Polysomnography and its parameters- a complete overview.
- 2. EEG Three channels of EEG, representing the frontal (F4), central (C4), and occipital (O2) regions referenced to the contralateral mastoid (M1), should be recorded. Backup electrodes (F3, C3, O1, M2) are also applied to avoid interruption during the study and anykind of malfunctions with the primary electrodes that can occur during the study. The EEG electrodes should be placed according to the International 10- 20 System of electrode placement. Gold or silver-silver chloride electrodes can be attached with either collodion or paste.
- 3. • However, since the PSG is a relatively long recording and patients may make multiple position changes during the night, collodion is a more secure application method and will help prevent artifact and the need to reattach electrodes during the night.
- 4. EOG The electrooculogram records vertical and horizontal eye movement and assists in identifying sleep onset and the differentiation of sleep stages. The cornea (front of the eye) has a positive charge when compared to the retina (back of the eye). When the patient looks towards one of the eye leads (E1 or E2), a positive charge is created and a downward deflection in the channel is recorded (when E1 or E2 is in input 1). At the same time, a negative charge is being recorded by the opposite eye lead causing an upward deflection. The morphology and duration of the eye movements help to discern the stages of sleep, particularly Stage R (REM) sleep and the transition from awake to Stage N1. The EOG leads should be applied using disposable self adhesive surface electrodes or silver-silver chloride electrodes attached with the tape.
- 5. The recommended placement for EOG electrodes are as follows: • E1 (left eye)—1 cm below the left outer canthus of the eye. • E2 (right eye)—1 cm above the right outer canthus of the eye. • Both E1 and E2 should be referenced to the same mastoid electrode
- 7. EMG The submental (chin) EMG recording is very important for determining sleep onset and stage R sleep. As the patient drifts to sleep, there should be a reduction in the amplitude of the muscle activity from the baseline. During stage R sleep, the chin EMG typically is at the lowest amplitude of the night. This channel may also assist in identifying arousals. Three electrodes should be securely applied to record chin EMG. Impedance for EMG channels should not exceed 10 kW. The recommended placement for the submental EMG electrodes is as follows • One electrode in the midline 1 cm above the inferior edge of the mandible (mental) • One electrode 2 cm below the inferior edge of the mandible and 2 cm to the right of the midline (submental) • One electrode 2 cm below the inferior edge of the mandible and 2 cm to the left of the midline (submental)
- 8. The standard recording should reference one of the electrodes below the mandible to the electrode above the mandible. The third electrode below the mandible will act as a backup. A sensitivity of 2 mV/mm typically provides an optimal recording that allows comparisons in the EMG level between awake, non-REM, and REM sleep.
- 9. Lower Extremity EMG • Abnormal limb movements at night are identified during the PSG by recording muscle activity from electrodes applied to the anterior tibialis muscle of the lower limbs. When these electrodes capture repetitive, periodic movements, it is often indicative of Periodic Limb Movement Disorder (PLMD); a relatively frequent problem that can be diagnosed in the sleep laboratory. • To locate the anterior tibialis muscle, the technologist should ask the patient to dorsiflex their foot after which the muscle can easily be located along the lateral side of the tibia. Two electrodes should be applied 2 to 3 cm apart longitudinally on the belly of the muscle.
- 10. ECG A single-channel, modified Lead II recording with standard ECG (peel and stick) electrodes is recommended to record basic heart rate and arrhythmias during the PSG. One electrode is placed on the chest below the right clavicular bone and a second electrode should be aligned in parallel to the left hip in the 6th intercostal space. Recording and careful monitoring of the ECG is crucial to ensure the patient’s safety during the study. Often times, ECG abnormalities are not documented in the patient’s history as they may only occur while the patient is sleeping and may be noted for the first time during the PSG. Thus, the technologist should be trained to recognize not only normal ECG patterns, but also arrhythmias, and be prepared to respond to cardiac emergencies.
