The Multiple Sleep Latency Test (MSLT) is a sleep disorder diagnostic tool. It used to measure the time it takes from the start of a nap period to the first signs of sleep. The test is based on the idea that the sleepier one is the faster they will fall asleep.
The Multiple Sleep Latency Test (MSLT) is a sleep disorder diagnostic tool. It used to measure the time it takes from the start of a nap period to the first signs of sleep. The test is based on the idea that the sleepier one is the faster they will fall asleep.
The test consists of four or five, twenty minute naps that are scheduled about two hours apart. The test is often done following an overnight sleep study. During the test things such as the patient's brain waves, EEG, muscle activity and eye movements are monitored and recorded. The entire test normally takes about 7 hours. The MSLT may also be used more extensively to test sleepiness in a number of other research and diagnostic protocols.
The Multiple Sleep Latency Test was created in 1975 by sleep pioneer William C. Dement and Mary Carskadon. It developed out of repeating a project done in 1970 by Dr. Dement called the 90-minute day. They informally called the 0-5 score range the twilight zone due to its indication of extreme physical and mental impairment.
Prepration: On the day of the test the patient is asked to not take any stimulants such as tea, coffee, colas and chocolate.
A neurologist or sleep specialist will review the results and inform the patient of the outcome.
Maintenance of Wakefulness Test or MWT is a test to measure a persons ability to stay awake in certain circumstances which are normally difficult to stay awake. These studies are mostly performed on people with professions that require them to be awake during potentially dangerous careers, such as truck drivers, and airplane pilots.
MWT can be performed in between MSLT naps. MWT's have no standard method for performing the test, yet it is each lab's responsibilty to establish a MWT protocol.
Rapid eye movement behavior disorder, or RBD was first described in 1986 as a parasomnia involving dissociation of the characteristic stages of sleep. The major and arguably only abnormal feature of RBD is loss of muscle atonia (paralysis) during otherwise intact REM sleep (the stage of sleep in which most vivid dreaming occurs).
This loss of motor inhibition leads to a wide spectrum of behavioural release during sleep. This extends from simple limb twitches to more complex integrated movements where sufferers appear to be unconsciously acting out their dreams. These behaviours are often violent in nature and commonly result in injury to either the patient or their bed partner. Injuries range from bruises and cuts to fractures, subdural hematoma and other serious injuries. In contrast, all other aspects of sleep appear similar to normal.
The most comprehensive assessment so far has estimated RBD prevalence to be around 0.5% in individuals aged 15-100[1]. It is far more common in males: most studies report that only around a tenth of sufferers are female. This may be due to a referral bias, as violent activity carried out by men is more likely to result in harm and injury and is more likely to be reported than injury to male bed partners by women, or it may reflect a true difference in prevalence as a result of genetic or androgenic factors. The mean age of onset is estimated to be around 60 years of age.
Various conditions are very similar to RBD in that sufferers exhibit excessive sleep movement and potentially violent behaviour. Such disorders include sleepwalking and sleep terrors, which are associated with other stages of sleep, nocturnal seizures and obstructive sleep apnea which can induce arousals from REM sleep associated with complex behaviours. Because of the similarities between the conditions, polysomnography plays an important role in confirming RBD diagnosis.
It is now apparent that RBD appears in association with a variety of different conditions. Narcolepsy has been reported as a related disorder. This is unsurprising, as both RBD and narcolepsy involve dissociation of sleep states probably arising from a disruption of sleep control mechanisms. RBD has also been reported following cerebrovascular accident and neurinoma (tumour), indicating that damage to the brain stem area may precipitate RBD. RBD is usually chronic, however may be acute and sudden in onset if associated with drug treatment or withdrawal (particularly with alcohol withdrawal) 60% of RBD is idiopathic. This includes RBD that is found in association with conditions such as Parkinson's disease and dementia with Lewy bodies, where it is often seen to precede the onset of neurodegenerative disease. Monoamine oxidase inhibitors, tricyclic antidepressants, serotonergic synaptic reuptake inhibitors, and noradrenergic antagonists can induce or aggravate RBD symptoms and should be avoided in patients with RBD.
RBD is a treatable condition. The standard therapy is the anti-convulsant drug clonazepam, and this is generally received very well. How this drug works to restore REM atonia is unclear, however it is thought to suppress muscle activity, rather than directly restoring atonia.
