Understanding Sleep Test Terms and Acronyms

Understanding Sleep Test Terms and Acronyms - A Brief Guide

By Admin

Whether you undergo a full sleep study in a lab, or use one of the many home-test options currently available, the resulting data will include terms and acronyms used to describe each of the measurements. These terms represent the parameters of sleep monitoring, and they include everything from general health markers like vital signs (temperature, heart rate, blood pressure, etc.) to the number and duration of sleep disruptions caused by disorders like sleep apnea. Sleep studies can involve a lot of recorded data, and neither patents nor doctors are expected to track and assess all of the information collected, but it is good to have a grasp of the most important highlights and how they relate to a possible sleep disorder diagnosis. Normally, a sleep lab technician will summarize test results in a condensed format, just as the sleep tracker apps do with charts or graphs, but in either case, it is important to understand what the measurements mean for both your general health and your sleep health. The following is a brief overview of the most common terms and acronyms used for sleep monitoring and diagnostic purposes.

Sleep Data Highlights: The Most Important Areas to Focus On

Sleep data is summarized in a variety of ways, depending on the focus of the test or application involved, and some results are easier to understand than others, but the majority will focus on aspects of sleep and health that are most important for diagnostic purposes. To fully understand these parameters, it is important to know not only what they mean, but also what the normal range is for healthy sleep.

Total Sleep Time (TST)

This measure quantifies sleep according to the total minutes spent unconscious. This is often the first thing people look at to see if they’re getting enough, or too much, sleep. Total sleep time is recorded using electrodes that are attached to the body (usually along the scalp). These electrodes are connected to electrophysiological monitoring devices such as the EEG, or electroencephalography, which records electrical activity in the brain (brain waves). By comparison. Sleep tracking apps, on the other hand, measure sleep time using motion sensors, along with an accompanying algorithm which estimates both the time and quality of a night of sleep. Called accelerometers, these sensors are sometimes combined with microphones, thermometers (thermisters), or other measuring tools to better assess physiological changes. While these methods have become extremely useful for assessing problems with sleep and health, a sophisticated medical device like an EEG will be more accurate and provide much more detail, especially when calculating the precise moments of sleep and waking.

Many people find that their total sleep time, when recorded, is different than they expected. According to recommendations from the National Sleep Foundation, most adults require 7-9 hours of sleep per night to maintain optimal health conditions (with slightly less for older adults).

Sleep Efficiency

Sleep efficiency is normally defined by the ratio of total sleep time to total bed time (TBT) or total recording time (TRT), which may vary depending on the specifics of the test. Most often in sleep studies, recording time begins when the patient is in bed and the lights are turned off as a cue to begin sleeping, often referred to as the “lights out” point. The “lights on” point signals the end of the recording time. In addition to the TST/TRT ratio, other considerations such as sleep behaviors or sleep onset latency may be observed as well. Sleep onset latency is the the time it takes to fall asleep once in bed or after the lights are turned off. A healthy sleeper will spend about 5-20 minutes falling asleep, based on testing norms, and tests will highlight short as well as long periods of latency as possible signs of a sleep problem. While people worry more about difficulties falling asleep, a brief onset period (less than 5 minutes) may result from lack of sleep, exhaustion, or other health problems.

Generally, over 80 percent Is considered a normal sleep efficiency ratio, but this will vary slightly by age and testing standards. This would be an average of about six and half hours of sleep time for an eight-hour period in bed (or during lights out). Sleep latency, of course, will affect this percentage, but most healthy adults do not have difficulty achieving over 80-percent efficiency.

One important note about sleep efficiency and latency is that not every factor is taken into account. For example, efficiency may not recognize brief episodes of wakefulness, however frequent, or a long sleep latency could offset the efficiency score regardless of quality sleep time. For this reason, some laboratories exclude sleep latency from the total wake time (TWT), which is the total time spent awake during the recording. By beginning wake time after sleep onset, it offers a variant perspective on sleep quality besides the efficiency score. Total wake time is also referred to as wake after sleep onset, or WASO, which is calculated as total recording time or time in bed minus sleep latency, minus total sleep time (TRT-SL-TST). A WASO below 20 percent of the TBT is considered normal for most adults.

