Nitric oxide and cardiac autonomic control in humans

Modulation of Heart Rate Variability and Brain Excitability through Acute Whole-Body Vibration: The Role of Frequency

This cross-over study aimed to explore effects of acute whole-body vibration (WBV) at frequencies of 5-35 Hz on heart rate variability and brain excitability. Thirteen healthy physically active college students randomly completed eight interventions under the following conditions: static upright standing without vibration (CON), static squat exercise (knee flexion 150°) on the vibration platform (SSE), and static squat exercise (knee flexion 150°) combined with WBV at vibration frequency of 5, 9, 13, 20, 25, and 35 Hz. Five bouts × 30 s with a 30-s rest interval were performed for all interventions. The brain's direct current potentials (DCPs), frequency domain variables (FDV) including normalized low frequency power (nLF), normalized high frequency power (nHF) and the ratio of LF to HF (LF/HF), along with the mean heart rate (MHR) were collected and calculated before and after the WBV intervention. Results suggested that WBV frequency at 5 Hz had a substantial effect on decreasing DCPs [-2.13 μV, t(84) = -3.82, p < 0.05, g = -1.03, large] and nLF [-13%, t(84) = -2.31, p = 0.04, g = -0.62, medium]. By contrast, 20-35 Hz of acute WBV intervention considerably improved DCPs [7.58 μV, t(84) = 4.31, p < 0.05, g = 1.16, large], nLF [17%, t(84) = 2.92, p < 0.05, g = 0.79, large] and the LF/HF [0.51, t(84) = 2.86, p < 0.05, g = 0.77, large]. A strong (r = 0.7, p < 0.01) correlation between DCPs and nLF was found at 5 Hz. In summary, acute WBV at 20-35 Hz principally activated the sympathetic nervous system and increased brain excitability, while 5-Hz WBV activated the parasympathetic nervous system and reduced brain excitability. The frequency spectrum of WBV might be manipulated according to the intervention target on heart rate variability and brain excitability.

Mechanisms of Cardiovascular Changes of Phototherapy in Newborns with Hyperbilirubinemia

During phototherapy of jaundiced newborns, vasodilation occurs in the skin circulation compensated by vasoconstriction in the renal and mesenteric circulation. Furthermore, there is a slight decrease in cardiac systolic volume, and blood pressure, as well as an increase in heart rate and discrete changes in the heart rate variability (HRV). The primary change during phototherapy is the skin vasodilation mediated by multiple mechanisms: 1) Passive vasodilation induced by direct skin heating effect of the body surface and subcutaneous blood vessels, modified by myogenic autoregulation. 2) Active vasodilation mediated via the mechanism provided by axon reflexes through nerve C-fibers and humoral mechanism via nitric oxide (NO) and endothelin 1 (ET-1). During and after phototherapy is a rise in the NO:ET-1 ratio. 3) Regulation of the skin circulation through the sympathetic nerves is unique, but their role in skin vasodilation during phototherapy was not studied. 4) Special mechanism is a photorelaxation independent of the skin heating. Melanopsin (opsin 4) - is thought to play a major role in systemic vascular photorelaxation. Signalling cascade of the photorelaxation is specific, independent of endothelium and NO. The increased skin blood flow during phototherapy is enabled by the restriction of blood flow in the renal and mesenteric circulation. An increase in heart rate indicates activation of the sympathetic system as is seen in the measures of the HRV. High-pressure, as well as low-pressure baroreflexes, may play important role in these adaptation responses. The integrated complex and specific mechanism responsible for the hemodynamic changes during phototherapy confirm adequate and functioning regulation of the neonatal cardiovascular system, including baroreflexes.

Vasoactive Biomarkers in Patients With Vasovagal Syncope During Head-Up Tilt Test: A Case-Control Study

Background:

Vasovagal syncope (VVS) is the most common cause of syncope. Some stages of its pathophysiological mechanisms remain unclear. Vasoactive substances such as nitric oxide metabolites (NOx) and endothelin (ET) may be involved during acute orthostatic stress.

Objective:

To analyze plasma changes in NOx and ET and heart rate variability (HRV) in the supine positions (T1) and during the head-up tilt test (HUTT) (T2), in patients with VVS (case group) and control group.

Methods:

Thirty-seven patients (17 in the case group and 20 in the control group), matched for age and sex (mean aged 31.8 years) underwent HUTT with simultaneous HRV recording and venipuncture. Blood samples were collected during phases T1 and T2 and the analysis was performed without knowledge of the HUTT result.

