Cardiac Baroreceptor Reflex Sensitivity Research Articles

Premedication of Oral Clonidine 2mcg/kg and 4mcg/kg for Analgesic and Pressure Response During First Twenty-four Hours After Upper Abdominal Surgery: A Comparative Study

Traditionally postoperative period analgesia was maintained by opoids and which frequently increasethe hospital stay time and cost by delayed bowel movement and others side effects. on the other handupper abdominal surgery is very much painful, usually Opiods are used as good analgesic, but havesome adverse effect and addiction effect; anaesthesiologists want to reduce its requirements. In upperabdominal surgery adequate analgesia, stable haemodynamic, early bowel movement, free from nauseaand vomiting is wanted, as a part of multimodal analgesic approach, premedication by clonidine is veryimportant for it analgesic, angiolytic and sedative properties. Alpha two (α–2) adrenoreceptor agonist,Clonidine exerts central sympatholytic effect for 8 to 10 hours as its half life is 9-12 h. So thatpremedication with oral clonidine causes reduction of anxiety, reduction of perioperative analgesicdrugs and also reduction of anaesthetic doses. In addition, clonidine increases cardiac baroreceptorreflex sensitivity to increase in systolic blood pressure, and thus stabilizes blood pressure. Clonidine israpidly and almost completely absorbed after oral administration with a time to maximum plasmaconcentration of between 1.5 and 2 hr and elimination half-life of 8 to 12 hr. But clonidine producesanalgesia in a dose dependent manner, achieving complete pain relief for up to 5 hours without sensoryor motor block at large doses (oral 7000 to 900 mcg) however large doss were associated withdisadvantage including hypotension, bradycardia and transient sedation. It also reported thatclonidine 150mcg intravenous (I/V) produce a similar analgesic effect to morphine 5mg in patient afterorthopedic surgery. Because of its dose, route, and surgical variation it is very much important tospecify the dose for upper abdominal surgery.The primary aim of this study to compare the effects of clonidine premedication at different doses (2 &4mcg/kg) on postoperative analgesia and hemodynamic status in upper abdominal surgery with largeincision area. (like- hepatobiliary surgery, gastrectomy, esophagectomy, hepatictomy, and whipplesoperations). JBSA 2022; 35 (2) : 17-21

Randomized controlled trials - mechanistic studies of testosterone and the cardiovascular system.

Testosterone deficiency is common in men with cardiovascular disease (CVD), and randomized placebo-controlled trials (RCTs) have reported beneficial effects of testosterone therapy on exercise-induced cardiac ischemia in chronic stable angina, functional exercise capacity, maximum oxygen consumption during exercise (VO2max) and muscle strength in chronic heart failure (CHF), shortening of the Q-T interval, and improvement of some cardiovascular risk factors. Testosterone deficiency is associated with an adverse CV risk profile and mortality. Clinical and scientific studies have provided mechanistic evidence to support and explain the findings of the RCTs. Testosterone is a rapid-onset arterial vasodilator within the coronary circulation and other vascular beds including the pulmonary vasculature and can reduce the overall peripheral systemic vascular resistance. Evidence has demonstrated that testosterone mediates this effect on vascular reactivity through calcium channel blockade (L-calcium channel) and stimulates potassium channel opening by direct nongenomic mechanisms. Testosterone also stimulates repolarization of cardiac myocytes by stimulating the ultra-rapid potassium channel-operated current. Testosterone improves cardiac output, functional exercise capacity, VO2max and vagally mediated arterial baroreceptor cardiac reflex sensitivity in CHF, and other mechanisms. Independent of the benefit of testosterone on cardiac function, testosterone substitution may also increase skeletal muscle glucose metabolism and enhance muscular strength, both factors that could contribute to the improvement in functional exercise capacity may include improved glucose metabolism and muscle strength. Testosterone improves metabolic CV risk factors including body composition, insulin resistance, and hypercholesterolemia by improving both glucose utilization and lipid metabolism by a combination of genomic and nongenomic actions of glucose uptake and utilization expression of the insulin receptor, glucose transporters, and expression on regulatory enzymes of key metabolic pathways. The effect on high-density lipoprotein-cholesterol (HDL-C) differs between studies in that it has been found to fall, rise, or have no change in levels. Testosterone replacement can suppress the levels of circulating pro-inflammatory cytokines and stimulate the production of interleukin-10 (IL-10) which has anti-inflammatory and anti-atherogenic actions in men with CVD. No effect on C-reactive protein has been detected. No adverse effects on clotting factors have been detected. RCTs have not clearly demonstrated any significant evidence that testosterone improves or adversely affects the surrogate markers of atherosclerosis such as reduction in carotid intima thickness or coronary calcium deposition. Any effect of testosterone on prevention or amelioration of atherosclerosis is likely to occur over years as shown in statin therapy trials and not months as used in testosterone RCTs. The weight of evidence from long-term epidemiological studies supports a protective effect as evidenced by a reduction in major adverse CV events (MACEs) and mortality in studies which have treated men with testosterone deficiency. No RCT where testosterone has been replaced to the normal healthy range has reported a significant benefit or adverse effect on MACE nor has any recent meta-analysis.

