Clinical Polysomnography

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Introduction

The assessment of patients for snoring and sleep apnea includes a comprehensive sleep history, physical examination, and a diagnostic sleep study. The compilation of this information allows for the formulation of a treatment plan that is tailored to the patient's specific issues and needs.

There is much more information on a sleep study report than just the Apnea/Hypopnea Index (AHI) and Respiratory Disturbance Index (RDI). The purpose of this chapter is to present a practical approach to looking at sleep study reports to get the most information out of them in an attempt to allow individualized treatment recommendations for our sleep patients.

Sleep studies can be performed either in a sleep laboratory or at home. There are advantages and disadvantages to both. The decision to do a study in the laboratory versus at home is sometimes dictated by the expertise and comfort level of the physician, the desires of the patient, or, unfortunately at times, by the edict of the insurance company.

This chapter will focus on in-laboratory sleep studies. Chapter 5 will review home sleep apnea testing.

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Data Acquisition for Polysomnography

The patient generally presents to the sleep laboratory in the evening. However, shift workers, who usually sleep during the day, are better served by having the test performed during the day in what would be their normal sleep period. After being checked in and changing into their sleep attire, a sleep laboratory technician will perform the setup by attaching all of the appropriate leads.

When ready, the patient will lie down and the technician will start the recording. The technician observes the data channel, for each lead, on a monitor in a different room. If a lead detaches during the study, the technician may enter the test room, at the appropriate time, and replace it. Generally, each technician will set up and monitor two patients during the course of a night.

The patients are being videotaped by a low-resolution video camera that serves three purposes. First, it allows the technician to record body position, that is, supine vs. nonsupine. Second, it allows monitoring of parasomnias, such as sleep walking, rapid eye movement (REM) behavior disorder (RBD) and seizures. Finally, it is there to protect both the patient and the sleep laboratory from inappropriate behaviors and/or accusations. There is also a microphone that allows patients to communicate with the sleep technician if they have any questions or concerns.

After the recording is finished in the morning, the raw data collected during the night will be “scored” by a respiratory polysomnography technologist. Scoring a sleep study generally entails analyzing all data channels on multiple passes. First, it is staged for wakefulness and sleep stages. Subsequently, it will be analyzed for respiratory, and other, events.

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Sleep Staging

The leads that are used during a sleep study include those that measure electroencephalography (EEG), electrooculography (EOG), electromyography (EMG), electrocardiography (ECG), nasal pressure, airflow, effort (chest and abdomen), and pulse oximetry.

The top half of the recording of sleep data is usually EEG, EOG, and chin EMG. This helps us determine if a patient is awake or asleep and, if asleep, what stage of sleep they are in. The bottom half of the data allows us to visualize events, such as respiratory events, snoring, and limb movements. The ECG is usually in the top half of the screen, which is best seen in a 30-second window, similar to the best way to visualize the EEG. The channels at the bottom half of the screen are usually viewed in a 2-minute screen ( Fig. 4.1 ).

There are three general states of being: wakefulness, non-REM sleep, and REM sleep. Normally, one proceeds from wakefulness into non-REM sleep and then into REM sleep. One cycles between non-REM and REM sleep approximately four to five times in a typical night before awakening in the morning.

As stated earlier, wakefulness and sleep on a sleep study are determined by EEG, EOG, and chin EMG leads.

Wakefulness and stages of sleep are artificially broken down into 30-second epochs. The epoch is scored as whatever stage of sleep or wakefulness makes up the majority of the 30 seconds. The chin EMG amplitude helps with the staging of sleep. It decreases from a high in wakefulness, decreases in non-REM sleep, down to a low in Stage REM.

Wakefulness, with the eyes closed, is characterized by alpha waves making up >50% of the epoch and a high chin EMG ( Fig. 4.2 ). Non-REM sleep is made up of three stages: Stage N1, Stage N2, and Stage N3. If you are looking at an old sleep study report, you may notice mention of Stage 4 sleep. In a revision of sleep staging by the American Academy of Sleep Medicine (AASM), 2007, Stage 3 and Stage 4 were combined into Stage N3.

Stage N1 is the transition between wakefulness and deeper stages of sleep. It is a very light sleep. If someone taps you on the shoulder during Stage N1 sleep, you may awaken easily and respond. It is typically 2% to 5% of a night's sleep. Increased Stage N1 sleep is seen with fragmented sleep where a patient has multiple awakenings. As they are frequently falling back to sleep, they may transition briefly through Stage N1. Stage N1 is characterized by low-amplitude, mixed-frequency EEG activity and alpha waves that make up <50% of the epoch ( Fig. 4.3 ).

Adults with normal sleep architecture generally spend more time in Stage N2 than in any other individual sleep stage. At times, it is a higher percentage of sleep than all of the other sleep stages combined. Normally, we spend 45% to 55% of the night in Stage N2. It is characterized by sleep spindles and K-complexes ( Fig. 4.4 ).

Stage N3 sleep is generally considered “deep sleep” and allows for “restorative sleep.” It is easy to recognize Stage N3 by its slow, rhythmic, high-amplitude delta waves ( Fig. 4.5 ). Delta waves are 1 to 4 Hz. Stage N3 sleep typically encompasses 3% to 20% of sleep. This stage of sleep slowly decreases as a percentage of sleep as we get older, more in men than in women.

Obviously, the classic, feature and basis for naming of Stage REM is the rapid eye movements (see Fig. 4.6 ). This is documented by the EOG leads. The EEG during Stage REM is also characterized by intermittent saw tooth waves.

The classic physiologic finding of Stage REM, other than the eye movements, is atonia. The only muscles that work during Stage REM are of the diaphragm, eyes and heart. This atonia is a protective mechanism that allows us to dream in Stage REM without getting out of bed and acting out our dreams. On the other hand, obstructive sleep apnea (OSA) is generally worse in Stage REM than in non-REM sleep because of this atonia and the increased collapsibility of the airway.

Lack of atonia during Stage REM, which is pathologic, is seen in RBD. There is a higher incidence of RBD in patients with Parkinson disease than in the general population. In fact, RBD sometimes precedes the diagnosis of Parkinson disease by several years.

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