Keywords

Introduction

A physician dealing with patients suffering from autonomic dysfunction must have a basic knowledge about a variety of sleep disorders that may occur in such patients. For this particular reason, it is essential to know when to order sleep laboratory tests, the rationale behind these tests, and the essential sleep laboratory findings in major conditions with autonomic failure manifesting significant sleep-related symptoms. It is incumbent upon the autonomic specialist to remember that there is an intimate relationship among the central autonomic network (CAN) in the brainstem with its reciprocal ascending and descending connections, hypnogenic neurons (located in the brainstem and hypothalamus), and brainstem respiratory neurons. Sleep has a profound effect on the function of the autonomic nervous system (ANS). Furthermore, dysfunction of the ANS significantly impacts human sleep and particularly breathing during sleep. It is, therefore, logical to expect sleep dysfunction and sleep disordered breathing (SDB) in patients with autonomic failure. In many patients with primary autonomic failure (e.g., multiple system atrophy [MSA], primary autonomic failure [PAF], familial dysautonomia [FD], idiopathic subtype of postural tachycardia syndrome [POTS]) and in some patients with secondary autonomic failure (e.g., diabetic autonomic neuropathy, Guillain-Barre syndrome, central neurodegenerative diseases, such as Parkinson’s disease [PD] and diffuse Lewy body disease with dementia [DLBD]), sleep dysfunction and SDB have been noted. In addition, Fatal Familial Insomnia, a rare prion disease, presents with severe sleep disturbances and dysautonomia. In this chapter, we will briefly describe a variety of sleep laboratory tests (e.g., overnight polysomnography [PSG], Home Sleep Apnea Test [HSAT], Multiple Sleep Latency Test [MSLT], Maintenance of Wakefulness Test [MSWT], and actigraphy) which are important for the diagnosis and monitoring of sleep dysfunction as well as SDB. Finally, we will briefly allude to consumer-oriented sleep technology (not of much practical use currently) and list sleep laboratory findings in some of the conditions with both autonomic and sleep dysfunction mentioned above.

Techniques to Measure Sleep-Disordered Breathing

Polysomnography

Clinical Utility

Attended overnight in-laboratory PSG remains the gold standard in the evaluation of OSA and other types of SDB including central sleep apnea and Cheyne-Stokes respirations (seen in many patients with autonomic failure) as well as ataxic breathing that may be seen in patients on opioid therapy or those with neurodegenerative diseases (e.g., MSA, DLBD, and PD) and demyelinating diseases such as multiple sclerosis [1]. In addition, the routine recording of multiple physiological characteristics in addition to respiratory function simultaneously during sleep, including electroencephalography (EEG), electro-oculography (EOG), and chin and limb muscle electromyography (EMG), allows for the evaluation of unusual behavior in sleep (parasomnias), including rapid eye movement (REM) sleep behavior disorder (RBD), as well as epileptiform activity and clinical seizures during sleep [2], especially when additional EEG and EMG channels are employed.

In general, during PSG recording, patients spend one entire night in the sleep laboratory with the goal of capturing a typical night’s sleep. Figure 11.1 depicts a typical 30-s epoch from an overnight PSG. The study assesses wakefulness and sleep stages, respiration, cardiopulmonary function, and body movements. Airflow and respiratory effort channels are used to score respiratory events including apneas and hypopneas. The finger pulse oximetry channel allows for scoring of event-related oxygen desaturations as well as sleep hypoxemia independent of apneic and hypopneic events. In patients undergoing continuous positive airway (CPAP) or bilevel titration for OSA, the C-flow channel provides the airflow signal, and PAP pressure is continuously adjusted during the night to eliminate respiratory events. EEG, EOG, and chin EMG channels are used to stage sleep, and limb (EMG ) electrodes are typically placed on the legs (usually the tibialis anterior muscle) for scoring and evaluation of limb movements. Additional EMG channels may be used in special montages, especially when it is necessary to determine the presence of REM sleep without atonia in patients with RBD. A single channel electrocardiography (EKG) channel and a snore channel are part of the typical PSG setup. Video and audio recording are essential for recording position and evaluating abnormal movements and behavior in sleep (such as bruxism, catathrenia, and various other parasomnias). Table 11.1 presents a standard set of montages for PSG recording, modified from the American Academy of Sleep Medicine (AASM) recommendations [3].