Differential Sympathetic Vasomotor Activation Induced by Liver Cirrhosis in Rats.

We tested the hypothesis that there is a topographical sympathetic activation in rats submitted to experimental cirrhosis. Baseline renal (rSNA) and splanchnic (sSNA) sympathetic nerve activities were evaluated in anesthetized rats. In addition, we evaluated main arterial pressure (MAP), heart rate (HR), and baroreceptor reflex sensitivity (BRS). Cirrhotic Wistar rats were obtained by bile duct ligation (BDL). MAP and HR were measured in conscious rats, and cardiac BRS was assessed by changes in blood pressure induced by increasing doses of phenylephrine or sodium nitroprusside. The BRS and baseline for the control of sSNA and rSNA were also evaluated in urethane-anesthetized rats. Cirrhotic rats had increased baseline sSNA (BDL, 102 vs control, 58 spikes/s; p<0.05), but no baseline changes in the rSNA compared to controls. These data were accompanied by increased splanchnic BRS (p<0.05) and decreased cardiac (p<0.05) and renal BRS (p<0.05). Furthermore, BDL rats had reduced basal MAP (BDL, 93 vs control, 101 mmHg; p<0.05) accompanied by increased HR (BDL, 378 vs control, 356; p<0.05). Our data have shown topographical sympathetic activation in rats submitted to experimental cirrhosis. The BDL group had increased baseline sSNA, independent of dysfunction in the BRS and no changes in baseline rSNA. However, an impairment of rSNA and HR control by arterial baroreceptor was noted. We suggest that arterial baroreceptor impairment of rSNA and HR is an early marker of cardiovascular dysfunction related to liver cirrhosis and probably a major mechanism leading to sympathoexcitation in decompensated phase.

Prospective Evaluation of Blood Pressure Monitoring and Baroreceptor Reflex Sensitivity (BRS) in Patients with AL Amyloidosis: Prognostic and Pathophysiologic Implications

