Baroreflex sensitivity in obesity: relationship with cardiac autonomic nervous system activity

Mechanisms mediating renal sympathetic nerve activation in obesity-related hypertension

Excessive renal sympathetic nerve activation may be one of the mechanisms underlying obesity-related hypertension. Impaired baroreflex sensitivity, adipokine disorders-such as leptin, adiponectin, and resistin-activation of the renin-angiotensin system, hyperinsulinemia, insulin resistance, and renal sodium retention present in obesity increase renal sympathetic nerve activity, thus contributing to the development of hypertension. Renal sympathetic denervation reduces both renal sympathetic activity and blood pressure in patients with obesity-related hypertension.

Does the sympathetic nervous system contribute to the pathophysiology of metabolic syndrome?

The metabolic syndrome (MS), formally known as syndrome X, is a clustering of several risk factors such as obesity, hypertension, insulin resistance, and dislypidemia which could lead to the development of diabetes and cardiovascular diseases (CVD). The frequent changes in the definition and diagnostic criteria of MS are indications of the controversy and the challenges surrounding the understanding of this syndrome among researchers. Obesity and insulin resistance are leading risk factors of MS. Moreover, obesity and hypertension are closely associated to the increase and aggravation of oxidative stress. The recommended treatment of MS frequently involves change of lifestyles to prevent weight gain. MS is not only an important screening tool for the identification of individuals at high risk of CVD and diabetes but also an indicator of suitable treatment. As sympathetic disturbances and oxidative stress are often associated with obesity and hypertension, the present review summarizes the role of sympathetic nervous system and oxidative stress in the MS.

Heart rate variability is reduced in underweight and overweight healthy adult women

Heart rate variability (HRV) is altered in obese subjects, but whether this is true also in underweight (UW) subjects is still under debate. We investigated the HRV profile in a sample of healthy adult women and its association with adiposity. Five-minute resting state electrocardiographic activity was recorded in 69 subjects grouped according to their body mass index, [23 normal weight (NW), 23 overweight/obese (OW) and 23 UW). Body fat mass (FM) was measured by bio-impedance. Frequency- and time-domain analyses were performed. Compared to NW, UW and OW subjects showed a significant decrease in HRV indices, as revealed by spectral analysis. No differences were observed between UW and OW subjects. A second-order polynomial regression unveiled an inverted U-shaped relationship between FM extent and HRV indices. A decrease of HRV indices was associated with changes in FM extent, proving that in UW and OW subjects, the adaptive flexibility of autonomic cardiac function was reduced. These findings provide important clues to guide future studies addressed to determine how changes in adiposity and autonomic cardiac function may contribute to health risk.

Obesity depresses baroreflex control of renal sympathetic nerve activity and heart rate in Sprague Dawley rats: role of the renal innervation

AIM

This study investigated the role of the renal innervation in arterial and cardiopulmonary baroreflex regulation of renal sympathetic nerve activity (RSNA) and heart rate (HR) in rats fed a high-fat diet to induce obesity.

METHODS

Rats received either a normal (12% kcal) or high (45% kcal) fat diet for 60 days. On day 61, rats were anesthetized and prepared for recording left RSNA. In one group, the renal nerves remained intact, while in the other, both kidneys were denervated. Baroreflex gain curves for RSNA and HR were generated by increasing and decreasing blood pressure. Low-pressure baroreceptors were challenged by infusing a saline load.

RESULTS

Mean blood pressure was 135 mmHg in the fat-fed and 105 mmHg (P < 0.05) in normal rats. Weight gain, adiposity index and creatinine clearance were 37, 82 and 55% higher (P < 0.05-0.001), but urine flow rate and fractional sodium excretions were 53 and 65% (both P < 0.001) lower, respectively, in the fat-fed compared to normal rats. In fat-fed rats with innervated kidneys, RSNA and HR arterial baroreflex sensitivities were reduced by 73 and 72% (both P < 0.05) but were normal in renally denervated rats. Volume expansion decreased RSNA by 66% (P < 0.001) in normal rats, but not in the intact fat-fed rats and by 51% (P < 0.01) in renally denervated fat-fed rats.

CONCLUSION

Feeding a high-fat diet caused hypertension associated with dysregulation of the arterial and cardiopulmonary baroreflexes which was dependent on an intact renal innervation. This suggests that in obese states neural signals arising from the kidney contribute to a deranged autonomic control.

Improvement of baroreflex sensitivity in patients with obstructive sleep apnea following surgical treatment

OBJECTIVE

Depressed baroreflex sensitivity (BRS) have been reported in patients with obstructive sleep apnea (OSA). This study aimed to determine if surgery can improve the clinical outcomes by investigating changes in BRS and in other cardiovascular autonomic parameters.

METHODS

Eighty-one OSA patients were enrolled. They were classified as mild OSA if their apnea-hypopnea index (AHI) was 5-15, moderate OSA if their AHI was 15-30, and sever OSA if their AHI was >30. Twenty-three subjects with AHI<5 were recruited as controls. For patients who received surgery, polysomnography (PSG) and autonomic tests were evaluated upon enrollment and six-months after surgery.

RESULTS

The patient number for mild, moderate, and severe OSA was 22, 22, and 37, respectively. BRS on enrollment showed significant difference among the four groups, with the highest BRS in the control group, follow by the mild, moderate, and severe OSA groups. There were significant correlations between BRS and all PSG parameters. The depressed BRS significantly improved after surgery.

CONCLUSIONS

Surgical modifications of the upper airways can improve the depressed BRS in OSA patients.

SIGNIFICANCE

The study offers the promise that surgical treatment for OSA not only improves the index of PSG, but also reduces the possibility of cardiovascular risk.

Integrative neurobiology of metabolic diseases, neuroinflammation, and neurodegeneration

Alzheimer's disease (AD) is a complex, multifactorial disease with a number of leading mechanisms, including neuroinflammation, processing of amyloid precursor protein (APP) to amyloid β peptide, tau protein hyperphosphorylation, relocalization, and deposition. These mechanisms are propagated by obesity, the metabolic syndrome and type-2 diabetes mellitus. Stress, sedentariness, dietary overconsumption of saturated fat and refined sugars, and circadian derangements/disturbed sleep contribute to obesity and related metabolic diseases, but also accelerate age-related damage and senescence that all feed the risk of developing AD too. The complex and interacting mechanisms are not yet completely understood and will require further analysis. Instead of investigating AD as a mono- or oligocausal disease we should address the disease by understanding the multiple underlying mechanisms and how these interact. Future research therefore might concentrate on integrating these by “systems biology” approaches, but also to regard them from an evolutionary medicine point of view. The current review addresses several of these interacting mechanisms in animal models and compares them with clinical data giving an overview about our current knowledge and puts them into an integrated framework.

Relevance of Sympathetic Nervous System Activation in Obesity and Metabolic Syndrome

Sympathetic tone is well recognised as being implicit in cardiovascular control. It is less readily acknowledged that activation of the sympathetic nervous system is integral in energy homeostasis and can exert profound metabolic effects. Accumulating data from animal and human studies suggest that central sympathetic overactivity plays a pivotal role in the aetiology and complications of several metabolic conditions that can cluster to form the Metabolic Syndrome (MetS). Given the known augmented risk for type 2 diabetes, cardiovascular disease, and premature mortality associated with the MetS understanding the complex pathways underlying the metabolic derangements involved has become a priority. Many factors have been proposed to contribute to increased sympathetic nerve activity in metabolic abnormalities including obesity, impaired baroreflex sensitivity, hyperinsulinemia, and elevated adipokine levels. Furthermore there is mounting evidence to suggest that chronic sympathetic overactivity can potentiate two of the key metabolic alterations of the MetS, central obesity and insulin resistance. This review will discuss the regulatory role of the sympathetic nervous system in metabolic control and the proposed pathophysiology linking sympathetic overactivity to metabolic abnormalities. Pharmacological and device-based approaches that target central sympathetic drive will also be discussed as possible therapeutic options to improve metabolic control in at-risk patient cohorts.

The role of insulin resistance in the association between body fat and autonomic function

BACKGROUND AND AIM

Excess body fat is associated with altered autonomic function. We investigated whether this association is mediated by insulin resistance.