Fig. 11.1
figure 1

A 30-s epoch depicting N2 sleep from the overnight polysomnogram of a 24-year-old woman with insomnia and snoring. Top eight channels; EEG recording with electrodes placed according to the 10–20 international electrode placement system. E1-M2, E2-M2; electro-oculogram channels. Chin1-Chin2; submental electromyogram (EMG). EKG; electrocardiogram. HR; heart rate. LTIB, RTIB; left and right tibialis anterior EMG. LGAST, RGAST; left and right gastrocnemius EMG. OroNs1-OroNS2; oronasal airflow. Pflw1-Pflw2; nasal pressure transducer recording. Chest and ABD; effort belts. SaO2; arterial oxygen saturation by finger oximetry. Also included is a snore channel

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Technical Considerations

Biological signals recorded during PSG are of very small amplitude (EEG, EOG, and EMG activities are in the microvolt range) and need to be amplified to be displayed and analyzed. Additionally, these waveforms also need to be filtered in order to best visualize activity of interest and exclude artifact. PSG equipment is, thus, a series of amplifiers that record and amplify this activity and then pass it through adjustable filters for display at different sensitivity settings.

PSG equipment uses differential amplifiers, which amplify the potential difference between the two amplifier inputs. The result of this is that unwanted extraneous environmental noise, which is likely to be seen at the two electrodes, is subtracted out and therefore cannot contaminate the recording.

The amplifiers used consist of both alternating current (AC) and direct current (DC) amplifiers. The AC amplifiers are used to record physiological characteristics showing high frequencies such as EEG, EOG, EMG, and EKG. The AC amplifier contains both high- and low-frequency filters. DC amplifiers have no low-frequency filters and are typically used to record potentials with slow frequency such as the output from the oximeter, the output from the pH meter, CPAP titration used for upper airway pressurization to eliminate apneic events, and for some special techniques such as intraesophageal pressure readings. AC or DC amplifiers may be used to record respiratory flow and effort. Sensitivity and filter settings vary according to the physiological characteristics recorded (Table 11.1 and 11.2).

Table 11.1 Typical overnight polysomnographic montage used in our laboratory
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Table 11.2 Filter and sensitivity settings for polysomnographic studies
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The standard speed for recording traditional PSG is 10 mm/s, so that each monitor screen is a 30-s epoch, making sleep staging easy to identify. A 30 mm/s speed is the traditional speed at which EEGs are analyzed, as they allow for easy identification of epileptiform activities. While reviewing the PSG at the traditional 10 mm/s speed, the polysomnographer may pick up EEG abnormalities that can be better analyzed by slowing the recording down to 30 mm/s. On the other hand, with experience, polysomnographers may choose a 5 mm/s speed, rendering a 60-s epoch, to better visualize respiratory events.

Electroencephalography

The main purpose of EEG recording incorporated into PSGs is twofold: to distinguish between wakefulness and the various stages of sleep and to recognize an arousal. EEG electrodes are placed as per the ten-twenty international electrode placement system (Fig. 11.2) [4,5,6,7]. The AASM recommends a minimum of three channels (F4-M1, C4-M1, O2-M1) representing the right frontal, central, and occipital electrodes referenced to the contralateral mastoid. While the above montage would theoretically be sufficient to detect a posterior dominant rhythm in wakefulness (best seen in occipital leads) and major sleep architecture (vertex waves, sleep spindles, and K complexes best seen in frontal and central derivations), there are serious limitations to adhering to this minimum recommended montage. Recording over only one hemisphere may result in inability to score sleep accurately if that hemisphere is affected by a pathological process (as in a patient with stroke or tumor) or in missing possible serious pathology in the contralateral hemisphere. Furthermore, the absence of a temporal lead may result in missing epileptiform activity which is most common in this region. Therefore, we use a montage that records over both hemispheres and includes the temporal regions (see Table 11.1), in addition to electrodes recommended by the AASM for the scoring of sleep. For patients in whom nocturnal seizures are suspected or likely to occur, a full seizure montage with parasagittal and temporal chains (not shown) is recommended [2].