The prognosis of patients with AL amyloidosis depends on the degree of cardiac dysfunction. Elevated cardiac troponin levels and of NTproBNP identify patients at high risk (stage 3 per Mayo stage); very high levels of NTproBNP are further associated with quite poor outcomes. Low blood pressure (BP) is associated with poor prognosis in patients with Mayo stage-3 disease (Wechalekar et al Blood 2013). BP depends on cardiac output and is tightly regulated by the autonomic nervous system (ANS), which is also commonly affected and deregulated in AL amyloidosis. However, the prognostic role of BP has not been evaluated prospectively and the measurement of BP in patients with AL has not been standardized as a prognostic factor. In addition, the importance of the deregulation of ANS in AL amyloidosis as a determinant of BP has not been evaluated. Baroreceptor reflex sensitivity (BRS) is implicated in the homeostatic regulation of the cardiovascular system and can be measured as a surrogate for the ANS effect on BP. In the current study we prospectively evaluated office and 24h ambulatory BP and calculated cardiac BRS in newly diagnosed patients with AL amyloidosis.All patients underwent office BP measurements, 24h ambulatory BP monitoring and a simultaneously electrocardiographic and non-invasive BP monitoring (Finometer), under standardized conditions for 15min. Standard office BP consisted of three BP measurements taken at a 1-min intervals, at sitting position, averaged to obtain a single systolic and diastolic office BP value. Ambulatory BP monitoring was performed on a usual working day. BP recordings were obtained automatically at 15-min intervals throughout the 24h period. Daytime was defined as the interval between 09:00h and 21:00h and nighttime was the interval between 01:00h and 06:00h. BRS was expressed as the alpha-index (a-index), which was estimated by means of power spectral analysis.This prospective analysis included 50 consecutive patients with biopsy confirmed AL amyloidosis. Median age was 65 (range 40-84) and 50% were males. Heart was involved in 64%, kidneys in 70% and nervous system in 20%. Per Mayo stage, 10% were stage-1, 60%-2 and 30%-3 and 12% had NTproBNP≥8500 ng/L. Median eGFR was 63 ml/min/1.73 m2 (by MDRD formula). Primary treatment was bortezomib-based (VD, VCD or BMDex) in 80% and 20% received MDex.Median office systolic BP (SBP) was 118 mmHg and median diastolic BP (DBP) was 72 mmHg. SBP was lower in stage 2 vs stage 1 and stage 3 vs either stage 2 or stage 1 patients (p=0.026); there was no significant difference in the DBP between groups. The median level of the mean 24h ambulatory SBP was 112.5 mmHg and for DBP was 69.5 mmHg; again, advanced Mayo stage was associated with lower mean 24h SBP (p=0.048). While 20% of patients had office SBP<100 mmHg and 24% had 24h SBP<100 mmHg, none of those with Mayo stage 1, 13% of patients with Mayo stage-2 and 33% of those with stage-3 had office SBP<100 mmHg. For 24h mean SBP, none with stage 1, 23% with stage 2 and 42% with stage 3 had SBP<100 mmHg. Lower levels of SBP were associated with inferior survival and this was more pronounced in patients with Mayo stage 2 or 3 disease. More specifically either office SBP<100 mmHg (6 months vs not reached) (p<0.001) or mean 24h SBP<90 mmHg (2 months vs not reached) (p<0.001) were associated with poor survival and early death. Analysis of 24h ambulatory BP monitoring provided data of higher BP fluctuations among patients with less severe or no heart involvement, while more often patients with Mayo stage 3 had higher nighttime vs daytime SBP values than stage 2 or stage 1 patients.Median a-index was 2.85 (range 0.4-5.85) and was lower in patients with advanced cardiac involvement. Importantly, a-index was lower in patients who had nerve involvement (median 1.6 vs 3.3, p=0.016). Thus, a-index reflected both cardiac and nerve involvement by AL amyloidosis. Low a-index was associated with early death: 25% of those with a-index<2.14 died within 3 months from initiation of therapy but there were no early deaths among patients with a-index ≥2.14.In conclusion, low BP, either measured in a sitting position as in standard office visits or by means of 24h ambulatory measurement, is associated with poor prognosis in patients with AL amyloidosis. Impaired BRS is associated with advanced cardiac and nerve involvement and risk of early death. Further analysis of the data obtained during 24h ambulatory BP monitoring and BRS is ongoing. DisclosuresTerpos:Amgen: Honoraria, Research Funding; Celgene: Honoraria; Novartis: Honoraria; Janssen: Honoraria. Dimopoulos:Celgene: Honoraria; Novartis: Honoraria; Genesis: Honoraria; Amgen: Honoraria; Onyx: Honoraria; Janssen: Honoraria; Janssen-Cilag: Honoraria.