Results:

In the total sample, there was an increase in NOx values (P = .014), however there was no increase in ET values from phase T1 to phase T2. Patients with VVS tended to increase plasma NOx values (P = .057) and had significantly higher plasma values compared to ET (P = .033) between phases T1 to T2. In the control group, there was no significant change in the values of these vasoactive substances. Regarding HRV, there were a decrease in the component HF (high frequency) and increased of the LF (low frequency)/HF ratio during HUTT.

Conclusions:

There was an increase in ET during HUTT occurred only in the case group. These patients are more likely to have an imbalance between antagonistic vasoactive biomarkers during orthostatic stress.

Does overnight duty affect vascular endothelial function?

BACKGROUND

The reactive hyperemia index (RHI), which is obtained from the measurement of peripheral arterial tonometry (PAT), is highly associated with the percentage change in the end-diastolic arterial diameter (%flow-mediated dilatation) at reactive hyperemia. Low RHI is reported to be a mortality risk in patients with a high risk of cardiovascular (CV) disease. CV events are thought to be induced by physical and mental stress, including long-term fatigue and lack of sleep. However, the relationship between fatigue, lack of sleep, and endothelial function has not yet been established.

METHODS

Healthy hospital workers (n = 13, 6 men and 7 women) with an average age of 31.6 years were assigned to this study after they provided written informed consent. During the study period, we conducted 72 measurements of reactive hyperemia-peripheral arterial tonometry (RH-PAT) in the morning before or after their duty. At each measurement of the RH-PAT, we recorded the participants' hours of sleep and evaluated their degree of fatigue using a visual analog scale (VAS).

RESULTS

Although the VAS was significantly less (36 ± 16% and 64 ± 12%, p < 0.001) and the hours of sleep were longer (6.0 ± 1.1 h and 2.3 ± 1.0 h, p < 0.001) before duty compared to those after duty, the RHI was comparable between them (2.12 ± 0.53 vs. 1.97 ± 0.50, p = 0.21). The VAS score was significantly higher in participants with low RHI (< 1.67) than in those with normal RHI (≥ 2.07) (59 ± 13% and 46 ± 21%, respectively, p < 0.05). However, binary logistic regression showed no significant association between low RHI and the VAS when adjusted for systemic blood pressure (SBP) and heart rate variability (HRV). In a simple regression analysis, the RHI was significantly correlated with the VAS score but not with sleep duration. A multiple linear regression analysis also showed no significant association between the RHI and VAS scores after adjustment for SBP and HRV.

CONCLUSIONS

Vascular endothelial function was not associated with overnight duty, hours of sleep, or degree of fatigue in healthy young adults. Since the RHI may be decreased in severe fatigue conditions through autonomic nerve activity, one should consider the physical and mental conditions of the examinee when evaluating the RH-PAT results.

Attenuation of baroreflex sensitivity and heart rate variability is linked to reduced levels of nitric oxide in pregnant women having risks of developing gestational hypertension

Purpose: Decreased baroreflex sensitivity (BRS) and sympathovagal imbalance (SVI) have been reported as a cardiovascular (CV) risk in gestational hypertension (GH). Nitric oxide (NO) has been implicated in pathophysiology of GH. In the present study, we assessed the link of CV risks (decreased BRS and SVI) to the plasma levels of NO in women having risk of developing GH. Materials and Methods: A total of 96 pregnant women having risk factors for GH were recruited for the study. The blood pressure variability (BPV), heart rate variability (HRV), plasma NO, marker of insulin resistance (HOMA-IR), lipid risk factors, inflammatory markers (hsCRP, interleukin-6), and malondialdehyde (MDA), the marker of oxidative stress (OS) were measured at 16^th and 36^th week. Link of various parameters to NO was assessed by correlation and multiple regression analysis. Results: Of HRV indices, parasympathetic components were decreased and sympathetic components were increased, BRS was decreased, NO was decreased, HOMA-IR, lipid risk factors, hsCRP, interleukin-6, and MDA were increased significantly at 36^th week compared to 16^th week of pregnancy. Most of the markers of cardiometabolic risk were correlated with NO. However, only the markers of CV risk (SVI and reduced BRS) were independently associated with decreased level of NO, but not the metabolic markers except interleukin-6. The independent contribution of BRS (β = 0.334, P < .001) to NO was found to be most significant. Conclusion: It was concluded that decreased BRS, SVI, and increased interleukin-6 are associated with reduction in NO in GH, which may possibly be linked to the development of CV risks in GH.

