Influence of vagal nervous activity on blood pressure variability.
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In our previous studies, it was shown that blood pressure variability was largely independent from the adrenergic nervous system. In the present work, vagal nervous influence on blood pressure variability was analysed both in dogs and in men. In eight chronically instrumented conscious dogs, striking fluctuations of blood pressure were observed when quietly resting; these fluctuations correlate well with fluctuation of heart rate. Atropine abolished all variations both of heart rate and of pressure. Reflex stimulation of vagal tone by neosynephrine increased variability of both parameters. Thus, in dogs, blood pressure variability is related to variability of heart rate which is largely influenced by vagal tone. The same question was approached in seven male volunteers; blood pressure and heart rate were measured automatically every 2 min, during 1 h, before and after atropine. In control conditions, no correlation between variability of heart rate and of blood pressure was observed. Atropine clearly decreased variability of heart rate and of diastolic blood pressure. These data confirm the animal results; however, the influence of vagal nerves on variability is less pronounced in man than in dogs.Keywords:
Vagal Tone
Mean blood pressure
Parasympathetic nervous system
Sympathetic nervous system
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OBJECTIVE To observe the effect of vagal stimulation of different frequencies on heart rate and heart rate variability in the toads. METHODS The animals were prepared to be models of isolated heart with right vagosympathetic trunks, then the nerves stimulated by different frequencies. Collected the electrocardiogram of isolated hearts and analyzed the data with HRV software. RESULTS Since the effect of sympathetic nerve had been diminished, vagal stimulation resulted in HR being markedly attenuated (P < 0.01), SDNN and RMSSD being significantly increased (P < 0.01). There was no significant difference in different levels of frequency. Contrast to group control, HR,SDNN and RMSSD each changed clearly. At the frequency of 0.2 Hz, HF increased markedly (P < 0.01), and LF/HF decreased obviously (P < 0.05) in group P + P. While at the frequency of 0.8 Hz, HF and LF/HF were both around the level of pre-stimulation. CONCLUSION These findings suggest that in the certain electrical stimulation frequency range, the effect of vagal on HR increases along with the frequency. Without the effect of sympathetic nerve, the modulation of vagal to HR and HRV may have different ways.
Autonomic nerve
Nerve stimulation
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Objective.Recent research suggests that percutaneous auricular vagus nerve stimulation (pVNS) beneficially modulates the autonomic nervous system (ANS). Bursted pVNS seems to be efficient for nerve excitation. Bursted pVNS effects on cardiac autonomic modulation are not disclosed yet.Approach.For the first time, the present study evaluates the effect of pVNS on cardiac autonomic modulation in healthy subjects (n = 9) using two distinct bursted stimulation patterns (biphasic and triphasic stimulation) and heart rate variability analysis (HRV). Stimulation was delivered via four needle electrodes in vagally innervated regions of the right auricle. Each of the two bursted stimulation patterns was applied twice in randomized order over four consecutive stimulation sessions per subject.Main results.Bursted pVNS did not change heart rate, blood pressure, and inflammatory parameters in study subjects. pVNS significantly increased the standard deviation of heart inter-beat intervals, from 46.39 ± 10.4 ms to 63.46 ± 22.47 ms (p < 0.05), and the total power of HRV, from 1475.7 ± 616.13 ms2to 3190.5 ± 2037.0 ms2(p < 0.05). The high frequency (HF) power, the low frequency (LF) power, and theLF/HFratio did not change during bursted pVNS. Both stimulation patterns did not show any significant differences in cardiac autonomic modulation. Stimulation intensity to reach a tingling sensation was significantly lower in triphasic compared to biphasic stimulation (p< 0.05). Bursted stimulation was well tolerated.Significance.Bursted pVNS seems to affect cardiac autonomic modulation in healthy subjects, with no difference between biphasic and triphasic stimulation, the latter requiring lower stimulation intensities. These findings foster implementation of more efficient pVNS stimulation.
Vagus Nerve Stimulation
Autonomic nerve
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Introduction: Changes in the heart rate variability are well known among patients with depression. Amongst others, a modulation of the autonomic nervous system is discussed. An investigation of heart rate variability during terms of stimulation could give some insight in the central nervous effect of vagus nerve stimulation (VNS) and possible cardiac side effects.
