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1.
Exploring the complexity: the interplay between the angiotensin-converting enzyme insertion/deletion polymorphism and the sympathetic response to hemodialysis.
Ribas Ribeiro, L, Flores de Oliveira, J, Bueno Orcy, R, Castilho Barros, C, Damé Hense, J, Santos, F, Irigoyen, MC, Gonzalez, MC, Oses, JP, Böhlke, M
American journal of physiology. Heart and circulatory physiology. 2018;(4):H1002-H1011
Abstract
Patients on hemodialysis (HD) are at increased risk for arrhythmias and sudden cardiac death. Autonomic nervous system (ANS) dysfunction seems to participate in the arrhythmogenic process. Genetic factors have an impact on ANS modulation, but the specific role of the insertion/deletion (I/D) polymorphism in the gene for angiotensin-converting enzyme (ACE) has not been investigated. Since the D allele increases gene expression, it is a candidate polymorphism to interact with the ANS. The aim of the present study was to compare the behavior of heart rate variability (HRV) during HD, as a surrogate for ANS response to stressors, between the ACE genotypes. In a sample of patients with chronic kidney disease I/D ACE genotypes were assessed with PCR and HRV was measured before, in the second hour, and after a HD session. HRV parameters in the time and frequency domains were analyzed by repeated-measures mixed models according to the time of measurement and ACE polymorphism. HRV parameters in the frequency domain presented significantly different variations during the HD session between patients with or without the D allele. Only patients with the II genotype presented an increase in low-frequency normalized units and in the low frequency-to-high frequency ratio throughout HD. Patients with the II genotype seemed to have a more physiological response to the volemic and electrolytic changes that occur during HD, with greater sympathetic activation than patients with ID and DD genotypes. NEW & NOTEWORTHY Adding to the effort to understand the complexity of cardiovascular system regulation, we have found that the autonomic nervous system response to the acute volume removal during hemodialysis may be different between angiotensin-converting enzyme insertion/deletion polymorphisms. To our knowledge, this is the first time that this specific interaction was analyzed during a volume removal intervention.
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2.
Neurohormonal Imbalance: A Neglected Problem-And Potential Therapeutic Target-In Acute Heart Failure.
Goldsmith, SR, Bart, BA, Pin A, IL
Current problems in cardiology. 2018;(7):294-304
Abstract
Decompensated or acute heart failure (AHF) is characterized by increased ventricular and atrial pressures which may lead to and be caused by circulatory congestion. Unless due to a primary decrease in cardiac function, congestion arises from volume expansion or vasoconstriction. In turn, volume expansion and vasoconstriction are due to neurohormonal imbalance since both result from activation of the sympathetic nervous system, the renin-angiotensin-aldosterone axis and excess secretion of arginine vasopressin. Outcomes in AHF remain dismal. Loop diuretics are the mainstay of therapy for AHF and may themselves aggravate neurohormonal imbalance. No adjunctive pharmacotherapy has yielded improvement in outcomes in AHF despite many attempts with various vasodilators and inotropes. We, therefore, propose that insufficient attention has been paid to neurohormonal imbalance in AHF. As in chronic HF, rectifying the effects of neurohormonal imbalance may lead to better outcomes. The use of alternative decongestive strategies or adjunctive pharmacotherapy directed at neurohormonal activation could yield benefit.
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3.
Polyphenols, Antioxidants and the Sympathetic Nervous System.
Bruno, RM, Ghiadoni, L
Current pharmaceutical design. 2018;(2):130-139
Abstract
BACKGROUND A high dietary intake of polyphenols has been associated with a reduced cardiovascular mortality, due to their antioxidant properties. However, growing evidence suggests that counteracting oxidative stress in cardiovascular disease might also reduce sympathetic nervous system overactivity. METHODS This article reviews the most commonly used techniques to measure sympathetic activity in humans; the role of sympathetic activation in the pathophysiology of cardiovascular diseases; current evidence demonstrating that oxidative stress is involved in the regulation of sympathetic activity and how antioxidants and polyphenols might counteract sympathetic overactivity, particularly focusing on preliminary data from human studies. RESULTS The main mechanisms by which polyphenols are cardioprotective are related to the improvement of vascular function and their anti-atherogenic effect. Furthermore, a blood pressure-lowering effect was consistently demonstrated in randomized controlled trials in humans, when the effect of flavonoid-rich foods, such as tea and chocolate, was tested. More recent studies suggest that inhibition of sympathetic overactivity might be one of the mechanisms by which these substances exert their cardioprotective effects. Indeed, an increased adrenergic traffic to the vasculature is a major mechanism of disease in a number of cardiovascular and extra-cardiac diseases, including hypertension, obesity, metabolic syndrome and heart failure. A considerable body of evidence, mostly from experimental studies, support the hypothesis that reactive oxygen species might exert sympathoexcitatory effects both at the central and at the peripheral level. Accordingly, supplementation with antioxidants might reduce adrenergic overdrive to the vasculature and blunt cardiovascular reactivity to stress. CONCLUSIONS While supplementation with "classical" antioxidants such as ROS-scavengers has many limitations, increasing the intake of polyphenol-rich foods seems to be a promising novel therapeutic strategy to reduce the deleterious effects of increased adrenergic tone, particularly in essential hypertension.