Arousals

Nearly all sleep studies begin the first sleep stage epoch after the latency period, which represents the transition from consciousness to sleep. In sleep study terms, sleep is defined as the “natural periodic suspension of consciousness” consisting of slowed metabolism and characteristic changes in brain electrical activity (brain waves). Thereafter, moments of temporary waking are referred to as arousals (sleep interruptions lasting 3 to 15 seconds). More specifically, arousals are defined according to EEG frequency changes with at least 10 seconds of stable sleep preceding. Beyond 15 seconds, an arousal becomes an awakening, as full consciousness is normally reached by that time.

Arousals have a variety of causes, but the most important arousals for sleep test purposes are those caused by health or sleep-health problems. Some of the most common health-related arousals are those caused by respiratory distress, heart conditions, and sleep disorders.

In both polysomnography (sleep study) and home sleep tests, arousals are assessed according to the arousal index (ArI), which is the number of arousals per hour of sleep (total arousals x 60/TST in minutes). While arousals are not often recalled, they can be very disruptive to sleep. Each arousal brings the sleeper out of the current sleep stage and back to the beginning of the sleep cycle, which makes it harder to get back to a deeper level of sleep. Sleep tests will record every arousal and awakening in the night, and make note of high index scores (over 20 per hour), but this tends to rise with age from just over 10 in the teen years to 20 or more in middle age. As with most measurements on sleep tests, age and health conditions are factored into the overall scores. Arousals, for example, should be viewed along with any respiratory issues that could be symptoms of sleep apnea or another sleep-related breathing (SDB) disorder. People with high arousal numbers tend to feel less refreshed in the morning, which can lead to daytime sleepiness or fatigue. For those with severe conditions such as chronic sleep apnea, arousals can be very frequent and extremely disruptive.

Sleep Behaviors and Movements

Sleep behaviors can be anything from snoring or movements to serious disruptions that cause awakenings. Sleep tests tend to focus on those behaviors that may be related to sleep disorders or other sleep problems. Some common examples include bruxism (teeth clenching or grinding), periodic limb movements (PLM), and other parasomnias such as hyperhidrosis (night sweats), sleep walking, or REM sleep behavior disorder (acting out dreams). Periodic movement events such as PLM have their own indices, calculated as the the number of events per hour of sleep (or total events x 60/TST in minutes). For limb movements to be considered periodic, they must occur regularly throughout the night (every 5-20 seconds).

In the case of full sleep studies, a separate count is made of those events that lead to arousals. For example, limb movents are considered normal below an index of 15 (average within an hour), but periodic limb movements with arousals (PLMAr) are considered more problematic than movements alone. The same can be said about bruxism. One or two instances of teeth clenching or grinding may not be a problem, but repeated instances or those leading to arousals are signs of a chronic issue. Severity is also noted, as the behaviors may be mild or severe depending on how robust the motions are, and how dangerous they may be to bed partners or the sleepers themselves.

While movements can be recorded with motion sensors, polysomnography, or PSG, utilizes a number of advanced technologies to record multiple physiologic parameters related to sleep behaviors. The electrooculogram (EOG) is a measures eye movement, which is extremely important for later stages, and electromyography (EMG) measures muscle movement with a high level of sensitivity for subtle, surface-level twitches or spasms. A portable version of the EMG, known as the Chin EMG, records muscle activity in a similar manner but is also used to measure bruxism and sleep stage transitions.

Sleep Architecture: The Stages of the Sleep Cycle

The rate of a sleeper’s passage through the stages of sleep is known as sleep architecture, and this is extremely important for sleep health considerations. Sleep architecture recordings generally include stage latencies, time spent in each stage, and body position, as well as the percent in each sleep stage of total sleep time. There are four main stages of sleep that make up each sleep cycle, and a normal cycle lasts about 90-120 minutes. Thus, an 8-hour night of sleep would included about 4-5 cycles through the stages. The stages begin with the passage from the wake stage (stage W) to the first stage of Non-REM sleep, or NREM1.