Vagus Nerve Stimulation
Vagal Tone
Depression
Parasympathetic nervous system
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Heart rate variability is used to assess cardiac autonomic tone. We bought to determine the relationship of graded direct stimulation of efferent cardiac autonomic nerves on heart rate variability in an anesthetized canine model. Time and frequency domain variables were measured at denervated baseline and during electrical stimulation of the vagi and ansae subclaviae over a wide range of frequencies. Vagal and ansae stimuli produced significant changes in heart rate that correlated with the intensity of stimulation. Vagal stimulation resulted in small increases in time domain indexes of heart rate variability and in the power spectrum from 0.04 to 0.40 Hz, but with no correlation between stimulus intensity and changes in these indexes. By contrast, ansae stimulation had no effect on time or frequency domain measures. In the absence of central modulation of autonomic outflow, indexes of heart rate variability reflect the presence of vagal input but do not correlate with the level of vagal tone and are unaffected by changes in mean sympathetic tone.
Vagal Tone
Autonomic nerve
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In our previous studies, it was shown that blood pressure variability was largely independent from the adrenergic nervous system. In the present work, vagal nervous influence on blood pressure variability was analysed both in dogs and in men. In eight chronically instrumented conscious dogs, striking fluctuations of blood pressure were observed when quietly resting; these fluctuations correlate well with fluctuation of heart rate. Atropine abolished all variations both of heart rate and of pressure. Reflex stimulation of vagal tone by neosynephrine increased variability of both parameters. Thus, in dogs, blood pressure variability is related to variability of heart rate which is largely influenced by vagal tone. The same question was approached in seven male volunteers; blood pressure and heart rate were measured automatically every 2 min, during 1 h, before and after atropine. In control conditions, no correlation between variability of heart rate and of blood pressure was observed. Atropine clearly decreased variability of heart rate and of diastolic blood pressure. These data confirm the animal results; however, the influence of vagal nerves on variability is less pronounced in man than in dogs.
Vagal Tone
Mean blood pressure
Parasympathetic nervous system
Sympathetic nervous system
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In normal healthy individuals, heart rate differs in various states and is influenced by many variables. At rest, heart rate is affected by neurological, humoral and metabolic factors. This article, however, reviews only the role of autonomic nervous system in modulating heart rate. Parasympathetic nerve, through Vagus nerve slows heart rate, whereas sympathetic nerve accelerates heart rate. Some reflexes mediated by baroreflex, chemoreflex and cardiopulmonary reflex also modulate heart rate. In addition, heart rate accelerates during inspiration and decelerates during expiration.
Expiration
Oculocardiac reflex
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Vagal Tone
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Changes in the function of the autonomic nervous system underlying changes in heart rate variability are not fully understood. Furthermore, decreased heart rate variability has been found to be related to poor prognosis, for example, in patients with coronary artery disease. Our aim was to study how modulation in sympathetic stimulation at various frequencies is transferred into heart rate variation, and how the interaction between sympathetic and parasympathetic inputs can affect the high‐frequency component of heart rate variability. We stimulated electrically cardiac sympathetic and vagal nerves in anaesthetized, vagotomized, spinal anaesthetized dogs. We controlled the frequency and magnitude of the modulation in programmed stimulation patterns and analysed the resulting changes in heart rate variability by power spectral analysis. We found that modulations in sympathetic stimulation were reflected in the high‐frequency component of heart rate variability, as well as in the low‐ and medium‐frequency components. In addition, a novel finding was that sympathetic stimulation reduced the magnitude of the high‐frequency variations caused by vagal stimulation. This suggests that, although the high‐frequency component of heart rate variability is mainly under parasympathetic regulation, it may also be influenced by the sympathetic nervous system.
Sympathetic activity
Sympathetic nervous system
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The authors present a prediction model of circadian variation of mean blood pressure employing the endocrine gland and the autonomic nervous system. Heart rate and mean blood pressure in 17 normal subjects and 17 essentially hypertensive subjects were measured and were simulated using the proposed model. Measured results of heart rate and mean blood pressure coincided with simulation results. Absolute errors between measured results and simulation results of heart rate and mean blood pressure were calculated, and found to be small. It is concluded that the proposed model can be used to estimate daily variations of heart rate and mean blood pressure in essentially hypertensive subjects.< >
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Sympathetic nervous system
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