Baroreceptor reflex sensitivity is associated with arterial stiffness in a population of normotensive and hypertensive patients

Baroreceptor reflex sensitivity (BRS) is an important factor in the homeostatic regulation of the cardiovascular system. Arterial stiffening also provides direct evidence of target organ damage in hypertensive patients. The aim of the present study was to evaluate a possible association between BRS and pulse wave velocity (PWV) in a population of normotensive and hypertensive patients. A consecutive series of 160 patients underwent office blood pressure (BP) measurements, 24-h ambulatory BP monitoring, a 15-min electrocardiographic and noninvasive BP monitoring, and carotid-femoral PWV measurements. Power spectral analysis was carried out to calculate cardiac BRS, expressed as the alpha-index. The study population was divided into two groups according to the office BP values: patients with systolic and diastolic BP<140/90 mmHg were defined as normotensives, whereas patients with systolic BP≥140 mmHg and/or diastolic BP≥90 mmHg were defined as hypertensives. Hypertensive patients (79%) had significantly higher PWV values (P=0.004) and a lower alpha-index (P<0.001) than the normotensive patients (21%). Multivariate linear regression analyses showed significant and independent associations of PWV with the following factors: age [0.510, 95% confidence interval (CI): 0.260-0.760; P<0.001], 24-h systolic BP (0.320, 95% CI: 0.120-0.520; P=0.002), and log(alpha-index) (-1.465, 95% CI: -2.686 to -0.244; P=0.019). A 1 ms/mmHg decrease in the log(alpha-index) correlated to an increment of 1.465 m/s (95% CI: 0.244-2.686) in the PWV of the study population. Increased arterial stiffness is significantly and independently associated with impaired BRS in normotensive and hypertensive patients.

A unified point process probabilistic framework to assess heartbeat dynamics and autonomic cardiovascular control.

In recent years, time-varying inhomogeneous point process models have been introduced for assessment of instantaneous heartbeat dynamics as well as specific cardiovascular control mechanisms and hemodynamics. Assessment of the model’s statistics is established through the Wiener-Volterra theory and a multivariate autoregressive (AR) structure. A variety of instantaneous cardiovascular metrics, such as heart rate (HR), heart rate variability (HRV), respiratory sinus arrhythmia (RSA), and baroreceptor-cardiac reflex (baroreflex) sensitivity (BRS), are derived within a parametric framework and instantaneously updated with adaptive and local maximum likelihood estimation algorithms. Inclusion of second-order non-linearities, with subsequent bispectral quantification in the frequency domain, further allows for definition of instantaneous metrics of non-linearity. We here present a comprehensive review of the devised methods as applied to experimental recordings from healthy subjects during propofol anesthesia. Collective results reveal interesting dynamic trends across the different pharmacological interventions operated within each anesthesia session, confirming the ability of the algorithm to track important changes in cardiorespiratory elicited interactions, and pointing at our mathematical approach as a promising monitoring tool for an accurate, non-invasive assessment in clinical practice. We also discuss the limitations and other alternative modeling strategies of our point process approach.

Relationships between baroreceptor cardiac reflex sensitivity and cognitive performance: Modulations by gender and blood pressure

This study aimed at replicating and extending previous results on the association between baroreceptor reflex sensitivity (BRS) and cognitive performance. Thirty men and 31 women performed an arithmetic task. After adjusting for numerical aptitude and effort, no predictors of performance were found in men. In women, the relationships between BRS and parameters related to correct responses were modulated by blood pressure (BP). BRS was inversely associated with these parameters for participants with BP>1 SD above the mean, whereas the associations were positive in participants with BP<1 SD below the mean. Also for women, BRS was positively associated with number of errors during the task. These results suggest that the relation between BRS and performance varies as a function of the type of cognitive processes assessed and that the central nervous system effects of the baroreceptors on cognitive functioning are modulated by gender and BP.