NREM1 is sometimes referred to as pre-sleep or light sleep. About 5-10 percent of total sleep time is spent in Stage 1 (1-5 minutes each cycle). The next stage is Non-REM stage 2, or NREM2, which is deeper sleep than stage 1 and lasts about 25 to 50 percent of total sleep. This stage is characterized by shifts in the EEG known as sleep spindles (bursts of activity) and K-complexes (spikes), which represent brief moments of neural activity as the sleeper falls further from consciousness. The third stage, or Non-REM stage 3 (NREM3), is the deepest stage of non-REM sleep, lasting about 20-25 percent of total sleep time. This later stage is sometimes called “deep sleep” or “slow-wave sleep,” (SWS) and is characterized by delta waves measured by the EEG, as opposed to the alpha waves or spindles of earlier stages. This stage of sleep is considered important not only for achieving restful or restorative sleep, but also for memory consolidation and other brain functions. In general, older individuals tend to have a lower percentage of deep or slow-wave sleep.

The fourth and final stage of the sleep cycle is rapid eye movement (REM) sleep, or stage R, lasting about 20-30 percent of sleep time with longer periods later in the night (though more for young children). The REM stage is when most people do the majority of their dreaming. REM sleep often is characterized by low amplitude, mixed frequency EEG activity and frequent wave changes. Some people with sleep disorders like sleep apnea have difficulty achieving REM sleep because of the arousals, and this can be very damaging to sleep health. In addition to measuring the amount of time spent in REM sleep, tests will also measure REM latency, which refers to the amount of time it takes a person to achieve REM sleep from the beginning of the sleep cycle (falling asleep). Most sleepers achieve their first period of REM sleep about 60-110 minutes after sleep onset (after the first hour), but this will vary according to age and health conditions. Sleep architecture changes are expected with age, and most tests will look at the overall picture to determine any signs of concern.

It should also be noted that the classification of sleep stages was updated in 2007 by the American Academy of Sleep Medicine (AASM). Before that, most experts referred to five sleep stages, including four in NREM and a final REM stage. Today, the AASM definitions of the four stages listed above represent the consensus among most sleep specialists.

Heart Rate and Cardiac Events

Sleep tests generally track heart and respiratory data throughout the sleep-wake cycle, focusing on any changes, abnormalities, or areas of concern for both health and sleep health. While polysomnography often includes an electrocardiogram (ECG) to record the electrical activity of the heart, home tests use a much simpler heart rate monitor to record the pulse alone, though most tests will include highlights such as the highest and lowest rate during sleep. Electrical activity is more in-depth than pulse numbers and provides a clearer picture of the heart’s beating patterns, especially at the micro-level.

Without EEG recordings of brain waves, some sleep trackers also use heart rates (and to an extent, respiration) to estimate REM sleep and other sleep stages, which is not as accurate but does give you an idea of when the stages occur, given the effects of sleep architecture on the autonomic nervous system. Tests can then keep track of when heart rate changes occur in the sleep cycle.

In addition to heart rate and heart electrical activity, sleep tests will track monitor any cardiac events or abnormalities, including any arrhythmias or atrial fibrillation (abnormal rates or rhythms), bradycardia (under 40 bpm for over 30 seconds) or tachycardia (over 90 bpm for over 30 seconds), as well as any moments of cardiac arrest.

Respiratory Measures

Respiration is considered the most important parameter of sleep physiology because it can accurately determine sleep disorders such as sleep apnea Because of this, sleep tests often record several respiration parameters including respiratory counts and averages, snoring levels, airflow and pressure parameters, blood-oxygen levels (pulse oximetry), respiratory effort, and sleep-related breathing events or arousals such as apneas or hypopneas.

When breathing stops due to sleep apnea, airflow is reduced by at least 80 percent for 10 or more seconds, while in a hypopnea, the reduction is 50 to 80 percent for 10 or more seconds. Tests will report the total number of times these event occurs, as well as an index of events per hour. This is known as the apnea-hypopnea index (AHI) (events x 60/TST). Based on the scoring standards of the AASM, up to 5 apnea or hypopnea events per hour is considered normal, between 5 and 15 events (per hour) is considered mild sleep apnea, between 16 and 30 is considered moderate, and anything above 30.

