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Sympathetic Modulation (sympathetic + modulation)
Selected AbstractsImpaired cardiovagal and vasomotor responses to baroreceptor stimulation in type II diabetes mellitusEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 7 2003E. O. Sanya Abstract Background In diabetic patients, impairment of the cardiovagal limb of the baroreflex has been well established. However, the role of sympathetic mediated baroreflex vasomotor control of the blood vessels is not well defined. We therefore assessed the vasomotor responses to sinusoidal baroreceptor stimulation in diabetic patients. Materials and methods We studied 14 type II diabetic patients (age; 57 ± 7 years) and 18 healthy controls (age; 59 ± 11 years). Oscillatory neck suction was applied at 0·1 Hz to assess the sympathetic modulation of the heart and blood vessels, and at 0·2 Hz to assess the effect of parasympathetic stimulation on the heart. Breathing was paced at 0·25 Hz. Spectral analysis was used to evaluate the oscillatory responses of RR-interval and blood pressure. Results The diabetic patients showed a significantly lower RR-interval response (P < 0·05) to the 0·1 Hz neck suction (2·52 ± 0·50,3·62 ± 0·54 ln ms2) than the controls (4·23 ± 0·31,6·74 ± 0·36 ln ms2). The increase in power of 0·1 Hz systolic blood pressure oscillations during 0·1 Hz suction was also significantly smaller (P < 0·05) in the diabetics (1·17 ± 0·44,1·69 ± 0·44 mmHg2) than in the controls (1·60 ± 0·29 mmHg2,5·87 ± 1·25 mmHg2). The magnitude of the peak of the 0·2 Hz oscillation in the RR-interval in response to 0·2 Hz neck stimulation was significantly greater (P < 0·05) in the controls (3·42 ± 0·46 ln ms2) than in the diabetics (1·58 ± 0·44 ln ms2). Conclusion In addition to cardiovagal dysfunction, baroreflex-mediated sympathetic modulation of the blood vessels is impaired in type II diabetic patients. [source] Effects of age on the cardiac and vascular limbs of the arterial baroreflexEUROPEAN JOURNAL OF CLINICAL INVESTIGATION, Issue 1 2003C. M. Brown Abstract Background Healthy ageing has several effects on the autonomic control of the circulation. Several studies have shown that baroreflex-mediated vagal control of the heart deteriorates with age, but so far there is little information regarding the effect of ageing on sympathetically mediated baroreflex responses. The aim of this study was to assess the effects of ageing on baroreflex control of the heart and blood vessels. Materials and Methods In 40 healthy volunteers, aged 20,87 years, we applied oscillatory neck suction at 0·1 Hz to assess the sympathetic modulation of the heart and blood vessels and at 0·2 Hz to assess the effect of parasympathetic stimulation on the heart. Breathing was maintained at 0·25 Hz. Blood pressure, electrocardiographic RR intervals and respiration were recorded continuously. Spectral analysis was used to evaluate the magnitude of the low-frequency (0·03,0·14 Hz) and high-frequency (0·15,0·50 Hz) oscillations in the RR interval and blood pressure. Responses to neck suction were assessed as the change in power of the RR interval and blood pressure fluctuations at the stimulation frequency from baseline values. Results Resting low- and high-frequency powers of the RR interval decreased significantly with age (P < 0·01). However, the low-frequency power of systolic blood pressure did not correlate with age. Spontaneous baroreflex sensitivity (alpha-index) showed a significant inverse correlation with age (r = ,0·46, P < 0·05). Responses of the RR interval and systolic blood pressure to 0·1 Hz neck suction stimulation were not related to age, however, the RR interval response to 0·2 Hz neck suction declined significantly with age (r = ,0·61, P < 0·01). Conclusions These results confirm an age-related decrease in cardiovagal baroreflex responses. However, sympathetically mediated baroreflex control of the blood vessels is preserved with age. [source] Heart Rate Variability in Emergency Department Patients with SepsisACADEMIC EMERGENCY MEDICINE, Issue 7 2002Douglas Barnaby MD Abstract Objective: To test the hypothesis that heart rate variability (HRV) can provide an early indication of illness severity among patients presenting to the emergency department (ED) with sepsis. Methods: The authors enrolled a convenience sample of 15 ED patients meeting the American College of Chest Physicians/Society of Critical Care Medicine criteria for sepsis. Each patient had continuous Holter monitoring performed in the ED. Acute Physiology and Chronic Health II (APACHE II) and Sequential Organ Failure (SOFA) scores were calculated for the day of presentation. Holter tapes obtained in the ED were analyzed off-line to calculate HRV variables for the 5-minute segment with