- 12. Airflow • Airflow monitoring helps to detect and differentiate sleeprelated breathing disorders that are frequently encountered in the sleep laboratory. Two separate airflow channels using different recording methods are recommended. • Apneas are identifed by using an oral-nasal thermal sensor, while hypopneas are detected with the use of an oral-nasal air pressure transducer. • The thermal sensor (thermistor or thermocouple) is a qualitative measurement that reflects temperature changes between the room air and the patient’s expired air.
- 13. • The nasal pressure transducer measures the volume of air expired through an oral-nasal cannula and converts that measurement into an electrical signal that is subsequently recorded as an airflow signal. • This is the recommended device for detection of hypopneas and respiratory effort–related arousals (RERA).
- 14. Snore Monitor • Snoring can be recorded several ways. A snore sensor records vibrations using a piezo crystal, which presents as a burst of fast activity that resembles muscles discharge. • The sensor should be placed on the anterior aspect of the neck in a location where vibrations are most prominent; often at the level of the larynx. • To find the best location, place two fingers on the patient’s throat and ask them to cough or hum. • The signal can be either superimposed on the airflow channel or recorded in a separate channel.
- 15. Oxymetry • Monitoring of the SpO2 (oxygen saturation) is a vital part of the sleep study as it is used to define the severity of respiratory event as well as monitor the safety of the patient. • The pulse oximeter is a DC device used to measure the SpO2 or the amount of saturated oxygen in the blood by using a light emitting diode (LED) that shines a red and infrared light into the tissue bed of a finger. • The sensor sends an electronic signal to the oximeter and the amount is displayed as a percentage, either linearly or numerically or both.
- 18. Body Position Precise body position monitoring is important in the diagnosis of sleep- disordered breathing and can be monitored with a body position sensor or by visual observation and documentation. A body position sensor may be attached to the center of the thoracic belt and recorded in a DC channel. The sensor typically detects supine, lateral, prone, and upright sleeping positions. Visual observation and documentation by the technologist should complement the position channel. Body position must be incorporated into the sleep report to allow for assessment of sleep-disordered breathing in relation to body position, as the supine position (due to the gravitation effects upon the Oropharynx) tends to be frequently associated with more severe and frequent pathological events.
- 19. ADDITIONAL RECORDING PARAMETERS • Capnography is commonly used during pediatric studies to diagnose nocturnal hypoventilation, while for adults it can provide evidence suggestive of hypoventilation. Capnographyis the measurement of carbon dioxide (CO2) in an exhaled breath or in the blood depending on the recording method. • End Tidal CO2 (EtCO2) monitoring is more commonly used during polysomnography and measures the peak concentration of carbon dioxide at the end of expiration. • Transcutaneous CO2 (TCO2) monitoring records the amount of CO2 in the blood using a heated sensor applied to the skin. • Oesophageal pressure is measured by inserting a balloon-tipped catheter through the nasal passage into the esophagus where it detects pressure changes in the thoracic cavity. It is recommended for diagnosing Upper Airway Resistance Syndrome (UARS).
- 20. Apnea-Hypopnea Index • The apnea-hypopnea index (AHI) is the combined average number of apneas and hypopneas that occur per hour of sleep • According to the American Academy of Sleep Medicine (AASM) it is categorized into mild (5-15 events/hour), moderate (15-30 events/hr), and severe (> 30 events/hr). • The apnea-hypopnea index (AHI) is calculated by dividing the total number of events (apneas and hypopneas) from the total sleep time. Apneas and hypopneas must last at least 10 seconds to count them as events and be associated with a decrease in the blood oxygen levels or cause an awakening. • It is a major tool for diagnosing OSA.
