Polysomnography
Polysomnography
Definition
Polysomnography is a set of tests performed while a patient sleeps. It is done to diagnose and evaluate sleep disorders , and examines at a minimum brain wave patterns, the movements of both eyes, and the tone of at least one skeletal muscle.
Purpose
Polysomnography is used to diagnose and evaluate many types of sleeping disorders, including disorders of initiating or maintaining sleep (dissomnias) and disorders during sleep (parasomnias), including medical, psychiatric, and dental disorders that have symptoms during sleep. A relatively common dissomnia is sleep apnea, a disorder most prevalent in middle-aged and elderly obese men, in which the muscles of the soft palate in the back of the throat relax and close off the airway during sleep. Sleep apnea may cause the patient to snore loudly and gasp for air at night, and to be excessively sleepy and doze off during the day.
Another dissomnia often evaluated by polysomnography is narcolepsy. Narcoleptics suffer from excessive daytime sleepiness, sudden attacks of muscle weakness (cataplexy), and hallucinations at sleep onset. Some parasomnias that can be detected using polysomnography include disorders of arousal or rapid-eye-movement (REM) sleep problems, such as nightmares. Medical conditions including sleep-related asthma , depression, and panic disorder can be evaluated. Teeth-grinding (bruxism ) or such neurological problems as restless leg syndrome show up during polysomnography. Finally, the tests can also be used to detect or evaluate seizures of sleep-related epilepsy that occur in the middle of the night, when the patient and his or her family are unlikely to be aware of them.
Precautions
Polysomnography is completely safe, and no special precautions need to be taken.
Description
Polysomnography is done during an overnight stay in a sleep laboratory. While the patient sleeps, a wide variety of tests can be performed.
One form of monitoring is electroencephalography (EEG), in which electrodes are attached to the patient's scalp in order to record his or her brain wave activity. The electroencephalograph records brain wave activity from different parts of the brain and charts them on a graph. The EEG not only helps doctors establish what stage of sleep the patient is in, but may also detect seizures. Standard tests have at least one central electrode attached to the scalp and one reference electrode attached to the ear. Other electrodes can be added in order to pinpoint the area of the brain where abnormal activity is occurring.
Another form of monitoring is continuous electrooculography (EOG), which records eye movement and is useful in determining when the patient is going through a stage of REM sleep. Both EEG and EOG can be helpful in determining sleep latency (the time that transpires between lights out and the onset of sleep); total sleep time; the time spent in each sleep stage; and the number of arousals from sleep.
The air flow through the patient's nose and mouth is measured by heat-sensitive devices called thermistors. This measurement can help detect episodes of apnea (stopped breathing), or hypopnea (inadequate breathing). Another test, called pulse oximetry, measures the amount of oxygen in the blood and can be used to assess the
degree of oxygen starvation during episodes of hypopnea or apnea.
The electrical activity of the patient's heart is also measured using electrocardiography (ECG or EKG). Electrodes are affixed to the patient's chest and pick up electrical activity from various areas of the heart. They help detect cardiac arrythmias (abnormal heart rhythms), which may occur during periods of sleep apnea. Blood pressure is also measured as episodes of sleep apnea sometimes dangerously elevate blood pressure.
A final standard measurement is the tone of at least one skeletal muscle, often a muscle of the chin (mentalis or submentalis). This is done using electromyography (EMG), which involves placing an electrode on the muscle to record its contractions. If normal, measurements will indicate the general atonia present during REM sleep. Other EMG channels can be placed, particularly on the leg (anterior tibialis), to indicate movement during sleep.
Depending on the suspected disorder, polysomnography can also include sound monitoring to record snoring; video monitoring to document body positions; core body temperature readings; incident light intensities; penile swelling (tumescence); and pressure and pH at various levels of the esophagus.
One test that is often performed in conjunction with polysomnography is a Multiple Sleep Latency Test (MSLT). This test is also performed in a sleep laboratory and involves the recording of the sleep of several naps during the day after the overnight test. The MSLT is particularly important for a complete diagnosis of narcolepsy.
Preparation
Patient preparation is necessary to ensure that the night or nights in the sleep laboratory are as close as possible to an unmediated night in the patient's own home. Patients should bring suitable sleepwear and make sure their hair is clean and free from gels or sprays that may interfere with electrode functioning. They should be advised to maintain usual awake-sleep cycles and avoid sleeping pills, alcohol, stimulants, and strenuous exercise before the test.