Heart rate fragmentation gives novel insights into non-autonomic mechanisms governing beat-to-beat control of the heart's rhythm

To demonstrate how heart rate fragmentation gives novel insights into non-autonomic mechanisms of beat-to-beat variability in cycle length, and predicts survival of cardiology clinic patients, over and above traditional clinical risk factors and measures of heart rate variability.

Approach: We studied 2893 patients seen by cardiologists with clinical data including 24-hour Holter monitoring. Novel measures of heart rate fragmentation alongside canonical time and frequency domain measures of heart rate variability, as well as an existing local dynamics score were calculated. A proportional hazards model was utilized to relate the results to survival.

Main results: The novel heart rate fragmentation measures were validated and characterized with respect to the effects of age, ectopy and atrial fibrillation. Correlations between parameters were determined. Critically, heart rate fragmentation results could not be accounted for by undersampling respiratory sinus arrhythmia. Increased heart rate fragmentation was associated with poorer survival (p ≪ 0.01 in the univariate model). In multivariable analyses, increased heart rate fragmentation and more abnormal local dynamics (p 0.045), along with increased clinical risk factors (age (p ≪ 0.01), tobacco use (p ≪ 0.01) and history of heart failure (p 0.019)) and lower low- to high-frequency ratio (p 0.022) were all independent predictors of 2-year mortality.

Significance: Analysis of continuous ECG data with heart rate fragmentation indices yields information regarding non-autonomic control of beat-to-beat variability in cycle length that is independent of and additive to established parameters for investigating heart rate variability, and predicts mortality in concert with measures of local dynamics, frequency content of heart rate, and clinical risk factors.

"Comparison of cardiovascular autonomic activity (heart rate variability and baroreceptor sensitivity) in young healthy females during fasting and hyperglycaemia"

BACKGROUND AND AIM

The present study compared cardiovascular autonomic activity and reactivity during fasting (FS) and hyperglycemia (HS) states in young healthy females.

METHODS

This case crossover study was conducted on 30 females recruited by convenient sampling. Blood glucose levels were measured in FS and after oral glucose load i.e., HS. Finger arterial blood pressure (BP) and ECG were recorded constantly to monitor baroreceptor sensitivity (BRS) and heart rate variability (HRV). Autonomic reactivity was tested with deep breathing (DB), Valsalva manoeuvre (VM), and head-up-tilt (HUT) test under FS and HS. HRV parameters not normally distributed were natural log (ln) transformed.

RESULTS

Significantly reduced Valsalva ratio and higher heart rate and BP were observed in HS that continued during HUT (P < 0.05). The lnSDNN (standard deviation of normal-to-normal intervals) and lnRMSSD (root mean square of successive differences) were significantly lower (p < 0.05) in HS during HUT. After HUT, lnRMSSD remained lower (P = 0.031), whereas lnLF/HF (low frequency/high frequency power) ratio (P = 0.042) and LFnu (normalized units) (P = 0.024) were higher in HS. BRS was significantly lower in supine position in HS compared to FS and further reduced in HUT position in both FS and HS (P < 0.05).

CONCLUSION

Compared to FS, the HS exhibited heightened sympathetic activity with attenuation of parasympathetic activity and this phenomenon was further accentuated by HUT. BRS was more sensitive indicator of autonomic effects of hyperglycemia in resting state. In addition to standard tests, autonomic reactivity in vulnerable young subjects could be useful to detect autonomic imbalance at an early stage.

Neurohumoral Control of Sinoatrial Node Activity and Heart Rate: Insight From Experimental Models and Findings From Humans

The sinoatrial node is perhaps one of the most important tissues in the entire body: it is the natural pacemaker of the heart, making it responsible for initiating each-and-every normal heartbeat. As such, its activity is heavily controlled, allowing heart rate to rapidly adapt to changes in physiological demand. Control of sinoatrial node activity, however, is complex, occurring through the autonomic nervous system and various circulating and locally released factors. In this review we discuss the coupled-clock pacemaker system and how its manipulation by neurohumoral signaling alters heart rate, considering the multitude of canonical and non-canonical agents that are known to modulate sinoatrial node activity. For each, we discuss the principal receptors involved and known intracellular signaling and protein targets, highlighting gaps in our knowledge and understanding from experimental models and human studies that represent areas for future research.