Fig. 11.2
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The international 10–20 system of electrode placement, superior (left) and lateral (right) views. (From Butkov [6], with permission Synapse Media, Medford, Oregon)

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Electro-oculography

Eye movements are generally characteristic of the sleep stage in which they occur and are an essential part of scoring. Eye blinks, seen only in wakefulness, are conjugate vertical eye movements occurring at 0.5–2 hertz with the eyes open or closed. Rapid eye movements (conjugate, irregular, sharp eye movements with an initial deflection of less than half a second) occur in wakefulness along with high chin EMG tone, eye blinks, and a posterior dominant rhythm, and also occur in REM sleep, especially in phasic REM where they occur in bursts seen in all directions (horizontal, oblique, and vertical) and are accompanied by low to absent chin tone (interspersed with similar phasic bursting) and a desynchronized, amorphous EEG pattern. Slow lateral eye movements (SEMs or SLEMs) are seen in drowsiness and light sleep and are defined as conjugate, sinusoidal, regular eye movements with an initial deflection of greater than half a second. These eye movements are not under voluntary control and cannot be volitionally simulated. In approximately 10–15% of subjects who do not generate a posterior dominant rhythm, the appearance of SLEMs heralds stage N1 sleep. While they may persist into stage N2 during the early part of the night, they generally disappear in stage N3 and REM sleep (although there is no formal publication in this regard, but this information is derived from day-to-day routine PSG interpretation); the SLEMs may, however, may persist in deeper stages of sleep in patients on antidepressant medication).

Electromyography

EMG channels provide important physiological characteristics that help determine sleep stage, as well as aiding in the diagnosis and classification of a variety of parasomnias. At a minimum, chin EMG channels recording activity from the mentalis and submental muscles (the mylohyoid and anterior belly of the digastric) and bilateral leg EMG channels recording activity from the tibialis anterior muscles should be included in PSG recordings.

Chin EMG tone aids in the staging of sleep. It follows a characteristic pattern as sleep progresses, decreasing with sleep onset and continuing to diminish through NREM sleep to a point where it is at its minimum and almost absent in REM sleep. Phasic bursts (myoclonic bursts) in the chin EMG (as well as limb EMG) are seen in phasic REM sleep.

Lower limb EMGs are generally recorded with electrodes placed over the tibialis anterior muscles 2–2.5 cm apart. The main utility of these channels is to detect periodic limb movements in sleep (PLMS) and are particularly useful when these movements occur as a result of respiratory events, as the correlation between these movements and the respiratory events can be easily appreciated on PSG. However, many patients with a history of abnormal movements or behavior in sleep require a more extended EMG montage (we call this a multiple muscle montage [MMM]) that includes extra channels recording from additional cranially innervated muscles (e.g., the sternocleidomastoideus, masseter, and mentalis), upper limb muscles (e.g., biceps, triceps, extensor digitorum communis, flexor digitorum Sublimis), lower limb muscles (e.g., quadriceps and gastrocnemius), and axial muscles (e.g., paraspinals, rectus abdominis, intercostals). The MMM is of particular utility in patients with suspected RBD, where REM without atonia may be missed if an adequate number of muscles is not sampled. While a standard montage for RBD has not yet been agreed upon, Fraucher et al. [8] found that simultaneous recording and quantitative analysis of the mentalis and flexor digitorum Sublimis in 3-s mini epochs was 100% specific for RBD, when activity was present in more than 31.9% of miniepochs. The heterogeneity of RBD appears to be expressed in the dissociated EMG findings in cranial as well as arm and the leg muscles, requiring recording from multiple muscles. The MMM recording may also be useful in patients with suspected restless legs syndrome (RLS or Willis-Ekbom disease) as PLMS may also occasionally occur in the arm muscles or, rarely, in the axial or cranially innervated muscles.

It is often helpful to also include external intercostal or diaphragmatic EMG (recording inspiratory muscle bursts) as well as rectus abdominis muscle (recording expiratory muscle activity). The intercostal EMG recorded from the seventh to ninth intercostal space with an active electrode on the anterior axillary line and the reference electrodes on the midaxillary line may also include some diaphragmatic muscle activity in addition to the intercostal activity. Diaphragmatic activity can be recorded by placing surface electrodes over the right or left side of the umbilicus or over the anterior costal margin, but these are contaminated by a mixture of intercostal activity and such noninvasive techniques are unreliable for quantitative assessment of diaphragmatic EMG. True diaphragmatic activity is typically recorded by intraesophageal recording. Intercostal or diaphragmatic EMG is useful in the differentiation between central and obstructive apneas, especially when the respiratory channels are unreliable; continued bursts of EMG activity in these channels would identify the event as obstructive while the absence of such bursts would indicate a central event.

Electrocardiography

The PSG generally includes a single channel of EKG recorded by placing one electrode over the sternum and the other electrode at a lateral chest location. This recording detects bradytachyarrhythmias or other cardiac arrhythmias which may be seen in many patients with autonomic failure and OSA; a standard EKG should be later obtained to characterize the exact nature of the arrhythmia.