The associated drops in blood oxygen levels, known as desaturations, are also measured and categorized. Normal saturation is around 95 percent. A desaturation to 86 percent is mild, a reduction to 80 to 85 percent is moderate, and a drop to 79 percent or less is severe. Aside from children, who are diagnosed if the AHI rises above a 5 per hour, most adults are scored according to this criteria. But there are other sleep-related arousals that do not meet the definitions of apneas or hypopneas, but do disrupt sleep and cause symptoms. The most common example of this is called a respiratory-effort related arousal (RERA), which is an increase of respiratory effort leading to arousal. Like apneas and hypopneas, RERAs have to last at least 10 seconds to be counted and have their own index, known as the RERA index. Some tests will create an index for each of these parameters as well as a combined index known as the respiratory disturbance index (RDI). The RDI counts all apneas, hypopneas, and RERAs per hour (or multiplied by 60/TST). To keep things clear, sleep lab technicians will often use the term “respiratory event” for apneas and hypopneas, while the term “respiratory disturbance” includes RERAS and any other unqualified arousal. Any other arousals not related to respiration are referred to as “spontaneous” arousals and are included in the arousal index mentioned above.

An additional measure, and an important one for sleep disorders, will distinguish the two main types of sleep apnea events. Obstructive sleep apnea (OSA) is the common form of sleep apnea, caused by physical obstruction of the airway, while central sleep apnea (CSA) is caused by disruptions in the brain’s breathing signals. When both OSA and CSA are present, it is known as mixed or complex sleep apnea. While a PSG will give patients the clearest picture of respiratory events, studies have found that some home tests, such as the WatchPAT, developed by Itamar Medical, can now distinguish central sleep apneas from obstructive apneas. This parameter is extremely important because sleep apnea is associated with numerous adverse clinical outcomes, including cardiovascular disease, morbidity, and mortality.

Oxygen Saturation

One of the most immediate effects of sleep disordered breathing is oxygen desaturation. Oxygen saturation, abbreviated as SaO2 (or SpO2 when recorded using oximetry), is the fraction of oxygen-saturated hemoglobin relative to total hemoglobin in the blood. A saturation level of 95 to 100 percent is considered normal, while anything below 90 percent represents a condition known as hypoxemia, which can very easily develop from respiratory disruptions in sleep. Over time, hypoxemia can cause tissue damage, as the parts of the body furthest from the heart begin to lose oxygen.

Pulse oximetry is a test used to measure the oxygen saturation level of blood, and is now available in portable, hom-test options. Because oximetry is an easy and highly accurate way to measure oxygen levels in the body, organizations like the AASM recommend using O2 levels as an additional criteria for respiratory events such as hypopnea, defined as a 3 or 4 percent desaturation (or an arousal under AHI criteria). As with the other parameters, oxygen levels have their own index, called the oxygen saturation index (ODI), calculated as the number of desaturations over 3 or 4 percent per hour (≥3 or ≥4 percent x 60/TST). Oximetry will track the ODI as well as the average oxygen level throughout the recording time, the nadir (lowest point), and hypoxemic burden (Cumulative percent of sleep time spent under 90 percent SpO2), also known as T90.

PAP Therapy Titration

When patients are diagnosed with sleep apnea, a titration service may follow initial testing procedures. This is often the case in full sleep studies when patients already show clear signs of a sleep disorder. Once it is established that apneas and/or hypopneas are occurring with regularity, the titration is performed to determine the best device and settings for positive airway pressure (PAP) therapy treatment. This includes machine type or mode, mask type, pressure settings, comfort settings (such as heated humidification or low starting pressures), and any other setting or accessory that could improve the treatment experience.

PAP machines can vary between models in settings or features, but the most important distinctions are the four main types of therapy. The most common types are continuous PAP (CPAP), automated PAP (APAP or AutoPAP), bilevel PAP (BiPAP), and adapto servo ventilation (ASV). CPAP uses a continuous pressure level, while BiPAP uses separate pressures for inhalations and exhalations. APAP, by comparison, uses an algorithm to shift pressures according respiration changes or alternating patterns, and ASV does this in real time, or on a breath-by-breath basis.

PAP Therapy Mask Options

PAP therapy masks are even more diverse than the machines, offering a range of designs, shapes, and variations, but the most distinct differences are those between full-face masks, nasal masks, and nasal-pillow masks. Full-face options are good for people who sleep in the supine position or move around a lot during the night, often preferred for their sturdiness and for higher pressures. Nasal masks, on the other hand, leave the mouth free and unobstructed, and are good for those experiencing discomfort with full-face options. Nasal-pillow masks are a high-comfort alternative that minimize contact and cushion the face. Each of these mask types have similar varieties available, and each is designed with patient needs in mind. The titration process can assess mask comfort and effectiveness as well as the machine settings to ensure that new patients receive the best possible therapy for their health needs.