the least artifact and non-sinus beats. These variables were correlated with APACHE II and SOFA scores. Results: LFnu (normalized low-frequency power), an assessment of the relative sympathetic contribution to overall HRV, was correlated with increased illness severity as calculated using APACHE II (r = -0.67, r2= 0.43) and SOFA (r = -0.80, r2= 0.64) scores. LF/HF ratio (low-frequency/high-frequency ratio), a measure of sympathovagal balance, was correlated with the SOFA score [r = -0.54 (95% CI = -0.83 to -0.01), r2= 0.29]. All five patients who required critical care monitoring or ventilatory support or who died during the first 5 days of their hospitalization had LFnu values below 0.5 and LF/HF ratios less than 1.0. None of the patients with measurements greater than these threshold values died or required these interventions during the five days following admission. Conclusions: A single variable, LFnu, which reflects sympathetic modulation of heart rate, accounted for 40-60% of the variance in illness severity scores among patients presenting to the ED with sepsis. HRV, as reflected in LFnu and the LF/HF ratio and measured with a single brief (5-minute) period of monitoring while in the ED, may provide the emergency physician with a readily available, noninvasive, early marker of illness severity. The threshold effect of LFnu and LF/HF in the prediction of early clinical deterioration was an unexpected finding and should be regarded as hypothesis-generating, pending further study. [source] Sympathetic control of short-term heart rate variability and its pharmacological modulationFUNDAMENTAL & CLINICAL PHARMACOLOGY, Issue 4 2007Jean-Luc Elghozi Abstract The static relationship between heart rate (HR) and the activity of either vagal or sympathetic nerves is roughly linear within the physiological range of HR variations. The dynamic control of HR by autonomic nerves is characterized by a fixed time delay between the onset of changes in nerve activity and the onset of changes in HR. This delay is much longer for sympathetically than for vagally mediated changes in HR. In addition, the kinetics of the HR responses shows the properties of a low-pass filter with short (vagal) and long (sympathetic) time constants. These differences might be secondary to differences in nervous conduction times, width of synaptic cleft, kinetics of receptor activation and post-receptor events. Because of the accentuated low-pass filter characteristics of the HR response to sympathetic modulation, sympathetic influences are almost restricted to the very-low-frequency component of HR variability, but the chronotropic effects of vagal stimulation usually predominate over those of sympathetic stimulation in this frequency band. Oscillations in cardiac sympathetic nerve activity are not involved in respiratory sinus arrhythmia (high-frequency component) and make a minor contribution to HR oscillations of approximately 10-s period (low-frequency component of approximately 0.1 Hz), at least in the supine position. In the latter case, HR oscillations are derived mainly from a baroreflex, vagally mediated response to blood pressure Mayer waves. Beta-blockers and centrally acting sympathoinhibitory drugs share the ability to improve the baroreflex control of HR, possibly through vagal facilitation, which might be beneficial in several cardiovascular diseases. [source] Assessment of autonomic cardiovascular changes associated with recovery from anaesthesia in children: a study using spectral analysis of blood pressure and heart rate variabilityPEDIATRIC ANESTHESIA, Issue 6 2000ISABELLE CONSTANT MD PhD Recovery from anaesthesia is associated with large changes in cardiovascular autonomic activity, which are poorly documented in children. This study was undertaken to investigate the cardiovascular autonomic activity in anaesthetized and recovering children, using a noninvasive approach based on spectral analysis of heart rate (HR) and blood pressure (BP) variability. Ten children (aged 5,13 years) undergoing major surgery were studied. Continuous HR and BP were recorded using a noninvasive device during deep anaesthesia and recovery. Spectral analysis was used to determine the main oscillatory components of HR and BP signals. For each power spectrum, the frequency components were identified as follows (i): the low frequency (LF) component (0.04,0.14 Hz) both parasympathetically and sympathetically mediated for HR and corresponding to vasomotor sympathetic modulation for BP; and (ii) the high frequency (HF) component (0.2,0.6 Hz) parasympathetically mediated for HR, and reflecting mechanical influence of ventilation on cardiac output for BP. In addition, the LF : HF ratio for HR, reflecting the cardiac sympathovagal balance, was calculated. Under deep