Dose-Response Association between Smoking Cessation and Arterial Stiffness: The Cardiovascular and Metabolic Diseases Etiology Research Center (CMERC) Cohort

Background and Objectives

Cigarette smoking has been reported to be associated with arterial stiffness. However, the clinical relevance of smoking cessation on arterial stiffness is debatable. Thus, we evaluated whether smoking cessation is associated with arterial stiffness.

Methods

A total of 1,169 male participants aged 30–64 years with absence of cardiovascular diseases in 2013–2017 were selected from the Cardiovascular and Metabolic Disease Etiology Research Center cohort study. The subjects were classified into the following 5 groups based on self-reporting: non-smokers, former smokers (<1, 1 to <10, and ≥10, years after cessation), and current smokers. Arterial stiffness was assessed using the augmentation index (AIx). The radial artery AIx was obtained from the peripheral artery waveform. The association was explored cross-sectionally.

Results

The AIx of former smokers did not differ from that of non-smokers (p=0.089). However, after former smokers were stratified by duration of smoking cessation, we noted a linear trend according to the smoking status (p<0.001). Men who quit smoking <1 year ago showed an elevated AIx (β=3.94, standard error=1.54, p=0.011) as much as ones of current smokers (β=4.39, standard error=0.74, p<0.001), while those who quit more than a decade ago showed an AIx similar to that of non-smokers (β=0.35, standard error=0.82, p=0.670) after controlling covariates.

Conclusions

A dose-response association between smoking cessation and AIx was revealed, which implies the possibility of a reversible effect of smoking cessation on arterial stiffness. Therefore, our findings may motivate current smokers to modify their smoking habits to delay or reverse disease progression.

Serum Asymmetric Dimethylarginine Levels in Patients with Vasovagal Syncope

Background and Objectives: Vasovagal syncope (VVS) is the most common cause of syncope and has multiple pathophysiological mechanisms. Asymmetric dimethylarginine (ADMA) is the major inhibitor of nitric oxide (NO). In this study, we aimed to investigate the relationship between plasma ADMA levels and syncope during the head-up tilt (HUT) test. Materials and Methods: Overall, 97 patients were included in this study. They were above 18 years of age and were admitted to our clinic with the complaint of at least one episode of syncope consistent with VVS. The HUT test was performed in all patients. Patients were divided into the following two groups based on the HUT test results: group 1 included 57 patients with a positive HUT test and group 2 included 35 patients with a negative HUT test. Blood samples were taken before and immediately after the HUT test to measure ADMA levels. Results: No significant intergroup differences were observed concerning gender and age (female gender 68% vs 60%; mean age 24.85 ± 4.01 vs 25.62 ± 3.54 years, respectively, for groups 1 and 2). ADMA values were similar between groups 1 and 2 before the HUT test [ADMA of 958 (544–1418) vs 951 (519–1269); p = 0.794]. In the negative HUT group, no significant differences were observed in ADMA levels before and after the HUT test [ADMA of 951 (519–1269) vs 951 (519–1566); p = 0.764]. However, in the positive HUT group, ADMA levels were significantly decreased following the HUT test [pretest ADMA of 958 (544–1418) vs post-test ADMA of 115 (67–198); p < 0.001]. Conclusion: ADMA levels significantly decreased after the HUT test in patients with VVS.

Subclinical inflammation and endothelial dysfunction are linked to cardiac autonomic neuropathy in type 2 diabetes

Purpose

The present study aimed to examine association between inflammatory and endothelial function biomarkers and indices of cardiac autonomic control in T2DM patients.

Methods

50 T2DM patients were recruited for this study. For cardiac autonomic function, cardiovascular autonomic reflex tests (CARTs) and heart rate variability (HRV) analysis was performed. Blood samples were collected for evaluating inflammatory and endothelial function biomarkers. Multivariable linear regression analysis adjusted for diabetes duration, glycemic control, waist circumference, hypertension, dyslipidemia, metformin, and statins was performed to examine the association between the biomarkers and cardiac autonomic function parameters.

Results

Interleukin-6 was inversely related to total power (p = .009) and low frequency power (p = .04). Interleukin-18 and high sensitivity C-reactive protein inversely correlated with measures of cardiac vagal control (p < .05). Both nitric oxide and endothelial nitric oxide synthase were positively linked with cardiac vagal control indices (p < .05) whereas endothelin-1 did not show any independent association with cardiac autonomic function parameters.