The Sleep Test Report

Whether using a portable home test, a mobile app, or a full sleep study option, the data will be presented in an organized fashion using tables, charts, summary lists, and special histograms called hypnograms that present the distribution of sleep stages over the total recording time of the test. These reports allow patients to interpret the data visually and have quick and easy reference points to look back on during treatment.

The Dictated Summary

Full PSG studies will provide what is known as a dictated summary, a concise but detailed summary of data highlights in a single document, often including patient health or treatment history for context. In some cases, this will also include a sleep disorder diagnosis or recommendations for further testing. These summaries can include a lot of information in a condensed form that is easy to read and understand. As with any test method, the report summary will highlight any areas of concern regarding sleep or general health parameters.

TERMS

Adapto-Servo Ventilation (ASV) - (See PAP).

Apnea Event - Complete cessation of airflow for at least 10 seconds,

Apnea-Hypopnea Index (AHI) - The number of apneas and hypopneas multiplied by 60 divided by total sleep time in minutes, or total/TST in hours).

Apnea Index - Number of apneas times 60 divided by total sleep time in minutes.

(sim to per hour)

Alpha Rhythm - An EEG pattern consisting of trains of sinusoidal 8 – 13 Hz activity.

Automated Positive Airway Pressure (APAP or AutoPAP) - (See PAP).

Arousal - An abrupt shift in EEG frequency lasting for at least 3 seconds with at least 10 seconds of stable sleep preceding the change (in N1, N2, N3, or R).

Scoring of arousal during REM requires a concurrent increase in submental EMG lasting at least 1 second.

Arousal Index - (ArI) - Number of arousals per hour of sleep or number of arousals x 60/TST in minutes.

Atrial fibrillation - Rapid beating of the heart due to insufficient blood flow.

Arrhythmia - Irregular or abnormal heart rhythm.

Awakening - An arousal lasting more than 15 seconds.

Beta Rhythm - An EEG rhythm consisting of 13-30 Hz activity.

BiLevel Positive Airway Pressure (BiPAP) - (See PAP).

Bradycardia - Slower than normal heart rate (< 40 bpm for >30 seconds).

Bruxism - Teeth clenching or grinding (2 or more events).

Cardiac Event - Significant change or abnormality in heart rate or heart electrical activity.

Central Sleep Apnea (CSA) - Type of sleep apnea caused by irregular messages from the brain, rather than physical obstruction of the airway.

Chin EMG - A recording of muscle activity from the mentalis and submentalis consisting of electrodes placed above and below the inferior mandible, utilized in the scoring of sleep stages and bruxism.

Circadian Clock - Biological clock determined by internal and external sleep-wake cues.

Circadian Rhythms - Biological sleep-wake cycle rhythms.

Complex Sleep Apnea (or Mixed Sleep Apnea) - Combination of OSA and CSA, often beginning with OSA and developing into CSA when the OSA is treated.

Continuous Positive Airway Pressure (CPAP) - (See PAP).

Delta Wave- Extremely slow waves with a frequency < 4 Hz.

Desaturation - Drop in blood-oxygen levels (artery or tissue, etc.).

Dictated Summary - Summary of sleep study report.

Electrocardiography (ECG) (produces electrocardiogram) - Monitor that records electrical signal from the heart to check for different heart conditions. Electrodes are placed on the chest to record the heart's electrical signals, which cause the heart to beat. The Electrocardiogram is a graph of voltage versus time of the electrical activity of the heart. (An EKG is an older acronym based on the Russian spelling of the original device).

Electroencephalography (EEG) (produces electroencephalogram) - An electrophysiological monitoring method to record electrical activity of the brain. It is typically noninvasive, with the electrodes placed along the scalp, although invasive electrodes are sometimes used, as in electrocorticography, sometimes called intracranial EEG.

Electromyography (EMG) (produces electromyogram) - Movement and muscle monitor that typically uses four electrodes to measure muscle tension in the body as well as to monitor for an excessive amount of leg movements during sleep (which may be indicative of periodic limb movement disorder).

Electrooculogram - (EOG) - Monitor of eye movement that uses two electrodes, one placed 1 cm above the outer canthus of the right eye and one placed 1 cm below the outer canthus of the left eye.

Enuresis - Night arousals to urinate, sometimes including bedwetting.

Epoch - A short interval of arbitrarily defined length (usually 20-60 seconds). The sleep stage or state of each consecutive epoch within a bedrest episode is determined by PSG.