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4.
Effects of a combined dietary, exercise and behavioral intervention and sympathetic system on body weight maintenance after intended weight loss: Results of a randomized controlled trial.
Mai, K, Brachs, M, Leupelt, V, Jumpertz-von Schwartzenberg, R, Maurer, L, Grüters-Kieslich, A, Ernert, A, Bobbert, T, Krude, H, Spranger, J
Metabolism: clinical and experimental. 2018;:60-67
Abstract
BACKGROUND Lifestyle based weight loss interventions are hampered by long-term inefficacy. Prediction of individuals successfully reducing body weight would be highly desirable. Although sympathetic activity is known to contribute to energy homeostasis, its predictive role in body weight maintenance has not yet been addressed. OBJECTIVES We investigated, whether weight regain could be modified by a weight maintenance intervention and analyzed the predictive role of weight loss-induced changes of the sympathetic system on long-term weight regain. DESIGN 156 subjects (age > 18; BMI ≥ 27 kg/m2) participated in a 12-week weight reduction program. After weight loss (T0), 143 subjects (weight loss > 8%) were randomized to a 12-month lifestyle intervention or a control group. After 12 months (T12) no further intervention was performed until month 18 (T18). Weight regain at T18 (regainBMI) was the primary outcome. Evaluation of systemic and tissue specific estimates of sympathetic system was a pre-defined secondary outcome. RESULTS BMI was reduced by 4.67 ± 1.47 kg/m2 during the initial weight loss period. BMI maintained low in subjects of the intervention group until T12 (+0.07 ± 2.98 kg/m2; p = 0.58 compared to T0), while control subjects regained +0.98 ± 1.93 kg/m2 (p < 0.001 compared to T0). The intervention group regained more weight than controls after ceasing the intervention (1.17 ± 1.34 vs. 0.57 ± 0.93 kg/m2) until T18. Consequently, BMI was not different at T18 (33.49 (32.64; 34.33) vs. 34.18 (33.61; 34.75) kg/m2; p=0.17). Weight loss-induced modification of urinary metanephrine excretion independently predicted regainBMI (R2 = 0.138; p < 0.05). The lifestyle intervention did not modify the course of urinary metanephrines after initial weight loss. CONCLUSIONS Our lifestyle intervention successfully maintained body weight during the intervention period. However, no long-term effect could be observed beyond the intervention period. Predictive sympathetic activity was not persistently modified by the intervention, which may partially explain the lack of long-term success of such interventions.
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5.
Pathophysiology of essential hypertension: an update.
Saxena, T, Ali, AO, Saxena, M
Expert review of cardiovascular therapy. 2018;(12):879-887
Abstract
Hypertension is caused by increased cardiac output and/or increased peripheral resistance. Areas covered: The various mechanisms affecting cardiac output/peripheral resistance involved in the development of essential hypertension are covered. These include genetics; sympathetic nervous system overactivity; renal mechanisms: excess sodium intake and pressure natriuresis; vascular mechanisms: endothelial cell dysfunction and the nitric oxide pathway; hormonal mechanisms: the renin-angiotensin-aldosterone system (RAAS); obesity, obstructive sleep apnea (OSA); insulin resistance and metabolic syndrome; uric acid; vitamin D; gender differences; racial, ethnic, and environmental factors; increased left ventricular ejection force and hypertension and its association with increased basal sympathetic activity - cortical connections. Expert commentary: Maximum association of hypertension is found with sympathetic overactivity which is directly or indirectly involved in different mechanisms of hypertension including RAAS, OSA, obesity, etc.. It is not overt sympathetic activity but disturbed basal sympathetic tone. Basal sympathetic tone arises from hypothalamus; possibly affected by cortical influences. Therefore, hypertension is not merely a disease of circulatory system alone. Its pathogenesis involves alteration in ANS (autonomic nervous system) and likely in cortical-hypothalamic connections. Assessment of ANS and cortical-hypothalamic connections may be required for better understanding of hypertension.
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6.
Evidence for Pressure-Independent Sympathetic Modulation of Central Pulse Wave Velocity.