Recording of Respiratory Effort

Intraesophageal pressure monitoring is the ideal method of detecting respiratory effort but is not routinely used in the usual sleep laboratory recording. The most commonly used channels measure respiratory effort by respiratory inductive plethysmography (RIP) belts, or by mercury-filled or piezoelectric strain gauges. Impedance pneumography and respiratory magnetometers are available but generally not used.

Respiratory Inductive Plethysmography (RIP)

This measures changes in thoracoabdominal cross-sectional areas and the sum of these two components is proportional to airflow. Inductance refers to resistance to current flow. Transducers across the chest and abdomen detect changes in the cross-sectional areas of the thorax and abdomen during breathing. These belts are prone to dislodgement during the night by patient movement, causing inaccuracy in measurements of the respiratory effort.

Measurement of Airflow

Airflow can be measured by oronasal thermal devices (thermistors or thermocouples) or nasal cannula–pressure transducers. Most standard PSGs use both types of devices due to limitations with using only one type.

Oronasal Temperature Monitoring

An oronasal thermal device (thermistor or thermocouple) placed between the nose and mouth is commonly used to monitor airflow by detecting changes in temperature (cool air flows during inspiration and warm air flows during expiration). A thermistor consisting of wires records changes in electrical resistance, and thermocouples consisting of dissimilar metals (e.g., copper and constantan) register changes in voltage that result from this temperature variation. Thermal devices are not as sensitive as nasal pressure transducers for detecting airflow limitation and, hence, may miss hypopneas. For this reason, the nasal pressure technique to detect airflow (described below) should also be used in addition routinely during PSG recording. The thermistors, however, are used to score apneas.

The temperature of the thermal device must be below body temperature in order to sense the temperature difference between expired and inspired air. These devices must therefore not be in contact with the skin. Because of this, they are easily displaced , causing false changes in airflow.

Nasal Pressure Monitoring

Nasal airway pressure decreases during inspiration and increases during expiration. In nasal pressure monitoring, a nasal cannula is connected to a pressure-sensitive transducer, which measures this pressure difference. This alternating decrement and increment of nasal pressure produce electrical signals, which indirectly register airflow.

Nasal pressure monitoring is more sensitive than the thermal devices in detecting airflow limitation and hypopneas. With increased upper airway resistance, the nasal pressure monitor will register a plateau indicating a flow limitation. A DC amplifier or an AC amplifier with a long time constant should be used. One disadvantage is that nasal pressure cannula cannot be used to measure airflow in mouth breathers and in patients with nasal obstruction. For this reason, nasal pressure transducers are not used to score apneas.

Oxygen Saturation

Finger pulse oximetry is used to noninvasively measure oxygen saturation during sleep (SaO2). It reflects the percentage of hemoglobin that is oxygenated (by measuring the difference in light absorption between oxyhemoglobin and deoxyhemoglobin), rather than the arterial partial pressure of oxygen. Continuous monitoring of SaO2 is crucial because it provides important information about the severity of respiratory dysfunction. PSG reports mention the time the patient spent with an SaO2 below 90%. Patients with OSA may have hyponea/apnea-related recurrent desaturations with a return of SaO2 to baseline at the termination of the event (“respiratory event related hypoxemia”).

Expired Carbon Dioxide

Capnography or end-tidal CO2 (EtCO2) monitoring detects the expired carbon dioxide (CO2) level, which closely approximates intra-alveolar CO2. Capnography detects both airflow and the partial pressure of CO2 in alveoli and is useful in evaluating OSA, sleep hypoventilation, and underlying pulmonary disease. An infrared analyzer over the nose and mouth detects CO2 in the expired air, which qualitatively measures the airflow. This is the best noninvasive method to detect alveolar hypoventilation. The method is costly and therefore not used in most laboratories, but it should be used routinely in children with suspected OSA.

Home Sleep Apnea Testing (HSAT)

In recent years , there has been a trend toward the increased use of portable monitoring devices for home sleep studies in preference to in-lab PSG. HSAT devices are classified into four types based on the number of characteristics they measure and the degree of attendance required. Type 1 devices are the traditional attended in-laboratory PSGs described above. Type 2 devices require a minimum of seven channels, including EEG/EOG, chin EMG, EKG, oximetry, and airflow and respiratory effort channels. Thus, they permit sleep scoring. Type 3 studies (also called “cardiopulmonary studies”) have a minimum of four channels (airflow, respiratory effort, pulse oximetry, and EKG); these studies can be attended or unattended. Sleep scoring cannot be performed with these devices. An example for a type 4 device is overnight ambulatory pulse oximetry (a single-channel device recording a single physiological characteristic). Type 4 devices may also have a channel to measure airflow.

