| Summary: | 碩士 === 慈濟大學 === 神經科學研究所 === 91 === Indirect evidence has suggested a relationship between high frequency component (HF) of heart rate variability (HRV) and parasympathetic nervous activity. Whether the HF represents vagal tone or vagal modulation has yet to be determined. We aimed to find a direct relationship between HF and vagal neurogram. Experiments were divided into three parts. To investigate the relationship between HF and the baroreflex related vagal activity (VA), Experimentation I was carried out in male adult Sprague-Dawley (SD) rats anesthetized with pentobarbital sodium. Baroreflex modulation was employed to alter vagus nerve activity using bolus phenylephrine (PE, 20 mg/kg iv) injection. On-line power spectral analysis of heart rate and neurogram was performed during acute vagal modulation. To investigate the differences between normotensive and hypertensive rats, the above-mentioned experiments were repeated in Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) in Experimentation II. The purpose of Experimentation III was to investigate the relationship between HF and vagal tone. Similar experiments were repeated in SD rats in Experimentation III. In order to stabilize systemic arterial pressure (SAP), PE was administered via continuous intravenous infusion instead. We found that SAP, R-R interval (RR), HF, and VA (70-3000 Hz of power spectral density of neurogram) increased significantly in response to baroreflex modulation. There was a significantly positive correlation between HF and VA (r = 0.77, P < 0.05). No difference was observed between the right and left vagus nerve recordings. The SHR had higher SAP, lower RR, and lower HF than the WKY. There were significantly positive correlations between HF and VA in both WKY (r = 0.83, P < 0.05) and SHR (r = 0.62, P < 0.05) with the correlation coefficient being lower in SHR. The delta SAP, delta RR, delta HF, and delta VA increased at different vagal tone levels. In each SD rat, there was a tendency toward heightened HF and increased VA. The present study provided direct evidence that HF correlate with VA in anesthetized rats. The HF domain of HRV represent not only vagal modulation but also vagal tone.
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