About Sleep Disorders

Glossary

• Apnea
  A period of time during which breathing stops or is markedly reduced.
• Apnea Index (AI)
  A measure of the severity of sleep apnea; the number of all types of apnea events per hour.
• Apnea/Hypopnea Index (AHI)
  The number of apneas and hypopneas per hour. Also known as the Respiratory Disturbance Index (RDI).
• Arousal
  Abrupt change from sleep to wakefulness or from a "deeper" stage of non-REM sleep to a "lighter" stage. These often correlate with changes in heart rate.
• Arrhythmia
  A deviation in the normal pattern of the heartbeat.
• Basic Sleep Cycle
  Progression through orderly succession of sleep states and stages. For the healthy adult, the first cycle begins in going from wakefulness to non-REM sleep. The initial REM period follows the first period of non-REM sleep, and the two sleep states alternate throughout the night with an average period of about 90 minutes. A night of normal human sleep usually consists of 4-6 non-REM/REM sleep cycles.
• Bi-Level
  Two level pressure device used to treat sleep apnea. A lower pressure is used during exhalation and a higher pressure during inhalation. Bi-Level machines are more expensive than a standard CPAP device, but some patients tolerate it better because they can exhale more comfortably against the constant inhalation pressure. (Sometimes called Bi-PAP, but that is a trademark name of one system).
• Body Mass Index (BMI)
  Abbreviation for body mass index, the most popular tool for defining what are healthy weight, overweight, and obesity in an individual.
• Body Position
  Positions in which the patient is sleeping. Often quantitated into supine (back), and non-supine categories. The percentage of time spent sleeping in each position is measured.
• Bradycardia
  Heart rhythm with a rate lower than 60 beats per minute in an adult.
• Central Apnea
  Absence of airflow caused by a complete cessation of all respiratory effort to breathe. Abnormalities of respiratory control in the brain or elsewhere can produce central apnea.
• Circadian Rhythm
  The inherent daily fluctuation of behavioral and physiological functions including the sleep/wake cycle, generally tied to the 24 hour day-night cycle but sometimes to a different periodicity especially when light/dark and other time cues are removed.
• Continuous Positive Airway Pressure (CPAP)
  Application of positive air pressure at a constant level to help keep an airway open by acting as a pneumatic "splint", thus preventing the airway from collapsing during sleep. Measured in cm of H2O pressure.
• Desaturation
  A reduction of the value of the oxygen saturation (SaO2).
• Epworth Sleepiness Scale
  An index of sleep propensity (tendency) during the day as perceived by a patient, and derived from the answers to 8 standardized questions.
• Excessive Daytime Sleepiness or Hypersomnolence (EDS)
  A subjective report of difficulty in staying awake, accompanied by a ready entrance into sleep or diminished consciousness when an individual is sedentary.
• Fragmentation (Pertaining to Sleep Architecture)
  The interruption of a sleep stage as a result of the appearance of a lighter stage, or to the occurrence of wakefulness, which leads to a disrupted non-REM to REM sleep cycle.
• Hypersomnia
  Sleep of excessive depth or abnormal duration often characterized by a state of confusion upon awakening. Usually caused by psychological rather than physical causes.
• Hypertension (HTN)
  A persistent elevated blood pressure that is often asymptomatic.
• Hyperventilation
  An increased rate and/or depth of breathing.
• Hypopnea
  A decrease in breathing in which the airflow in and out of the airway is less than half of normal--usually associated with oxygen desaturation and commonly caused by partial airway obstruction. The presence of some airflow distinguishes this event from apneic episodes.
• Hypoventilation
  A reduced rate and/or depth of breathing.
• Hypoxemia
  Reduced oxygen tension in arterial blood.
• Hypoxia
  The condition in which an inadequate amount of oxygen reaches the tissues of the body. The tissues most sensitive to hypoxia are the brain, heart, pulmonary vessels and liver.
• Insomnia
  The chronic inability to fall asleep or remain asleep during the night.
• Laser Assisted Uvulopalatoplasty (LAUP)
  Laser removal of soft palate tissue which can eliminate or decrease snoring but has not been shown to be effective in the treatment of severe sleep apnea.
• Mixed Apnea
  An interruption in breathing during sleep beginning as a central apnea then becoming an obstructive apnea.
• Narcolepsy
  A sleep disorder often characterized by sudden sleep attacks and an abnormal tendency to pass directly from wakefulness into REM sleep in a short time.
• Obstructive Apnea
  The cessation of airflow for at least 10 seconds in the presence of continued inspiratory effort. In sleep these are often caused by a mechanical obstruction, such as a semi-collapsed airway, a tongue relaxing in the back of the throat, or large tissue in the uvula area.
• Obstructive Sleep Apnea Syndrome (OSA)
  A clinical spectrum of chronic disease caused by repeated apneic or hypopneic events during sleep.
• Oral Dental Devices
  Oral appliances, available from dentists specializing in treating dental sleep medicine, may be used in selected patients alone or in combination with other means to treat OSA. These devices work by bringing the lower jaw forward, and/or elevating the soft palette, and/or retaining the tongue from falling back into the airway.
• Oxygen Desaturation
  A decreased amount of oxygen carried by hemoglobin in the arterial blood.
• Oxygen Saturation (SaO2)
  A measure of oxygen carried by hemoglobin in the arterial blood. It is expressed as a ratio of the oxygenated hemoglobin molecules to all of the hemoglobin molecules (oxygenated and non-oxygenated). Values of arterial oxygen saturation in a young healthy adult are typically above 95%.
• Oximeter (Pulse)
  An instrument that gives estimates of arterial oxyhemoglobin saturation (SaO2) by measuring absorption of selected wavelengths of light in blood non-invasively. It is usually measured in peripheral tissues such as the fingers or earlobes.
• Periodic Limb Movement Disorder (PLMD)
  A syndrome also known as periodic leg movements or nocturnal myoclonus. Characterized by periodic episodes of repetitive and highly stereotyped limb movements occurring during sleep. The movements are often associated with a partial arousal or awakening; however, the patient is usually unaware of the limb movements or frequent sleep disruption. Between the episodes, the legs are still. There can be marked night-to-night variability in the number of movements or in the existence of movements.
• Pulmonary Hypertension
  High blood pressure in the vessels supplying blood to and from the lungs.
• Radiofrequency Tissue Ablation
  A procedure (Somnoplasty) for treating nasal obstruction, snoring and in some cases, sleep apnea. Uses radiowave energy to reduce snoring and the size of the soft palate.
• REM Sleep
  Rapid Eye Movement sleep. Sleep characterized by the most active brain activity, flitting motions of the eyes, and weakness of the muscles. Most dreaming occurs in this stage, which accounts for about 20 - 25% of sleep in adults.
• Respiratory Disturbance Index (RDI)
  An index that includes all respiratory events (apneas and hypopneas) per hour.
• Restless Legs Syndrome (RLS)
  A sleep disorder characterized by a deep creeping, or crawling sensation in the legs that manifests itself as unilateral or bilateral twitches in the legs. Episodes generally last from five minutes to two hours and can alternate with periods of normal sleep. Leg movement relieves the sensations.
• Sleep
  A state marked by lessened consciousness, lessened movement of the skeletal muscles, and depressed metabolism.
• Sleep Debt
  The result of recurrent sleep deprivation which occurs over time when an individual does not experience a sufficient amount of the restorative daily sleep that is required to maintain a sense of feeling rested and refreshed.
• 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 factors extrinsic to the sleep process.
• Sleep Walking
  — also known as somnambulism — usually involves getting up and walking around while asleep. Most common in children between the ages of 8 and 12, sleepwalking often is a random event that doesn't signal any serious problems or require treatment.
  