The advantages of HSAT include reduced cost; easier access to these devices for patients who are immobile, cannot travel, or who live far away from sleep laboratories; and quicker turnaround time for results. On the other hand, there are several disadvantages, including reduced sensitivity, especially with type 3 and 4 devices, which may miss mild or positional OSA, or may produce false negative results in patients who sleep poorly during the test. Additionally, type 3 and 4 devices cannot evaluate abnormal movements or seizures in sleep due to lack of EEG and EMG channels. A negative study in a patient in whom the clinical suspicion for sleep disordered breathing is high leads to an in-laboratory PSG anyway. In-lab PSG, rather than portable monitoring, should be used for the diagnosis of OSA in patients with significant cardiorespiratory disease (such as chronic obstructive pulmonary disease [COPD] or congestive heart failure [CHF]), potential respiratory muscle weakness due to neuromuscular condition, awake hypoventilation or suspicion of sleep-related hypoventilation, chronic opioid medication use, history of stroke, or severe insomnia.

Tests for Daytime Hypersomnolence

Although they are both tests for excessive daytime sleepiness, the MSLT and the MWT assess different functions. The MSLT unmasks physiologic sleepiness, which depends on both circadian and homeostatic factors; in contrast, the MWT is a reflection of the individual’s capability to resist sleep and is influenced by physiologic sleepiness.

Multiple Sleep Latency Testing

The MSLT, developed by Carskadon and Dement in the late 1970s [9], is an objective test of hypersomnolence, which measures the rapidity with which a subject can fall asleep under standard conditions during the day. The MSLT has become the standard clinical method for objectively measuring excessive daytime sleepiness [10,11,12]. It is also used to document sleep-onset REM periods (SOREMPS), defined as the onset of REM sleep within 15 min of sleep initiation, one of the critical findings in narcolepsy. Therefore, the AASM has indicated that the MSLT should be used as part of an evaluation of suspected narcolepsy, which remains the single most important indication for performing the MSLT, and that it may be helpful in the evaluation of suspected idiopathic hypersomnia [13, 14]. The MSLT is not routinely recommended in patients with OSA, circadian rhythm disorders, or insomnia; however, those patients previously diagnosed with OSA, PLMS, or mood disorders who continue to have excessive sleepiness despite optimal treatment may require evaluation by the MSLT to exclude associated narcolepsy. Additionally, the MSLT is also often used to determine the efficacy of treatment in patients with narcolepsy. For patients with initially negative studies, following are the recommended indications for repeat MSLT: extraneous circumstances or inappropriate conditions affecting the initial MSLT, presence of ambiguous or uninterpretable finding, and initial MSLT without polygraphic confirmation in a patient suspected to have narcolepsy.

MSLT Guidelines

Guidelines for performing the MSLT have been standardized [15] and should be followed without deviation from protocol by all sleep laboratories. Where deviations are unavoidable, they should be justified by the technician and included in the final report. The sleep specialist must then make a determination with regard to whether the deviation from protocol invalidates the results.

The general procedures before the actual recording include keeping a sleep diary for 1–2 weeks before the test, which records information about usual bedtime, time of rising, napping, and any drug use. The test is mandatorily preceded by an overnight PSG, and the MSLT is scheduled about 2–3 h after the conclusion of the overnight PSG study. On the PSG, additional sleep disorders that may contribute to hypersomnolence (such as OSA) or insufficient sleep (less than 360 min) would invalidate any MSLT results, and the MSLT should be deferred until the underlying sleep disorders are addressed.

