Keiji Ishii

Power Spectral Analysis of Heart Rate Variability as a New Method for Assessing Autonomic Activity in the Rat

The authors studied power spectral analysis of heart rate variability in the rat, hypothesizing that the quantitative information provided by this analysis reflects the interaction between sympathetic and parasympathetic regulatory activities. For this purpose, an electrocardiogram was recorded from conscious and unrestrained Wistar rats (Nippon, Shizuoka) (12-16 weeks old) by a telemetry system and analyzed by a power spectrum. Because it was thought that the electrocardiogram recorded by the telemetry system could provide more reliable data to assess autonomic nervous activity than the tethering system, the telemetry recording system was used. There were two major spectral components in the 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 defined 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. Atropine (2 mg/kg intraperitoneally) significantly reduced both HF and LF power. Propranolol (4 mg/kg intraperitoneally) also significantly reduced LF power; however, it had no significant effect on HF power. Thus, this study in the rat confirmed earlier observations in the conscious dog and human. Furthermore, the decrease in the parasympathetic mechanism produced by atropine was reflected by a slight increase in the LF/HF ratio. The LF/HF ratio appeared to follow the reductions of sympathetic activity produced by propranolol. From these results, the LF/HF ratio seemed to be a convenient index of parasympathetic and sympathetic interactions in the rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of autonomic nervous function by power spectral analysis of heart rate variability in the horse

We studied power spectral analysis of heart rate (HR) variability in the horse, with the hypothesis that the quantitative information provided by the spectral analysis of HR variability reflects the interaction between sympathetic and parasympathetic regulatory activities. For this purpose, electrocardiogram, blood pressure (BP) and respiratory (Resp) waveform were simultaneously recorded from Thoroughbred horses (3-5 years old) and analyzed by power spectrum. There were two major spectral components at low-frequency (LF) and high-frequency (HF) bands for HR variability. The peak of Resp variability clearly occurred at the HF range. In contrast to Resp variability, the power spectra of BP variability occurred at lower frequencies. The maximum coherence between HR and Resp variabilities and HR and BP variabilities occurred at approximately 0.15 and approximately 0.03 Hz, respectively. These relationships were similar to the ensemble spectra. On the basis of these data, we have defined two frequency bands of interest: LF (0.01-0.07 Hz) and HF (0.07-0.6 Hz). Therefore, we believe that power spectral analysis of HR variability provides a very powerful technique for assessing autonomic nervous activity in the horse.

Autonomic nervous function in mice and voles (Microtus arvalis): investigation by power spectral analysis of heart rate variability

We have studied the autonomic nervous function in voles (Microtus arvalis) and mice. For this purpose, ECGs were recorded from conscious and unrestrained voles and mice using radiotelemetry and the autonomic nervous function was investigated by the power spectral analysis of heart rate variability. Heart rate in voles was lower than mice and the coefficient of variance was larger in voles. In the power spectra of voles and mice, there were two major spectral components with the high frequency (HF) peak generally appearing between 2.0 and 4.0 Hz, and the low frequency (LF) peak appearing below 0.6 Hz. On the basis of this data, we set the two frequency bands as LF (0.1-1.0 Hz) and HF (1.0-5.0 Hz) to evaluate autonomic nervous function. The LF and HF powers were larger in voles than mice. The LF/HF ratio was thought to provide a convenient index of autonomic nervous balance and was smaller in voles than mice. The LF powers in both species were reduced by atropine, but propranolol reduced the LF power only in mice. The HF power was reduced by atropine only in voles. The intrinsic heart rate produced by a double blockade with atropine and propranolol in voles was almost the same as control levels, but in mice was lower than controls. The ratio of the LF and HF powers by a double blockade were almost the same as those of the administration of atropine in voles, but nearer to propranolol in mice. These results suggested that the parasympathetic nervous function was predominant in voles, but the sympathetic one was predominant in mice.

Role of the autonomic nervous system in emetic and cardiovascular responses in Suncus murinus

To clarify the role of the autonomic nervous system in cardiovascular and emetic responses, we studied the influence of drugs that act on autonomic nervous function on emetic and cardiovascular responses induced by chemical or mechanical stimulation to the stomach in two strains of Suncus murinus, Jic:SUN-Her and Jic:SUN-Ler. Latency to the first retching in Jic:SUN-Her was significantly shorter than that in Jic:SUN-Ler to both mechanical and chemical stimulation. This result indicated that there are different sensitivities to mechanical and chemical stimulation to the stomach in these two strains of suncus. However, the numbers of emetic episodes were almost the same in these two strains. Mean blood pressure significantly increased from baseline prior to retching in both strains. Heart rate decreased in Jic:SUN-Her and increased in Jic:SUN-Ler prior to retching, suggesting that a different baroreflex responsiveness might exist in these two strains of suncus. Administration of acetylcholine and phenylephrine affected emetic response induced by mechanical and chemical stimulation. Although the baseline values of mean blood pressure and heart rate after administration of these drugs were different, changes in mean blood pressure and heart rate prior to retching were unaffected. This result suggested that the state of autonomic activity before the emetic response might be important in the development of the emetic response. Pretreatment with hexamethonium suppressed the cardiovascular response prior to retching and prolonged the latency to the first retching. This result indicated that there was an interaction between the mechanisms involved in cardiovascular and emetic responses. The change in autonomic function during the emetic response, especially enhancement of sympathetic activity prior to retching, may be relevant to emetic and cardiovascular responses. Moreover, these results suggest that different autonomic function or different baroreflex responsiveness in Jic:SUN-Her and Jic:SUN-Ler may be involved in emetic responses.

Role of autonomic nervous system for development and suppression of motion sickness in Suncus murinus

To clarify the role of autonomic nervous function in motion sickness, the effect of agents that act on the autonomic nervous system on the motion stimuli-induced emesis was studied in two strains of Suncus murinus (Jic:SUN-Her and Jic:SUN-Ler) with congenitally different sensitivity to veratrine sulfate. We demonstrated significant differences between the two strains in sensitivity to motion stimuli. Isoproterenol (2.5 mg kg(-1), s.c.) significantly prolonged the latency to the first emetic episode induced by motion stimuli and significantly decreased the number of emetic episodes in Jic:SUN-Her suncus. Hexamethoium (2.0 mg kg(-1), s.c.) tended to shorten the latency in Jic:SUN-Ler. Acetylcholine (1.2 mg kg(-1), s.c.) enhanced the emetic response in Jic:SUN-Ler, but atropine (4.0 mg kg(-1), s.c.) suppressed motion stimuli-induced emetic response in Jic:SUN-Her. These results suggest that the predominance of parasympathetic nervous activity is relevant to the enhancement of motion stimuli-induced emetic response, whereas the predominance of sympathetic nervous activity suppresses motion stimuli-induced emetic response. Norepinephrine (0.8 mg kg(-1), s.c.) enhanced motion stimuli-induced emesis contrary to isoproterenol in Jic:SUN-Ler although both drugs are adrenergic agents. However, atropine pretreatment (4.0 mg kg(-1), s.c.) inhibits norepinephrine-induced emetic response. It was considered that norepinephrine-induced emetic response might be dependent on a secondary increase of parasympathetic nervous activity due to bororeflex. Moreover, the different emetic response in Jic:SUN-Her and Jic:SUN-Ler suncus to motion stimuli and drug administration mentioned above indicated that different participation of autonomic nervous activity and/or afferent information from the baroreceptor in the emetic response may exist between these animal groups.