Aftercare
Once the test is over, the monitors are detached from the patient. No special measures need to be taken after polysomnography.
Complications
The greatest limitations to polysomnography are the differences between the recording conditions and those that are present in the patient's home. The differences between the sleep laboratory and home have the highest effect on the first night of testing. Detection and elimination of this "first night effect" can be accomplished by the rather costly step of recording for multiple nights. Multiple night recordings are also sometimes necessary to obtain information about problems that appear only sporadically.
Results
Standard analysis still involves the tedious and time-consuming review and scoring of either paper tracings or recordings projected on a computer monitor. However, automatic computer-based systems are becoming more and more common in clinical and research settings.
Results are interpreted in light of recorded overnight parameters such as the times of lights on/off, total time in bed, and total sleep time. The overnight recording is divided into time periods of approximately 30 seconds. The standard EEG, EMG, and EOG recordings are evaluated, and the predominant stage of sleep, according to the manual of Rechtschaffen and Kales, is assigned to the entire time period.
These data are used to calculate total time and relative proportion of the night spent in each of the six stages of sleep, including REM and non-REM. Latencies to REM and slow-wave sleep (SWS) are also recorded.
Special note is made of such neurophysiologic events as epileptic events, intrusion of alpha-type brain waves into sleep, or periodic activity of the tibialis anterior. Respiratory activities, including apneic or hypopneic episodes and oxygen saturation, are correlated with sleep stages. Other parameters that are being measured, such as body position, gastroesophageal reflux, bruxism, and penile tumescence, are recorded.
If a sleep apnea syndrome is diagnosed, primarily through a demonstration of periodic breathing stoppage and effects on the pulse and heart, a trial of continuous positive airway pressure or a trial of an oral appliance may be undertaken, either in a partial-night or second-night polysomnography recording.
KEY TERMS
Cataplexy —A condition characterized by sudden loss of muscle tone brought on by emotions, often associated with narcolepsy.
Electrocardiography (ECG) —Recording of the electrical activity from various regions of the heart muscle.
Electroencephalography (EEG) —Recording of the electrical activity from various regions of the brain.
Electrooculography (EOG) —Recording of the electrical activity of the muscles that control eye movement.
Narcolepsy —A sleep disorder characterized by attacks of sleep, cataplexy, sleep paralysis, or hallucinations with the onset of sleep.
Sleep apnea —A sleep disorder characterized by lapses in breathing during sleep.
Sleep latency —The time it takes to fall asleep once the lights are out.
Health care team roles
Polysomnography is often performed by a specially trained technician called a polysomnographic technologist. Training programs for this position can involve one–to two–year programs in training as an electrodiagnostic technologist, with additional time for the polysomnography courses. Some typical courses in this area include:
- fundamentals of polysomnography
- sleep disorders
- infant and pediatric polysomnography
- polysomnography instrumentation
- polysomnography recording and monitoring
- polysomnography record scoring
Registration in polysomnography is available from the Board of Registered Polysomnography Technologists. The certification requires passing a written test.
Resources
BOOKS
Misulis, Karl E. "Polysomnography Basics." In Essentials of Clinical Neurophysiology. Boston, MA: Butterworth–Heinemann, 1997.
PERIODICALS
Grandjean, Cynthia and Susanne Gibbons. "Assessing Ambulatory Geriatric Sleep Complaints." The Nurse Practitioner (September 2000).
ORGANIZATIONS
Association of Polysomnographic Technologists. PO Box 14861, Lexena, KS, 66285. (913) 541-1991 ext. 477. <http://www.aptweb.org>.
National Sleep Foundation. 1522 K St. NW, Suite 500, Washington, DC 20005. (202) 347-3471. <http://www.sleepfoundation.org>.
OTHER
Nowack, William J. "Polysomnography: Overview and Clinical Applications."eMedicine Journal 11 April 2001. 3 July 2001 <http://www.emedicine.com/neuro/topic566.htm>.
Michelle L. Johnson, M.S., J.D.
