Colin Snow
Sleep studies, formally known as polysomnograms, are diagnostic tests that track and record the activity of multiple body systems, including the brain, heart, and respiratory system. This is done through various sensors and monitoring methods, such as electroencephalography (EEG), which involves placing sensors with a sticky, electrically conductive gel coating on the head to detect brain wave activity. Other methods include electrooculography (EOG) to measure eye movement, electromyography (EMG) for muscle movement, and electrocardiography (EKG or ECG) to examine heart activity. These sensors provide healthcare providers with comprehensive data to assess sleep quality and diagnose or rule out health issues. Sleep studies are typically conducted during a person's normal sleeping hours, with overnight sleep studies being the most common.
| Characteristics | Values |
|---|---|
| Formal Name | Polysomnogram |
| Purpose | To track and record how multiple body systems work while asleep |
| Sensors | Electrodes, video cameras, and other devices |
| Sensor Placement | Head, chest, face, leg |
| Sensor Functions | Detecting and recording electrical activity of the brain, tracking muscle movement, measuring eye movement, recording electrical activity of the heart |
| Preparation | No caffeine, alcohol, lotions or oils, filling out sleep questionnaires |
| Post-Study | Removal of electrodes and other devices, results available in several days |
| Sleep Study Types | Overnight, daytime, at-home |
| Sleep Disorders Diagnosed | Sleep apnea, narcolepsy, restless legs syndrome, seizures, epilepsy, sleep paralysis, parasomnias, sleep behavior-related disorders |
| Brain Scanning Techniques | EEG, fMRI, PET, SPECT |
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What You'll Learn
Electroencephalography (EEG)
EEG is typically non-invasive, with electrodes placed on the scalp using the International 10-20 system or its variations. The electrodes detect bio-signals representing the postsynaptic potentials of pyramidal neurons in the neocortex and allocortex. Each electrode pair measures the voltage difference between them, and the entire array forms a montage. The EEG can be displayed in various montages to highlight specific features.
The rhythmic activity captured by EEG is divided into frequency bands, with certain bands associated with specific scalp distributions or biological significance. Most cerebral signals observed in scalp EEG fall within the 1-20 Hz range, with activity outside this range likely being artifactual. EEG provides insights into particular neuron types, locations, and orientations, but it should not be used to make claims about global brain activity due to its bias towards certain neuron types.
During a sleep study, participants may be asked to avoid napping, caffeine, and sedatives to ensure accurate results. EEG sensors are coated with a sticky, electrically conductive gel to help them adhere to the head. The sensors detect and record brain wave activity, which differs depending on the sleep stage, enabling healthcare providers to identify any sleep disorders or issues.
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Electrooculogram (EOG)
A sleep study, formally known as a polysomnogram, is a diagnostic test that tracks and records how multiple body systems work while a person is asleep. This test involves sensors that track the activity of multiple body systems, including the brain, heart, and respiratory system, giving healthcare providers a comprehensive view of the quality of a person's sleep.
An Electrooculogram (EOG) is a test that is conducted during a sleep study to measure eye movement. It is an electrophysiologic test that measures the existing resting electrical potential between the cornea and Bruch's membrane. The patient's eye movement is recorded during 15 minutes of dark adaptation and 15 minutes of light adaptation. During the dark adaptation phase, the standing potential usually reaches a minimum level (dark trough/DT) at 10-15 minutes. During the light adaptation phase, the standing potential achieves the highest value at 7-12 minutes, called a light peak/LP. The light peak results from increased free intracellular calcium released from the endoplasmic reticulum.
EOG is also used to determine the function of the outer retina and RPE. It has a positive waveform in the light and a negative waveform in the dark. The wave form of FO is sinusoidal compared to the EOG, which has a shape of a plateau after post hoc DC restoration by digital integration. The light-insensitive component accounts for the dark trough and is dependent on the integrity of the retinal pigment epithelium (RPE), as well as the cornea, lens, and ciliary body. The light-sensitive component is the slow light rise of the EOG and is generated by the depolarization of the basal membrane of the RPE.
EOG is also used in some cases as a tool to diagnose hereditary macular diseases, particularly Best Disease. It is used in conjunction with an ERG to diagnose various progressive retinal disorders. The test was first described and named by Elwin Marg in 1951, and the first clinical applications were described by Geoffrey Arden in 1962.
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Electromyography (EMG)
Sleep studies, or polysomnograms, are diagnostic tests that track and record the activity of multiple body systems, including the brain, heart, and respiratory system. This is done to give healthcare providers a comprehensive view of an individual's sleep quality and to diagnose or rule out health issues.
One of the sensors used in sleep studies is Electromyography (EMG), which is a technique for evaluating and recording the electrical activity produced by skeletal muscles. EMG sensors are attached to the skin, usually on the face and a leg, to track muscle movement. This is done by measuring the electrical signals given off by muscles when they contract and relax.
