Quantitative Sleep Monitoring - Quantitative EEG Analysis Methods and Clinical Applications - page 272

An LM is defined as an increase in the EMG signal of a least one-fourth the
amplitude exhibited during biocalibration that is 0.5 to 5 seconds in duration [39].
Periodic LMs (PLMs) should be differentiated from bursts of spike-like phasic activ-
ity that occur during REM sleep. To be considered a PLM, the movement must
occur in a group of four or more movements, each separated by more than 5 and less
than 90 seconds (measured onset to onset). To be scored as a PLM in sleep, an LM
must be preceded by at least 10 seconds of sleep. In most sleep centers, LMs associ-
ated with termination of respiratory events are not counted as PLMs. Some may
score and tabulate this type of LM separately. The PLM index is the number of
PLMs divided by the hours of sleep (TST in hours). Rough guidelines for the PLM
index are as follows: 50, severe

[40]. A PLM arousal is an arousal that occurs simultaneously with or following
(within 1 to 2 seconds) a PLM. The PLM arousal index is the number of PLM arous-
als per hour of sleep. A PLM arousal index of

> 5to < 25 per hour, mild; 25 to < 50, moderate; and =

25 per hour is considered severe.
LMs that occur during wake or after an arousal are either not counted or tabulated
separately. For example, the PLMW (PLMwake) index is the number of PLMs per
hour of wake. Of note, frequent LMs during wake, especially at sleep onset, may
suggest the presence of the restless legs syndrome. The latter is a clinical diagnosis
made on the basis of patient symptoms.

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10.13 Polysomnography, Biocalibrations, and Technical Issues

A summary of the signals monitored in polysomnography is listed in Table 10.7. In
addition, body position (using low-light video monitoring) and treatment level (con-
tinuous positive airway pressure, bilevel pressure) are usually added in comments by
the technologists. In most centers, a video recording is also made on traditional vid-
eotape or digitally as part of the digital recording. It is standard practice to perform
amplifier calibrations at the start of recording. In traditional paper recording, a cali-
bration voltage signal (square wave voltage) was applied and the resulting pen
deflections, along with the sensitivity, polarity, and filter settings on each channel,
were documented on the paper. Similarly, in digital recording, a voltage is applied,
although it is often a sine-wave voltage. The impedance of the head electrodes is also

Table 10.7 Polysomnography—Respiratory Variables

Variables Purpose Methods

Airflow Classify apneas and

hypopneas

Nasal-oral thermistor
Nasal pressure
RIPsum (changes approximate tidal volume)
Exhaled CO 2

Respiratory
effort

Classify apneas and
hypopneas

Chest and abdominal bands (RIP, piezo bands)
Intercostal EMG
Esophageal pressure

Pulse oximetry Arterial oxygen saturation Pulse oximetry

End-tidal PCO 2 Estimate of arterial PCO 2

(detect hypoventilation)

Capnography—exhaled CO 2

Transcutaneous PCO 2 Estimate of arterial PCO 2
(detect hypoventilation)

Transcutaneous PCO 2