Polysomnography
Polysomnography
Definition
Polysomnography is a set of tests performed while a patient sleeps. It is done to diagnose and evaluate sleep disorders, and examines at a minimum brain wave patterns, the movements of both eyes, and the tone of at least one skeletal muscle.
Purpose
Polysomnography is used to diagnose and evaluate many types of sleeping disorders, including disorders of initiating or maintaining sleep (dissomnias) and disorders during sleep (parasomnias), including medical, psychiatric, and dental disorders that have symptoms during sleep. A relatively common dissomnia is sleep apnea, a disorder most prevalent in middleaged and elderly obese men, in which the muscles of the soft palate in the back of the throat relax and close off the airway during sleep. Sleep apnea may cause the patient to snore loudly and gasp for air at night, and to be excessively sleepy and doze off during the day.
Another dissomnia often evaluated by polysomnography is narcolepsy. Narcoleptics suffer from excessive daytime sleepiness, sudden attacks of muscle weakness (cataplexy), and hallucinations at sleep onset. Some parasomnias that can be detected using polysomnography include disorders of arousal or rapid-eye-movement (REM) sleep problems, such as nightmares. Medical conditions including sleep-related asthma, depression, and panic disorder can be evaluated. Teeth-grinding (bruxism ) or neurological problems such as restless leg syndrome show up during polysomnography. Finally, the tests can also be used to detect or evaluate seizures of sleep-related epilepsy that occur in the middle of the night, when the patient and his or her family are unlikely to be aware of them.
Precautions
Polysomnography is completely safe, and no special precautions need to be taken.
Description
Polysomnography is performed during an overnight stay in a sleep laboratory. While the patient sleeps, a wide variety of tests can be performed.
One form of monitoring is electroencephalography (EEG), in which electrodes are attached to the patient's scalp in order to record his or her brain wave activity. The electroencephalograph records brain wave activity from different parts of the brain and charts them on a graph. The EEG not only helps doctors establish what stage of sleep the patient is in, but may also detect seizures. Standard tests have at least one central electrode attached to the scalp and one reference electrode attached to the ear. Other electrodes can be added in order to pinpoint the area of the brain where abnormal activity is occurring.
Another form of monitoring is continuous electrooculography (EOG), which records eye movement and is useful in determining when the patient is going through a stage of REM sleep. Both EEG and EOG can be helpful in determining sleep latency (the time that transpires between lights out and the onset of sleep), total sleep time, the time spent in each sleep stage, and the number of arousals from sleep.
The air flow through the patient's nose and mouth is measured by heat-sensitive devices called thermistors. This measurement can help detect episodes of apnea (stopped breathing), or hypopnea (inadequate breathing). Another test, called pulse oximetry, measures the amount of oxygen in the blood and can be used to assess the degree of oxygen starvation during episodes of hypopnea or apnea.
The electrical activity of the patient's heart is also measured using electrocardiography (ECG or EKG). Electrodes are affixed to the patient's chest and pick up electrical activity from various areas of the heart. They help detect cardiac arrythmias (abnormal heart rhythms), which may occur during periods of sleep apnea. Blood pressure is also measured as episodes of sleep apnea sometimes dangerously elevate blood pressure.
A final standard measurement is the tone of at least one skeletal muscle, often a muscle of the chin (mentalis or submentalis). This is done using electromyography (EMG), which involves placing an electrode on the muscle to record its contractions. If normal, measurements will indicate the general atonia present during REM sleep. Other EMG channels can be placed, particularly on the leg (anterior tibialis), to indicate movement during sleep.
Depending on the suspected disorder, polysomnography can also include sound monitoring to record snoring; video monitoring to document body positions; core body temperature readings; incident light intensities; penile swelling (tumescence); and pressure and pH at various levels of the esophagus.
One test that is often performed in conjunction with polysomnography is a Multiple Sleep Latency Test (MSLT). This test is also performed in a sleep laboratory and involves the recording of the sleep of several naps during the day after the overnight test. The MSLT is particularly important for a complete diagnosis of narcolepsy.
Preparation
Patient preparation is necessary to ensure that the night or nights in the sleep laboratory are as close as possible to an unmediated night in the patient's own home. Patients should bring suitable sleepwear and make sure their hair is clean and free from gels or sprays that may interfere with electrode functioning. They should be advised to maintain usual awake-sleep cycles and avoid sleeping pills, alcohol, stimulants, and strenuous exercise before the test.