The actual test consists of four to five opportunities for napping at 2-h intervals and each recording session is scheduled to last for 20 min. Between tests, subjects must remain awake. The subjects must not smoke for 30 min before lights are turned off. The patient is instructed to relax and fall asleep, and the lights are turned off. The test must be conducted in a quiet, dark room. The specific recording includes a minimum of three channels of EEG (F3-A2, C3-A2, O1-A2, and C4-A1 are recommended to document alpha activity in relaxed wakefulness in adults and its disappearance at sleep onset), submental EMG to evaluate chin tone, and EOG recordings for detection of rapid eye movements. For each nap opportunity, the measurements recorded include sleep-onset latency (the time in minutes from lights out to the first epoch of any stage of sleep) and the presence of SOREMPs. If sleep is recorded, the test is run for an additional 15 min to provide an opportunity for a SOREMP to occur; if a SOREMP does occur, the nap is immediately terminated. If the technician is unclear about whether a SOREMP has occurred, then it is better to continue the test than to end it prematurely. If no sleep occurs, then the test is concluded 20 min after lights are turned off. A total of four to five nap opportunities is provided to the subject (only four need to be recorded if the patient develops two SOREMPs in those four naps or has a SOREMP on the preceding night PSG and at least one additional SOREMP on one of the first four naps) [16]. Mean sleep latency (MSL) is calculated as the average sleep latencies of each of the four or five individual naps.

MSLT Interpretation, Limitations, and Pitfalls

Based on AASM practice parameters, a mean sleep latency of 8 min or less indicates pathological hypersomnolence; a mean sleep latency of 10 min or more is considered normal and latencies between these two means are considered borderline pathologic [17]. The diagnosis of narcolepsy requires a mean sleep latency of 8 min or less and 2 SOREMPs; where insufficient SOREMPs are seen, the diagnosis of idiopathic hypersomnia may be made.

The sensitivity and specificity of the MSLT in detecting sleepiness have not been clearly determined. While the test-retest reliability of the MSLT has been documented to be high in normal subjects [18, 19], it was found to be poor in patients with diseases of central hypersomnolence [20]. In subjects with sleepiness caused by circadian rhythm sleep disorders, sleep deprivation, and ingestion of hypnotics and alcohol, pathologic sleepiness has been validated by MSLT [14]. However, there is poor correlation between the MSLT and subjective measures of sleepiness such as the Epworth Sleepiness Scale [21,22,23]. The patient’s psychological and behavioral state also interferes with the MSLT results. If the patient suffers from severe anxiety or psychological disturbances causing behavioral stimulation, MSLT may not show sleepiness even in a patient complaining of EDS. Day-to-day variability in the degree of sleepiness and an inability to cooperate or understand instructions are other factors for unreliability. Use of centrally active stimulating medications (methylphenidate, amphetamines, modafinil, armodafinil, etc.) and REM suppressants (selective serotonin reuptake inhibitors, tricyclic antidepressants, monoamino oxidase inhibitors, etc.) may produce falsely increased sleep latencies or suppress SOREMPs. Furthermore, pathological sleepiness with two or more SOREMPS may occasionally be seen in other conditions (e.g., OSA, REM sleep dysregulation, circadian rhythm sleep disorders). In addition, the MSLT measures propensity to fall asleep in an environment (e.g., sleep laboratory) conducive to sleep but not in other conditions (e.g., work or driving). One should also be aware of false-positive and false-negative test results. Aldrich et al. [24] found that the sensitivity of the combination of two or more SOREMPs with a mean sleep latency of <5 min on an initial MSLT was 70% with a specificity of 97%, but 30% of all subjects with this combination of findings did not have narcolepsy. Repeat MSLT in those patients with narcolepsy with an initially negative study may yield positive findings in up to 20% of cases [25].

Maintenance of Wakefulness Testing

The MWT, which is performed less frequently than the MSLT, measures the ability of the subject to remain awake, and in contrast to MSLT, the instruction provided is to resist, rather than attempt, sleep [11, 12, 26]. The test protocol requires four trials (“wake opportunities”) at 2-h intervals to test an individual’s ability to stay awake. Based on studies published in the peer-reviewed literature, the Standards of Practice Committee of the AASM [13] recommends the MWT 40-min protocol. Unlike the MSLT, the MWT does not require prior overnight polysomnography. The test is performed about 1.5–3 h after the individual’s usual wake-up time. The recording montage and patient calibrations are similar to those used for the MSLT. Prior to the beginning of the recording, subjects are asked to sit still in bed with a back and headrest and remain awake as long as possible. They are not allowed to read, use headphones to listen to music, use a mobile phone, watch television or use any digital device to read during each trial of 40 min. Sleep onset is defined as the time between lights off in the beginning of the recording and the onset of three consecutive epochs of stage 1 sleep or one epoch of any other stage of sleep. The trial should be terminated after sleep onset or after 40 min if no sleep occurs. A mean sleep latency (the arithmetic mean of the individual sleep latencies of four trials) of less than 8 min is considered abnormal as recommended by the standards of practice committee of the AASM [13]; values greater than this but less than 40 min are of uncertain significance.