Heart Rate Monitor (HRM) - A personal monitoring device that allows one to measure/display heart rate in real time.

Histogram - Visual representation of the distribution of numerical data (i.e. graph).

Home Sleep Apnea Test (HSAT) - Home test specifically for the diagnosis of sleep apnea.
Home Sleep Test (HST) - Simplified sleep test taken in the home setting.

Note: Home Test Terms Have Redundancy - HSAT, HST, Ambulatory Test, Portable Test, Portable Sleep Apnea Test, Out of Center, etc.

Hypopnea Event - Reduction of airflow by > 50 percent for at least 10 seconds,

- can cause oxygen levels in the blood to drop. It commonly is due to partial obstruction of the upper airway. shallow breathing, or an abnormally low respiratory rate

Hyperventilation (overbreathing) - During hyperventilation the rate of removal of carbon dioxide from the blood is increased. Excessive breathing creates a low level of carbon dioxide in your blood.

Hypoventilation - (underbreathing) - The state in which a reduced amount of air enters the alveoli in the lungs, resulting in decreased levels of oxygen and increased levels of carbon dioxide in the blood. Hypoventilation can be due to breathing that is too shallow (hypopnea) or too slow (bradypnea), or to diminished lung function.

Hypnogram - A graph that represents the stages of sleep as a function of time.

Hypoxemia - abnormally low level of oxygen in the blood. More specifically, it is oxygen deficiency in arterial blood. Hypoxemia has many causes, and often causes hypoxia as the blood is not supplying enough oxygen to the tissues of the body.

Hypoxemic Burden: Defined as the time a patient spends with an oxygen saturation below 90 percent (called T90) (i. e. percent of study O2 sat < 90 percent).

Hypoxia - a condition in which the body or a region of the body is deprived of adequate oxygen supply at the tissue level.

K-Complex - A well-delineated negative sharp wave immediately followed by a positive component standing out from the background EEG (spike), with total duration ≥ 0.5 seconds usually maximal in amplitude. Generally, they are large waves that stand out from the background and often occur in response to stimuli, either external or internal.

Lateral position - on side (vs. supine).

Mean Sleep Latency - Average sleep onset latency over a period (testing period).

Nadir saturation - Lowest saturation point in test.

Nadir O2 Saturation - Lowest oxygen percentage in test.

Obstructive Sleep Apnea (OSA) - The most common form of sleep apnea, caused by soft-palate obstruction of the upper airway during sleep.

Out of Center Sleep Test - (OCST) (see home test redundancy)

Oximetry (often Overnight) - A noninvasive method for monitoring a person's oxygen saturation (finger attachment, etc.). Peripheral oxygen saturation (SpO2) readings from oximetry are often preferred to the more invasive arterial blood gas analysis.

Oxygenation Desaturation Index (ODI) - Number of times per hour of sleep that the blood's oxygen level drop by a certain degree from baseline (≥3 percent or ≥4 percent x 60/TST).

Oxygen Saturation (SO2) (SpO2) - Measure of the concentration of oxygen that is dissolved - or - amount of oxygen-carrying hemoglobin in the blood - specifically, the fraction of oxygen-saturated hemoglobin relative to total hemoglobin (unsaturated + saturated) in the blood. SaO2, by comparison, is the oxygen saturation as measured by blood analysis (e.g. blood gas).

Paradoxical Breathing - Paradoxical breathing is often a sign of breathing problems. It causes the chest to contract during inhaling and to expand during exhaling, the opposite of how it should move.

Periodic Limb Movements (PLM or PLMS) - defined via frequency parameters or Periodic Limb Movement Index (PLMI or PLMSI) - Number of PLM events x 60/TST.

Polysomnography (PSG) (produces polysomnogram) - A multi-parametric test used in the study of sleep and as a diagnostic tool in sleep medicine. Uses: EEG, EOG, EMG, and ECG (EKG), and additional audio/video recordings for observational purposes.

