POWER SPECTRAL-ANALYSIS OF HEART-RATE-VARIABILITY AS A NEW METHOD FORASSESSING AUTONOMIC ACTIVITY IN THE RAT

The authors studied power spectral analysis of heart rate variability in the rat, hypothesizing that the quantitative information provided b y this analysis reflects the interaction between sympathetic and paras ympathetic regulatory activities. For this purpose, an electrocardiogr am was recorded from conscious and unrestrained Wistar rats (Nippon, S hizuoka) (12-16 weeks old) by a telemetry system and analyzed by a pow er spectrum. Because it was thought that the electrocardiogram recorde d by the telemetry system could provide more reliable data to assess a utonomic nervous activity than the tethering system, the telemetry rec ording system was used. There were two major spectral components in th e power spectrum at low frequency (LF) (0.6 Hz) and high frequency (HF ) (approximately 1.4 Hz). On the basis of these data, the authors defi ned two frequency bands of interest: LF (0.04-1.0 Hz) and HF (1.0-3.0 Hz). The power of LF was higher than that of HF in the normal rat. Atr opine (2 mg/kg intraperitoneally) significantly reduced both HF and LF power. Propranolol (4 mg/kg intraperitoneally) also significantly red uced LF power; however, it had no significant effect on HF power. Thus , this study in the rat confirmed earlier observations in the consciou s dog and human. Furthermore, the decrease in the parasympathetic mech anism produced by atropine was reflected by a slight increase in the L F/HF ratio. The LF/HF ratio appeared to follow the reductions of sympa thetic activity produced by propranolol. From these results, the LF/HF ratio seemed to be a convenient index of parasympathetic and sympathe tic interactions in the rat. Therefore, power spectral analysis of hea rt rate variability may provide a very powerful noninvasive technique for assessing autonomic nervous activity in the rat.