Study on Heart rate Variability and Heart Rate under General Anesthesia in Rats of Both Sexes

Objectives: It is known that general anesthesia weakens autonomic function and baroreflex control. Intravenous anesthetics may have different qualitative and quantitative effects on the peripheral autonomic nervous system (ANS) and, can thus, alter the activity of sympathetic or parasympathetic divisions of the ANS. Presently, there are relatively little data regarding sex differences in ANS activity or sex differences in ANS activities during anesthesia.

Aims: The primary objective of this study was to determine the impact of spectral powers of heart rate variability (HRV) on changes in heart rate (HR), total spectral power of HRV, and low-frequency (LF)/high-frequncy (HF) ratio in healthy, sexually mature rats of both sexes spontaneously breathing under zoletil anesthesia in the light (inactive) and the dark (active) period of their regimen day.

Materials and Methods: Experiments were performed using male and female zoletil-anesthetized (30 mg/kg [intraperitoneal]) Wistar rats after a four-week adaptation to a light-dark (LD) cycle (12h:12h). The animals were divided into four experimental groups (n=20 each) according to sex and light period. HR, spectral powers of HRV (very low frequency, LF, and HF), as well as LF/HF ratio were evaluated 20 min after administration of anesthesia.

Results and Conclusions: Zoletil exerted a tachycardic effect in both sexes and in both light periods of the regimen day. In females, the autonomic nervous system was involved in HR changes in both light periods, while in males, HR exhibited no dependence on autonomic nervous system activity; as such, the authors speculate that it was predominantly determined by other factors. In females, HRV was determined by sympathetic and baroreflex activity in both light periods, while in males, HRV was determined by parasympathetic activity. LF significantly influenced LF/HF ratio in females, but not in males, while the effect of HF on the LF/HF ratio was negligible in both sexes and in both light periods.