Aftercare
Once the test is over, the monitors are detached from the patient. No special measures need to be taken after polysomnography.
Complications
The greatest limitation to polysomnography are the differences between the recording conditions and those that are present in the patient's home. The differences between the sleep laboratory and home have the highest effect on the first night of testing. Detection and elimination of this "first night effect" can be accomplished by the rather costly step of recording for multiple nights. Multiple night recordings are also sometimes necessary to obtain information about problems that only appear sporadically.
Results
Standard analysis still involves the tedious and time-consuming review and scoring of either paper tracings or recordings projected on a computer monitor. However, automatic, computer-based systems are becoming more and more common in clinical and research settings.
Results are interpreted in light of recorded overnight parameters such as the times of lights on/off, total time in bed, and total sleep time. The overnight recording is divided into time periods of approximately 30 seconds. The standard EEG, EMG, and EOG recordings are evaluated, and the predominant stage of sleep, according to the manual of Rechtschaffen and Kales, is assigned to the entire time period.
This data is used to calculate total time and relative proportion of the night spent in each of the six stages of sleep, including REM and non-REM. Latencies to REM and slow-wave sleep (SWS) are also recorded.
Special note is made of such neurophysiologic events as epileptic events, intrusion of alpha-type brain waves into sleep, or periodic activity of the tibialis anterior. Respiratory activities, including apneic or hypopneic episodes and oxygen saturation, are correlated with sleep stages. Other parameters that are being measured, such as body position, gastroesophageal reflux, bruxism, and penile tumescence, are recorded.
If a sleep apnea syndrome is diagnosed, primarily through a showing of periodic breathing stoppage and effects on the pulse and heart, a trial of continuous positive airway pressure or a trial of an oral appliance may be undertaken, either in a partial-night or second-night polysomnography recording.
Health care team roles
Polysomnography is often performed by a specially trained technician called a polysomnographic technologist. Training programs for this position can involve one-to-two-year programs in training as an electrodiagnostic technologist, with additional time for the polysomnography courses. Some typical courses in this area include:
- fundamentals of polysomnography
- sleep disorders
- infant and pediatric polysomnography
- polysomnography instrumentation
- polysomnography recording and monitoring
- polysomnography record scoring
Registration in polysomnography is available from the Board of Registered Polysomnography Technologists. The certification requires passing a written test.
KEY TERMS
Cataplexy— A condition characterized by sudden loss of muscle tone brought on by emotions, often associated with narcolepsy.
Electrocardiography (ECG)— Recording of the electrical activity from various regions of the heart muscle.
Electroencephalography (EEG)— Recording of the electrical activity from various regions of the brain.
Electrooculography (EOG)— Recording of the electrical activity of the muscles that control eye movement.
Narcolepsy— A sleep disorder characterized by attacks of sleep, cataplexy, sleep paralysis, or hallucinations with the onset of sleep.
Sleep apnea— A sleep disorder characterized by lapses in breathing during sleep.
Sleep latency— The time it takes to fall asleep once the lights are out.
Resources
BOOKS
Misulis, Karl E. "Polysomnography Basics." In Essentials of Clinical Neurophysiology. Boston: Butterworth-Heinemann, 1997.
PERIODICALS
Grandjean, Cynthia and Susanne Gibbons. "Assessing Ambulatory Geriatric Sleep Complaints." The Nurse Practitioner (September 2000).
ORGANIZATIONS
Association of Polysomnographic Technologists. PO Box 14861, Lexena, KS, 66285. (913) 541-1991 ext. 477. 〈http://www.aptweb.org〉.
National Sleep Foundation. 1522 K St. NW, Suite 500, Washington, DC 20005. (202) 347-3471. 〈http://www.sleepfoundation.org〉.
OTHER
Nowack, William J. "Polysomnography: Overview and Clinical Applications." eMedicine Journal 11 April 2001. 3 July 2001 〈http://www.emedicine.com/neuro/topic566.htm〉.