The AASM Standards of Practice Committee recommended the following indications for the MWT [13]:

  • Assessment of the individuals employed in occupations involving public transportation or safety for their ability to remain awake

  • Assessment of response to treatment (e.g., response to stimulants in narcolepsy and CPAP titration in OSA patients)

Recently in an important study of MWT [27] concluded tha for driving impairment a sleep onset latency (SOL) of 0–19 minutes may be considered pathological( highl vulnerable) but those with a SOL of 20–33 minutes may also be vulneral but to a lesser extent whereas those with a SOL of 34–40 minutes are considered alert.

Techniques to Measure Body Movements/Sleep-Wake Cycles

Actigraphy

An actigraph , also known as an actometer or actimeter, monitors body movements and other activities continuously for days, weeks, or even months, and thereby indirectly obtains information about sleep-wake cycles [12, 28, 29]. These devices can be worn on the wrist or alternatively on the ankle for recording arm, leg, and body movements. Actigraphs use piezoelectric sensors which function as accelerometers to record acceleration or deceleration of movements rather than the actual movements. The mechanical movements are converted into electrical signals, which are then sampled every tenth second over a predetermined time or epoch and then retrieved and analyzed in a computer. The principle of analysis is based on the fact that increased movements (as indicated by black bars in the actigraph) are seen during wakefulness in contrast to markedly decreased movements or no movements (as indicated by the white area interrupting the black bars) during sleep, although normal physiological body and limb movements and postural shifts during sleep will cause interruptions (black bars of the white background) (Fig. 11.3).

Fig. 11.3
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Actigraphy showing normal sleep-wake schedule in a 55-year-old healthy woman without sleep complaints. This recording shows a fairly regular sleep-wake schedule except one weekend night (third from the top). She goes to bed between 10:30 PM and 11:00 PM and wakes up around 7:00 AM except on the third day. Physiological body shifts and movements during sleep are indicated by a few black bars in the white areas. The waking period is indicated by black bars. (From Chokroverty [12], with permission from Elsevier)

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Actigraphy has been shown to compare favorably with PSG recordings in distinguishing sleep from wakefulness [30]. Compared to PSG, actigraphs have several advantages including easy accessibility, inexpensive recording over extended periods for days, weeks, or even months; recording of 24-h activities at all sites (home, work, or laboratories); usefulness in uncooperative and demented patients when laboratory PSG study is not possible; and ability to conduct longitudinal studies during therapeutic intervention (behavioral or pharmacological treatment) in patients with insomnia. However, actigraphy has several limitations compared to PSG: these include inability to diagnose sleep apnea and to clarify the etiology of insomnia; overestimation of sleep when some insomniacs may lie down in bed for prolonged periods without moving; and an inability to identify subjects who are feigning sleep problem and to discriminate types of movements such as PLMS from other body movements and provide any information about other physiological characteristics (e.g., EEG, EOG, respiration).

Consumer-Oriented Sleep Technology

In recent years, there has been an explosion of inexpensive, consumer-oriented, readily available technology that is meant to monitor, among other parameters, sleep quality and duration. Entries into this category include standalone wearable devices (e.g., FitBit, Jawbone) as well as smartphone-based software programs (“apps”) [31, 32]. While they all essentially use accelerometry-based techniques, as does actigraphy, to score sleep or wake (and in some cases distinguish between “light” and “deep” sleep) based on body movement, in most cases, the exact technology is proprietary, which limits detailed evaluation. “No-contact” bedside devices that detect sleep through radio waves have recently become available [33]. Several smartphone apps that screen for OSA have also been marketed [34, 35]. Although the use of consumer-oriented sleep technology is undoubtedly likely to become more prevalent in the near future, its widespread clinical application is currently limited by the very little data validating it against established means of evaluating sleep [36]. Recently published studies do suggest that this technology, while showing variable correlation with PSG-based scoring, has a sensitivity and specificity for sleep-wake detection that may be comparable to actigraphy [37, 38]. However, the data are preliminary and much more research in the area is required. The AASM Position Statement on consumer-oriented sleep technology [39] recommends that, given the lack of validation and US Food and Drug Administration (FDA) clearance, this technology not be utilized for the diagnosis or treatment of sleep disorders currently.