IMPAIRED BARORECEPTOR SENSITIVITY IS ASSOCIATED WITH INCREASED COMMON CAROTID ARTERY INTIMA-MEDIA THICKNESS IN HYPERTENSIVE PATIENTS: PP.2.88

Objective: Recent studies have clearly demonstrated that hypertension, even in early stages, is associated with impaired baroreceptor reflex sensitivity (BRS). Common carotid artery intima-media thickness (CCA-IMT) represents a surrogate marker of subclinical atherosclerosis. Aim of our study was to evaluate the relationship between BRS and CCA-IMT in hypertensive subjects. Design and Method: A total of 15 untreated hypertensive patients underwent 24-hour ambulatory blood pressure (BP) monitoring and carotid ultrasonographic measurements. All patients underwent a 15-min electrocardiographic and non-invasive BP monitoring (Finometer). Cardiac BRS was calculated from the combined a-index. Subjects with daytime ambulatory BP values more than 135/85 mmHg were defined as hypertensives. Statistical analysis was performed by means of bivariate correlations. Results: The mean age of the study population was 52 ± 11 years. The mean daytime systolic and diastolic ambulatory BP values were 145 ± 13 mmHg and 90 ± 9 mmHg, respectively. The CCA-IMT was 0.71 ± 0.16 mm and the combined a-index was 3.32 ± 1.60 ms/mmHg. CCA-IMT values were significantly correlated with the combined a-index (r = −0.590, p = 0.021). Conclusions: Our finding suggests that impaired BRS is significantly correlated with increased CCA-IMT values in hypertensive patients.

Comparison of baroreceptor cardiac reflex sensitivity estimates from inter-systolic and ECG R-R intervals

Baroreceptor reflex sensitivity (BRS) is frequently evaluated using the spontaneous sequence method. Many of these studies use the inter-systolic interval (ISI) derived from a blood pressure monitor (e.g., Finapres) as interbeat interval measure instead of the traditionally recommended R-R series derived from the ECG. In this study, we examine possible differences between estimates of BRS from ISI and ECG R-R intervals. BRS was evaluated in 35 participants under three conditions: rest, mental arithmetic, and recovery periods. Although correlations between the two estimates are very high (all rs>.9), small but significant differences were found: the measures from ISI systematically yield higher BRS values and result in the detection of a greater number of reflex sequences. The higher BRS values from measures of ISI are due to the effects of pulse transit time fluctuations associated with the sequences of change in blood pressure.

Testosterone Benefits Men With Heart Failure

Kate Johnson is a freelance writer in Montreal. Long-acting testosterone injections improved exercise capacity and insulin sensitivity in elderly men with heart failure, reported Dr. Giuseppe Caminiti of the Istituto di Ricovero e Cura a Carattere Scientifico San Raffaele Pisana in Rome and colleagues. “The increase in functional capacity and muscle strength is related to the increase in plasma levels of testosterone and not related to changes in left ventricular function,” noted the authors (J. Am. Coll. Cardiol. 2009 54: 919-27). The study randomized 70 elderly patients, median age 70 years, with stable chronic heart failure (CHF) to either long-acting testosterone undecanoate (1,000 mg) or placebo intramuscular injections given at baseline, 6, and 12 weeks, in addition to optimal medical therapy. Echocardiographic examination, muscle strength assessment, and cardiopulmonary exercise testing, as well as a 6-minute walk test (6MWT) were performed at the same three time points. Blood samples also were to measure testosterone and insulin, among other parameters. Baroreceptor cardiac reflex sensitivity (BRS) was assessed at the start and end of the study. At baseline, 21 patients in the testosterone group and 9 in the placebo group had total and free testosterone levels below the normal range—a phenomenon that has been well documented in CHF patients. Baseline testosterone levels correlated with peak oxygen consumption (VO2), distance reached in the 6MWT, and isometric strength. As expected, testosterone levels normalized in the treatment group but not the placebo group, and improved testosterone levels correlated with improved VO2 and quadriceps maximal voluntary contraction. Insulin resistance was significantly reduced in the treated group, BRS improved with treatment but not with placebo. There were no significant changes in left ventricular function in either group. The authors suggested that testosterone's ability to improve such extra-cardiac problems of muscle performance and glucose metabolism might not only improve the symptoms but possibly the pathophysiology and worsening of heart failure syndrome.

