Quantitative Sleep Monitoring - Quantitative EEG Analysis Methods and Clinical Applications - page 273

checked prior to recording. An ideal impedance is < 5,000 Ω . Electrodes with higher

impedances should be changed.
A biocalibration procedure is performed (Table 10.8) while signals are acquired
with the patient connected to the monitoring equipment [4, 5]. This procedure per-
mits checking of amplifier settings and integrity of monitoring leads/transducers. It
also provides a record of the patient's EEG and eye movements during wakefulness
with eyes closed and open. A summary of typical commands and their utility is
listed in Table 10.8.

10.14 Quantitative Polysomnography

As mentioned previously, the polysomnograph is traditionally used to conduct sleep
studies. The polysomnograph records electrical activity that represents specific
physiological characteristics during sleep. It can be made up of bioelectrical poten-
tials, transduced signals, and signals that are derived from ancillary equipment [41].
The EEG, EOG, and EMG are some of the measurements taken in a
polysomnograph. These measurements can be used for sleep state detection. Each of
these devices monitors different physiological characteristics: The EEG measures
brain activity, the EOG measures eye movement, and the EMG measures muscle
activity. Each device gives insight into the sleep stage that the patient is currently in.

10.14.1 EEG
According to the Rechtschaffen and Kales [1] sleep-staging system, certain
bandwidths appear or disappear within the EEG signal depending on the sleep state
the patient is in. In addition, certain neurophysiological activity (sleep spindles and
K complexes) can be used to distinguish the stage of sleep from the EEG.
The main points of the R&K classification [1] system were discussed previ-
ously. To summarize, during wakefulness, alpha activity exists, as well as low-volt-
age mixed-frequency activity. The alpha waves exist in the wake state and decrease
when the patient enters the first stage of NREM sleep. Sleep spindles and K com-
plexes are an indication of stage 2 NREM sleep. Then delta waves appear in stages 3

Table 10.8 Biocalibration Procedure

Eyes closed EEG: alpha EEG activity

EOG: slow eye movements

Eyes open EEG: attenuation of alpha rhythm

EOG: REMs, blinks

Look right, look left,
look up, look down

Integrity of eye leads, polarity, amplitude
Eye movements should cause out-of-phase
deflections

Grit teeth Chin EMG

Breathe in, breathe out Airflow, chest, abdomen movements adequate

gain? Tracings in phase? (Polarity of inspiration
is usually upward)

Deep breath in, hold breath Apnea detection

Wiggle right toe, left toe Leg EMG, amplitude reference to evaluate LMs