Spirometry (meaning the measuring of breath) is the most common of the Pulmonary Function Tests (PFTs), measuring lung function, specifically the measurement of the amount (volume) and/or speed (flow) of air that can be inhaled and exhaled. Spirometry is an important tool used for assessing conditions such as asthma, cystic fibrosis, and COPD.
Generally, the patient is asked to take the deepest breath they can, and then exhale into the sensor as hard as possible, for as long as possible. It is sometimes directly followed by a rapid inhalation (inspiration), in particular when assessing possible upper airway obstruction. Sometimes, the test will be preceded by a period of quiet breathing in and out from the sensor (tidal volume), or the rapid breath in (forced inspiratory part) will come before the forced exhalation.During the test, soft nose clips may be used to prevent air escaping through the nose. Filter mouthpieces may be used to prevent the spread of microorganisms, particularly for inspiratory maneuvers.
The maneuver is highly dependent on patient cooperation and effort, and is normally repeated at least three times to ensure reproducibility. Since results are dependent on patient cooperation, FEV1 and FVC can only be underestimated, never overestimated. Due to the patient cooperation required, spirometry can only be used on children old enough to comprehend and follow the instructions given (typically about 4-5 years old), and only on patients who are able to understand and follow instructions - thus, this test is not suitable for patients who are unconscious, heavily sedated, or have limitations that would interfere with vigorous respiratory efforts.
Spirometry can also be part of a bronchial challenge test, used to determine bronchial hyperresponsiveness to either rigorous exercise, inhalation of cold/dry air, or with a pharmaceutical agent such as methacholine or histamine. Sometimes, to assess the reversibility of a particular condition, a bronchodilator is administered before performing another round of tests for comparison. This is commonly referred to as a reversibility test, or a post bronchodilator test (Post BD), and is an important part in diagnosing asthma versus COPD.
| Abbreviation | Name | Description |
FVC |
Forced Vital Capacity |
This is the total amount of air that you can forcibly blow out after full inspiration, measured in liters. |
FEV1 |
Forced Expiratory Volume in 1 Second |
This is the amount of air that you can forcibly blow out in one second, measured in liters. Along with FVC it is considered one of the primary indicators of lung function. |
FEV1 / FVC |
.... |
This is the ratio of FEV 1 to FVC. In healthy adults this should be approximately 75 - 80%. |
PEF |
Peak Expiratory Flow |
This is the speed of the air moving out of your lungs at the beginning of the expiration, measured in liters per second. |
FEF 25-75% or 25-50% |
Forced Expiratory Flow 25-75% or 25-50% |
This is the average flow (or speed) of air coming out of the lung during the middle portion of the expiration (also sometimes referred to as the MMEF, for maximal mid-expiratory flow). |
FIF 25-75% or 25-50% |
Forced Inspiratory Flow 25%-75% or 25%-50% |
This is similar to FEF 25%-75% or 25%-50% except the measurement is taken during inspiration. |
FET |
Forced Expiratory Time |
This measures the length of the expiration in seconds. |
SVC |
Slow Vital capacity |
.... |
TV |
Tidal Volume |
During the respiratory cycle, a specific volume of air is drawn into and then expired out of the lungs. This volume is tidal volume. |
MVV |
Maximum Voluntary Ventilation |
.... |
Electroencephalography is the neurophysiologic measurement of the electrical activity of the brain by recording from electrodes placed on the scalp or, in special cases, subdurally or in the cerebral cortex. The resulting traces are known as an electroencephalogram (EEG) and represent an electrical signal (postsynaptic potentials) from a large number of neurons. These are sometimes called brainwaves, though this use is discouraged. The EEG is a brain function test, but in clinical use it is a "gross correlate of brain activity". Electrical currents are not measured, but rather voltage differences between different parts of the brain.
EEGs are frequently used in experimentation because the process is non-invasive to the research subject. The subject does not need to make a decision or behavioral action in order to log data, and it can detect covert responses to stimuli, such as reading. The EEG is capable of detecting changes in electrical activity in the brain on a millisecond-level. It is one of the few techniques available that has such high temporal resolution. The other common technique is MEG.
