
Sleep Apnea - Cessation of breathing for 10 or more seconds during
sleep. There are two basic types of sleep apnea: Obstructive Apnea is
caused by a closure of the air passage despite efforts to breathe; Central
Apnea is a lack of effort to breathe. Obstructive Sleep Apnea is by far the
most common type.
Sleep Architecture - The sequence and duration of each sleep stage and
awakening during a sleep period. Often displayed in the form of a histogram.
Sleep Cycle - The progression through an orderly succession of sleep
states and stages. In a healthy adult, the first cycle is always initiated by
going from wakefulness to non-REM sleep. The first REM period follows the first
period of non-REM sleep to complete the first sleep cycle. The two sleep states
continue to alternate throughout the night with an average cycle period of
about 90 minutes. A full night of normal human sleep will usually consist of
4-6 non-REM/REM sleep cycles.
Sleep Debt - The result of recurrent sleep deprivation that occurs over
time, when an individual does not obtain a sufficient amount of restorative
daily sleep. Sleep debt is like a monetary debt; it must be paid back at some
time. The larger the sleep debt, the stronger the tendency to fall asleep. This
accumulation of "lost sleep" may contribute to a decreased quality of
life, the onset of related health problems, and the increased risk of injury
and/or accident. See Sleep Deprivation.
Sleep Deprivation - An acute or chronic lack of sufficient sleep, which
causes a person to feel unrefreshed during wakefulness.
Sleep Disorders - A broad range of illnesses arising from many causes,
including; dysfunctional sleep mechanisms, abnormalities in physiological
functions during sleep, abnormalities of the biological clock, and sleep
disturbances that are induced by external factors.
Sleep Efficiency (or Sleep Efficiency Index) - The ratio of total sleep
time to time in bed. The proportion of sleep in the period potentially filled
by sleep.
Sleep Episode - A total interval of sleep that may be voluntary or
involuntary.
Sleep Extension - Extending sleep time by increasing the time in bed.
Extended sleep alleviates the chronic sleep debt and provides an accompanying
increase in alertness. It is common for many people to extend, or "catch
up" on their sleep debt by sleeping for longer periods on the weekend.
Sleep Fragmentation - Brief arousals that occur throughout the night,
that reduce the total amount of time spent in the deeper levels of sleep.
Frequent episodes of sleep fragmentation lead to sleep deprivation.
Sleep Hygiene - Behavioral activities that either contribute to or
detract from restorative sleep. Good sleep hygiene would include activities
such as going to bed the same time each night, restricting caffeine intake, and
avoiding napping during the day.
Sleep Hyperhydrosis - Excessive sweating during sleep.
Sleeping Pills (hypnotics) - Compounds that have a sedative effect are
often used to produce sleepiness. If taken frequently, development of tolerance
to the medication is common.
Sleep Inertia - Feelings of grogginess and sleepiness that persist up to
20 minutes after waking up. This results in poor performance upon awakening.
Sleep Latency - The length of time it takes to go from full wakefulness
to the moment of sleep.
Sleep Log (Diary) - A daily, written record of a person's sleep-wake
pattern containing such information as time of retiring and arising, time in
bed, estimated total sleep time, number and duration of sleep interruptions,
quality of sleep, daytime naps, use of medications or caffeine beverages, and
nature of waking activities.
Sleep Mentation - All thoughts, feelings, images, perceptions,
hallucinations, and active dreams that take place during sleep.
Sleep Onset - The time from when a person attempts to fall asleep until
the onset of sleep. This sleep onset normally leads to NREM stage 1 sleep, but
in certain conditions, such as infancy and narcolepsy, may lead to REM stage
sleep.
Sleep Onset Imagery - A kaleidoscope of images and experiences during
the moments following the transition from wake to sleep.
Sleep Onset REM Period (SOREMP) - REM periods within 15 minutes of sleep
onset, considered to confirm the diagnosis of narcolepsy. As a result,
narcoleptics often experience Hypnagogic Hallucinations as they are
falling asleep.
