Regression Analysis Between Heart Rate Variability and Baroreflex‐Related Vagus Nerve Activity in Rats

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Abstract
Introduction: Many previous studies have suggested that the high‐frequency (HF) power of the heart rate variability may represent cardiac vagal activity although direct evidence of a correlation between the HF and vagal neuronal activity is still lacking. In the present study, we performed a regression analysis of the HF and vagal neurograms. Methods and Results: Experiments were carried out on adult male Sprague‐Dawley rats anesthetized with a continuous infusion of pentobarbital sodium. The baroreflex‐related vagus neuronal activities were obtained by nerve or single‐fiber recordings. The transient baroreflex response was employed to alter vagus neuronal activities using a bolus injection of phenylephrine (PE). On‐line power spectral analysis of the heart rate and a vagal neurogram was performed during the acute baroreflex response. During the test period, systemic arterial pressure immediately increased in response to the PE injection, after which the R–R interval (RR), HF (0.6–2.4 Hz), and vagus nerve and unit activities all dramatically increased. Both nerve and unit activities exhibited good correlations (r ≥ 0.7 in all nerve recordings and r ≥ 0.6 in 91% of single‐fiber recordings) with the HF. There were insignificant differences between the right‐ and left‐side baroreflex‐related vagus nerve recordings. Conclusion: Our present study provides a direct linkage between the HF and vagus neuronal electrical activity in anesthetized rats.

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