METHODS AND RESULTS

Cross-sectional analysis of a subgroup of the Netherlands Epidemiology of Obesity study with measurements of autonomic function (heart rate variability calculated as mean interbeat interval, standard deviation of all normal intervals (SDNN), low frequency (LF) power and high frequency (HF) power). We measured BMI(kg/m²), total body fat(%) and waist circumference(cm), and calculated the HOMA-index of insulin resistance (HOMA-IR). We examined the association between body fat and heart rate variability with multivariate linear regression analysis. To investigate whether the association was mediated by insulin resistance, we additionally adjusted for HOMA-IR. After exclusion of participants with glucose lowering medication (n = 19), 466 participants were included. Per SD of BMI, the difference in SDNN was -2.7% (95%CI: -5.5, 0.1) in the multivariate model. Additional adjustment for HOMA-IR attenuated this association to -1.2% (95%CI: -4.2, 1.7), suggesting that 55% of the association between BMI and SDNN was mediated by HOMA-IR. All measures of body fat were associated with mean interbeat interval, SDNN and LF power. Depending on the parameter of body fat or heart rate variability, 29-81% of the association was mediated by HOMA-IR.

CONCLUSION

In this cross-sectional study, body fat was associated with heart rate variability. This association may at least partially be mediated by insulin resistance. Future studies should investigate whether a reduction in obesity and insulin resistance may prevent the adverse cardiovascular consequences of altered autonomic function.

Intensive blood pressure control during the hyperacute phase of intracerebral hemorrhage in patients at risk for resistant hypertension: a retrospective cohort study

INTRODUCTION

There are limited data evaluating intensive systolic blood pressure (SBP) control during the hyperacute phase of intracerebral hemorrhage (ICH) in patients with multiple risk factors for resistant hypertension. We evaluated the feasibility and safety of this intervention in a primary population that includes patients with multiple risk factors for resistant hypertension.

MATERIALS AND METHODS

We conducted a retrospective analysis of ICH patients for which intensive SBP control (<140 mm Hg)- i.e. less than or equal to 140 was targeted. All patients possessed at least 2 risk factors that have been associated with resistant hypertension. Our primary objective was to determine the percentage of patients who achieved goal SBP within 1 hour of ICH diagnosis. Secondary objectives included identifying predictors of achieving goal SBP within 6 hours.

RESULTS

Goal SBP within 1 hour was achieved in 8.1% of patients. The total number of risk factors a patient possessed was found to negatively predict ability to achieve goal SBP. For each risk factor possessed, the odds of achieving goal SBP within 6 hours are reduced by 31% (odds ratio, 0.69 [95% confidence interval, 0.54-0.89]).

CONCLUSION

Intensive SBP control after ICH was difficult to achieve within 1 hour in those with risk factors for resistant hypertension. Patients' total risk factors were found to reduce the odds of achieving goal SBP within 6 hours.

Impaired baroreflex sensitivity in subjects with impaired glucose tolerance, but not isolated impaired fasting glucose

Impaired baroreflex sensitivity (BRS) is associated with adverse cardiovascular outcomes. There are currently no studies on BRS changes in subjects with different glycemic statuses, including normal glucose tolerance (NGT), isolated impaired fasting glucose (IFG), impaired glucose tolerance (IGT), and newly diagnosed diabetes (NDD). The aim of this study was to investigate the effects of NDD, IGT and isolated IFG on BRS, based on a community-based data. A total of 768 subjects were classified as NGT (n = 498), isolated IFG (n = 61), IGT (n = 126) and NDD (n = 83). Spontaneous BRS was determined by the spectral α coefficient method, i.e., the square root of the ratio between the power of the RR interval and the power of systolic blood pressure in the LF frequency region (0.04-0.15 Hz) after the subjects had rested in a supine position for 5 min. Valsalva ratio was calculated as the longest RR interval after release of the Valsalva maneuver, divided by the shortest RR interval during the maneuver. As compared with NGT subjects, NDD (p = 0.039) and IGT (p = 0.041) subjects had a reduced spontaneous BRS in multivariate analysis based on analysis of covariance. NDD subjects exhibited a lower Valsalva ratio than NGT subjects (p = 0.043). However, there were no significant differences in spontaneous BRS and Valsalva ratio between subjects with isolated IFG and NGT. In conclusion, NDD and IGT subjects had an impaired BRS as compared to NGT subjects. However, reduced BRS was not apparent in subjects with isolated IFG.

Carotid chemoreceptor afferent projections to leptin receptor containing neurons in nucleus of the solitary tract

Neurons expressing the leptin receptor (Ob-R) exist within the caudal nucleus of the solitary tract (NTS). Additionally, afferent neurons expressing the Ob-R have been identified within the nodose ganglion and NTS. Furthermore, systemic injections or focal injections of leptin directly into NTS potentiate the response of NTS neurons to carotid chemoreceptor activation. However, the distribution of carotid body afferents in relation to Ob-R containing neurons within NTS is not known. In this study, chemoreceptor afferent fibers were labeled following microinjection of the anterograde tract tracer biotinylated dextran amine (BDA) into the carotid body or petrosal/nodose ganglion of Wistar rats. After a survival period of 10-14 days, the NTS was processed for BDA and Ob-R immunoreactivity. Afferent axons originating in the carotid body were found to project to the lateral (Slt), gelantinosa (Sg), and medial (Sm) subnuclei of the NTS complex. A similar, but more robust distribution of BDA labeled fibers was observed in the NTS complex after injections into the petrosal/nodose ganglion. Carotid body BDA labeled fibers were observed in close apposition to Ob-R immunoreactive neurons in the region of Slt, Sg and Sm. In addition, a small number of carotid body afferents were found to contain both BDA and express Ob-R-like immunoreactivity within the regions of Slt, Sg and Sm. Taken together, these data suggest that leptin may modulate carotid chemoreceptor function not only through direct effects on NTS neurons, but also through a direct effect on carotid body primary afferent fibers that innervate NTS neurons.

Cardiorespiratory anomalies in mice lacking CB1 cannabinoid receptors

Cannabinoid type 1 (CB1) receptors are expressed in the nervous and cardiovascular systems. In mice, CB1 receptor deficiency protects from metabolic consequences of a high-fat diet (HFD), increases sympathetic activity to brown fat, and entails sleep anomalies. We investigated whether sleep-wake and diet-dependent cardiorespiratory control is altered in mice lacking CB1 receptors. CB1 receptor knock-out (KO) and intact wild-type (WT) mice were fed standard diet or a HFD for 3 months, and implanted with a telemetric arterial pressure transducer and electrodes for sleep scoring. Sleep state was assessed together with arterial pressure and heart rate (home cage), or breathing (whole-body plethysmograph). Increases in arterial pressure and heart rate on passing from the light (rest) to the dark (activity) period in the KO were significantly enhanced compared with the WT. These increases were unaffected by cardiac (β1) or vascular (α1) adrenergic blockade. The breathing rhythm of the KO during sleep was also more irregular than that of the WT. A HFD increased heart rate, impaired cardiac vagal modulation, and blunted the central autonomic cardiac control during sleep. A HFD also decreased cardiac baroreflex sensitivity in the KO but not in the WT. In conclusion, we performed the first systematic study of cardiovascular function in CB1 receptor deficient mice during spontaneous wake-sleep behavior, and demonstrated that CB1 receptor KO alters cardiorespiratory control particularly in the presence of a HFD. The CB1 receptor signaling may thus play a role in physiological cardiorespiratory regulation and protect from some adverse cardiovascular consequences of a HFD.

Body fat, especially visceral fat, is associated with electrocardiographic measures of sympathetic activation

OBJECTIVE

Obesity is associated with sympathetic activation, but the role of different fat depots is unclear. The association between body fat, specifically visceral fat, and electrocardiographic measures of sympathetic activation in a population with structurally normal hearts was investigated.

METHODS

In this cross-sectional baseline analysis of the Netherlands Epidemiology of Obesity study, body fat percentage was assessed with BIA and abdominal subcutaneous (SAT) and visceral adipose tissue (VAT) with magnetic resonance (MR) imaging. Mean heart rate (HR) and five other electrocardiographic measures of sympathetic activation were calculated. We performed multivariate linear regression analyses.

RESULTS

In 868 participants with a mean age(SD) of 55(6) years, BMI of 26(4) kg/m(2) , 47% men, body fat was associated with HR and two other measures of sympathetic activation. Per sex-specific SD total body fat, the difference in HR was 1.9 beats/min (95% CI: 1.0, 2.9; P < 0.001) and per SD waist circumference 2.1 beats/min (95% CI: 1.3, 2.9; P < 0.001). The difference in HR per SD VAT was 2.1 beats/min (95% CI: 1.3, 3.0; P < 0.001).