EEG in various forms is most useful as a tool for monitoring and diagnosis in certain clinical situations:
It is sometimes useful in assessing dementia, when other examinations are equivocal. In some jurisdictions it has a legal significance and formal criteria are used to assess brain death. Current research is being done to determine if EEG may also be used to help monitor clinical depression treatment, but such studies are still in the clinical stages. In conventional scalp EEG, the recording is obtained by placing electrodes on the scalp, usually after preparing the scalp area by light abrasion and application of a conductive gel to reduce impedance. Modern EEG systems have the subject wear a plastic cap where the electrodes are inserted in small holes.
Electrode placement is determined by measuring and marking the scalp using a system called the 10-20 system. This system ensures a system of placement that is reliable and reproducible. This was especially important before the advent of computer imaging because EEG was the primary method of tumor localization. This is less important today where MRI and CT scans are used for localizing many lesions. Each electrode is connected to an input of a differential amplifier (one amplifier per pair of electrodes), which amplifies the voltage between them (typically 1,000-100,000 times, or 60-100 dB of voltage gain). The resulting voltage signal is filtered by a high-pass filter and a low-pass filter, typically set at 0.5 Hz and 35-70 Hz, respectively. The high-pass filter typically filters out slow electrogalvanic signals, whereas the low-pass filter filters out electromyographic signals.
The filtered signal is then output on paper (in older systems), or displayed on a computer screen. The amplitude of the EEG is about 100 μV when measured on the scalp, and about 1-2 mV when measured on the surface of the brain.
Historically four major types of continuous rhythmic sinusoidal EEG activity are recognized (alpha, beta, delta and theta). There is no precise agreement on the frequency ranges for each type.
Delta is the frequency range up to 4 Hz and is often associated with the very young and certain encephalopathies and underlying lesions. It is seen in stage 3 and 4 sleep
Theta is the frequency range from 4 Hz to 8 Hz and is associated with drowsiness, childhood, adolescence and young adulthood. This EEG frequency can sometimes be produced by hyperventilation. Theta waves can be seen during hypnagogic states such as trances, hypnosis, deep day dreams, lucid dreaming and light sleep and the preconscious state just upon waking, and just before falling asleep.
Alpha (Berger's wave) is the frequency range from 8 Hz to 12 Hz. It is characteristic of a relaxed, alert state of consciousness. Alpha rhythms are best detected with the eyes closed. Alpha attenuates with drowsiness and open eyes, and is best seen over the occipital (visual) cortex. An alpha-like normal variant called mu is sometimes seen over the motor cortex (central scalp) and attenuates with movement, or rather with the intention to move.
Sensorimotor Rhythm (SMR) is a middle frequency (about 12-16 Hz) associated with physical stillness and body presence.
Beta is the frequency range above 12 Hz. Low amplitude beta with multiple and varying frequencies is often associated with active, busy or anxious thinking and active concentration. Rhythmic beta with a dominant set of frequencies is associated with various pathologies and drug effects, especially benzodiazepines.
Gamma is the frequency range approximately 26-100 Hz. Gamma rhythms may be involved in higher mental activity, including perception, problem solving, fear, and consciousness.
Rhythmic slow activity in wakefulness is common in young children, but is abnormal in adults. In addition to the above types of rhythmic activity, individual transient waveforms such as sharp waves, spikes, spike-and-wave complexes occur in epilepsy, and other types of transients occur during sleep.
In the transition from wakefulness, through Stage I sleep (drowsiness), Stage II (light) sleep, to Stage III and IV (deep) sleep, first the alpha becomes intermittent and attenuated, then disappears. Stage II sleep is marked by brief bursts of highly rhythmic beta activity (sleep spindles) and K complexes (transient slow waves associated with spindles, often triggered by an auditory stimulus). Stage III and IV are characterized by slow wave activity. After a period of deep sleep, the sleeper cycles back to stage II sleep and/or rapid eye movement (REM) sleep, associated with dreaming. These cycles may occur many times during the night.
EEG under general anesthesia depends on the type of anesthetic employed. With halogenated anesthetics and intravenous agents such as propofol, a rapid (alpha or low beta), nonreactive EEG pattern is seen over most of the scalp, especially anteriorly; in some older terminology this was known as a WAR (widespread anterior rapid) pattern, contrasted with a WAIS (widespread slow) pattern associated with high doses of opiates. Anesthetic effects on EEG signals are beginning to be understood at the level of drug actions on different kinds of synapses and the circuits that allow synchronized neuronal activity.