Nardone, M, Incognito, AV, Millar, PJ
Journal of the American Heart Association. 2018;(3)
Abstract
BACKGROUND Whether the sympathetic nervous system can directly alter central aortic stiffness remains controversial, mainly because of the difficulty in experimentally augmenting peripheral vasoconstrictor activity without changing blood pressure. METHODS AND RESULTS To address this limitation, we utilized low-level cardiopulmonary baroreflex loading and unloading shown previously to alter sympathetic outflow without evoking parallel hemodynamic modulation. Blood pressure and carotid-femoral aortic pulse wave velocity (cf-PWV) were measured in 32 healthy participants (24±2 years; women: n=15) before and during 12-minute applications of low-level lower body negative pressure; -7 mm Hg) and lower body positive pressure; +7 mm Hg), applied in a random order. Fibular nerve microneurography was used to collect muscle sympathetic nerve activity (MSNA) in a subset (n=8) to confirm peripheral sympathetic responses. During lower body negative pressure, heart rate, blood pressure, stroke volume, cardiac output, and total peripheral resistance were not statistically different (all P>0.05); MSNA burst frequency (+15%; P=0.007), total MSNA (+44%; P=0.006), and cf-PWV (∆+0.3±0.2 m/s; P<0.001) increased. In total, 28 (88%) of participants observed an increase in cf-PWV greater than the baseline typical error of measurement. During lower body positive pressure, heart rate, stroke volume, cardiac output, and total peripheral resistance were not statistically different (all P>0.05), though blood pressure increased (P<0.05) and pulse pressure decreased (P=0.01); MSNA burst frequency (-4%; P=0.37), total MSNA (-7%; P=0.89), and cf-PWV (∆0.0±0.2 m/s; P=0.68) were not statistically different. CONCLUSIONS These findings provide evidence that acute elevations in peripheral sympathetic activity can increase central aortic PWV in young participants independent of a change in distending or pulsatile blood pressure or heart rate.
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7.
Impact of an exercise training program on cardiac neuronal function in heart failure patients on optimal medical therapy : A randomized Iodine-123 metaiodobenzylguanidine scintigraphy study.
Valborgland, T, Isaksen, K, Munk, PS, Grabowski, ZP, Larsen, AI
Journal of nuclear cardiology : official publication of the American Society of Nuclear Cardiology. 2018;(4):1164-1171
Abstract
BACKGROUND The syndrome of heart failure (HF) is characterized by left ventricular dysfunction and a compensatory chronic over activation of the sympathetic nervous system. We wanted to investigate if the beneficial effects of exercise training (ET) in HF patients on optimal medical therapy (OMT) are associated with alterations in cardiac sympathetic activity. METHODS Cardiac sympathetic activity was evaluated at baseline and after 12 weeks using metaiodobenzylguanidine scintigraphy in 23 patients with stable HF participating in the SmartEx trial. Patients with HF in New York Heart Association class II or III and left ventricular ejection fraction <35 % were randomized to three different ET groups. RESULTS We found no statistically significant changes in cardiac sympathetic activity after 12 weeks of ET. Heart to mediastinum (H/M) ratio at 15 minutes (0.00174 ± 0.0841, P = 0.922), H/M ratio at 4 hours (-0.00565 ± 0.1163, P = 0.818) and washout ratio (WR) (-1.2666 ± 16.5412, P = 0.717). A further group-wise analysis of the three ET groups did not show any difference between the groups. CONCLUSION A 12-week ET program did not alter the abnormal cardiac sympathetic activity in stable HF patients on modern OMT.
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8.
High-molecular-weight adiponectin is inversely associated with sympathetic activity in polycystic ovary syndrome.