Sleep Paralysis - Sleep paralysis is a common part of REM sleep itself
but is a disorder when it strikes outside REM sleep. Usually, people with sleep
paralysis are unable to perform voluntary movements either right before they go
to sleep or upon waking in the morning. One of the symptoms of narcolepsy, but
also experienced by some non-narcoleptic individuals.
Sleep Period - The time it takes to complete one cycle of sleep activity.
Sleep Related Accidents - Accidents caused by individuals who were sleep
deprived and had impaired judgment.
Sleep Restriction - A limitation of the number of hours in bed.
Sleep Spindle - A synchronized, rhythmic EEG waveform, with a duration
of about ½ second and a frequency of 12 to 14 Hz. Sleep spindles are observed
most frequently during stage 2 sleep.
Sleep Stage Demarcation - The significant polysomnographic
characteristics that distinguish the boundaries of the sleep stages.
Sleep Stages - Distinctive stages of sleep as demonstrated by EEG
patterns. See Stages 1-4; REM Sleep.
Sleep Stage 1 (NREM Stage 1) - A stage of NREM sleep that ensues
directly from the awake state. Its criteria consist of a low-voltage EEG
tracing with well defined alpha activity and theta frequencies in the 3 to 7
cps range, occasional vertex spikes, and slow rolling eye movements (SEMs), and
includes the absence of sleep spindles, K complexes, and REMS. Stage 1 normally
represents 4-5% of total sleep.
Sleep Stage 2 (NREM Stage 2) - A stage of NREM sleep characterized by
the advent of sleep spindles and K complexes against a relatively low-voltage,
mixed frequency EEG background. High voltage delta waves may comprise up to 20%
of stage 2 epochs. Stage 2 usually accounts for 45-55% of total sleep time.
Sleep Stage 3 (NREM Stage 3) - A stage of NREM sleep defined by at least
20% and not more than 50% of the period consisting of EEG waves of 2 cps or
slower, with amplitudes of more than 75 mV (high-amplitude delta waves). It
constitutes "deep" NREM sleep, or, so-called slow wave sleep (SWS),
and is often combined with stage 4 NREM sleep because of the lack of documented
physiological differences between the two. It normally appears usually only in
the first third of the sleep episode, and usually compromises 4-6% of total
sleep time.
Sleep Stage 4 (NREM Stage 4) - All statements concerning NREM sleep
stage 3 apply to stage 4 except that high-voltage, slow EEG waves cover 50% or
more of the record. NREM sleep stage 4 usually represents 12-15% of total sleep
time. Sleepwalking, sleep terrors, and sleep-related enuresis episodes
generally start in stage 4 or during arousals from this stage.
Sleep Starts - See Hypnic jerks.
Sleep talking - Talking in sleep that usually occurs in the course of
transitory arousals from NREM sleep. Can occur during REM sleep, at which time
it represents a motor breakthrough of dream speech. Full consciousness is not
achieved and no memory of the event remains. Sleep talking probably carries no
psychological or psychiatric significance, and the content should be taken very
lightly.
Sleep walking (Somnambulism) - Arising from bed during a period when
there is a simultaneous occurrence of incomplete wakefulness and NREM sleep.
The eyes are usually open, but appear not to be focusing. If victims do not
awaken during the episode, they do not remember the event. An extremely common
phenomenon, occurring in up to 40 percent of children, with a peak incidence at
12 years of age. Sleepwalking typically occurs in the first third of the night
during deep NREM sleep (stages 3 and 4).
Sleep-Wake Cycle - The clock hour relationships of the major sleep and
wake episodes in the 24-hour cycle. See Phase Transition, Circadian Rhythm.
Sleep-Wake Shift (Change, Reversal) - When sleep as a whole or in part
is moved to a time of customary waking activity, and wakefulness is moved to
the time of the major sleep episode. This is common in jet lag and shift work.
