Riesgo y Delito

A PSG typically records a minimum of 12 channels requiring a minimum of 22 wires to be attached to each patient. This varies between different sleep

laboratories according to the requirements of physicians, patient needs, and budgetary constraints. In this study, a minimum of three channels were set aside for the EEG, one to two measured airflow, one to two for chin muscle tone, one or more for leg movements, two for eye movements (EOG), one to two for heart rate and rhythm, one for oxygen saturation, and one each for the belts that measured chest wall movement and upper abdominal wall movement. The movement of the belts was measured with piezoelectric sensors or respiratory inductance plethysmography. This movement was equated to effort and produced a low-frequency sinusoidal waveform as the patient inhaled and exhaled. Wires for each channel of recorded data led from the patient and converged into the “jack-box”, which in turn was connected to a computer system for recording, storing, and displaying the data (see Figure 6). During sleep the computer monitor displayed multiple channels continuously. In addition, each sleep laboratory

had a small video camera in the room so the sleep technician could observe each patient visually (Iber, Ancoli-Israel, Chesson, & Quan, 2007).

The electroencephalogram (EEG). Eight electrodes (six exploratory and two

reference) were applied to each patient. The exploratory electrodes were attached to the frontal, central, and occipital areas of the patient’s head using a conducting gel. These electrodes provided information on brain activity that was “scored” into different stages of sleep (Iber et al., 2007).

The electrooculogram (EOG). Two electrodes, one placed above the corner of the right eye and one below the corner of the left eye, monitored and recorded activity of the eyes. This information provided data relating to the onset of REM sleep (Iber et al., 2007).

The electromyogram (EMG). Six electrodes were applied, two to each anterior tibia of each leg to measure muscle tension (to determine periodic limb movement disorder) and two on the chin (one above the jaw line and one below to establish sleep onset and REM sleep) (Iber et al., 2007).

The electrocardiogram (ECG or EKG). For a standard PSG, two to three electrodes were applied either under the collar bone on each side of the chest or one under the collar bone and the other above either waist to record the electrical activity of the heart (i.e., “P” wave, “QRS” complex, and “T” wave) (Iber et al., 2007).

Respiration. Pressure transducers and/or a thermocouple were generally fitted near the nostrils to measure nasal and oral airflow. These were applied to measure the rate of respiration and identify interruptions in breathing. Belts that expanded and contracted upon breathing effort were also applied to measure respiratory effort (Iber et al., 2007).

Oximetry. A senior was fitted over the finger or ear lobe to determine changes in blood oxygen levels that often occur with sleep apnoea and other respiratory problems (Iber et al., 2007).

Figure 6. Patient connected to a polysomnography. Adapted from Benefits of a Polysomnography, Patrick, 2013, Sleep Solutions, Retrieved from

On completion of the PSG, the results were collected and analysed to provide information on the following sleep-related data:

• Sleep efficiency–the number of minutes of sleep divided by the number of minutes in bed. This is normally calculated to be approximately 85 to 90% or higher;

• Sleep onset latency–onset of sleep from time the lights were turned off. This is normally less than 20 minutes and is measured by EEG results;

• Stage of sleep–determined by the data collected from the EEG, EOG, and EMG and recorded in 30-second epochs. It is normally recorded as “awake”, non-REM sleep (sleep Stages 1, 2, 3) or REM sleep. Non-REM sleep Stage 1 and 2 are referred to as “light sleep”, and sleep Stage 3 is referred to as “deep sleep” or “slow wave sleep” and is demonstrated by wide brain waves

compared to other stages (see Figures 7 and 8; Table 12);

• Apnoeas and hypopnoea–identified by the complete or partial cessation of airflow for at least 10 seconds followed by an arousal and/or a decrease in oxygen desaturation;

• Arousals or sudden shifts in brain wave activity–generally as a result of breathing abnormalities, leg movements and environmental noises;

• Cardiac rhythm abnormalities;

• Leg movements;

• Body position during sleep; and

Interpretations were made by a sleep medicine physician/doctor taking into account the patient’s medical history, a complete list of medications the patient was taking, and any other relevant information that might impact the sleep study such as napping done before the PSG. A report was completed and sent to the referring physician with specific recommendations based on the test results.

Figure 7. Polysomnography results. Results highlighting Alpha wave, Theta waves, Sleep spindles, K-complex and Delta wave from Stage 1 sleep through to Stage 4 sleep including REM. Adapted from Control of Sleep and Wakefulness, by R. Brown, R. Basheer, J. McKenna, R. Strecker, R. McCarley, 2012, Physiological Reviews 1(92), 1087-1187. Copyright 2014 by the American Physiological Society. Adapted with permission.

Alpha waves

Delta waves Theta waves

Figure 8: Parameters monitored during a PSG. The recorded variables are shown over 30-second epochs. Data exhibits passive breathing during stage 2 sleep, followed by an arousal (apnoea) resulting in increased EMG, EOG, and EEG activity. From Cardiac and respiratory activity at arousal from sleep under controlled ventilation conditions, by J. Trinder et al., 2001, Journal of Applied Physiology, 90(4), 1455- 1463. Copyright 2001 the American Physiological Society. Reprinted with

Table 12 Stages of Sleep

Stage

Total Sleep, %

EEG Wave Defining Traits

1 2–5% Theta wave Light sleep, hypnic jerks, conscious awareness.

2 45–55% Sleep spindles and K complexes

Consolidated sleep, loss of conscious

awareness, slowed heart rate, decreased body temperature.

3 & 4 3–8% Delta/slow wave Deep/restorative sleep, difficult to arouse. REM 20–25% Alpha (wakefulness) Dream sleep, paradoxical sleep, paralysis,

high cortical activity.

CHAPTER 3