anaesthesia, HR variability and BP variability were very low and mainly due to mechanical influence of intermittent positive pressure ventilation. Conversely, the recovery period was associated with a marked increase of HR and BP overall variability. Compared to anaesthesia, spectral analysis of HR and BP revealed that the LF component of BP and HR spectra increased 40-fold during recovery; the LF : HF ratio of HR was also increased during recovery (0.1 ± 0.1 versus 1.3 ± 1.2, P=0.008). The results of this study demonstrate that the recovery period is associated with an increase of cardiovascular sympathetic drive in children after major surgery. [source] Relationship Between Myocardial Beta-Adrenergic Sensitivity and Heart Rate VariabilityANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2000Philippe Cabrol M.D. Background: In congestive heart failure, despite activation of the sympathetic nervous system, heart rate variability parameters reflecting sympathetic modulation on sinus node are decreased. Our goal was to assess the role of beta-adrenergic sensitivity in the modulation of heart rate variability (HRV) in patients with valvular heart diseases. Methods and results: Ten patients with aortic stenosis, 10 patients with heart failure, and 12 controls were included. Baroreflex sensitivity was calculated by the sequency method. Noradrenaline plasma levels were assayed by HPLC. HRV was studied using 24-hour Holter monitoring. Cardiac beta-adrenergic receptivity was assessed by the chronotropic response to dobutamine. Right auricular samples were obtained for determination of beta-adrenergic receptor density by binding study with [125I]-iodocynaopindolol, and beta 1 and beta 2 densities, measured by competition between 125ICP binding by isoprenaline. In multivariate analysis, the dose of dobutamine that increases basal heart rate for 25 beats/min (ED25) is correlated with a parameter of global HRV: SDNN (r = 0.6, P < 0.001) and with indexes reflecting rather sympathetic modulation of HRV: SDANN (r = 0.62, P < 0.001) or SD (r = 0.47, P < 0.0001). All these relations were independent from mean NN, spontaneous baroreflex sensitivity, and noradrenaline plasma levels. No significant correlation existed between dobutamine ED25 and HRV indexes reflecting parasympathic tone. No relationship existed between HRV and beta-adrenergic receptor-binding characteristics. Conclusion: Cardiac beta-adrenergic sensitivity explored by dobutamine ED25 is an important determinant of HRV independent from mean NN, spontaneous baroreflex sensitivity, and noradrenaline plasma levels. [source] IDENTIFICATION OF BLOOD PRESSURE CONTROL MECHANISMS BY POWER SPECTRAL ANALYSISCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 4 2007Harald M Stauss SUMMARY 1Blood pressure and organ perfusion are controlled by a variety of cardiovascular control systems, such as the baroreceptor reflex and the renin,angiotensin system (RAS), and by local vascular mechanisms, such as shear stress-induced release of nitric oxide (NO) from the endothelium and the myogenic vascular response. Deviations in arterial blood pressure from its set point activate these mechanisms in an attempt to restore blood pressure and/or secure organ perfusion. However, the response times at which different cardiovascular mechanisms operate differ considerably (e.g. blood pressure control by the RAS is slower than blood pressure control via the baroreceptor reflex). 2Owing to these different response times, some cardiovascular control systems affect blood pressure more rapidly and others more slowly. Thus, identifying the frequency components of blood pressure variability (BPV) by power spectral analysis can potentially provide important information on individual blood pressure control mechanisms. 3Evidence is presented that the RAS, catecholamines, endothelial-derived NO and myogenic vascular function affect BPV at very low frequencies (0.02,0.2 Hz) and that low-frequency (LF) BPV (0.2,0.6 Hz) is affected by sympathetic modulation of vascular tone and endothelial-derived NO in rats. In humans, LF BPV (0.075,0.15 Hz) is affected by sympathetic modulation of vascular tone and myogenic vascular function. The impact of the RAS and endothelial-derived NO on BPV in humans requires further investigation. 4In conclusion, power spectral analysis is a powerful diagnostic tool that allows identification of pathophysiological mechanisms contributing to cardiovascular diseases, such as hypertension, heart failure and stroke, because it can separate slow from fast cardiovascular control mechanisms. The limitation that some cardiovascular control mechanisms affect the same frequency components of BPV requires the combination of blood pressure spectral analysis with other techniques. [source] | ||||||||||