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Table 1 Definitions of Sleep Variables Measured in the Study [1, 2]

From: Nocturnal sleep, daytime sleepiness, and quality of life in stable patients on hemodialysis

Brief Arousal – An abrupt change (3 to 14 seconds) from a "deeper" stage of NREM sleep to a "lighter" stage, or from REM sleep to wakefulness.
Brief Arousal Index – number of brief arousals/hour of sleep; normally < 15/hour
Excessive Daytime Sleepiness – Difficulty in maintaining the alert, awake state. Can be measured subjectively using questionnaires (such as the Epworth Sleepiness Scale; see text) or objectively (polysomnographically) using the Multiple Sleep Latency Test (see text).
Insomnia/Sleep Fragmentation (subjective) – difficulty initiating or maintaining sleep; often characterized by difficulty falling and/or staying asleep, early morning awakenings, or unrefreshing sleep.
Mean Sleep Latency – the average period of time from the start of a nap opportunity to the first epoch of sleep as measured by the Multiple Sleep Latency Test.
Periodic Limb Movement – a rapid partial flexion of the foot at the ankle, extension of the big toe, and partial flexion of the knee and hip[ that occurs during sleep. The movements occur with a periodicity of 5 to 90 seconds, lasting 0.5 to 5.0 seconds.
Periodic Limb Movement Index (PLMI) – number of periodic limb movements/hour of sleep.
Periodic Limb Movement with Arousal Index – number of limb movements/hour of sleep associated with an abrupt change from a deeper stage of NREM sleep to a lighter stage, or from REM sleep to wakefulness
Respiratory disturbance – Cessation (apnea) or reduction in breathing (hypopnea; airflow reduced by at least 50%) during sleep, lasting 10 seconds or longer, often associated with a fall in blood oxygen saturation.
Respiratory Disturbance Index (RDI) – number of apneas/hypopneas per hour of sleep.
Sleep Efficiency (SE) – The proportion of sleep in the episode filled by sleep; the ratio of TST to time in bed. Normal values range typically from 80% to 95% and decrease with age.
Sleep Latency (SL) – The onset of sleep defined as the first of three consecutive epochs of Stage 1 sleep or the first epoch of any other stage of sleep. Normal sleep latency averages < 20 minutes.
Total Sleep Time (TST) – The amount of actual sleep time in a sleep episode; the time is equal to the total sleep episode less the awake time; average normal TST is 7.5 hours.