[Hypopnea according to various definitions and coexisting arousal response in patients with sleep-disordered breathing].

Hypopnea is a type of sleep-disordered breathing, and the apnea plus hypopnea index (AHI) is usually computed to diagnose this condition. Nevertheless, there is no consensus on the definition of hypopnea. To arrive at a reasonable definition, we examined the relationship between arousal response and hypopnea as defined in various ways, in polysomnographs of 20 patients with sleep-disordered breathing. Hypopnea was defined as a 50% reduction in thoraco-abdominal movement of various durations (all of which were more than 10 sec) and coexisting oxygen desaturation of various degree. The ratio of coexisting arousal response for hypopneas was higher when hypopnea was defined as having a relatively long duration and relatively deep desaturation, but more arousal responses were missed. 1) When the threshold duration for hypopnea was fixed at 10 sec, the following results were obtained: With desaturation thresholds of 4% and 2%, the mean ratios of missed arousals were 37% (range, 1-85%) and 12% (range, 0.5-35%), respectively. The hypopneas with only 2% desaturation had coexisting arousal responses with a mean frequency of 49% (range, 27-89%). 2) When desaturation was not included in the definition, the following results were obtained: Hypopneas lasting less than 15 sec had lower frequencies of a coexisting arousal response than did those of longer duration. When the threshold duration for hypopnea was 15 sec, the mean ratio of missed arousal was 16.2% (range, 1.6-32.9%).(ABSTRACT TRUNCATED AT 250 WORDS)