Polysomnography
Polysomnography
Definition
Polysomnography is a series of tests performed on patients while they sleep. Polysomnography is a comprehensive overnight procedure that evaluates sleep disorders . It generally includes monitoring of the patient’s airflow through the nose and mouth, blood pressure, heartbeat as measured by an electrocardiograph, blood oxygen level, brain wave patterns, eye movements, and the movements of respiratory muscles and limbs. The word polysomnography is derived from the Greek root poly meaning “many,” the Latin noun somnus meaning “sleep,” and the Greek verb graphein meaning “to write.”
Purpose
Polysomnography is used to help diagnose and evaluate a number of sleep disorders. For instance, it can help diagnose sleep apnea, a common disorder in middle-aged and elderly obese men, in which the muscles of the soft palate in the back of the throat relax and close off the airway during sleep. Sleep apnea may cause the person to snore loudly and gasp for air at night. It may also cause the person to be excessively drowsy and likely to fall asleep during the day. Another syndrome often uncovered by polysomnography is narcolepsy . Persons with narcolepsy have sudden attacks of sleep and/or cataplexy (temporary loss of muscle tone caused by moments of emotion, such as fear, anger, or surprise, which causes people to slump or fall over), sleep paralysis or hallucinations while they are falling asleep.
Polysomnography is often used to evaluate such parasomnias (abnormal behaviors or movements during sleep)as sleepwalking; talking in one’s sleep; nightmares; and bed-wetting. It can also be used to detect or evaluate seizures that occur in the middle of the night, when the patient and his or her family are unlikely to be aware of them.
Other problems uncovered by polysomnography include sleep-related psychiatric depression , asthma, and panic disorder . Polysomnography is generally not used if the sleep disorder has been clearly identified by the treating physician. It is also not used in cases of insomnia that have simple and obvious causes.
Precautions
Polysomnography is extremely safe, and no special precautions need to be taken.
Description
Polysomnography requires an overnight stay in a sleep laboratory. While the patient sleeps, he or she is monitored in a number of ways that can provide useful information.
One form of monitoring is electroencephalogra-phy (EEG), which involves the attachment of electrodes to the patient’s scalp to record his or her brain wave activity. The electroencephalograph records brain wave activity from different parts of the brain and charts them on a graph. The EEG not only helps doctors establish what stage of sleep the patient is in, but may also detect seizures.
Another form of monitoring is continuous elec-tro-oculography (EOG), which records eye movements. EOG is used to determine the time periods
during which the patient is going through a stage of sleep called rapid-eye-movement (REM) sleep. Both EEG and EOG can be helpful in determining sleep latency (the time period between getting into bed and the onset of sleep); total sleep time; the time spent in each sleep stage; and the number of arousals from sleep.
The airflow through the patient’s nose and mouth are measured by heat-sensitive devices called thermistors. The thermistors can help detect episodes of apnea (stopped breathing), or hypopnea (inadequate or too-shallow breathing). Another test called pulse oximetry measures the amount of oxygen in the patient’s blood. Pulse oximetry can be used to assess the degree of oxygen starvation during episodes of hypopnea or apnea.
The electrical activity of the patient’s heart is also measured on an electrocardiogram, or ECG. Electrodes are attached to the patient’s chest. The electrodes pick up electrical activity from various areas of the heart. They help to detect cardiac arrythmias (abnormal heart rhythms), which may occur during periods of sleep apnea. The patient’s blood pressure is also measured, because some episodes of sleep apnea can raise blood pressure to dangerously high levels.
In some cases, sleep laboratories monitor the movement of the patient’s arms and legs during sleep. This measurement can be helpful in detecting such sleep disorders as periodic limb movements. Some sleep laboratories perform an additional test called multiple sleep latency testing (MSLT), which records several naps throughout the day. In addition, many sleep researchers prefer to evaluate the patient over a period of a few days rather than just one night. This approach is based on the recognition that the patient may need more than one night to adjust to the unfamiliar surroundings of the sleep laboratory.
Preparation
The patient may be asked to discontinue taking any medications, and avoid alcohol and strenuous exercise the day before the sleep analysis is performed. Before the patient goes to sleep, the technician hooks him or her up to all of the monitors being used.
Aftercare
After the test is completed, the monitors are detached from the patient. No special measures need to be taken after polysomnography. On occasion, skin irritation from the adhesive can develop in the areas where the electrodes have been attached to the patient.
KEY TERMS
Apnea —A brief suspension or interruption of breathing.
