Polysomnography

Polysomnography is a systematic way of collecting physiological measurements during sleep [1]. A full study uses electroencephalography (brain waves), electro-oculography (eye movements), electromyography (muscle activity), electrocardiography (heart) and pulse oximetry (blood oxygen), along with sensors for airflow and breathing effort [1]. In clinical practice it is considered the gold standard for diagnosing sleep-related breathing disorders [1].

The recordings are scored into the measures that sleep trials report: total sleep time, sleep efficiency, sleep onset latency (the time taken to fall asleep), wake after sleep onset, and the share of each sleep stage, such as N2, N3 and REM sleep [2]. A meta-analysis of normal values included only studies scored with American Academy of Sleep Medicine criteria (2007 or 2012) during an overnight in-laboratory study [2].

Polysomnography is expensive and burdensome, so existing normal values for healthy adults had been based on small samples [2]. That meta-analysis pooled 169 studies of healthy adults (5,273 participants) and reported normal values by age and sex [2]. Comparing across studies, samples with older participants had shorter total sleep time, lower sleep efficiency and more wake after sleep onset for each decade of age, while the shares of N2, N3 and REM sleep did not change significantly with age [2]. Samples with a higher share of men had a shorter REM latency (the time until the first REM sleep) [2].

Age and sex therefore matter when a trial's sleep results are compared with another trial's. A supplement trial that uses polysomnography can report these scored measures, including sleep stages [2], while a sleep-quality questionnaire records how people rate their own sleep.

NootropicsWork names the measurement method in every sleep finding: polysomnography, actigraphy or a questionnaire.

Actigraphy, sleep latency, meta-analysis.