CONCLUSIONS

Body fat, especially visceral fat, was associated with electrocardiographic measures of sympathetic activation. Our study implies that already before the onset of cardiovascular disease, excess (visceral) body fat is associated with sympathetic activation.

Aerobic exercise during pregnancy influences infant heart rate variability at one month of age

BACKGROUND

Previously, we reported that regular maternal aerobic exercise during pregnancy was associated with lower fetal heart rate (HR) and higher heart rate variability (HRV) at 36weeks gestation. We now report the effect of maternal exercise on infant HR and HRV in subjects who remained active in the study at the one-month follow up visit.

AIMS

We aimed to determine whether differences in fetal cardiac autonomic control related to maternal physical activity were an in utero phenomenon or would persist 1month after birth.

STUDY DESIGN

Magnetocardiograms (MCGs) of infants born to regularly exercising (≥30min of aerobic activity, 3 times per week; N=16) and non-exercising (N=27) pregnant women were recorded using a fetal biomagnetometer. Normal R-peaks were marked to derive infant HR and HRV in time and frequency domains, including the root mean square of successive differences (RMSSD), the standard deviation of normal-to-normal interbeat intervals (SDNN), and power in the low frequency (LF) and high frequency (HF) bands. Group differences were examined with Student's t-tests.

RESULTS

Infants born to exercising women had significantly higher RMSSD (P=0.010), LF power (P=0.002), and HF power (P=0.004) than those born to women who did not engage in regular physical activity while pregnant.

CONCLUSION

Infants born to women who participated in regular physical activity during pregnancy continued to have higher HRV in the infant period. This suggests that the developing cardiac autonomic nervous system is sensitive to the effects of maternal physical activity and is a target for fetal programming.

Effect of atorvastatin on baroreflex sensitivity in subjects with type 2 diabetes and dyslipidaemia

In this prospective study, we examined the effect of atorvastatin treatment on baroreflex sensitivity (BRS) in subjects with type 2 diabetes. A total of 79 patients with type 2 diabetes with dyslipidaemia were recruited. A total of 46 subjects were enrolled to atorvastatin 10 mg daily and low-fat diet and 33 patients to low-fat diet only. BRS was assessed non-invasively using the sequence method at baseline, 3, 6 and 12 months. Treatment with atorvastatin increased BRS after 12 months (from 6.46 ± 2.79 ms/mmHg to 8.05 ± 4.28 ms/mmHg, p = 0.03), while no effect was seen with low-fat diet. Further sub-analysis according to obesity status showed that BRS increased significantly only in the non-obese group (p = 0.036). A low dose of atorvastatin increased BRS in non-obese subjects with type 2 diabetes and dyslipidaemia after 1-year treatment. This finding emphasizes the beneficial effect of atorvastatin on cardiovascular system, beyond the lipid-lowering effects.

Cerebral blood flow links insulin resistance and baroreflex sensitivity

Insulin resistance confers risk for diabetes mellitus and associates with a reduced capacity of the arterial baroreflex to regulate blood pressure. Importantly, several brain regions that comprise the central autonomic network, which controls the baroreflex, are also sensitive to the neuromodulatory effects of insulin. However, it is unknown whether peripheral insulin resistance relates to activity within central autonomic network regions, which may in turn relate to reduced baroreflex regulation. Accordingly, we tested whether resting cerebral blood flow within central autonomic regions statistically mediated the relationship between insulin resistance and an indirect indicator of baroreflex regulation; namely, baroreflex sensitivity. Subjects were 92 community-dwelling adults free of confounding medical illnesses (48 men, 30-50 years old) who completed protocols to assess fasting insulin and glucose levels, resting baroreflex sensitivity, and resting cerebral blood flow. Baroreflex sensitivity was quantified by measuring the magnitude of spontaneous and sequential associations between beat-by-beat systolic blood pressure and heart rate changes. Individuals with greater insulin resistance, as measured by the homeostatic model assessment, exhibited reduced baroreflex sensitivity (b = -0.16, p < .05). Moreover, the relationship between insulin resistance and baroreflex sensitivity was statistically mediated by cerebral blood flow in central autonomic regions, including the insula and cingulate cortex (mediation coefficients < -0.06, p-values < .01). Activity within the central autonomic network may link insulin resistance to reduced baroreflex sensitivity. Our observations may help to characterize the neural pathways by which insulin resistance, and possibly diabetes mellitus, relates to adverse cardiovascular outcomes.

Chronic baroreflex activation restores spontaneous baroreflex control and variability of heart rate in obesity-induced hypertension

The sensitivity of baroreflex control of heart rate is depressed in subjects with obesity hypertension, which increases the risk for cardiac arrhythmias. The mechanisms are not fully known, and there are no therapies to improve this dysfunction. To determine the cardiovascular dynamic effects of progressive increases in body weight leading to obesity and hypertension in dogs fed a high-fat diet, 24-h continuous recordings of spontaneous fluctuations in blood pressure and heart rate were analyzed in the time and frequency domains. Furthermore, we investigated whether autonomic mechanisms stimulated by chronic baroreflex activation and renal denervation-current therapies in patients with resistant hypertension, who are commonly obese-restore cardiovascular dynamic control. Increases in body weight to ∼150% of control led to a gradual increase in mean arterial pressure to 17 ± 3 mmHg above control (100 ± 2 mmHg) after 4 wk on the high-fat diet. In contrast to the gradual increase in arterial pressure, tachycardia, attenuated chronotropic baroreflex responses, and reduced heart rate variability were manifest within 1-4 days on high-fat intake, reaching 130 ± 4 beats per minute (bpm) (control = 86 ± 3 bpm) and ∼45% and <20%, respectively, of control levels. Subsequently, both baroreflex activation and renal denervation abolished the hypertension. However, only baroreflex activation effectively attenuated the tachycardia and restored cardiac baroreflex sensitivity and heart rate variability. These findings suggest that baroreflex activation therapy may reduce the risk factors for cardiac arrhythmias as well as lower arterial pressure.

The sympathetic nervous system in obesity hypertension

Abundant evidence supports a role of the sympathetic nervous system in the pathogenesis of obesity-related hypertension. However, the nature and temporal progression of mechanisms underlying this sympathetically mediated hypertension are incompletely understood. Recent technological advances allowing direct recordings of renal sympathetic nerve activity (RSNA) in conscious animals, together with direct suppression of RSNA by renal denervation and reflex-mediated global sympathetic inhibition in experimental animals and human subjects have been especially valuable in elucidating these mechanisms. These studies strongly support the concept that increased RSNA is the critical mechanism by which increased central sympathetic outflow initiates and maintains reductions in renal excretory function, causing obesity hypertension. Potential determinants of renal sympathoexcitation and the differential mechanisms mediating the effects of renal-specific versus reflex-mediated, global sympathetic inhibition on renal hemodynamics and cardiac autonomic function are discussed. These differential mechanisms may impact the efficacy of current device-based approaches for hypertension therapy.

Improvement in cardiovascular indices after Roux-en-Y gastric bypass or sleeve gastrectomy for morbid obesity

BACKGROUND

Morbidly obese patients display cardiac abnormalities which are partially reversed after weight loss. The aim of the present study was to assess the potential difference in cardiovascular disease indices between patients who underwent either gastric bypass surgery or sleeve gastrectomy.

METHODS

Thirty-seven morbidly obese patients who underwent either Roux-en-Y gastric bypass (RYGB) (n = 14) or SG (n = 23) were examined before, 3 and 6 months after surgery. Indices of cardiac autonomic nervous system activity were evaluated, namely baroreflex sensitivity (BRS) and heart rate variability (HRV). A complete echocardiographic study was performed in a subgroup of 17 patients (RYGB 8, SG 9) preoperatively and 6 months after surgery, evaluating epicardial fat thickness, aortic distensibility, left ventricular (LV) Tei index, left atrium diameter, ejection fraction, and LV mass.

RESULTS

All subjects experienced significant (p < 0.001) and similar weight loss independently of the type of operation. BRS and HRV indices improved significantly and to the same degree after surgery in both groups. In the echocardiographic study, all parameters improved significantly at 6 months in comparison with the baseline values. In addition, the RYGB group displayed significantly greater reduction in epicardial fat thickness (p = 0.007) and also tended to have a better LV performance as expressed by the lower values of the Tei index (p = 0.06) compared to the SG group 6 months after surgery.