Arrhythmia —Any disturbance in the normal rhythm of the heartbeat.
Bruxism —Habitual, often unconscious, grinding of the teeth.
Hypopnea —Breathing that is too shallow to maintain adequate levels of oxygen in the blood.
Narcolepsy —A disorder characterized by frequent and uncontrollable attacks of deep sleep.
Oximetry —The measurement of blood oxygen levels.
Parameter —A characteristic or factor that is measured during a test of a complex process or activity like sleep.
Parasomnia —A type of sleep disorder characterized by abnormal changes in behavior or body functions during sleep, specific stages of sleep, or the transition between sleeping and waking.
Thermistor —An electrical device whose resistance decreases with rises in temperature.
Normal results
A normal result in polysomnography shows normal results for all parameters (EEG, ECG, blood pressure, eye movement, air flow, pulse oximetry, etc.) that were monitored throughout all stages of sleep.
Abnormal results
Polysomnography may yield a number of abnormal results, indicating one or more potential sleep disorders. For instance, abnormal transitions into and out of various stages of sleep, as documented by the EEG and the EOG, may be signs of narcolepsy. Reduced air flow through the nose and mouth, along with a fall in blood oxygen levels, may indicate apnea or hypopnea. If apnea is accompanied by abnormal patterns on the ECG or elevations in blood pressure, then the sleep apnea may be producing harmful effects. Frequent movements of the patient’s arms and legs may suggest a sleep disorder called periodic limb movement. A related condition that affects sleep as well as daytime movement is called restless legs syndrome. Polysomnography can also be used to diagnose bruxism, which is the chronic grinding of the teeth during sleep.
See alsoBreathing-related sleep disorder.
Resources
BOOKS
Czeisler, C. A. and others, eds. Harrison’s Principles of Internal Medicine. 15th Ed. New York: McGraw-Hill, 2001.
PERIODICALS
“Practice parameters for the indications for polysomnogra-phy and related procedures.” Sleep 1997 (Reviewed 2000); 20: 406-22.
ORGANIZATIONS
American Sleep Disorders Association. 6301 Bandel Road NW, Suite 101, Rochester, MN 55901. http://www.asda.org
National Heart, Lung and Blood Institute. P.O. Box 30105, Bethesda, MD 20824-0105. (301) 251-1222. http://www.nhlbi.nih.gov
Robert Scott Dinsmoor
Polysomnography
Polysomnography
Definition
Polysomnography is a series of tests performed on patients while they sleep. Polysomnography is a comprehensive overnight procedure that evaluates sleep disorders . It generally includes monitoring of the patient's airflow through the nose and mouth, blood pressure, heartbeat as measured by an electrocardiograph, blood oxygen level, brain wave patterns, eye movements, and the movements of respiratory muscles and limbs. The word polysomnography is derived from the Greek root poly meaning "many," the Latin noun somnus meaning "sleep," and the Greek verb graphein meaning "to write."
Purpose
Polysomnography is used to help diagnose and evaluate a number of sleep disorders. For instance, it can help diagnose sleep apnea, a common disorder in middle-aged and elderly obese men, in which the muscles of the soft palate in the back of the throat relax and close off the airway during sleep. Sleep apnea may cause the person to snore loudly and gasp for air at night. It may also cause the person to be excessively drowsy and likely to fall asleep during the day. Another syndrome often uncovered by polysomnography is narcolepsy . Persons with narcolepsy have sudden attacks of sleep and/or cataplexy (temporary loss of muscle tone caused by moments of emotion, such as fear, anger, or surprise, which causes people to slump or fall over), sleep paralysis or hallucinations while they are falling asleep.
Polysomnography is often used to evaluate such parasomnias (abnormal behaviors or movements during sleep) as sleepwalking; talking in one's sleep; night-mares; and bed-wetting (enuresis ). It can also be used to detect or evaluate seizures that occur in the middle of the night, when the patient and his or her family are unlikely to be aware of them.
Other problems uncovered by polysomnography include sleep-related psychiatric depression, asthma, and panic disorder . Polysomnography is generally not used if the sleep disorder has been clearly identified by the treating physician. It is also not used in cases of insomnia that have simple and obvious causes.
Precautions
Polysomnography is extremely safe, and no special precautions need to be taken.