Sleep-Wake Transition Disorder - Parasomnia disorders that occur during
the transition from wakefulness to sleep or from one sleep stage to another.
These disorders include rhythmic movement disorders, hypnic jerks (sleep
starts), sleep talking, and nocturnal leg cramps.
Slow Eye Movements (SEM) - Slow, rolling movements of the eyes under
closed eyelids that occur as one drifts to sleep in stage 1.
Slow Wave Sleep (SWS) - Stage of sleep in which EEG delta waves are
present. Synonymous with sleep stages 3 and 4.
SmartPAP (Smart CPAP) - (Smart [Continuous] Positive Airway Pressure) A
medical device used in the treatment of obstructive sleep apnea that provides a
range of preset levels of continuous airflow, and automatically adjusts to keep
the breathing passages open by sensing changes in airway integrity. The air flows
from the device through a tube that connects to a nose or facemask.
Snoring - Sounds made during sleep caused by breathing vibrations in the
pharynx. In the diagnosis of obstructive sleep apnea, snoring volume and
frequency of occurrence often correlate with the severity of the condition.
Snoring noise is recorded in both diagnostic sleep studies and CPAP titration
studies.
Snoring Noise - This is recorded in both diagnostic sleep studies and
titration studies, and often correlates with the severity of airway obstruction
and apnea.
Soft Palate - The membranous and muscular fold on the roof of the mouth
that extends back from the hard palate and partially separates the oral cavity
from the pharynx.
Somatic Complaints - Awareness of pain or problems in the body.
Somnambulism - See Sleep Walking
Somnifacient - Inducing sleep; hypnotic, as in a drug.
Somnolence - Oppressive drowsiness or inclination to sleep.
Somnoplasty - The commercial name for radiofrequency treatment of
snoring, nasal obstruction and some cases of mild sleep apnea. (see
Radiofrequency Procedure).
Soporific - Causing or tending to induce sleep, such as a hypnotic drug.
Stages of Non-REM Sleep - Four sleep stages associated with mixed
frequency, mixed amplitude brain waves, an absence of rapid eye movements and
the continuous tonic presence of low-level EMG activity from the neck and jaw
muscles.
Stage 1 (NREM Stage 1) - The lightest phase of NREM sleep that directly
follows the awake state. It is a transition between wakefulness and sleep, and
an individual is easily aroused from this stage. It is characterized by mixed
frequency, low-voltage EEG patterns with bursts of alpha activity and theta
frequencies in the 3 to 7 cps range, occasional vertex spikes. Another feature
is slow, rolling eye movements (SEMs). There is an absence of sleep spindles, K
complexes, and REMS. In adults, stage 1 normally represents 4-5% of total
sleep. However, in some sleep disorders, such as sleep apnea, this percentage
of stage 1 increases. A person with sleep apnea must wake up to breath, and
stage 1 follows every arousal.
Stage 2 (NREM Stage 2) - Stage of NREM sleep characterized by the advent
of sleep spindles and K complexes against a low-voltage, mixed frequency EEG
background similar to stage 1. Stage 2 sleep is usually free of slow rolling
eye movements. A more intense stimulus is required to wake someone from stage 2
than from stage 1. In adults, stage 2 typically accounts for 45-55% of total
sleep time.
Stage 3 (NREM Stage 3, Delta Sleep, Slow Wave Sleep) - Stage 3, along
with stage 4 sleep is often called Delta Sleep or Slow Wave sleep. The Stage 3
EEG record consists of 20% to 50% delta EEG waves. These delta waves have a
slow frequency of 2 cps or slower, and amplitudes of more than 75 mV (high
amplitude delta waves). Stage 3 sleep is deeper than stages 1 or 2; it takes a
more intense stimulus to awaken someone in this sleep state. Stage 3 primarily
appears in the first half of the sleep episode in adults.
