Sleep Definitions Dictionary A through M


AHI -- Apnea Hypopnea Index -- The number of apneic episodes (obstructive, central, and mixed) plus hypopneas per hour of sleep, as determined by all-night polysomnography. (JSD); Normal AHI is <5, mild 5-14, moderate 15-30, severe >30.” (Sleepydave)

Apnea -- Cessation of airflow at the nostrils and mouth lasting at least 10 seconds (JSD)

Arousal -- An abrupt change from a ‘deeper’ stage of non-REM (NREM) sleep to a ‘lighter’ stage, or from REM sleep toward wakefulness, with the possibility of awakening as the final outcome. Arousal may be accompanied by increased tonic electromyographic activity and heart rate, as well as by an increased number of body movements. (JSD)

Awakening -- The return to the polysomnographically defined awake state from any NREM or REM sleep stages. (JSD)

Circadian Rhythms -- Circadian rhythms are our bodies natural rhythms that influence a number of biological / physiological processes, such as sleep and wake patterns, body temperature and certain hormonal changes. Circadian rhythms generally follow a cycle that lasts approximately 24 hours. (CCH)

Hypercapnia -- Hypercapnia is the presence of an abnormally high level of carbon dioxide in the circulating blood. (CCH)

Hypopnea -- Hypopnea is partial (30-50%) cessation of airflow at the nose and / or mouth. (CCH); An episode of shallow breathing (airflow reduced by at least 50%) during sleep, lasting 10 seconds or longer, usually associated with a fall in blood oxygen saturation. (JSD)

Hypoxemia -- Hypoxemia is reduced oxygen in the circulating blood. (CCH)