Description
Polysomnography requires an overnight stay in a sleep laboratory. While the patient sleeps, he or she is monitored in a number of ways that can provide useful information.
One form of monitoring is electroencephalography (EEG), which involves the attachment of electrodes to the patient's scalp to record his or her brain wave activity. The electroencephalograph records brain wave activity from different parts of the brain and charts them on a graph. The EEG not only helps doctors establish what stage of sleep the patient is in, but may also detect seizures.
Another form of monitoring is continuous electrooculography (EOG), which records eye movements. EOG is used to determine the time periods during which the patient is going through a stage of sleep called rapid-eye-movement (REM) sleep. Both EEG and EOG can be helpful in determining sleep latency (the time period between getting into bed and the onset of sleep); total sleep time; the time spent in each sleep stage; and the number of arousals from sleep.
The airflow through the patient's nose and mouth are measured by heat-sensitive devices called thermistors. The thermistors can help detect episodes of apnea (stopped breathing), or hypopnea (inadequate or too-shallow breathing). Another test called pulse oximetry measures the amount of oxygen in the patient's blood. Pulse oximetry can be used to assess the degree of oxygen starvation during episodes of hypopnea or apnea.
The electrical activity of the patient's heart is also measured on an electrocardiogram, or EKG. Electrodes are attached to the patient's chest. The electrodes pick up electrical activity from various areas of the heart. They help to detect cardiac arrythmias (abnormal heart rhythms), which may occur during periods of sleep apnea. The patient's blood pressure is also measured, because some episodes of sleep apnea can raise blood pressure to dangerously high levels.
In some cases, sleep laboratories monitor the movement of the patient's arms and legs during sleep. This measurement can be helpful in detecting such sleep disorders as periodic limb movements. Some sleep laboratories perform an additional test called multiple sleep latency testing (MSLT), which records several naps throughout the day. In addition, many sleep researchers prefer to evaluate the patient over a period of a few days rather than just one night. This approach is based on the recognition that the patient may need more than one night to adjust to the unfamiliar surroundings of the sleep laboratory.
Preparation
The patient may be asked to discontinue taking any medications, and avoid alcohol and strenuous exercise the day before the sleep analysis is performed. Before the patient goes to sleep, the technician hooks him or her up to all of the monitors being used.
Aftercare
After the test is completed, the monitors are detached from the patient. No special measures need to be taken after polysomnography. On occasion, skin irritation from the adhesive can develop in the areas where the electrodes have been attached to the patient.
Normal results
A normal result in polysomnography shows normal results for all parameters (EEG, EKG, blood pressure, eye movement, air flow, pulse oximetry, etc.) that were monitored throughout all stages of sleep.
Abnormal results
Polysomnography may yield a number of abnormal results, indicating one or more potential sleep disorders. For instance, abnormal transitions into and out of various stages of sleep, as documented by the EEG and the EOG, may be signs of narcolepsy. Reduced air flow through the nose and mouth, along with a fall in blood oxygen levels, may indicate apnea or hypopnea. If apnea is accompanied by abnormal patterns on the EKG or elevations in blood pressure, then the sleep apnea may be producing harmful effects. Frequent movements of the patient's arms and legs may suggest a sleep disorder called periodic limb movement. A related condition that affects sleep as well as daytime movement is called restless legs syndrome. Polysomnography can also be used to diagnose bruxism, which is the chronic grinding of the teeth during sleep.
See also Breathing-related sleep disorder
Resources
BOOKS
Czeisler, C. A. and others, eds. Harrison's Principles of Internal Medicine. 15th Ed. New York: McGraw-Hill, 2001.
PERIODICALS
"Practice parameters for the indications for polysomnography and related procedures." Sleep 1997 (Reviewed 2000); 20: 406-22.
ORGANIZATIONS
American Sleep Disorders Association. 6301 Bandel Road NW, Suite 101, Rochester, MN 55901. <http://www.asda.org>.
National Heart, Lung and Blood Institute. P.O. Box 30105, Bethesda, MD 20824-0105. (301) 251-1222. <http://www.nhlbi.nih.gov>.