The EMG technique has its roots in the 17th century, with the discovery that a specific type of electric ray fish (Electric Eel) could generate electricity. Over the next two centuries, researchers demonstrated that electricity could initiate muscle contraction and that it was possible to record electrical activity during voluntary muscle contraction. The term "electromyography" was introduced in 1890 when the first actual recording of this activity was made.
Today, EMG is used to check how well an individual's muscles and the nerves that control them are working. A healthy muscle should not give off any electrical signals when at rest. However, a damaged muscle may show electrical activity while at rest or abnormal activity while in use. EMG tests can also be used in conjunction with nerve conduction studies to determine if symptoms are caused by a muscle or nerve disorder.
There are two main types of EMG: needle EMG and surface EMG. Needle EMG is an electrodiagnostic medicine technique commonly used by neurologists to detect fibrillations, which represent the isolated activation of individual muscle fibers, usually due to nerve or muscle disease. Surface EMG, on the other hand, is a non-medical procedure used to assess muscle activation and is employed by professionals such as physiotherapists, kinesiologists, and biomedical engineers.
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Electrocardiogram (ECG)
A sleep study, formally known as a polysomnogram, is a diagnostic test that tracks and records how multiple body systems work while you sleep. This test involves sensors that track the activity of multiple body systems, including the heart, brain, and respiratory system, to give healthcare providers a comprehensive view of the quality of your sleep.
An Electrocardiogram (ECG) is a tool used in sleep studies to record the electrical activity of the heart. During a sleep study, a single ECG sensor is worn on the chest to pick up the electrical activity of the heart. Examining heart activity allows a healthcare provider to see if there are any issues with the heart's beating pattern (rhythm) and internal electrical system.
The use of an ECG in sleep studies is particularly important in the detection of sleep apnea. Transient changes in heart rate associated with obstructive apneas have been suggested for screening of sleep disordered breathing (SDB). An automated algorithm was applied to a single-channel ECG obtained during standard overnight polysomnography to obtain an apnea-hypopnea index (AHI) estimate. The results of this study suggest the utility of the system as a screening tool for subjects with suspected OSAS, as overnight ECGs can be obtained relatively easily using a Holter monitor.
The advantages of using an ECG monitor as an OSA screening tool include:
- Reducing the number of electrodes attached to patients, making it significantly easier for them as there are only three electrodes that need to be attached for a one-lead ECG.
- The algorithm is completely automated, so no time-consuming manual scoring is needed, which also avoids inter-scorer discrepancies.
- The CPC technique can also provide valuable measures (e.g., HFC, LFC) that are related to sleep structure and quality.
It is important to note that there are some preparations to be made before a sleep study. For example, you may be asked to limit your sleep before the study by avoiding naps. It is also important to inform your healthcare provider about any medications, herbal supplements, or alcohol consumption before the study, as these may change the test results. Caffeine should also be avoided for several days before the test, as it may cause you to take longer to fall asleep.
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Positron Emission Tomography (PET)
PET scans are used mostly in patients with brain or heart conditions and cancer. They are often used by oncologists, neurologists, neurosurgeons and cardiologists. However, as the technology advances, PET scans are becoming more widely used in other areas.
During a PET scan, a tiny amount of a radioactive substance, called a radiopharmaceutical (or radionuclide/radioactive tracer), is administered into a vein through an intravenous (IV) line. The PET scanner then moves over the part of the body being examined. Positrons are emitted by the breakdown of the radionuclide, and when these collide with electrons, gamma rays are created. These gamma rays are detected by the scanner, and a computer then analyses them to create an image map of the organ or tissue being studied. The amount of the radionuclide collected in the tissue indicates how brightly the tissue appears on the image, and also shows the level of organ or tissue function.
PET scans are often used in conjunction with other diagnostic tests, such as computed tomography (CT) or magnetic resonance imaging (MRI) scans. This combination of PET and CT or MRI can provide more definitive information about malignant tumours and other lesions.
In the context of sleep studies, PET scans can be used to study cerebral physiological and biochemical processes. They have been used to investigate a variety of sleep disorders, including narcolepsy, fatal familial insomnia, and continuous spike-and-wave discharges during slow sleep. PET scans have also been used to study regional cerebral glucose metabolism in children with deterioration of cognitive functions during sleep.
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Frequently asked questions
Electroencephalography (EEG) is used to measure brain wave activity during sleep studies. EEG sensors are coated in a sticky, electrically conductive gel that helps them stick to the head.
Sleep studies also measure eye movement (Electrooculogram or EOG), muscle movement (Electromyography or EMG), and heart electrical activity (Electrocardiogram or ECG). Video recordings are sometimes made of the patient while they sleep.
Sleep studies are used to diagnose sleep disorders such as sleep apnea, narcolepsy, restless leg syndrome, and sleepwalking. They can also be used to determine whether sleep disorder treatments are effective.
Your healthcare provider may ask you to limit your sleep before the study and refrain from consuming caffeine, alcohol, or sedatives. You should also disclose any medications or supplements you are taking.