Tonic blood pressure modulates the relationship between baroreceptor cardiac reflex sensitivity and cognitive performance

This study explored the effects of tonic blood pressure on the association between baroreceptor cardiac reflex sensitivity and cognitive performance. Sixty female participants completed a mental arithmetic task. Baroreceptor reflex sensitivity was assessed using sequence analysis. An interaction was found, indicating that the relationship between baroreceptor reflex sensitivity and cognitive performance is modulated by blood pressure levels. Reflex sensitivity was inversely associated to performance indices in the subgroup of participants with systolic blood pressure above the mean, whereas the association was positive in participants with systolic values below the mean. These results are in accordance with the findings in the field of pain perception and suggest that tonic blood pressure modulates the inhibitory effects of baroreceptor stimulation on high central nervous functions.

Relationship between baroreceptor cardiac reflex sensitivity and pain experience in normotensive individuals

In the present study, the relationship between cardiac baroreceptor function and the perception of acute pain was investigated in 60 normotensive subjects. Baroreceptor reflex sensitivity was determined using the sequence method based on continuous blood pressure recordings. A cold pressor test was used for pain induction. Visual analogue scales and a questionnaire were applied in order to quantify sensory and affective pain experience. Moderated multiple regression analysis revealed an inverse relationship between baroreceptor reflex sensitivity assessed during painful stimulation and the intensity of experienced pain. This relationship was moderated by resting blood pressure, with decreasing blood pressure being accompanied by a decrease in the magnitude of the association. Furthermore, resting blood pressure was inversely related to pain intensity. The inverse association between baroreceptor reflex sensitivity and pain experience is discussed as reflecting the well-established pain-inhibiting effect of baroreceptor activity. The finding that this relationship was less pronounced in the case of lower blood pressure suggests that baroreceptor-mediated pain attenuation is reduced in this population.

WITHDRAWN: Relationships between baroreceptor cardiac reflex sensitivity and pain experience in normotensive individuals

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Short-Term Effects of a Brief Respiratory Training on Baroreceptor Cardiac Reflex Function in Normotensive and Mild Hypertensive Subjects

Baroreceptor cardiac reflex sensitivity is reduced in hypertension and is considered a powerful prognostic factor in cardiovascular health. This study analyzes the acute effects of a brief respiratory training on baroreceptor sensitivity and on two new proposed baroreflex parameters: baroreceptor power (i.e., the percentage of cardiac beats regulated by the baroreflex) and effectiveness (i.e., the frequency in which the baroreflex responds to transient alterations in blood pressure). Twenty-two participants, 10 primary mild hypertensives and 12 normotensives, learned and practiced a respiratory pattern characterized by breathing at 6 bpm, with time of expiration being twice time of inspiration, predominantly abdominal, and with pursed lips. Baroreceptor parameters are differentiated in terms of increases ("up" sequences) or decreases ("down" sequences) in blood pressure. Irrespective of the groups, the breathing manipulation increased baroreceptor sensitivity (only in the "up" sequences), power, and effectiveness (only in the "down" sequences). These results suggest that this type of respiratory training could be used as a promising intervention to increase baroreceptor cardiac function in primary hypertension.

Comparison of the Effects of VVI Versus DDD Pacing on Cardiac Baroreflex Function

Conventional baroreceptor-heart rate (HR) reflex sensitivity cannot be examined in chronotropically incompetent patients or in pacemaker recipients. However, cardiac baroreceptor reflex sensitivity (BRS)-stroke volume (SV), which is closely and linearly correlated with BRS-HR, may be an alternative in that population. The aim of this study was to compare the BRS-SV in pacemaker recipients with a fixed HR paced in VVI versus DDD modes in the supine and upright positions. The pacing mode was set randomly to DDD or VVI with complete atrial and/or ventricular capture, then crossed over to the alternate mode in 9 recipients of dual-chamber pacemakers with atrioventricular (AV) block. Beat-to-beat mean blood pressure and SV were measured in the supine and upright positions, using a tilt table. The BRS-SV, expressed in %/mmHg, was the ratio of low-frequency (LF) power to total power (TP) of SV variability, measured by spectral analysis of spontaneous variations in mean blood pressure and SV. BRS-SV was significantly lower in the VVI than in the DDD mode in the supine (37.2 +/- 26.7 vs 14.5 +/- 7.7%/mmHg) and upright (22.9 +/- 16.9 vs 10.6 +/- 6.6%/mmHg) positions (P < 0.05 for both comparisons). VVI pacing is adverse from the standpoint of cardiac autonomic baroreflex function. A decreased BRS-SV may be one of the factors involved in the hemodynamic intolerance associated with VVI pacing.

