The Evoked Heart Rate Response During Sleep

Heart rate responses evoked by a 3‐sec auditory stimulus were averaged within stages of sleep for five subjects. Although there were some individual differences, the evoked HR response is generally diphasic, with the peak of the acceleratory component occurring on the fourth post‐stimulus beat and the trough of the deceleratory component occurring on the 10th post‐stimulus beat. Unlike other variables, which are depressed during the rapid eye movement (REM) stage, the HR response tends to be larger during the REM stage than during other stages of sleep. The size of the response is not appreciably affected by time of night, since HR is non‐habituating during sleep, but is affected by the respiratory cycle phase, being largest when the stimulus occurs during inspiration or the period immediately prior to inspiration, and smallest when the stimulus occurs during the expiratory phase.