Cyclic alternating pattern and spectral analysis of heart rate variability during normal sleep RAFFAELE FERRI 1,2 , LIBORIO PARRINO 3 , ARIANNA SMERIERI 3 , MARIO G. TERZANO 3 , MAURIZIO ELIA 2 , SEBASTIANO A. MUSUMECI 2 andSALVATOREPETTINATO 1 1 Sleep Research Center, 2 Department of Neurology, Oasi Institute for Research on Mental Retardation and Brain Aging (IRCCS), Troina, 3 Sleep Disorders Center, Department of Neurology, University of Parma, Parma, Italy Accepted in revised form 24 October 1999; received 23 December 1998 INTRODUCTION The natural electroencephalographic (EEG) arousal rhythm of non-rapid eye movement (NREM) sleep is known as the cyclic alternating pattern (CAP) (Terzano et al. 1985, 1988). CAP consists of arousal-related phasic events (Phase A) that interrupt, at intervals of 20±40 s, the tonic theta/delta activities of NREM sleep (Phase B). Functionally, CAP translates a condition of sustained arousal instability while the comple- mentary EEG pattern, i.e. non-CAP (NCAP), characterized by a rhythmic background activity with few, randomly distributed SUMMARY The natural arousal rhythm of non-rapid eye movement (NREM) sleep is known as the cyclic alternating pattern (CAP), which consists of arousal- related phasic events (Phase A) that periodically interrupt the tonic theta/ delta activities of NREM sleep (Phase B). The complementary condition, i.e. non-CAP (NCAP), consists of a rhythmic electroencephalogram background with few, randomly distributed arousal-related phasic events. Recently, some relation between CAP and autonomic function has been preliminarily reported during sleep in young adults by means of spectral analysis of heart rate variability (HRV). The present study was aimed at analysing the eects of CAP on HRV in a group of normal children and adolescents. Six normal children and adolescents (age range 10.0±17.5 y) were included in this study. All-night polygraphic recordings were performed after adaptation to the sleep laboratory. Six 5-min epochs were selected from sleep Stage 2 and six from Stages 3 and 4 (slow-wave sleep), both in CAP and NCAP conditions. From such epochs, a series of parameters describing HRV was then calculated, in both time and frequency domains, on the electrocardiographic R±R intervals. Statistical comparison between CAP and NCAP epochs revealed a signi®cant dierence for most of the frequency domain parameters (increase of the low-frequency band, increase of the low-frequency/high-frequency ratio and decrease in the high-frequency band during CAP) both in Stage 2 and in slow-wave sleep. Our results demonstrate that the physiological ¯uctuations of arousal during sleep described as CAP are accompanied by subtle, but signi®cant, changes in balance between the sympathetic and vagal components of the autonomic system. KEYWORDS autonomic function, cyclic alternating pattern, heart rate variability, sleep, spectral analysis Correspondence: Dr R. Ferri, Sleep Research Center, Oasi Institute, Via Conte Ruggero 73, 94018 Troina, Italy. Tel.: +39 935 936 111; fax: +39 935 653 327; e-mail: rferri@oasi.en.it. J. Sleep Res. (2000) 9, 13±18 Ó 2000 European Sleep Research Society 13