- 21. • People with OSA experience a collapse of their airways during sleep. When this causes their breathing to completely stop or reduce to 10% of normal levels for at least 10 seconds, it is called an Apnea. • Hypopneas occur when your airways partially collapse, resulting in shallow breathing. If your airflow decreases by more than 30% for at least 10 seconds, it can be considered as a Hypopnea. • Apneic and Hypopneic events disrupt sleep and lead to lower blood oxygen levels, contributing to long-term health complications
- 22. • If you score moderate or severe on the AHI, you might need to use a CPAP (continuous positive airway pressure) machine while you sleep. With a CPAP, you wear a mask over your nose that’s attached to a machine with a hose. It blows air into your nose, and that should help keep you from waking often during the night. It also may record your AHI. • The respiratory disturbance index (RDI) is similar to AHI. In addition to apneas and hypopneas, it counts the number of times those events that disturb your sleep, called respiratory effort-related arousals. • A sleep study will also check for low blood oxygen levels, called desaturation. The oxygen desaturation index (ODI) is the number of times your blood oxygen falls for more than 10 seconds, divided by the number of sleep hours.
- 23. • Children are less likely to have sleep apnea episodes. Most specialists see an AHI above 1 as unusual for them. A child typically needs treatment if their AHI is higher than 5. • Certain lifestyle changes that will keep your airways open are quitting smoke, losing weight, exercising, sleeping on your side or stomach instead of your back.
- 24. Sleep Staging Rules • Sleep stages are scored in 30-second sequential epochs based on EEG, EOG, and EMG findings. If two or more stages are seen in one epoch, the epoch is assigned the stage comprising the greatest portion of the epoch. • Sleep in infants is variable and the following guidelines for sleep stage scoring are recommended. If there are no recognizable sleep spindles, K-complexes, or high-amplitude 0.5- to 2-Hz slow-wave activity, all epochs of non-REM sleep are scored as stage N.
- 26. • Stage N2 - non-REM epochs that contain sleep spindles or K- complexes. • Stage N - non-REM epochs having 20 percent or more of slow-wave sleep. • Stage N3 - non-REM epochs with more than 20 percent slow-wave sleep. • Stage N - non-REM epochs having no K-complexes or sleep spindles. • If non-REM sleep has some epochs containing sleep spindles or K- complexes and other epochs contain sufficient slow-wave activity, it is scored as either N1, N2, or N3.
- 27. Arousal Rules • Arousals are scored during N1, N2, or N3, or R if there is an abrupt shift in EEG frequency, including alpha, theta, and/or other frequencies exceeding 16 Hz that last at least 3 seconds, preceded by at least 10 seconds of stable sleep. • Arousal during stage R needs concurrent increase in chin EMG tone lasting at least 1 second.
- 28. Respiratory Rules • Apnea in adults is scored when there is a drop in the peak signal excursion by ≥ 90% of pre-event baseline using an oronasal thermal sensor (diagnostic study), for ≥ 10 seconds. • Hypopnea in adults is scored when the peak signal excursions drop by ≥ 30% of pre-event baseline using nasal pressure (diagnostic study), for ≥ 10 seconds, in association with either ≥ 3% arterial oxygen desaturation or an arousal.
- 29. Sleep Study Times, Formulas and Calculations • Total Recording Time (TRT) Total time in minutes from lights out to lights on. • Total Sleep Time (TST) Total time spent asleep. Calculated by adding the time spent in each sleep stage or by subtracting total wake time from total recording time. • Sleep Efficiency (SE) Percentage of total recording time spent asleep. SE=TST/TRT
- 30. • Apnea Hypopnea Index (AHI) Total number of apneas and hypopneas per hour of sleep. AHI= (apneas+hypopneas)/TST • Respiratory Disturbance Index (RDI) Total number of apneas, hypopneas, and RERAs per hour ofsleep. RDI=(apneas+hypopneas+RERAs)/TST
- 31. • Arousal Index Total number of arousals per hour of sleep. AI=EEG arousals/TST in hours. • Periodic Limb Movement Index The total number of limb movements that are part of a PLM sequence per hour of sleep.