Portable Sleep Apnea Test (PSAT) - Similar to home test options (see home test redundancy)

Portable Sleep Test (PST or PT) - Similar to home test (see home test redundancy)

Positive Airway Pressure (PAP) Therapy - Abbreviated as PAP therapy, this form of treatment applies air pressure via mask and tube to stop the airway from collapsing during OSA. Common forms include continuous PAP (CPAP), automated PAP (APAP), bilevel PAP (BiPAP), and adapto servo ventilation (ASV). CPAP uses a continuous pressure, while BiPAP uses separate pressures for inhalations and exhalations. APAP, by comparison, uses an algorithm to shift pressures according to respiration changes, and ASV does this in real time, or on a breath-by-breath basis.

Pulse Oximeter - Method for measuring arterial oxygen saturation (SaO2) in clinical use. Note SaO2 = oxygen saturation as measured by blood analysis (e.g. a blood gas) SpO2 is blood-oxygen saturation reading indicates the percentage of hemoglobin. (See Oximetry).

PaO2 - Partial pressure of oxygen in the blood, as measured by blood analysis

Pulse Transit Time (PTT) - Pulse transit time measures the time it takes for the arterial pulse pressure wave to travel from the aortic valve to the periphery. PTT increases during the inspiratory fall in blood pressure and decreases during arousal induced increases in blood pressure.

Rapid Eye Movement - Rapid, shifting eye movements with an initial deflection usually lasting <500 msec. These eye movements are characteristic of Stage R sleep (REM sleep).

Rapid Eye Movement Sleep (REM Sleep Stage 4 or Stage R) - Sleep that is characterized by low amplitude, mixed frequency EEG activity and sometimes sawtooth waves; low chin EMG tone; and rapid eye movements. This sleep stage is associated with dreaming.

REM Latency - Another crucial reported parameter is rapid eye movement latency also known as REM latency. Rapid eye movement latency is the time from the sleep onset to the first epoch of REM sleep; therefore, it depends on the patient's sleep latency. The REM sleep cycles every 90 to 120 min intervals throughout the night.

Respiratory Disturbance - Apnea, hypopnea, or RERA.

Respiratory Disturbance Index/ or Respiratory Distress Index (RDI) - The number of apneas, hypopneas and RERAs per hour of sleep.

(RDI = (RERAs + Hypopneas + apneas) X 60 / TST (in minutes) OR total/TST in hours). That is, RDI means the average number of episodes of apnea, hypopnea, and respiratory event-related arousal per hour of sleep.[7] (TST is "total sleep time".)

Respiratory Effort - Making effort to breathe, often monitored using belts that are placed around the chest and abdomen attached to a sensor that generates a respiratory effort signal that provides an indirect representation of respiratory effort based on chest and abdominal movement.

Respiratory Event - Apnea or hypopnea

Respiratory Event Index (REI) - Total number of respiratory events × 60 divided by monitoring time (MT)(/recording time (TRT) (versus TST of AHI).

Respiratory-effort related arousal (RERA) - Arousals from sleep that do not technically meet the definitions of apneas or hypopneas, but do disrupt sleep and cause symptoms. - A RERA is characterized by increasing respiratory effort (and thus decreasing esophageal pressures) for 10 seconds or more leading to an arousal from sleep, but one that does not fulfill the criteria for a hypopnea or apnea.

RERA index - Record of respiratory events during sleep, but unlike the AHI, it also includes respiratory-effort related arousals (RERAs)

Restorative Sleep - High quality sleep that leaves the body rested and refreshed.

Saturation levels - For someone who's healthy, the normal blood oxygen saturation level will be around 95–100 percent. If the oxygen level is below this, it can be an indicator that there is a lung problem. People with low oxygen level may need additional oxygen or other treatment.

Sleep Definition - Sleep is the natural periodic suspension of consciousness characterized by slowed metabolism and characteristic changes in brain electrical activity (brain waves).

Sleep Disordered Breathing (SDB) - Patterns of abnormal breathing including snoring, RERAS, hypopneas, and apneas

Sleep Architecture - Time and character of an individual’s sleep cycle (passage through the stages and cycling between). Sleep architecture parameters generally include latencies, summation of time spent in each sleep stage and body position, and the percent of total sleep time spent in each sleep stage.

Sleep Debt - Sleep deprivation over time.

Sleep Efficiency - Percent sleep efficiency = (TST/TRT x 100) (percentage)

Sleep Fragmentation - The interruption of sleep with frequent, brief arousals characterized by increases in EEG frequency or bursts of alpha activity (and occasionally, transient increase in skeletal muscle tone.

Sleep Hygiene -Behavioral patterns that are consistent with quality sleep.