Stage 4 (NREM Stage 4, Delta Sleep, Slow Wave Sleep) - Stage 4 has
similar attributes to stage 3, except there are a greater proportion of EEG
delta waves. These high-voltage, slow EEG waves make up 50% or more of the
record. This is the deepest stage of sleep; a more intense stimulus is needed
to wake someone from stage 4 sleep than any other stage of NREM sleep. Young
children have more stage 4 sleep and are much more difficult to arouse than
adults. Both stages 3 and 4 decline with age and many older people report that
their sleep is lighter than when they were young. Children typically spend
20-25% of sleep in stages 3 and 4 slow wave sleep; this decreases to less than
10% by age 60. Sleepwalking, sleep terrors, and sleep-related enuresis episodes
generally occur in stages 3 or 4, or during arousals from this stage.
Stanford Sleepiness Scale (SSS) - A self-rating scale developed to
quantify subjective levels of sleepiness. It consists of seven numbered
statements.
Subjective Sleepiness - Feelings of sleepiness.
Substance Abuse - The excessive use of alcohol or drugs. These
substances can cause sleep disturbances.
Sudden Infant Death Syndrome (SIDS, Crib Death) - The sudden and
unexpected death of an apparently healthy infant, whose death remains
unexplained after an adequate postmortem investigation. Death usually occurs
during sleep. SIDS is the leading cause of death in infants in their first year
of life, with the peak occurrence at 2 - 4 months. Although the majority of
SIDS victims do not have identifiable risk factors, groups of infants at a
somewhat higher risk include siblings of SIDS victims and infants born to
substance-abusing mothers.
Synchronization - Two or more biological rhythms that have a 1:1
relation and maintain the same phase relationship. An example is the timing of
sleep onset with respect to body temperature; sleep onset tends to occur at the
same time of each temperature cycle, usually close to the minimum temperature.
Synchrony - Scheduling sleep to synchronize with the biological clock.
Tachycardia - Rapid heart rate. In adults, usually defined by a heart
rate of over 100 beats per minute (bpm).
Thermocouples - Small devices placed near the nostrils to measure
airflow by sensing temperature changes; expired air is warmer than inspired
air.
Thermoregulation - The regulation of body temperature in mammals.
Theta Activity - EEG brain wave activity with a frequency of 4-8 Hz. It
is most prominent over the central and temporal cortex.
Thoracic Excursion - Thoracic (chest) movement, which indicates
respiratory effort. This is recorded in diagnostic sleep studies, and is
typically measured by the placement of a sensor band around the chest. The
sensor band records chest wall movement associated with respiration. This
measurement is used in differentiating the type of sleep apnea.
Tidal Volume - The amount of air that passes in and out of the lungs in
an ordinary breath. Usually expressed in liters.
Titration - A method of determining optimal CPAP (continuous positive
airway pressure) treatment parameters for sleep apnea. This involves automatic
or manual adjustment of the CPAP device to a level that eliminates airway
blockage.
Transient Insomnia - Difficulty sleeping for only a few nights..
Tolerance - In pharmacology, refers to the reduced responsiveness to a
drug's action as the result of previous continued use.
Tonic (Event/Activity) - Physiological events that are constant or
continuous. In sleep, atonia refers to the lack of muscle tone during REM
sleep.
Tonsils - A pair of prominent masses of lymphoid tissue which are
located opposite each other in the throat between the anterior and posterior
pillars of the fauces (the narrow passage from the mouth to the pharynx
situated between the soft palate and the base of the tongue). Composed of lymph
follicles grouped around one or more deep crypts. Also called the palatine
tonsil.
Tonsillectomy - Surgical removal of the tonsils.
Toothgrinding (Bruxism) - Grinding one's teeth while asleep. This occurs
at some time in approximately 70% of people; most have no noticeable side
effects. However, 5% of victims develop symptoms such as tooth wear, jaw pain
and headaches. Episodes of grinding are more severe after stressful days.