CONCLUSIONS

Both RYGB and SG exert comparable effects on weight loss and improvement of cardiovascular parameters. RYGB displays a more beneficial influence on epicardial fat thickness and left ventricular performance than SG.

Plasma leptin inhibits the response of nucleus of the solitary tract neurons to aortic baroreceptor stimulation

Leptin receptors have been identified within the nucleus of the solitary tract (NTS) and leptin injections into the caudal NTS inhibit the baroreceptor reflex. However, whether plasma leptin alters the discharge of NTS neurons mediating aortic baroreceptor reflex activity is not known. A series of electrophysiological single unit recording experiments was done in the urethane-chloralose anesthetized, paralyzed and artificially ventilated Wistar and Zucker obese rat with either their neuroaxis intact or with mid-collicular transections. Single units in NTS antidromically activated by electrical stimulation of depressor sites in the caudal ventrolateral medulla (CVLM) were found to display a cardiac cycle-related rhythmicity. These units were tested for their responses to stimulation of the aortic depressor nerve (ADN) and intra-carotid injections of leptin (50-200ng/0.1ml). Of 63 single units tested in NTS, 33 were antidromically activated by stimulation of CVLM depressor sites and 18 of these single units responded with a decrease in discharge rate after intracarotid injections of leptin. Thirteen of these leptin responsive neurons (∼72%) were excited by ADN stimulation. Furthermore, the excitatory response of these single units to ADN stimulation was attenuated by about 50% after the intracarotid leptin injection. Intracarotid injections of leptin (200ng/0.1ml) in the Zucker obese rat did not alter the discharge rate of NTS-CVLM projecting neurons. These data suggest that leptin exerts a modulatory effect on brainstem neuronal circuits that control cardiovascular responses elicited during the reflex activation of arterial baroreceptors.

The effects of omega-3 polyunsaturated fatty acids on cardiac rhythm: a critical reassessment

Although epidemiological studies provide strong evidence for an inverse relationship between omega-3 polyunsaturated fatty acids (n-3 PUFAs) and cardiac mortality, inconsistent and often conflicting results have been obtained from both animal studies and clinical prevention trials. Despite these heterogeneous results, some general conclusions can be drawn from these studies: 1) n-PUFAs have potent effects on ion channels and calcium regulatory proteins that vary depending on the route of administration. Circulating (acute administration) n-3 PUFAs affect ion channels directly while incorporation (long-term supplementation) of these lipids into cell membranes indirectly alter cardiac electrical activity via alteration of membrane properties. 2) n-3 PUFAs reduce baseline HR and increase HRV via alterations in intrinsic pacemaker rate rather than from changes in cardiac autonomic neural regulation. 3) n-3 PUFAs may be only effective if given before electrophysiological or structural remodeling has begun and have no efficacy against atrial fibrillation. 5) Despite initial encouraging results, more recent clinical prevention and animal studies have not only failed to reduce sudden cardiac death but actually increased mortality in angina patients and increased rather than decreased malignant arrhythmias in animal models of regional ischemia. 6) Given the inconsistent benefits reported in clinical and experimental studies and the potential adverse actions on cardiac rhythm noted during myocardial ischemia, n-3 PUFA must be prescribed with caution and generalized recommendations to increase fish intake or to take n-3 PUFA supplements need to be reconsidered.

Leptin in nucleus of the solitary tract alters the cardiovascular responses to aortic baroreceptor activation

Recent data suggests that neurons expressing the long form of the leptin receptor form at least two distinct groups within the caudal nucleus of the solitary tract (NTS): a group within the lateral NTS (Slt) and one within the medial (Sm) and gelantinosa (Sg) NTS. Discrete injections of leptin into Sm and Sg, a region that receives chemoreceptor input, elicit increases in arterial pressure (AP) and renal sympathetic nerve activity (RSNA). However, the effect of microinjections of leptin into Slt, a region that receives baroreceptor input is unknown. Experiments were done in the urethane-chloralose anesthetized, paralyzed and artificially ventilated Wistar or Zucker obese rat to determine leptin's effect in Slt on heart rate (HR), AP and RSNA during electrical stimulation of the aortic depressor nerve (ADN). Depressor sites within Slt were first identified by the microinjection of l-glutamate (Glu; 0.25M; 10nl) followed by leptin microinjections. In the Wistar rat leptin microinjection (50ng; 20nl) into depressor sites within the lateral Slt elicited increases in HR and RSNA, but no changes in AP. Additionally, leptin injections into Slt prior to Glu injections at the same site or to stimulation of the ADN were found to attenuate the decreases in HR, AP and RSNA to both the Glu injection and ADN stimulation. In Zucker obese rats, leptin injections into NTS depressor sites did not elicit cardiovascular responses, nor altered the cardiovascular responses elicited by stimulation of ADN. Those data suggest that leptin acts at the level of NTS to alter the activity of neurons that mediate the cardiovascular responses to activation of the aortic baroreceptor reflex.

Autonomic cardiac innervation: development and adult plasticity

Autonomic cardiac neurons have a common origin in the neural crest but undergo distinct developmental differentiation as they mature toward their adult phenotype. Progenitor cells respond to repulsive cues during migration, followed by differentiation cues from paracrine sources that promote neurochemistry and differentiation. When autonomic axons start to innervate cardiac tissue, neurotrophic factors from vascular tissue are essential for maintenance of neurons before they reach their targets, upon which target-derived trophic factors take over final maturation, synaptic strength and postnatal survival. Although target-derived neurotrophins have a central role to play in development, alternative sources of neurotrophins may also modulate innervation. Both developing and adult sympathetic neurons express proNGF, and adult parasympathetic cardiac ganglion neurons also synthesize and release NGF. The physiological function of these “non-classical” cardiac sources of neurotrophins remains to be determined, especially in relation to autocrine/paracrine sustenance during development.

 

Cardiac autonomic nerves are closely spatially associated in cardiac plexuses, ganglia and pacemaker regions and so are sensitive to release of neurotransmitter, neuropeptides and trophic factors from adjacent nerves. As such, in many cardiac pathologies, it is an imbalance within the two arms of the autonomic system that is critical for disease progression. Although this crosstalk between sympathetic and parasympathetic nerves has been well established for adult nerves, it is unclear whether a degree of paracrine regulation occurs across the autonomic limbs during development. Aberrant nerve remodeling is a common occurrence in many adult cardiovascular pathologies, and the mechanisms regulating outgrowth or denervation are disparate. However, autonomic neurons display considerable plasticity in this regard with neurotrophins and inflammatory cytokines having a central regulatory function, including in possible neurotransmitter changes. Certainly, neurotrophins and cytokines regulate transcriptional factors in adult autonomic neurons that have vital differentiation roles in development. Particularly for parasympathetic cardiac ganglion neurons, additional examinations of developmental regulatory mechanisms will potentially aid in understanding attenuated parasympathetic function in a number of conditions, including heart failure.

Effects of clozapine on heart rate dynamics and their relationship with therapeutic response in treatment-resistant schizophrenia

Previous studies have suggested the utility of nonlinear complexity measures of heart rate variability (HRV) in evaluating the regulatory capacity of the neuroautonomic system. The purpose of the present study was to investigate the effects of clozapine on the nonlinear complexity measures of HRV in patients with treatment-resistant schizophrenia to find novel electrophysiological markers that indicate response to clozapine treatment. Forty patients with treatment-resistant schizophrenia were evaluated during 8 weeks of clozapine monotherapy. For nonlinear complexity measures of HRV, the approximate entropy (ApEn) and sample entropy (SampEn) values were obtained. The response rate to clozapine was 37.5%. The results of multivariate analysis of covariance revealed that the ApEn and the SampEn values of HRV at week 8 were significantly higher in the responders than in the nonresponders. Repeated-measures analysis of covariance showed a significant group by time interaction effect in the ApEn and SampEn indices. The responder group showed an increasing pattern of change in these complexity measures after administration of clozapine, whereas the nonresponder group showed a decreasing pattern of change. These results suggest that the nonlinear dynamic complexity measures of HRV, which indicate the irregularity and complexity of the biosystem, may be useful in evaluating the therapeutic changes of neuroautonomic function in schizophrenia. The response to clozapine treatment is expected to be more favorable when the plasticity of the neuroautonomic system reflected in the nonlinear complexity measures is high.

