Quantitative Sleep Monitoring - Quantitative EEG Analysis Methods and Clinical Applications - page 259

during a given epoch, the stage present for the majority of the time names the epoch.
When the tracings used to stage sleep are obscured by artifact for more than
one-half of an epoch, it is scored as movement time (MT). When an epoch of what
would otherwise be considered MT is surrounded by epochs of wake, the epoch is
also scored as wake. Some sleep centers consider MT to be wake and do not tabu-
late it separately.

10.2 Sleep Architecture Definitions

The term sleep architecture describes the structure of sleep. Common terms used in
sleep monitoring are listed in Table 10.1.
The normal range of the percentage of sleep spent in each sleep stage varies with
age [2, 3] and is impacted by sleep disorders (Table 10.2). Chronic insomnia (diffi-
culty initiating or maintaining sleep) is characterized by a long sleep latency and
increased WASO. The amount of stages 3 and 4 and REM sleep is commonly
decreased as well. The REM latency is also affected by sleep disorders and
medications.

10.3 Differential Amplifiers, Digital Polysomnography, Sensitivity, and

Filters

EEG, EOG, and EMG activity is recorded by differential ac amplifiers that amplify
the difference in voltage between two inputs. Signals common to both inputs are not
amplified (common mode rejection). This permits the recording of very small sig-
nals that are superimposed upon larger scalp-voltage changes and 60-cycle interfer-
ence from nearby ac power lines. Common mode rejection depends on the
impedance at input 1 and input 2 being relatively equal [4, 5]. A poorly conducting
electrode (high impedance) will result in a large amount of 60-Hz artifact being
present. By convention in EEG recording, if input 1 is negative relative to input 2,
the deflection is upward (up polarity). In modern digital sleep monitoring, one may
record the activity of numerous electrodes against a common electric reference (ref-

Table 10.1 Sleep Architecture Definitions
Lights out—start of sleep recording
Lights on—end of sleep recording
TBT (total bedtime time)—time from lights out to lights on
TST (total sleep time)—minutes of stages 1, 2, 3, 4, and REM
WASO (wake after sleep onset)—minutes of wake after first sleep but before the final awakening
SPT (sleep period time)—TST WASO

Sleep latency—time from lights out until the first epoch of sleep
REM latency—time from first epoch of sleep to the first epoch of REM sleep
Sleep efficiency—(TST

+

100)/TBT
Stages 1, 2, 3, 4, and REM as % TST—percentage of TST occupied by each sleep stage
Stages 1, 2, 3, 4, and REM, WASO as % SPT—percentage of SPT occupied by sleep stages and WASO

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