Total Recording Time - The duration of time from the beginning of a
sleep recording ("lights out") to final awakening. In addition to
total sleep time, it is comprised of the time taken up by wakeful periods.
Total Sleep Time - The amount of actual sleep time in a sleep episode.
This is equal to the total sleep episode less the awake time. Total sleep time
is the total of all REM and NREM sleep in a sleep episode.
Tracheotomy - Surgical procedure to create an opening in the trachea
(windpipe) through which breathing can occur. Occasionally used to treat severe
obstructive sleep apnea that is non-responsive to other treatment.
Tracheostomy - Refers to the opening in the trachea. As a treatment for
severe obstructive sleep apnea, this opening bypasses an obstruction in the
airway.
Transducer - A device designed to convert energy from one form to
another.
Transient Arousals - Brief awakenings from sleep.
Transient Insomnia - Difficulty sleeping for only a few nights.
Tricyclic Antidepressants (Antidepressants) - A class of medications
most commonly used in the treatment of depression. Tricyclic refers to
the three-ring chemical structure. Most tricyclic antidepressants also reduce
REM sleep. In sleep disorders, they are used to control cataplexy, hypnagogic
hallucinations, and sleep paralysis.
Turbinate - Small, shelf-like, cartilaginous structures covered by
mucous membranes, which protrude into the nasal airway to help warm, humidify,
and cleanse inhaled air on its way to the lungs.
Twilight Zone - A slang term that describes the waking state of
individuals whose MSLT scores are 5 minutes or less. Such individuals are
usually sleep deprived or suffer from a sleep disorder.
Twitch (Body Twitch) - A very small body movement such as a foot or
finger jerk that is not usually associated with an arousal.
Unattended CPAP Titration Study - An automatic calibration
test performed with a CPAP machine that measures the patient's airway pressure
requirements during sleep. This is performed after determining that a patient
has a sleep related breathing disorder such as OSA or Upper Airway Resistance
Syndrome, and is likely to benefit from CPAP therapy. These findings are then
used to prescribe the appropriate pressure the patient will use with their CPAP
therapy.
Unintended Sleep Episode - A sleep episode that is not planned and may
happen during an activity in which such an episode is hazardous, such as when
driving a car or working with machinery.
Upper Airway - The part of the respiratory anatomy that includes the
nose, nostrils, sinus passages, septum, turbinates, tongue, jaw, and palate.
Upper Airway Resistance Syndrome - Part of the spectrum of obstructive
sleep-related breathing disorders in which repetitive increases in resistance
to airflow in the upper airway lead to brief arousals and daytime fatigue.
Usually associated with loud snoring. Apneas and hypopneas (see RDI) may be
totally absent. Blood oxygen levels can be in the normal range.
Uvula - Small soft structure hanging from the bottom of the soft palate
in the midline above the back of the tongue. It is composed of connective
tissue and mucous membrane.
Uvulopalatopharyngoplasty (UPPP) - Surgical treatment for obstructive
sleep apnea and snoring. This procedure is designed to open the airway behind
the palate. The uvula, tonsils, and excess palatal tissue are removed. The
incision is closed with sutures. The procedure is performed under general
anesthesia and usually requires a one or two day hospital stay.
Wake Time - The total time scored as wakefulness in a polysomnogram
occurring between "lights out" and final awakening.
White Noise - A mixture of sound waves extending over a wide frequency
range that may be used to mask unwanted noise that interferes with sleep. Also
called white sound.
Wilkinson Addition Test - A performance test in which the subjects add
numbers for one hour. Often included in a battery of tests to measure the
impact of acute or chronic sleep loss.
Withdrawal - The negative effects experienced when a person stops taking
sleeping pills.
Zeitgeber - An environmental time cue that entrain biological rhythms
to a specific periodicity. Known Zeitgebers are light, melatonin and physical
activity. To be effective, these signals must occur when the biological clock
is in a responsive phase.