  However, sleepwalking can occur at any age and may involve unusual, even dangerous behaviors, such as climbing out a window or urinating in closets or trash cans.
• Snoring
  The noise produced primarily with inspiratory respiration during sleep coming from the vibration of the soft palate and the pillars of the oropharyngeal inlet. Many people having this symptom have incomplete obstruction of the upper airway, and may develop obstructive sleep apnea.
• Soft Palate
  The membranous and muscular fold suspended from the posterior margin of the hard palate and partially separating the oral cavity from the pharynx.
• Somnoplasty
  The common name for radiofrequency ablation of tissues in certain sleep disorders.
• Tachycardia
  A sustained rapid heart rate, usually defined by a pulse rate of over 100 beats per minute (bpm).
• Titration
  The progressive, stepwise increase or decrease in CPAP pressure to find the minimal pressure needed to keep the airway open in a sleep apnea patient.
• Upper Airway
  The parts of the respiratory anatomy that include the nose, nostrils, sinus passages, septum, turbinates, tongue, jaws, hard and soft palate, muscles of the tongue, and throat.
• Upper Airway Resistance Syndrome (UARS)
  A 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 hypersomnolence. Apneas and hypopneas may be totally absent. Blood oxygen levels and peripheral saturations can be in the normal range.
• Uvula
  A soft tissue structure hanging from the posterior aspect of the soft palate in the midline at the back of the tongue. It is frequently enlarged in sleep apnea patients.
• Uvulopalatopharyngoplasty (UPPP)
  Surgical resection of the uvulas, soft palate, and posterior tonsillar pillars.