Conclusions

Biomarkers of inflammation and endothelial function are associated with measures of cardiac vagal control and global HRV which suggest that there is some pathophysiological link between subclinical inflammation, endothelial dysfunction and cardiac autonomic dysfunction in T2DM.

Arterial Stiffness is Associated With Moderate to Vigorous Physical Activity Levels in Post-Myocardial Infarction Patients

PURPOSE

Arterial stiffness has shown independent predictive value for all-cause and cardiovascular mortalities, as well as fatal and nonfatal coronary events. Physical activity (PA) is associated with reduced cardiovascular morbidity and mortality. The study aims to analyze the cross-sectional association of arterial stiffness with objectively measured PA in patients following acute myocardial infarction.

METHODS

One hundred patients were consecutively recruited after experiencing an acute myocardial infarction. Central arterial stiffness was measured through carotid-femoral pulse wave velocity (cf-PWV) and daily PA was assessed objectively during 7 consecutive days with accelerometers. To be valid, data required recordings of at least 8 hr/d on 5 d.

RESULTS

The cf-PWV showed a negative and significant association with total weekly time spent in moderate to vigorous PA (MVPA) (r = -0.416, P < .001). Patients classified as having higher risk according to arterial stiffness values (cf-PWV ≥10 m/sec) showed significantly lower time spent in MVPA than those below that threshold. The cf-PWV was significantly lower in patients performing >300 min of MVPA/wk than in those performing <150 min/wk (8.53 ± 2.08 vs 10.3 ± 2.44 m/sec, P = .021). Differences remained significant after adjustment for several confounders.

CONCLUSIONS

Moderate to vigorous PA was inversely associated with arterial stiffness and time spent in MVPA was lower in patients after acute myocardial infarction, with cf-PWV above the risk threshold value (≥10 m/sec). These results seem to reinforce the importance of PA as a nonpharmacological tool for secondary cardiovascular prevention.

Cross-Sectional Associations between Homoarginine, Intermediate Phenotypes, and Atrial Fibrillation in the Community-The Gutenberg Health Study

Homoarginine has come into the focus of interest as a biomarker for cardiovascular disease. Atrial fibrillation (AF) causes a substantial increase in morbidity and mortality. Whether circulating homoarginine is associated with occurrence or persistence of AF and may serve as a new predictive biomarker remains unknown. We measured plasma levels of homoarginine in the population-based Gutenberg health study (3761 patients included, of them 51.7% males), mean age 55.6 ± 10.9 years-old. Associations between homoarginine and intermediate electrocardiographic and echocardiographic phenotypes and manifest AF were examined. Patients with AF (124 patients, of them 73.4% males) had a mean age 64.8 ± 8.6 years-old compared to a mean age of 55.3 ± 10.9 in the population without AF (p-value < 0.001) and showed a less beneficial risk factor profile. The median homoarginine levels in individuals with and without AF were 1.9 μmol/L (interquartile range (IQR) 1.5–2.5) and 2.0 μmol/L (IQR 1.5–2.5), respectively, p = 0.56. In multivariable-adjusted regression analyses homoarginine was not statistically significantly related to electrocardiographic variables. Among echocardiographic variables beta per standard deviation increase was −0.12 (95% confidence interval (CI) −0.23–(−0.02); p = 0.024) for left atrial area and −0.01 (95% CI −0.02–(−0.003); p = 0.013) for E/A ratio. The odds ratio between homoarginine and AF was 0.91 (95% CI 0.70–1.16; p = 0.45). In our large, population-based cross-sectional study, we did not find statistically significant correlations between lower homoarginine levels and occurrence or persistence of AF or most standard electrocardiographic phenotypes, but some moderate inverse associations with echocardiographic left atrial size and E/A. Homoarginine may not represent a strong biomarker to identify individuals at increased risk for AF. Further investigations will be needed to elucidate the role of homoarginine and cardiac function.