The impact of metabolic syndrome and endothelial dysfunction on exercise-induced cardiovascular changes

OBJECTIVE

There is limited information regarding the synergistic or additive effects of metabolic syndrome (MS) and endothelial dysfunction (ED) on cardiovascular disease (CVD). Altered cardiovascular responses to exercise have been shown to predict future cardiovascular events as well as assess autonomic function. The present study evaluated the impact of MS and brachial artery reactivity (a proxy of ED) on peak exercise-induced cardiovascular changes.

DESIGN AND METHODS

Individuals (n = 303) undergoing a standard nuclear medicine exercise stress test were assessed for MS. Participants underwent a Forearm Hyperaemic Reactivity test and were considered to have dysfunctional reactivity if their rate of uptake ratio (RUR) was <3.55. Resting and peak blood pressure (BP) and heart rate (HR) were measured. Reactivity was calculated as the difference between peak and resting measures.

RESULTS

Analyses, adjusting for age, sex, resting HR, total metabolic equivalents (METs), and a history of major CVD, revealed a main effect of MS (F = 5.51, η(2) = 0.02, P = 0.02) and RUR (F = 6.69, η(2) = 0.02, P = 0.01) on HR reactivity, such that patients with MS and/or poor RUR had reduced HR reactivity. There were no interactive effects of RUR and MS. There were no effects of RUR or MS on systolic BP (SBP) or diastolic BP (DBP) reactivity or rate pressure product (RPP) reactivity.

CONCLUSIONS

The presence of decreased HR reactivity among participants with MS or poor brachial artery reactivity, combined with the lack of difference in other exercise-induced cardiovascular changes, indicates that these patients may have some degree of parasympathetic dysregulation. Further longitudinal studies are needed to understand the long-term implications of MS and endothelial abnormalities in this context.

Altered heart rate dynamics associated with antipsychotic-induced subjective restlessness in patients with schizophrenia

BACKGROUND

Antipsychotic-induced subjective inner restlessness is one of the common and distressing adverse effects associated with antipsychotics; however, its underlying neurobiological basis is not well understood. We examined the relationship between antipsychotic-induced subjective inner restlessness and autonomic neurocardiac function.

METHODS

Twenty-two schizophrenia patients with antipsychotic-induced subjective restlessness, 28 schizophrenia patients without antipsychotic-induced subjective restlessness, and 28 matched healthy control subjects were evaluated. Assessments of the linear and nonlinear complexity measures of heart rate dynamics were performed. Multivariate analysis of variance and correlation analysis were conducted.

RESULTS

The mean interbeat (RR) interval value was significantly higher in control subjects than in patients with and without antipsychotic-induced subjective restlessness (P < 0.05). The low frequency/high frequency ratio was significantly higher in patients with antipsychotic-induced subjective restlessness than in control subjects and in patients without antipsychotic-induced subjective restlessness (P < 0.05), while the approximate entropy value was significantly lower in patients with antipsychotic-induced subjective restlessness than in control subjects and in patients without antipsychotic-induced subjective restlessness (P < 0.05). Correlation analyses controlling for psychotic symptom severity showed that the degree of antipsychotic-induced restlessness had a significant negative correlation with the value of approximate entropy (P < 0.05).

CONCLUSION

The results indicate that antipsychotic-induced subjective restlessness is associated with altered heart rate dynamics parameters, particularly the nonlinear complexity measure, suggesting that it might adversely affect autonomic neurocardiac integrity. Further prospective research is necessary to elucidate the precise interrelationships and causality.

Changes in baroreflex control of renal sympathetic nerve activity in high-fat-fed rats as a predictor of hypertension

There is evidence that obesity is associated with increased sympathetic activity and hypertension. However, the mechanisms responsible for these changes are not fully understood. Therefore, the aim of the present study was to evaluate the cardiovascular function and the baroreceptor reflex control of renal sympathetic nerve activity (rSNA) in rats exposed to a high-fat diet over different periods (10 and 20 weeks) compared to control rats. Serum leptin levels were assessed for all time points. Male Wistar rats weighing 150-180 g were used. Four groups of rats were studied: control 10 weeks (Ct10), obese 10 weeks (Ob10), control 20 weeks (Ct20), and obese 20 weeks (Ob20). Blood pressure (BP) and rSNA were recorded in urethane-anesthetized rats (1.4 g/kg, intravenous).The sensitivity of rSNA responses to baroreceptor reflex was assessed by changes in BP induced by increasing doses of phenylephrine or sodium nitroprusside. Significant and progressive increases in serum leptin levels were found in the obese rats, but not in the control rats. No changes in basal BP or rSNA were found in the Ob10 and Ob20 groups; however, a significant impairment in the baroreceptor sensitivity was observed in the Ob20 group for phenylephrine (slope Ob20: -0.78 ± 0.12 vs. Ct20: -1.00 ± 0.08 potential per second (pps)/mm Hg, P < 0.05) and sodium nitroprusside (slope Ob20: -0.82 ± 0.09 vs. 1.13 ± 0.13 pps/mm Hg, P < 0.05). The results suggest that the baroreceptor dysfunction that controls the rSNA is an initial change in the obesity induced in high-fat-fed rats, which might be a predictor of sympathoexcitation and hypertension associated to obesity.

Baroreflex sensitivity is associated with sleep-related breathing problems in adolescents

OBJECTIVES

To examine the relationship between sleep-related breathing problems (SRBPs) and baroreflex sensitivity (BRS) among adolescents and assesses whether body mass influences this relationship.

STUDY DESIGN

SRBPs were assessed in 106 adolescents aged 11-14 years using the Pediatric Sleep Questionnaire. Body mass index (BMI) was calculated, and 5 minutes of continuous beat-to-beat blood pressure (Finapres) and R-R interval were recorded (standard electrocardiogram) after 15 minutes of supine rest. Spectral indices were computed using fast Fourier transform, and transfer function analysis was used to compute BRS.

RESULTS

Regression analyses indicate an interaction between BMI and SRBPs (b=-.151, P=.015) on BRS. Graphing the interaction showed that those with higher SRBP scores had lower BRS but that this effect was stronger for those with higher BMI.

CONCLUSIONS

Adolescents with elevated SRBP scores had lower BRS. In addition, higher BMI amplified the risk of higher SRBP scores on BRS.

Diet-induced obesity severely impairs myelinated aortic baroreceptor reflex responses

Diet-induced obesity (DIO) attenuates the arterial cardiac baroreceptor reflex, but the mechanisms and sites of action are unknown. This study tested the hypothesis that DIO impairs central aortic baroreceptor pathways. Normal chow control (CON) and high-fat-chow obesity-resistant (OR) and obesity-prone (OP) rats were anesthetized (inactin, 120 mg/kg) and underwent sinoaortic denervation. The central end of the aortic depressor nerve (ADN) was electrically stimulated to generate frequency-dependent baroreflex curves (5-100 Hz) during selective activation of myelinated (A-fiber) or combined (A- and C-fiber) ADN baroreceptors. A mild stimulus (1 V) that activates only A-fiber ADN baroreceptors induced robust, frequency-dependent depressor and bradycardic responses in CON and OR rats, but these responses were completely abolished in OP rats. Maximal activation of A fibers (3 V) elicited frequency-dependent reflexes in all groups, but a dramatic deficit was still present in OP rats. Activation of all ADN baroreceptors (20 V) evoked even larger reflex responses. Depressor responses were nearly identical among groups, but OP rats still exhibited attenuated bradycardia. In separate groups of rats, the reduced heart rate (HR) response to maximal activation of ADN A fibers (3 V) persisted in OP rats following pharmacological blockade of β(1)-adrenergic or muscarinic receptors, suggesting deficits in both parasympathetic nervous system (PNS) and sympathetic nervous system (SNS) reflex pathways. However, the bradycardic responses to direct efferent vagal stimulation were similar among groups. Taken together, our data suggest that DIO severely impairs the central processing of myelinated aortic baroreceptor control of HR, including both PNS and SNS components.