Brief Review of Sleep Laboratory Findings in Selected Cases of Autonomic Failure

Multiple System Atrophy (Formerly Known as the Shy-Drager Syndrome)

Sleep dysfunction is very common in MSA and PSG findings may include the following [40]: sleep onset and maintenance insomnia with repeated awakenings and sleep fragmentation; decreased sleep efficiency (SE); reduced slow wave sleep (SWS) and REM sleep; a variety of respiratory dysrhythmias (almost in 100% of cases in advanced stage of illness) consisting of OSA with oxygen desaturation; dysrhythmic breathing (irregular rate, rhythm, and amplitude of breathing becoming worse in sleep); Cheyne-Stokes breathing (CSB) and Cheyne-Stokes Variant breathing (hypopnea substituting apnea); prolonged period of central apneas accompanied by mild oxygen desaturation in relaxed wakefulness as if the respiratory center forgot to breathe; in occasional patients inspiratory gasps, apneustic breathing, and periodic breathing in the erect posture accompanied by postural fall of blood pressure; RBD (in 80–95% of cases characterized by violent behavior in about 80% of cases but non-violent in the remaining percentage as captured in the video-audio recordings which are part of the routine PSG recording in most of the laboratories); motor behavior accompanied by REM without atonia (RWA), which is the physiological signature of RBD; and nocturnal stridor which may be inspiratory, expiratory (due to an obstruction in the intrathoracic region), or both and gives rise to a striking noise likened to a “donkey braying.” MSLT may show pathological excessive daytime sleepiness (EDS).

Postural Tachycardia Syndrome (POTS)

Sleep dysfunction is often an important component of this entity but has largely been neglected. PSG findings reflect heterogeneity (as is also noted in the spectrum of clinical presentation) and may include sleep onset and maintenance insomnia, PLMS, decreased or absent REM sleep, abnormal sweating in REM sleep, rarely OSA and CSA with ataxic breathing, and circadian dysrhythmia (e.g., delayed sleep phase syndrome). An important common presentation is fatigue, which may be difficult to differentiate from EDS.

Familial Dysautonomia (FD, Riley-Day Syndrome)

Approximately 85% of adults and 91% of pediatric patients with FD have some degree of SDB which, when untreated, is a risk factor for sudden unexpected death during sleep (SUDS), a leading cause of death in FD. Both CSA and OSA occur in about 50% of patients and hypoventilation is noted in 60% of cases without accompanying apnea in many of them [41]. Other PSG findings include increased arousals and awakenings, prolonged sleep onset, and reduced total REM sleep time as well as dysrhythmic breathing. MSLT may show hypersomnolence. In addition, one infant with FD was found to have periodic somnolence lasting for 4–15 h during the neonatal period.

Diabetic and Amyloidotic Polyneuropathies and Guillain-Barre Syndrome

Sleep and breathing disturbances characterized by PSG-documented obstructive and central apneas-hypopneas accompanied by oxygen desaturation and repeated awakenings have been described in some patients, particularly those with autonomic dysfunction.

Neurodegenerative Diseases (Synucleopathies, e.g., PD and DLBD)

Sleep dysfunction is present in 70–90% of cases of PD. PSG findings may include evidence of RBD (noted in about 40–50% of cases with dream-enacting behavior [DEB] which may precede, occur simultaneously, or after the onset of classic parkinsonian motor manifestations) accompanied by RWA (the physiological signature of RBD), insomnia and irregular sleep-wake schedule (circadian dysrhythmia) noted clearly in actigraphic study, as well as respiratory dysrhythmias in PSG characterized by OSA, hypoventilation, CSB and Cheyne-Stokes variant pattern of breathing, nocturnal stridor, and dysrhythmic breathing. Other breathing problems observed in PD during PSG recordings (video-audio) include laryngeal spasms associated with off-states as well as dystonic episodes and diaphragmatic dyskinesias related to the end-of-the dose and peak-dose levodopa medications. Additional PSG findings in PD may include PLMS, sleep onset blinking, REM onset blepharospasm, and intrusion of REMs into NREM sleep.

An important PSG finding in DLBD is RBD (REM motor dyscontrol with DEB and RWA) noted in 100% of cases and often preceding the onset of the illness. Other PSG findings include sleep apnea and insomnia. These patients may also have nocturnal visual hallucinations during PSG recording. MSLT may document hypersomnolence.

Fatal Familial Insomnia (FFI)

This is a rare autosomal dominant prion disease presenting with prominent sleep and autonomic dysfunction. The most prominent finding in the PSG is progressive decrease in the amount of NREM and REM sleep, eventually leading to patients having only brief episodes of REM sleep. PSG with video-audio recording shows oneiric episodes (RBD-like episodes with enactment of ordinary day-to-day activities).