The aim of the present study was to determine the effect of ketamine/ xylazine and pentobarbital anaesthesia on heart rate variability as a marker of autonomic nervous system activity. The experiments were performed in ketamine/ xylazine (10 mg/kg/15 mg/kg) and pentobarbital (40 mg/kg, i.p.) anaesthetized female Wistar rats, after adaptation to a light-dark cycle of 12 hours light: 12 hours dark. Heart rate variability parameters (RR interval, power VLF (very low frequency), power LF (low frequency), power HF (high frequency) and relative powers) were evaluated during spontaneous breathing as a function of the light-dark cycle (LD cycle). Significant LD differences were found in the duration of RR intervals in ketamine/xylazine compared with pentobarbital-anaesthetized rats. Correlation analysis revealed moderate dependency between the RR interval duration and HF and LF power parameters in ketamine/xylazine anaesthesia in both light and dark parts of the cycle. In pentobarbital-anaesthetized rats, correlation analysis demonstrated a moderate dependence between RR interval duration and HF and VLF power parameters, but only in the dark part of the LD cycle. Ketamine/xylazine anaesthesia increased parasympathetic activity, and suppressed sympathetic and baroreceptor activity independently of the light-dark cycle. LD differences in RR interval duration were not eliminated. Pentobarbital anaesthesia increased parasympathetic activity, decreased sympathetic and baroreceptor activity, and eliminated LD differences in RR interval duration.

Department of Physiology Faculty of Medicine Pavol Jozef Šafárik University Košice Slovak Republic

Department of Physiology Faculty of Medicine University of Ostrava Ostrava Czech Republic

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