Blood Pressure Control at Rest and during Exercise in Obese Children and Adults

The hemodynamic responses to exercise have been studied to a great extent over the past decades, and an exaggerated blood pressure response during an acute exercise bout has been considered as an indicator of cardiovascular risk. Obesity is a major factor influencing the blood pressure response to exercise since evidence indicates that the arterial pressure response to exercise is exacerbated in obese compared with lean adults. Signs of augmented responses (such as an exaggerated blood pressure response) to physical exertion appear early in life (from the prepubertal years) in obese individuals. Understanding the mechanisms that drive the altered hemodynamic responses during exercise in obese individuals and prevent the progression to hypertension is vitally important. This paper focuses on the evidence linking obesity with alterations of the autonomic nervous system and discusses the potential mechanisms and consequences of the altered sympathetic nervous system behavior in obese individuals at rest and during exercise. Furthermore, this paper presents the alterations in the reflex regulatory mechanisms ("exercise pressor reflex" and baroreflex) in obese children and adults and addresses the effects of training on obesity-related disturbances.

Baroreflex sensitivity is reduced in adolescents with probable developmental coordination disorder

Developmental coordination disorder (DCD) is a neurodevelopmental condition characterized by poor motor skills leading to a significant impairment in activities of daily living. Compared to typically developing children, those with DCD are less fit and physically active, and have increased body fat. This is an important consequence as both sedentary lifestyle and obesity are risk factors for cardiovascular disease. One indicator of cardiovascular health is baroreflex sensitivity (BRS), which is a measure of short term blood pressure (BP) regulation and is partly accomplished through changes in heart rate. Diminished BRS is predictive of future cardiovascular morbidity and mortality. The purpose of this study was to compare BRS in typically developing (TD) adolescents with probable DCD (pDCD) or suspect pDCD (spDCD) adolescents (13-14 years of age). Percentile scores on the Movement Assessment Battery for Children, 2nd edition, assessed at two time points were averaged and used to classify participants into the following groups: pDCD ≤ 5th percentile, spDCD > 5th percentile and ≤16th percentile and TD>16th percentile. Following 15 min of supine rest, 5 min of continuous beat-by-beat blood pressure (Finapres) and R-R interval were recorded (standard ECG). Spectral indices were computed using Fast Fourier Transform with transfer function analysis used to compute BRS in the low frequency region (0.04-0.15 Hz). BRS was compared between groups with an ANOVA and post hoc Bonferroni correction. BRS was reduced in the pDCD compared to the TD groups. In multivariate regression analyses predicting BRS, when pDCD and spDCD were entered as the only variables, pDCD was found to be a significant predictor of BRS (b=-6.74, p=0.016). However, when sex, VO(2) peak, and percent body fat (PBF) were entered as covariates, pDCD was no longer a predictor, while PBF approached significance (-0.32, p=0.056). Therefore, in this sample, BRS was reduced in adolescents with pDCD principally due to increased PBF.

Neuromuscular complications in HIV: effects of aging

There has been speculation that chronic HIV infection is a condition of accelerated aging that may lead to early onset of disease in multiple organ systems. The neuromuscular disorders of HIV, in particular distal symmetric polyneuropathy and myopathies, are also seen in the general population among older patients. As the HIV-infected population ages, there may be deleterious synergistic effects of age and chronic HIV infection on the brain, peripheral nerve, and muscle. In this review, we explore commonalities between the clinical features and putative mechanisms of neuromuscular disorders and HIV.

Heart rate variability - a historical perspective

Heart rate variability (HRV), the beat-to-beat variation in either heart rate or the duration of the R-R interval - the heart period, has become a popular clinical and investigational tool. The temporal fluctuations in heart rate exhibit a marked synchrony with respiration (increasing during inspiration and decreasing during expiration - the so called respiratory sinus arrhythmia, RSA) and are widely believed to reflect changes in cardiac autonomic regulation. Although the exact contributions of the parasympathetic and the sympathetic divisions of the autonomic nervous system to this variability are controversial and remain the subject of active investigation and debate, a number of time and frequency domain techniques have been developed to provide insight into cardiac autonomic regulation in both health and disease. It is the purpose of this essay to provide an historical overview of the evolution in the concept of HRV. Briefly, pulse rate was first measured by ancient Greek physicians and scientists. However, it was not until the invention of the "Physician's Pulse Watch" (a watch with a second hand that could be stopped) in 1707 that changes in pulse rate could be accurately assessed. The Rev. Stephen Hales (1733) was the first to note that pulse varied with respiration and in 1847 Carl Ludwig was the first to record RSA. With the measurement of the ECG (1895) and advent of digital signal processing techniques in the 1960s, investigation of HRV and its relationship to health and disease has exploded. This essay will conclude with a brief description of time domain, frequency domain, and non-linear dynamic analysis techniques (and their limitations) that are commonly used to measure HRV.

Heart rate variability and baroreceptor sensitivity following exercise-induced hyperthermia in endurance trained men

We evaluated the effect of exercise-induced hyperthermia (EIH) on autonomic nervous system (ANS) function in the early (<80 min) and late (24 and 48 h) stages of recovery. Eight males underwent three repeated 6 min 70° head-up tilts (HUT1, HUT2 and HUT3), each separated by 10-min supine rest in a non-exercise/non-heat stress control state (NHS). On a separate day, three 6 min 70° HUT were performed following EIH (esophageal temperature ≥ 40°C) and repeated after 24 and 48 h of recovery. Heart rate, stroke volume (SV), mean arterial pressure and cardiac output ([Formula: see text]) were evaluated during the last min prior to a change in posture. Responses to 70° HUT were compared to the same challenge performed without prior exercise and under a NHS condition. Relative to NHS, [Formula: see text] was maintained during the repeated HUT's following EIH, despite significant reductions in SV and sustained elevations in esophageal temperature (p < 0.05). The preserved [Formula: see text] appears to be due to increased HR (HUT1: NRS = 76 ± 3 beats min(-1), EIH = 126 ± 6 beats min(-1)) stemming from modulation of the ANS toward sympathetic dominance. Parasympathetic withdrawal was evidenced by a reduction in root mean squared successive difference (i.e., HUT1: NHS = 66 ± 12 ms, EIH = 9 ± 1 ms) of heart rate variability and paralleled by a reduction in baroreceptor sensitivity for all HUT's following EIH (p < 0.05). Despite significant modulation in ANS activity, Q is maintained and participants do not become orthostatic intolerant/syncopal during the short-term recovery period following EIH. Normal ANS and cardiovascular function is restored following 24 h of recovery.

Attenuation of age- and sucrose-induced insulin resistance and syndrome X by a synergistic antioxidant cocktail: the AMIS syndrome and HISS hypothesis

Absence of meal-induced insulin sensitization (AMIS) results in a predictable progression of dysfunctions, including postprandial hyperglycemia, compensatory hyperinsulinemia, resultant hyperlipidemia, increased oxidative stress, and obesity, progressing to syndrome X and diabetes. To one year of age, rats show a slow development of AMIS, but this can be potentiated by addition of a low-dose sucrose supplement to the diet. Provision of a synergistic antioxidant cocktail consisting of S-adenosylmethionine, vitamin E, and vitamin C (Samec) attenuates the rate and extent of development of AMIS in both normal aging animals and in aging animals on the sucrose diet. Adiposity, assessed from weighed regional fat masses and from bioelectrical impedance to estimate whole-body adiposity, correlated strongly with AMIS (r2 = 0.7-0.8). Rats given the sucrose supplement had accelerated AMIS and developed fasting hyperinsulinemia and postprandial hyperglycemia, hyperlipidemia, hyperinsulinemia, and adiposity. Samec completely compensated for the negative impact of this sucrose supplement and attenuated development of the associated dysfunctions. AMIS is explained by the HISS (hepatic insulin-sensitizing substance) hypothesis, which is outlined in the paper.

Heart rate variability - a historical perspective

Heart rate variability (HRV), the beat-to-beat variation in either heart rate or the duration of the R-R interval - the heart period, has become a popular clinical and investigational tool. The temporal fluctuations in heart rate exhibit a marked synchrony with respiration (increasing during inspiration and decreasing during expiration - the so called respiratory sinus arrhythmia, RSA) and are widely believed to reflect changes in cardiac autonomic regulation. Although the exact contributions of the parasympathetic and the sympathetic divisions of the autonomic nervous system to this variability are controversial and remain the subject of active investigation and debate, a number of time and frequency domain techniques have been developed to provide insight into cardiac autonomic regulation in both health and disease. It is the purpose of this essay to provide an historical overview of the evolution in the concept of HRV. Briefly, pulse rate was first measured by ancient Greek physicians and scientists. However, it was not until the invention of the "Physician's Pulse Watch" (a watch with a second hand that could be stopped) in 1707 that changes in pulse rate could be accurately assessed. The Rev. Stephen Hales (1733) was the first to note that pulse varied with respiration and in 1847 Carl Ludwig was the first to record RSA. With the measurement of the ECG (1895) and advent of digital signal processing techniques in the 1960s, investigation of HRV and its relationship to health and disease has exploded. This essay will conclude with a brief description of time domain, frequency domain, and non-linear dynamic analysis techniques (and their limitations) that are commonly used to measure HRV.