Abnormalities in cardiac baroreceptor sensitivity in acute ischaemic stroke patients are related to aortic stiffness

Cardiac BRS (baroreceptor reflex sensitivity) is impaired following ischaemic stroke and predicts the risk of subsequent long-term death and disability. Impaired cardiac BRS may be due to impaired central processing of baroreceptor information following stroke or reduced baroreceptor activity due to increased large artery stiffness. We evaluated the relationship between large (aortic) artery stiffness and cardiac BRS during the acute phase of ischaemic stroke and in comparison with a group of stroke-free control subjects. Thirty-one ischaemic stroke patients were studied within 48 h of onset and again on day 14, along with 26 control subjects free of cerebrovascular disease. Cardiac BRS (determined by spectral analyses) and arterial stiffness estimated by PWVcf (carotid-femoral pulse wave velocity) using applanation tonometry were obtained. At baseline, cardiac BRS was lower in the stroke compared with the control group (4.3+/-2.3 compared with 6.5+/-4.2 ms/mmHg; P < 0.05). Cardiac BRS values were correlated with PWVcf at < 48 h (r = -0.51, P < 0.01) and on day 14 (r = -0.54, P < 0.01), but not in the control group (r = -0.27, P = not significant). In quantile regression models, taking into account the effect of all cardiovascular variables, cardiac BRS was independently related to PWVcf at baseline and on day 14 in the stroke patients, but stroke was not related to cardiac BRS level when other cardiovascular variables were considered. Wall stiffness of the arterial vessels involved in the baroreflex arc may account for, at least in part, the reduced cardiac BRS observed in acute stroke patients.

Relationship of neurovascular compression to central sympathetic discharge and essential hypertension

ObjectivesWe planned to examine the relationship between neurovascular compression (NVC) of the rostral ventrolateral medulla (RVLM) and the magnitude of central sympathetic hyperactivity in normal subjects and in patients with untreated and uncomplicated essential hypertension (EHT). BackgroundPreviously it has not been possible to establish a definitive relationship between EHT and NVC of the RVLM, a location containing efferent sympathetic vasoconstrictor neurons. Furthermore, the relationship between NVC and magnitude of sympathetic nerve hyperactivity has not been adequately examined, despite the knowledge that hyperactivity varies according to EHT severity. MethodsIn 83 subjects, we used magnetic resonance imaging to detect NVC and, independently, peroneal microneurography to quantify muscle sympathetic nerve activity (MSNA), expressed as the mean frequency of multi-unit discharge (m-MSNA) and of single units (s-MSNA). Subjects were classified according to arterial pressure values into groups with normal (NT) (n = 24) or high-normal (HN) (n = 14) arterial pressure and mild (EHT-1) (n = 26) or severe (EHT-2/3) (n = 19) EHT. ResultsA significantly greater sympathetic activity was found in 23 subjects with NVC, compared with 60 subjects without NVC. The prevalence of NVC and the magnitude of sympathetic hyperactivity were greater in the EHT-1 group (p < 0.05) than in the other three groups. There was no significant difference in confounding variables between the groups. Although increased sympathetic activity was strongly predictive of NVC, this was not significantly related to baroreceptor sensitivity controlling the pulse interval (cardiac baroreceptor reflex sensitivity). ConclusionsNeurovascular compression of the RVLM may cause central sympathetic activation in normal and hypertensive populations and therefore has significant implications regarding the pathogenesis of EHT.