Robert Scott Dinsmoor
Polysomnography
Polysomnography
Definition
The word polysomnography, derived from the Greek roots "poly," meaning many, "somno," meaning sleep, and "graphy" meaning to write, refers to multiple tests performed on patients while they sleep. Polysomnography is an overnight test to evaluate sleep disorders. Polysomnography generally includes monitoring of the patient's airflow through the nose and mouth, blood pressure, electrocardiographic activity, blood oxygen level, brain wave pattern, eye movement, and the movement of respiratory muscle and limbs.
Purpose
Polysomnography is used to help diagnose and evaluate a number of sleep disorders. For instance, it can help diagnose sleep apnea, a common disorder in middle-aged and elderly obese men, in which the muscles of the soft palate in the back of the throat relax and close off the airway during sleep. This may cause the person to snore loudly and gasp for air at night, and to be excessively sleepy and doze off during the day. Another syndrome often evaluated by polysomnography is narcolepsy. In narcolepsy, people have sudden attacks of sleep and/or cataplexy (temporary loss of muscle tone caused by moments of emotion, such as fear, anger, or surprise, which causes people to slump or fall over), sleep paralysis or hallucinations at the onset of sleep. Polysomnography is often used to evaluate parasomnias (abnormal behaviors or movements during sleep), such as sleep walking, talking in one's sleep, nightmares, and bedwetting. It can also be used to detect or evaluate seizures that occur in the middle of the night, when the patient and his or her family are unlikely to be aware of them.
Precautions
Polysomnography is extremely safe and no special precautions need to be taken.
Description
Polysomnography requires an overnight stay in a sleep laboratory. During this stay, while the patient sleeps, he or she is monitored in a number of ways that can provide very useful information.
One form of monitoring is electroencephalography (EEG), in which electrodes are attached to the patient's scalp in order to record his or her brain wave activity. The electroencephalograph records brain wave activity from different parts of the brain and charts them on a graph. The EEG not only helps doctors establish what stage of sleep the patient is in, but may also detect seizures.
Another form of monitoring is continuous electro-oculography (EOG), which records eye movement and is used to determine when the patient is going through a stage of sleep called rapid-eye-movement (REM) sleep. Both EEG and EOG can be helpful in determining sleep latency (the time that transpires between lights out and the onset of sleep), total sleep time, the time spent in each sleep stage, and the number of arousals from sleep.
The air flow through the patient's nose and mouth are measured by heat-sensitive devices called thermistors. This can help detect episodes of apnea (stopped breathing), or hypnopea (inadequate breathing). Another test called pulse oximetry measures the amount of oxygen in the blood, and can be used to assess the degree of oxygen starvation during episodes of hypnopea or apnea.
The electrical activity of the patient's heart is also measured on an electrocardiogram, or ECG. Electrodes are affixed to the patient's chest and they pick up electrical activity from various areas of the heart. They help detect cardiac arrythmias (abnormal heart rhythms), which may occur during periods of sleep apnea. Blood pressure is also measured: sometimes episodes of sleep apnea can dangerously elevate blood pressure.
In some cases, sleep laboratories monitor the movement of limbs during sleep. This can be helpful in detecting such sleep disorders as periodic limb movements.
Preparation
The patient may be asked to discontinue taking any medications used to help him/her sleep. Before the patient goes to sleep, the technician hooks him or her up to all of the monitors being used.
Aftercare
Once the test is over, the monitors are detached from the patient. No special measures need to be taken after polysomnography.
Normal results
A normal result in polysomnography shows normal results for all parameters (EEG, ECG, blood pressure, eye movement, air flow, pulse oximetry, etc.) monitored throughout all stages of sleep.
Abnormal results
Polysomnography may yield a number of abnormal results, indicating a number of potential disorders. For instance, abnormal transitions in and out of various stages of sleep, as documented by the EEG and the EOG, may be a sign of narcolepsy. Reduced air flow through the nose and mouth, along with a fall in oxygenation of the blood, may indicate apnea or hypopnea. If apnea is accompanied by abnormalities in ECG or elevations in blood pressure, this can indicate that sleep apnea may be particularly harmful. Frequent movement of limbs may indicate a sleep disorder called periodic limb movement.
Resources
ORGANIZATIONS
National Heart, Lung and Blood Institute. P.O. Box 30105, Bethesda, MD 20824-0105. (301) 251-1222. 〈http://www.nhlbi.nih.gov〉.