A longitudinal study of blood pressure variability in African-American and European American youth

OBJECTIVES

High blood pressure variability is increasingly used as a predictor of target-organ damage and cardiovascular events. However, little is known about blood pressure variability changes with age and its possible sociodemographic, anthropometric, and genetic moderators.

METHODS

Twenty-four-hour ambulatory blood pressure was measured up to 12 times over a 15-year period in 344 European Americans and 297 African-Americans with an average age of 14 years at the initial visit. Blood pressure variability was indexed by the weighted 24-h standard deviation of ambulatory blood pressure recordings.

RESULTS

Both systolic and diastolic blood pressure variability increased with age and ambulatory blood pressure mean values. Men had higher levels of blood pressure variability (P < 0.001) and showed steeper linear increase rates with age than women. African-Americans showed higher values of blood pressure variability (P < 0.05) than European Americans. Body mass index and waist circumference were also associated with higher blood pressure variability levels (P < 0.001). Individuals with higher father's education level showed lower blood pressure variability. In the full model which included all the above factors, ethnic difference in systolic blood pressure variability was no longer significant.

CONCLUSION

The results of the present study suggest that men and African-Americans have higher blood pressure variability than women and European Americans. Apart from these ethnicity and sex effects, blood pressure variability increases with increases in age (especially in men), ambulatory blood pressure mean values and adiposity as well as decreased socioeconomic status.

Biological basis of depression in adults with diabetes

Diabetes and depression are common comorbid conditions. Although certain health behaviors and risk factors partially explain the association of depression and diabetes, other potential mechanisms have yet to be elucidated. Certain neuroendocrine alterations such as activation of the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic nervous system (SNS) may contribute to the association. Additionally, presence of a proinflammatory state shown in recent literature in both diabetes and depression may contribute to this as well. The objectives of this review are to summarize and review the recent evidence showing alterations of these three biological systems-HPA axis, SNS, and inflammatory cascade--in depression, diabetes, and diabetes-related risk factors.

Altered hemodynamic regulation and reflex control during exercise and recovery in obese boys

The aims of the present study were to assess in obese and lean boys 1) the hemodynamic responses and baroreflex sensitivity (BRS) to isometric handgrip exercise (HG) and recovery and 2) the muscle metaboreflex-induced blood pressure response and the variables that determine this response. Twenty-seven boys (14 obese and 13 lean boys, body mass index: 29.2 ± 0.9 vs. 18.9 ± 0.3 kg/m(2), respectively) participated. The testing protocol involved 3 min of baseline, 3 min of HG (30% maximum voluntary contraction), 3 min of circulatory occlusion, and 3 min of recovery. The same protocol was repeated without occlusion. At baseline, no differences were detected between groups in beat-to-beat arterial pressure (AP), heart rate (HR), and BRS; however, obese boys had higher stroke volume and lower total peripheral resistance than lean boys (P < 0.05). During HG, lean boys exhibited higher HR and lower BRS compared with their obese counterparts. In lean boys, BRS decreased during HG compared with baseline, whereas in obese boys, it was not significantly modified. In lean boys, TPR was elevated during HG and declined after exercise, whereas in obese boys, TPR did not significantly decrease after exercise cessation. In the postexercise period, BRS in lean boys returned to baseline, whereas an overshoot was observed in obese boys. Postexercise BRS was correlated with body mass index (R = 0.56, P < 0.05). Although the metaboreflex-induced increase in AP was similar between obese and lean children, it was achieved via different mechanisms: in lean children, total peripheral resistance was the main contributor to AP maintenance during the metaboreflex, whereas in obese children, stroke volume significantly contributed to AP maintenance during the metaboreflex. In conclusion, obese normotensive children demonstrated altered cardiovascular hemodynamics and reflex control during exercise and recovery.

Trigonometric regressive spectral analysis reliably maps dynamic changes in baroreflex sensitivity and autonomic tone: the effect of gender and age

Background

The assessment of baroreflex sensitivity (BRS) has emerged as prognostic tool in cardiology. Although available computer-assisted methods, measuring spontaneous fluctuations of heart rate and blood pressure in the time and frequency domain are easily applicable, they do not allow for quantification of BRS during cardiovascular adaption processes. This, however, seems an essential criterion for clinical application. We evaluated a novel algorithm based on trigonometric regression regarding its ability to map dynamic changes in BRS and autonomic tone during cardiovascular provocation in relation to gender and age.

Methodology/Principal Findings

We continuously recorded systemic arterial pressure, electrocardiogram and respiration in 23 young subjects (25±2 years) and 22 middle-aged subjects (56±4 years) during cardiovascular autonomic testing (metronomic breathing, Valsalva manoeuvre, head-up tilt). Baroreflex- and spectral analysis was performed using the algorithm of trigonometric regressive spectral analysis. There was an age-related decline in spontaneous BRS and high frequency oscillations of RR intervals. Changes in autonomic tone evoked by cardiovascular provocation were observed as shifts in the ratio of low to high frequency oscillations of RR intervals and blood pressure. Respiration at 0.1 Hz elicited an increase in BRS while head-up tilt and Valsalva manoeuvre resulted in a downregulation of BRS. The extent of autonomic adaption was in general more pronounced in young individuals and declined stronger with age in women than in men.

Conclusions/Significance

The trigonometric regressive spectral analysis reliably maps age- and gender-related differences in baroreflex- and autonomic function and is able to describe adaption processes of baroreceptor circuit during cardiovascular stimulation. Hence, this novel algorithm may be a useful screening tool to detect abnormalities in cardiovascular adaption processes even when resting values appear to be normal.

Sympathetic nervous system overactivity and its role in the development of cardiovascular disease

This review examines how the sympathetic nervous system plays a major role in the regulation of cardiovascular function over multiple time scales. This is achieved through differential regulation of sympathetic outflow to a variety of organs. This differential control is a product of the topographical organization of the central nervous system and a myriad of afferent inputs. Together this organization produces sympathetic responses tailored to match stimuli. The long-term control of sympathetic nerve activity (SNA) is an area of considerable interest and involves a variety of mediators acting in a quite distinct fashion. These mediators include arterial baroreflexes, angiotensin II, blood volume and osmolarity, and a host of humoral factors. A key feature of many cardiovascular diseases is increased SNA. However, rather than there being a generalized increase in SNA, it is organ specific, in particular to the heart and kidneys. These increases in regional SNA are associated with increased mortality. Understanding the regulation of organ-specific SNA is likely to offer new targets for drug therapy. There is a need for the research community to develop better animal models and technologies that reflect the disease progression seen in humans. A particular focus is required on models in which SNA is chronically elevated.

Dysregulation of heart rhythm during sleep in leptin-deficient obese mice

STUDY OBJECTIVES

sleep deeply affects cardiac autonomic control, the impairment of which is associated with cardiovascular mortality. Obesity entails increased cardiovascular risk and derangements in sleep and cardiac autonomic control. We investigated whether cardiac autonomic control is impaired during sleep in ob/ob mice with morbid obesity caused by congenital leptin deficiency.

DESIGN

indexes of cardiac autonomic control based on spontaneous cardiovascular fluctuations were compared between ob/ob and lean wild-type (+/+) mice during wakefulness, non-rapid eye movement sleep (NREMS), and rapid eye movement sleep (REMS).

SETTING

N/A PATIENTS OR PARTICIPANTS: 7 ob/ob and 11 +/+ male mice.

INTERVENTIONS

instrumentation with electrodes for sleep recordings and a telemetric transducer for measuring blood pressure and heart period.

MEASUREMENTS AND RESULTS

In ob/ob mice, the variability of heart period and cardiac baroreflex sensitivity (sequence technique) were significantly lower than in +/+ mice during each wake-sleep state. The vagal modulation of heart period was significantly weaker in ob/ob than in +/+ mice during NREMS and REMS. In ob/ob mice, the cross-correlation function between heart period and blood pressure suggested that the baroreflex contribution to cardiac control was lower than in +/+ mice during wakefulness and NREMS, whereas the contribution of central autonomic commands was lower than in +/+ mice during NREMS and REMS.

