RPSGT key terms

A continuous overnight recording of brain waves, eye movements, muscle tone, breathing, oxygen levels, and heart rhythm used to diagnose sleep disorders and to evaluate response to treatment.

The opposition to current flow at the skin-electrode interface, measured in ohms before recording begins; high values indicate poor contact and must be lowered by cleaning, light abrasion, or conductive paste.

A pre-recording check in which the patient performs instructed maneuvers such as eye blinks, jaw clenching, and leg lifts so the technologist can confirm each channel responds and is labeled correctly.

An international method of locating scalp electrodes by measuring from bony landmarks so that positions such as C3, C4, O1, and O2 are consistent from patient to patient and between recordings.

A short questionnaire in which the patient rates the chance of dozing in eight everyday situations, producing a score from 0 to 24 that screens for excessive daytime sleepiness.

A circuit that amplifies the voltage difference between two active inputs while canceling voltages common to both, which is why each polysomnographic channel records activity between an exploring and a reference electrode.

The number of times per second an analog signal is measured and stored digitally; it must be at least twice the highest frequency of interest to avoid distorting the waveform.

A narrow filter that removes signal at one specific frequency, usually 50 or 60 Hz, to reduce electrical mains interference without disturbing the surrounding EEG, EOG, and EMG frequencies.

A low-frequency filter setting that determines how quickly a slowly changing signal decays toward baseline; short values remove slow waves, while longer values preserve them for accurate EEG and respiratory recording.

The amount of amplification applied to a signal, usually expressed as microvolts per millimeter of display height, which determines how large a waveform appears on the screen.

A noninvasive method that uses light absorption through a finger or earlobe probe to estimate arterial oxygen saturation and pulse rate continuously throughout the night.

A cannula placed at the nostrils that senses airflow by converting pressure changes into an electrical signal; it detects hypopneas better than a thermistor because it is more sensitive.

A sensor placed at the nose and mouth that changes resistance with temperature, registering the difference between warm exhaled air and cooler inhaled air in order to mark airflow.

A method using elastic belts around the chest and abdomen whose inductance changes with circumference, allowing estimation of respiratory effort and detection of paradoxical thoracoabdominal movement.

Surface electrodes placed under the chin that record muscle tone, helping to identify wakefulness, the atonia of REM sleep, arousals, and movements during the night.

Surface electrodes placed on the lower legs that record muscle activity, allowing detection of periodic limb movements and other leg movements during sleep.

Electrodes placed near the outer canthi of both eyes that record eye movements and help identify wakefulness, the slow eye movements of sleep onset, and the rapid eye movements of REM sleep.

Any recorded signal that comes from a source other than the intended biological activity, such as sweat, movement, electrical interference, or a loose electrode, and must be recognized before scoring.

An abrupt shift of EEG frequency during sleep lasting at least three seconds, with a concurrent rise in muscle tone required during REM, that fragments sleep even when the patient does not fully wake.

A reduction in airflow lasting at least ten seconds that is accompanied by a fall in oxygen saturation or by an arousal, scored only when the flow signal drops by the required percentage.

A complete pause in airflow lasting at least ten seconds while respiratory effort continues, showing that the upper airway is blocked rather than that the drive to breathe has stopped.

A pause in airflow lasting at least ten seconds with no respiratory effort, indicating that the brain temporarily failed to signal the muscles that produce breathing.

The number of apneas plus hypopneas divided by the hours of sleep, used to grade sleep apnea severity as mild, moderate, or severe and to guide treatment decisions.

A run of increasing respiratory effort ending in an arousal after at least ten seconds that does not meet criteria for an apnea or hypopnea; scoring often requires a pressure-based flow signal or esophageal manometry.

The number of oxygen desaturations of at least three or four percent per hour of recording, an oximetry-based measure commonly used to screen for sleep-disordered breathing.

Total sleep time divided by time in bed and multiplied by 100, expressing what percentage of the time spent in bed was actually spent asleep.

The time from lights out to the first epoch scored as sleep, a key measure on the overnight study and the primary endpoint of the multiple sleep latency test.

The total minutes spent awake after sleep has begun and before final awakening, reflecting sleep fragmentation and difficulty staying asleep through the night.

The time from sleep onset to the first epoch of REM sleep; a very short latency suggests narcolepsy or another condition in which REM sleep is disinhibited.

A sharply negative then positive EEG wave lasting at least half a second and maximal over frontal regions, marking stage N2 sleep and sometimes elicited by a sudden sound.

A burst of 11 to 16 Hz activity lasting at least half a second, usually maximal over central regions, that helps define stage N2 sleep and reflects thalamocortical activity.

Stage N3 sleep, defined by waves of 0.5 to 2 Hz and more than 75 microvolts occupying at least 20 percent of an epoch, and associated with deep, restorative sleep.

A background rhythm of 8 to 13 Hz seen over the occipital regions when the eyes are closed, whose presence and attenuation on eye opening help identify wakefulness.

Repetitive, stereotyped leg movements lasting 0.5 to 10 seconds that occur in series during sleep, scored from the anterior tibialis EMG and summarized by a movement index.

A supervised study in which the delivered pressure is adjusted until apneas, hypopneas, and desaturations are eliminated while the patient remains comfortable and asleep in all body positions.

The degree to which a patient uses positive airway pressure as prescribed, usually judged by average nightly hours of use and the percentage of nights the device was used.

Unintended escape of air at the interface between mask and face, which lowers delivered pressure, disturbs sleep, and can produce artifacts or unreliable airflow and pressure readings.

A daytime test of four or five nap opportunities spaced two hours apart that measures mean sleep latency and the presence of sleep-onset REM periods, used mainly to evaluate narcolepsy.