Sleep Latency (or Sleep Onset Latency) (SL) - The period between lights-out and sleep onset, recorded in minutes (defined as the first epoch of any stage of sleep). Also referred to as the mean sleep latency (MSL) when the mean/average is used.

Sleep Onset - The start of the first epoch scored as any stage other than stage W (Wake). (In most subjects this will usually be the first epoch of stage N1).

Sleep Spike - A transient fast frequency (20-70 msec.) waveform with a pointed peak that is recorded in the EEG channels, and can be interpreted as epileptiform activity.

Sleep Spindle - Spindles represent brief bursts of fast activity with wave frequency between 11 – 16 Hz - most commonly 12 – 14 Hz) that rapidly increase in amplitude and then rapidly decay (duration ≥0.5 seconds). Like K-complexes, spindles are high/maximal in amplitude.

Sleep Stages: NREM 1-3 and REM 4 (NREM or N1-4, R/R4 etc.) (Waking Stage = Stage W).

Sleep Starts - Sudden brief contractions of multiple muscles of the legs, arms or trunk at sleep onset; may be asymmetric or associated with a brief impression of falling. They are a normal phenomenon and may occur in as many as 60 percent of subjects of all ages.

Slow Wave Activity - Waves of frequency 0.5–2 Hz and peak-to-peak amplitude >75 μV, measured over the frontal regions referenced to the contralateral ear or mastoid (F4-M1, F3-M2).

Slow Wave Sleep (deep sleep) - Slow-wave sleep (SWS) refers to phase 3 sleep, which is the deepest phase of non-rapid eye movement (NREM) sleep, and is characterized by delta waves (measured by EEG). Dreaming and sleepwalking can occur during SWS. SWS is thought to be important for memory consolidation.

Stage T - A transitional sleep state seen in infants at sleep onset, during arousals, or when the infant is transitioning between active and quiet sleep. Stage T is analogous to the previously used terminology of “indeterminate sleep.” Stage T (Transitional) is scored when 3 NREM and 2 REM or 2 NREM and 3 REM characteristics are present.

Supine - The position of lying on one’s back when sleeping (vs. lateral).

Tachycardia - Faster than normal heart beat (esp. when out of proportion to a person’s activity or level of exertion), normally defined as: > 90 bpm for > 30 seconds.

Thermister - Thermistor elements are the most sensitive temperature sensors available. A thermistor is a semiconductor device with an electrical resistance that is proportional to temperature.

Time in Bed (TIB) - The elapsed time between “lights off” and “lights on” in minutes.

Total Bedtime (TBT) - Total time spent in bed attempting to sleep (similar to TIB/TRT).

Total Recorded time (TRT) Normally the time between lights out and lights on in minutes (similar to TIB or TBT)

Total Sleep Time (TST) - All the time scored as NREM and REM sleep during the recording.

Total Wake Time (TWT) - Total time spent awake during the recording time or between sleep onset and lights out (note that in this case, it would begin after latency and therefore not include wake time before sleep).

Wake After Sleep Onset (WASO) - Measure of arousals that includes total recorded time minus sleep time, minus the sleep latency period (TRT-SL-TST, in minutes).

Watch PAT - (also Embletta and Stardust II sleep screeners/monitors) - A portable/home sleep test and diagnostic device for the detection of sleep apnea.

Sources

Term Reference: AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications, Version 2.3. - http://www.aasmnet.org

AASTweb.org - https://www.aastweb.org/hubfs/International%20Congress%20Presentations/4%20Atkinson%20Polysomnography%20Reports.pdf?t=1543258915420

Journal of Clinical Sleep Medicine - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2564772/

National Sleep Foundation - https://www.sleephealthjournal.org/article/S2352-7218(15)00015-7/fulltext

Physiological Reviews - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3768102/

Sleep - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6519908/

Sleep and Breathing - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7127995/

Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem - https://www.ncbi.nlm.nih.gov/books/NBK19956/

Sleep Medicine Pearls (3rd Edition) - https://www.sciencedirect.com/science/article/pii/B9781455770519000176

StatPearls - https://www.ncbi.nlm.nih.gov/books/NBK537023/

Thoracic.org - Interpreting Sleep Studies - https://www.thoracic.org/professionals/clinical-resources/sleep/sleep-modules/resources/interpreting-sleep-studies-primer.pdf