CONCLUSIONS

These data indicate a dysregulation of cardiac autonomic control during sleep in ob/ob mice. Ob/ob mice may represent a useful tool to understand the molecular pathways that lead to cardiac autonomic dysregulation during sleep in obesity.

Mechanism of impaired baroreflex sensitivity in Wistar rats fed a high-fat and -carbohydrate diet

Both high-fat and high-carbohydrate diets have been considered in association with the impairment of baroreflex sensitivity. However, the mechanisms are unclear. In the present study, the effects of a complex high-fat and high-carbohydrate diet (HFCD) on baroreflex circuitry were investigated. A HFCD emulsion was formulated and orally administered to rats for 30 d. Rats were then anaesthetised and baroreflex sensitivity was measured following intravenous injection of phenylephrine (PE) and sodium nitroprusside (SNP) at various doses. Morphological changes of the brainstem were detected by transmission electron microscopy. Baroreflex sensitivity-associated gene and protein expression was determined by quantitative RT-PCR and Western blot analysis. We found that: (1) the HFCD significantly attenuated heart rate responses to arterial blood pressure (ABP) increases induced by PE, but had no effect on heart rate responses to ABP decreases induced by SNP; (2) the HFCD induced medullary sheath thickening, myelinated nerve atrophy and hyaloplasm dissolving; (3) protein levels of substance P, calcitonin gene-related peptide, GlutR2 and γ-aminobutyric acid A receptors were all markedly decreased in the brainstems of rats administered with the HFCD. These findings conclude that a HFCD could impair the baroreflex sensitivity of rats. Remodelled morphology and decreased neurotransmitters and receptors in the domains of the nucleus tractus solitarii and nucleus ambiguus are participating in this process.

Lower cardiac vagal tone in non-obese healthy men with unfavorable anthropometric characteristics

OBJECTIVES

to determine if there are differences in cardiac vagal tone values in non-obese healthy, adult men with and without unfavorable anthropometric characteristics.

INTRODUCTION

It is well established that obesity reduces cardiac vagal tone. However, it remains unknown if decreases in cardiac vagal tone can be observed early in non-obese healthy, adult men presenting unfavorable anthropometric characteristics.

METHODS

Among 1688 individuals assessed between 2004 and 2008, we selected 118 non-obese (BMI <30 kg/m(2)), healthy men (no known disease conditions or regular use of relevant medications), aged between 20 and 77 years old (42 +/- 12-years-old). Their evaluation included clinical examination, anthropometric assessment (body height and weight, sum of six skinfolds, waist circumference and somatotype), a 4-second exercise test to estimate cardiac vagal tone and a maximal cardiopulmonary exercise test to exclude individuals with myocardial ischemia. The same physician performed all procedures.

RESULTS

A lower cardiac vagal tone was found for the individuals in the higher quintiles - unfavorable anthropometric characteristics - of BMI (p=0.005), sum of six skinfolds (p=0.037) and waist circumference (p<0.001). In addition, the more endomorphic individuals also presented a lower cardiac vagal tone (p=0.023), while an ectomorphic build was related to higher cardiac vagal tone values as estimated by the 4-second exercise test (r=0.23; p=0.017).

CONCLUSIONS

Non-obese and healthy adult men with unfavorable anthropometric characteristics tend to present lower cardiac vagal tone levels. Early identification of this trend by simple protocols that are non-invasive and risk-free, using select anthropometric characteristics, may be clinically useful in a global strategy to prevent cardiovascular disease.

Interval hypoxic training improves autonomic cardiovascular and respiratory control in patients with mild chronic obstructive pulmonary disease

OBJECTIVES

Chronic obstructive pulmonary disease (COPD) is associated with cardiac autonomic nervous system dysregulation. This study evaluates the effects of interval hypoxic training on cardiovascular and respiratory control in patients with mild COPD.

METHODS

In 18 eucapnic normoxic mild COPD patients (age 51.7 +/- 2.4 years, mean +/- SEM), randomly assigned to either training or placebo group, and 14 age-matched healthy controls (47.7 +/- 2.8 years), we monitored end-tidal carbon dioxide, airway flow, arterial oxygen saturation, electrocardiogram, and continuous noninvasive blood pressure at rest, during progressive hypercapnic hyperoxia and isocapnic hypoxia to compare baroreflex sensitivity to hypoxia and hypercapnia before and after 3 weeks of hypoxic training. In double-blind fashion, both groups received 15 sessions of passive intermittent hypoxia (training group) or normoxia (placebo group). For the hypoxia group, each session consisted of three to five hypoxic (15-12% oxygen) periods (3-5 min) with 3-min normoxic intervals. The placebo group inhaled normoxic air.

RESULTS

Before training, COPD patients showed depressed baroreflex sensitivity, as compared with healthy individuals, without evident chemoreflex abnormalities. After training, in contrast to placebo group, the training group showed increased (P < 0.05) baroreflex sensitivity up to normal levels and selectively increased hypercapnic ventilatory response (P < 0.05), without changes in hypoxic ventilatory response.

CONCLUSION

Eucapnic normoxic mild COPD patients already showed signs of cardiovascular autonomic abnormalities at baseline, which normalized with hypoxic training. If confirmed in more severe patients, interval hypoxic training may be a therapeutic strategy to rebalance early autonomic dysfunction in COPD patients.

Cardiac autonomic neural remodeling and susceptibility to sudden cardiac death: effect of endurance exercise training

Sudden cardiac death resulting from ventricular tachyarrhythmias remains the leading cause of death in industrially developed countries, accounting for between 300,000 and 500,000 deaths each year in the United States. Yet, despite the enormity of this problem, both the identification of factors contributing to ventricular fibrillation as well as the development of safe and effective antiarrhythmic agents remain elusive. Subnormal cardiac parasympathetic regulation coupled with an elevated cardiac sympathetic activation may allow for the formation of malignant ventricular arrhythmias. In particular, myocardial infarction can reduce cardiac parasympathetic regulation and alter beta-adrenoceptor subtype expression enhancing beta(2)-adrenoceptor sensitivity that can lead to intracellular calcium dysregulation and arrhythmias. As such, myocardial infarction can induce a remodeling of cardiac autonomic regulation that may be required to maintain cardiac pump function. If alterations in cardiac autonomic regulation play an important role in the genesis of life-threatening arrhythmias, then one would predict that interventions designed to either augment parasympathetic activity and/or reduce cardiac adrenergic activity would also protect against ventricular fibrillation. Recently, studies using a canine model of sudden death demonstrate that endurance exercise training (treadmill running) enhanced cardiac parasympathetic regulation (increased heart rate variability), restored a more normal beta-adrenoceptor balance (i.e., reduced beta(2)-adrenoceptor sensitivity and expression), and protected against ventricular fibrillation induced by acute myocardial ischemia. Thus exercise training may reverse the autonomic neural remodeling induced by myocardial infarction and thereby enhance the electrical stability of the heart in individuals shown to be at an increased risk for sudden cardiac death.

HISS-dependent insulin resistance (HDIR) in aged rats is associated with adiposity, progresses to syndrome X, and is attenuated by a unique antioxidant cocktail

The hypotheses were: HISS-dependent insulin resistance (HDIR) accounts for insulin resistance that occurs with aging; HDIR is the initiating metabolic defect that leads progressively to type 2 diabetes and the metabolic syndrome; a synergistic antioxidant cocktail in chow confers protection against HDIR, subsequent symptoms of diabetes, and the metabolic syndrome. Male Sprague Dawley rats were tested at 9, 26, and 52 weeks to determine their dynamic response to insulin, the HISS (hepatic insulin sensitizing substance)-dependent component of insulin action, and the HISS-independent (direct) insulin action using a dynamic insulin sensitivity test. In young rats, the HISS component accounted for 52.3+/-2.1% of the response to a bolus of insulin (50mU/kg) which decreased to 29.8+/-3.4% at 6 months and 17.0+/-2.7% at 12 months. HISS action correlated negatively with whole body adiposity and all regional fat depots (r(2) = 0.67-0.87). The antioxidants (vitamin C, vitamin E, and S-adenosylmethionine) conferred protection of HISS action, fat mass at all sites, blood pressure, postprandial insulin and glucose. Data are consistent with the hypotheses. Early detection and therapy directed towards treatment of HDIR offers a novel therapeutic target.