Autonomic cardiovascular changes during and after 14 days of head-down bed rest

A 14-day, 6° head-down bed rest (HDBR) study was conducted with 12 healthy young men to determine whether there are transient responses of the cardiovascular autonomic regulatory system including cardiovascular, autonomic nervous, and cardiac baroreceptor reflex functions in the acute phases of HDBR and post-HDBR. Compared with the supine position before bed rest, the high-frequency band power (HF RRI) of RR intervals (RRIs) decreased significantly at 3, 6, and 24 h of HDBR. This tendency went on until 24 h post-HDBR. Three kinds of cardiac baroreceptor reflex sensitivity (BRS) were estimated from closed-loop approaches to simultaneously recorded spontaneous RRI and systolic arterial pressure (SAP) fluctuations. BRS sequence is based on the simultaneous changes between RRI and SAP. α LF and α HF are based on a cross-spectrum analysis for low- and high-frequency bands of RRI and SAP. Although BRS sequence decreased significantly at acute phases of both HDBR and post-HDBR, neither α LF nor α HF decreased significantly at any of the acute phases of HDBR and post-HDBR. Our results suggest that HF RRI and BRS sequence can be used effectively to reveal reductions in cardiac vagal nervous modulation on the sinus node and cardiac BRS within 24 h of both HDBR and post-HDBR.

Sympathetic neural mechanisms in white-coat hypertension.

This study planned to establish whether sympathetic hyperactivity exists in white-coat hypertension (WHT) in the clinical setting, relative to matched groups with normotension (NT) and untreated essential hypertension (EHT). White-coat hypertension differs from EHT by the presence of normal ambulatory blood pressure. Sympathetic hyperactivity exists in patients with EHT in the clinical setting and is believed to contribute to the development of target organ damage. Similar organ damage has been reported in WHT, yet little is known about sympathetic neural activity in this condition. Using microneurography, we examined groups of 12 matched subjects with WHT, EHT and NT during the same clinical setting to quantify muscle sympathetic nerve activity as multiunit discharge (MSNA) and single units (s-MSNA). The s-MSNA in WHT (54 +/- 4.2 impulses/100 beats) was greater (p < 0.05) than in NT (37 +/- 5.4 impulses/100 beats) despite similar age and body mass index (BMI). The EHT values of s-MSNA (73 +/- 5.2 impulses/100 beats) were significantly (p < 0.05) greater than in WHT despite similar age, BMI and blood pressure levels. The MSNA followed a similar trend. White-coat hypertension had a similar cardiac baroreceptor reflex sensitivity to NT, but this was impaired in EHT relative to both NT and WHT. It was shown, in the clinical setting, that central sympathetic hyperactivity exists in WHT, albeit to a lesser degree than EHT. These findings suggest that WHT may not be entirely benign and that the observed sympathetic hyperactivity may be responsible for development of target organ damage in this group of patients.

Down-regulation of basal Fos expression at nucleus tractus solitarii underlies restoration of baroreflex response after antihypertensive treatment in spontaneously hypertensive rats

Antihypertensive therapy not only normalizes the elevated blood pressure but also restores the reduced baroreceptor reflex response associated with hypertension, although the underlying mechanism is not fully understood. We assessed the hypothesis that a reversal of the enhanced basal Fos expression seen during hypertension in nucleus tractus solitarii, the terminal site of baroreceptor afferents, underlies the restoration of baroreceptor reflex sensitivity after antihypertensive treatment. Male adult spontaneously hypertensive or normotensive Wistar–Kyoto rats received for 3 weeks captopril (100 mg/kg/day) added to their drinking water. Evaluated subsequently under pentobarbital anesthesia, captopril-treated spontaneously hypertensive rats exhibited significantly lowered systolic blood pressure and restoration of the sensitivity in baroreceptor reflex control of heart rate to levels comparable with Wistar–Kyoto rats. Reverse transcription-polymerase chain reaction analysis and immunohistochemical evaluation revealed concomitant down-regulation of basal expression in nucleus tractus solitarii of c- fos gene at both mRNA and protein levels. Captopril treatment, on the other hand, elicited no discernible effect on systolic blood pressure, cardiac baroreceptor reflex sensitivity or basal expression of Fos protein at the nucleus tractus solitarii of normotensive Wistar–Kyoto rats. From these findings we suggest that a down-regulation of basal Fos expression in nucleus tractus solitarii may contribute to the restoration of baroreceptor reflex sensitivity in spontaneously hypertensive rats that received antihypertensive treatment such as captopril.