Sleep Stages and Scoring Technique

Chapter 3


Sleep Stages and Scoring Technique




Introduction to Sleep Stage Scoring


The original Rechtschaffen and Kales sleep scoring manual of 1968, commonly known as the R and K rules, was used until 2007, at which point the American Academy of Sleep Medicine (AASM) updated the scoring manual in what is commonly known as the AASM scoring manual. The Rechtschaffen and Kales method divides sleep into five distinct stages: non–rapid eye movement (non-REM [NREM]) stages 1, 2, 3, and 4 and stage REM sleep. The AASM scoring manual recognizes four sleep stages: Stage N1 (formerly stage 1 sleep), stage N2 (formerly stage 2 sleep), stage N3 (formerly stages 3 and 4 sleep), and stage R sleep (formerly stage REM sleep). The reader is reminded that sleep stages should not be viewed as distinct entities, but rather as a gradual transition of a waveform. The scoring rules were devised to allow uniformity between sleep laboratories and to offer a conceptual simplicity rather than a rigid framework.


Particular signals of interest for sleep scoring include those generated from the cerebral cortex (electroencephalogram [EEG]), eye movements (electro-oculogram [EOG]), and the muscles of the face (picked up by chin electromyographic activity). Electrode placement for EEG scoring rules follows the international 10-20 system, which assigns a number to each EEG electrode to specify the location in the left or right hemisphere (Table 3.1).



Figures 3.1 and 3.2 depict the updated AASM-recommended derivations for recording the EEG.




This chapter will include a discussion of the specific parameters required for staging sleep and a summary of the various EEG activity needed to score sleep. This discussion will be followed by a discussion of the stages of sleep using specific polysomnographic (PSG) records.


The following abbreviations are used in the PSG samples provided in this chapter:



Electro-oculogram electrodes (EOG): Left outer canthus: LOC-A2; right outer canthus: ROC-A1; LOC-A2, ROC-A1, left and right electro-oculogram referred to right and left mastoid leads; M2, right mastoid electrode location; M1, left mastoid electrode location; L/ROC-AVG, left and right electro-oculogram referred to an average reference electrode; E1, left outer canthus eye electrode; E2, right outer canthus eye electrode.


Electroencephalogram electrodes (EEG): C3-A2, C4-A1, O1-A2, O2-A1, left central, right central, left occipital, right occipital; electrode location: ground (FPZ), reference (CZ), A1 or M1 and A2 or M2; C3 and O1, left central and occipital, respectively, EEG electrodes; C4 and O2, right central and occipital, respectively, EEG electrodes. The exploring reference electrode (F3, F4, C3, C4, O1, and O2) is chosen on the opposite side of the head from the mastoid electrode (M1, M2) or average (AVG).


Electromyogram electrodes (EMG): LtTib1-LtTib2 and RtTib1-RtTib2, left and right tibialis anterior EMG electrodes; Chin1-Chin2, submental EMG signal; chin EMG, Chin1-Chin2; limb EMG (left leg, right leg), LtTib1-LtTib2, RtTib1-RtTib2.


Electrocardiogram electrodes (ECG): ECG1-ECG2, ECG2-ECG3.


Respiratory electrodes: SNORE, snore sensor sound; OroNs, oronasal airflow or oronasal thermistor; PFLOW, nasal pressure transducer; THOR/CHEST and ABD, chest and abdominal walls motion effort; THOR1-THOR2, thoracic effort channel; ABD1-ABD2, abdominal effort channel; CFLOW, continuous positive airway pressure (CPAP) airflow channel; PCO2, mm Hg of carbon dioxide; SpO2, oxygen saturation by pulse oximetry by finger probe; Pleth, plethysmography; Pt Position, patient position (supine, left, right, prone).




Parameters for Staging Human Sleep


Common to all PSG monitoring is the measure of the following three physiological parameters:




Eye Movements (Electro-oculogram Activity)


The EOG signals measure changes in the electrical potential of the positive anterior aspect of the eye, the cornea, relative to the negative posterior aspect, the retina. Horizontal axis electrodes are placed near the outer canthi and vertical axis electrodes 1 cm below (LOC) and 1 cm above (ROC) the eye to measure transient changes in potential during the actual eye movement (Fig. 3.3). During any eye movement the cornea moves toward one electrode, while the retina moves away. When the eye is not moving, the change in relative position is zero, and the eye leads do not record a signal.



Slow rolling eye movements (SREMs) occur during drowsiness and light sleep and are recorded as long gentle waves, whereas rapid jerking movements are represented by sharply contoured fast waves. Blinking of the eyes produces rapid vertical movements. During REM sleep, eye movements again become active and jerky. The intensity of the bursts of activity is used to describe the density of REM sleep.




Electroencephalographic Recording


Wakefulness and sleep are determined by the characteristic patterns of the scalp EEG signals and are of fundamental importance in interpreting PSG studies. EEG records electrical potentials generated by the cortex but can reflect the influence of deeper brain structures, such as the thalamus. Measurement of the EEG signal is possible because of the relative difference in potential between two recording electrodes in grid 1 and grid 2 of the channel. A negative discharge in grid 1 relative to grid 2, by convention, is represented by an upwardly deflecting wave in grid 1 of the channel. The PSG references the left or right electrodes to electrodes on the opposite right and left ears (A2, A1) or mastoids (M2, M1). The general rule is to read only from the right cortical channel. However, when this channel develops artifact or the validity of the signal is suspected, comparison is made with the left channel.




Electromyographic Recording


The EMG signals are muscle twitch potentials, which are used in PSG to distinguish between sleep stages based on the fact that EMG activity diminishes during sleep. Specifically, during REM sleep, muscle activity is minimal. Compounding the problem of interpreting EMG channels is occasional intrusion of EMG artifact into the record. Some of these intrusions are in the form of yawns, swallows, and teeth grinding (bruxism).




Electroencephalographic Activity During Wakefulness and Sleep


Six EEG wave patterns are used to differentiate wake and sleep states and classify sleep stages: (1) alpha activity, (2) theta activity, (3) vertex sharp waves, (4) sleep spindles, (5) K complexes, and (6) slow wave activity. These are summarized in Tables 3.2 and 3.3.




Cortical activity can be characterized by specific frequencies. Frequency is defined as the number of times a repetitive wave recurs in a specific time period (typically 1 second). Frequency is noted as cycles per second (i.e., Hertz [Hz]). EEG activity has been divided into four bands based on the frequency and amplitude of the waveform, and the bands are assigned Greek letters (alpha, beta, theta, and delta). The EEG frequencies are defined slightly differently according to the reference used. The following convention is used to define EEG frequencies: beta is greater than 13 Hz; alpha is between 8 and 13 Hz; theta is between 4 and less than 8 Hz, and delta is the slowest activity at less than 4 Hz. Another EEG activity is gamma, which ranges from 30 to 45 Hz.

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Jul 16, 2016 | Posted by in NEUROLOGY | Comments Off on Sleep Stages and Scoring Technique

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