Recovery cycle of the evoked heart rate response in sleeping humans

Paired auditory stimuli, presented during sleep, evoked biphasic heart rate responses of greater than 10-second duration. The magnitude of the response to a second stimulus varies with the time between stimuli. The recovery cycle for human subjects exhibits a subnormal period for both HR peak and trough components at 5-or 6-second interstimulus intervals, and a supernormal period for the HR peak at 9-or 10-second interstimulus intervals. Thus, subnormal and supernormal periods coincide with the peak and trough, respectively, of the biphasic evoked heart rate response.