Diagnosis and Treatment of all Sleep Disorders

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Sleep Study Terminology

Learn these terms and their meaning so that you can understand your sleep study results

    1. Sleep Efficiency

The percentage of bed time actually staying asleep. Usually >80%.

    1. Sleep Onset Latency

The time taken from ‘lights out,’ to the onset of sleep.

    1. Sleep Architecture

This is the proportionate and timing of the different sleep stages.


Stage I & Stage II are ‘light sleep’
Stage III & IV = ‘deep’ or ‘slow wave’ sleep’
(usually 20% of sleep time and decreases with age)
REM = ‘dream sleep’ (usually 20% of sleep)

Normally, you will go through 3-5 cycles of light to deep back to light sleep. As the night goes on REM episodes grow progressively longer, so that slow wave sleep predominates in the first third of the night and REM in the last third Sleep disorders often disrupt this normal pattern leading to a reduced REM and slow wave sleep, leaving predominantly the lighter stages of sleep.

    1. AHI (Apnoea-Hypopnoea Index)

Measure of how severe your sleep apnoea is. It is the average number of abnormal breathing events per hour of sleep.

5 is normal; 5 to 14 is mild; 15 to 29 is moderate; more than 30 is severe.

    1. Apnea

No airflow through both the nose and mouth for more than 10 seconds. It may be obstructive (related to the throat), central (related to the controllers of breathing) or mixed (a combination).

    1. Hypopnea

A significant reduction in breathing but not complete cessation. These often result in a drop in oxygen or cause a disruption in the brain’s sleep pattern (ie. an arousal).

    1. Arousal

An abrupt change in the brain activity, often causing change from ‘deeper’ stage of sleep to a ‘lighter’ one. Sometimes they lead to awakening as the final outcome. An Arousal Index >20/hr is abnormal.

    1. Oxygen Saturation (SaO2)

A measure of how much oxygen is available to the body at a given time. Normally, this is 94-100%.