Shorakae, S, Abell, SK, Hiam, DS, Lambert, EA, Eikelis, N, Jona, E, Sari, CI, Stepto, NK, Lambert, GW, de Courten, B, et al
Fertility and sterility. 2018;(3):532-539
Abstract
OBJECTIVE To examine the role of high-molecular-weight (HMW) adiponectin and its relationship to sympathetic activity in women with polycystic ovary syndrome (PCOS). DESIGN Cross sectional study using biobanked samples. SETTING Not applicable. PATIENT(S): Premenopausal women with PCOS (n = 46, Rotterdam diagnostic criteria) and without PCOS (n = 22). INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): High-molecular-weight adiponectin levels with secondary outcomes of sympathetic activity and leptin levels. RESULT(S): The high-molecular-weight adiponectin level was lower in women with PCOS (median 2.2 [interquartile range (IQR)2.3] μg/mL) than in controls (median 3 [IQR2.5] μg/mL) (age and BMI adjusted), and it correlated inversely with the values measured for homeostatic model of assessment of insulin resistance (HOMA-IR), fasting insulin, triglycerides, and free androgen index and positively with sex hormone-binding globulin (SHBG) and high-density lipoprotein cholesterol in all participants and in the PCOS group. In the PCOS group, sympathetic activity (burst frequency) was statistically significantly higher than in controls (median 26 [IQR11] vs. median 22 [IQR14], respectively) and correlated inversely with HMW adiponectin (r = -0.230). The leptin levels were similar between the women with PCOS and controls and did not statistically significantly correlate with HMW adiponectin or sympathetic activity. On multiple regression analysis, burst frequency and SHBG explained 40% of the HMW adiponectin variability (B = -0.7; 95% CI -1.2 to -0.2; and B = 0.01; 95% CI 0.004-0.01) in PCOS. CONCLUSION(S): Alongside insulin resistance, increased sympathetic activity is associated with and may modulate HMW adiponectin levels in women with PCOS.
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9.
Ischemic preconditioning does not alter muscle sympathetic responses to static handgrip and metaboreflex activation in young healthy men.
Incognito, AV, Doherty, CJ, Lee, JB, Burns, MJ, Millar, PJ
Physiological reports. 2017;(14)
Abstract
Ischemic preconditioning (IPC) has been hypothesized to elicit ergogenic effects by reducing feedback from metabolically sensitive group III/IV muscle afferents during exercise. If so, reflex efferent neural outflow should be attenuated. We investigated the effects of IPC on muscle sympathetic nerve activity (MSNA) during static handgrip (SHG) and used post-exercise circulatory occlusion (PECO) to isolate for the muscle metaboreflex. Thirty-seven healthy men (age: 24 ± 5 years [mean ± SD]) were randomized to receive sham (n = 16) or IPC (n = 21) interventions. Blood pressure, heart rate, and MSNA (microneurography; sham n = 11 and IPC n = 18) were collected at rest and during 2 min of SHG (30% maximal voluntary contraction) and 3 min of PECO before (PRE) and after (POST) sham or IPC treatment (3 × 5 min 20 mmHg or 200 mmHg unilateral upper arm cuff inflation). Resting mean arterial pressure was higher following sham (79 ± 7 vs. 83 ± 6 mmHg, P < 0.01) but not IPC (81 ± 6 vs. 82 ± 6 mmHg, P > 0.05), while resting MSNA burst frequency was unchanged (P > 0.05) with sham (18 ± 7 vs. 19 ± 9 bursts/min) or IPC (17 ± 7 vs. 19 ± 7 bursts/min). Mean arterial pressure, heart rate, stroke volume, cardiac output, and total vascular conductance responses during SHG and PECO were comparable PRE and POST following sham and IPC (All P > 0.05). Similarly, MSNA burst frequency, burst incidence, and total MSNA responses during SHG and PECO were comparable PRE and POST with sham and IPC (All P > 0.05). These findings demonstrate that IPC does not reduce hemodynamic responses or central sympathetic outflow directed toward the skeletal muscle during activation of the muscle metaboreflex using static exercise or subsequent PECO.
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10.
Understanding the Two Faces of Low-Salt Intake.
Braam, B, Huang, X, Cupples, WA, Hamza, SM
Current hypertension reports. 2017;(6):49
Abstract
Fierce debate has developed whether low-sodium intake, like high-sodium intake, could be associated with adverse outcome. The debate originates in earlier epidemiological studies associating high-sodium intake with high blood pressure and more recent studies demonstrating a higher cardiovascular event rate with both low- and high-sodium intake. This brings into question whether we entirely understand the consequences of high- and (very) low-sodium intake for the systemic hemodynamics, the kidney function, the vascular wall, the immune system, and the brain. Evolutionarily, sodium retention mechanisms in the context of low dietary sodium provided a survival advantage and are highly conserved, exemplified by the renin-angiotensin system. What is the potential for this sodium-retaining mechanism to cause harm? In this paper, we will consider current views on how a sodium load is handled, visiting aspects including the effect of sodium on the vessel wall, the sympathetic nervous system, the brain renin-angiotensin system, the skin as "third compartment" coupling to vascular endothelial growth factor C, and the kidneys. From these perspectives, several mechanisms can be envisioned whereby a low-sodium diet could potentially cause harm, including the renin-angiotensin system and the sympathetic nervous system. Altogether, the uncertainties preclude a unifying model or practical clinical guidance regarding the effects of a low-sodium diet for an individual. There is a very strong need for fundamental and translational studies to enhance the understanding of the potential adverse consequences of low-salt intake as an initial step to facilitate better clinical guidance.