The acute effects of different spironolactone doses on cardiac function in streptozotocin-induced diabetic rats

Currently, cardiovascular diseases are the leading cause of global mortality, while diabetes mellitus remains an important cause of cardiovascular morbidity. A recent study showed that patients with diabetes mellitus treated with mineralocorticoid receptor antagonists have improved coronary microvascular function, leading to improved diastolic dysfunction. In this study, we evaluated the influence of acute administration of spironolactone on myocardial function in rats with streptozotocin-induced diabetes mellitus, with special emphasis on cardiodynamic parameters in diabetic rat hearts. The present study was carried out on 40 adult male Wistar albino rats (8 weeks old). Rats were randomly divided into 4 groups (10 animals per group): healthy rats treated with 0.1 μmol/L of spironolactone, diabetic rats treated with 0.1 μmol/L of spironolactone, healthy rats treated with 3 μmol/L of spironolactone, and diabetic rats treated with 3 μmol/L of spironolactone. Different, dose-dependent, acute responses of spironolactone treatment on isolated, working diabetic and healthy rat heart were observed in our study. In healthy rats, better systolic function was achieved with higher spironolactone dose, while in diabetic rats, similar effects of low and high spironolactone dose were observed.

Mineralocorticoid receptor blockade: new insights into the mechanism of action in patients with cardiovascular disease

Mineralocorticoid receptor (MR) blockade is effective in reducing total mortality and the incidence of heart failure in patients with systolic left ventricular dysfunction (SLVD) associated with chronic heart failure or post myocardial infarction.

Pre-clinical and clinical studies in SLVD have shown that MR blockade reduces sudden cardiac death, left ventricular remodelling, left ventricular hypertrophy, endothelial dysfunction, autonomic imbalance, renal dysfunction and improves fibrinolysis.

While MR blockade promotes sodium excretion and the combination of an angiotensin-converting enzyme inhibitor and a MR blocker have been shown to be more effective than either alone in causing natriuresis, it is unlikely that their beneficial effects can be explained solely on this basis.

Aldosterone has been shown to have a number of adverse effects, including activation of other neurohumeral mediators, stimulation of active reactive oxygen species (ROS), activation of the NF-κβ and AP-1 signalling pathways, vascular inflammation and fibrosis, myocardial hypertrophy, autonomic imbalance, and a decrease in fibrinolysis. MR blockade is, however, effective both in situations with and without an increase in serum aldosterone level, since the MR can be occupied and activated by cortisol as well as by aldosterone.

In view of these mechanisms, MR blockade may play an important role not only on SLVD, but also in essential hypertension with normal systolic function, diastolic heart failure, valvular heart disease, vascular stiffening with ageing, progression of renal disease, and diabetes mellitus. This hypothesis will, however, require further prospective evaluation.

A Review of Cardiovascular Autonomic Control in Cluster Headache

OBJECTIVE

This review aims to evaluate existing literature concerning cardiovascular autonomic function and CH. Suggestions about future research are offered and known difficulties in investigating the autonomic nervous system in cluster headache are discussed.

BACKGROUND

Little is known of the pathophysiological mechanisms behind cluster headache. Cranial autonomic features are an inherent and diagnostic feature; however, a number of studies and clinical observations support the involvement of systemic autonomic control in its pathophysiology. Further, cluster headache attacks are apparently more easily triggered during periods of parasympathetic dominance. A better understanding of this interaction may provide insight into central autonomic regulation and its role in cluster headache.

METHODS

A PubMed search was performed in April 2015 using the search terms "cluster headache," "cardiovascular," "autonomic nervous system," and "cardiac." References of identified articles were also searched for relevant articles. Studies were included if they contained data on cardiovascular or autonomic responses to autonomic tests, induced or spontaneous attacks.

RESULTS

In total, 22 studies investigating cardiac autonomic control in cluster headache were identified. Three overall categories of investigations exist: (1) Those studying changes in heart rate, blood pressure, and electrocardiographic changes; (2) those employing various clinical autonomic tests; and finally (3) those using spectral and nonlinear analysis of heart rate variability. Although not completely congruent, overall, results suggest ictal hyperactivation of the parasympathetic branch and a sympathetic deficit. Subclinical autonomic dysregulation is also present in the pain-free state.

CONCLUSION

Cardiac autonomic control is subclinically affected in cluster headache. The changes could be attributed to the suggested central dysregulation present in this disorder.

Two weeks of high-intensity interval training improves novel but not traditional cardiovascular disease risk factors in adolescents

High-intensity interval training (HIIT) improves traditional cardiovascular disease (CVD) risk factors in adolescents, but no study has identified the influence of HIIT on endothelial and autonomic function in this group. Thirteen 13- to 14-yr-old adolescents (6 girls) completed six HIIT sessions over 2 wk. Each training session consisted of eight to ten 1-min repetitions of cycling at 90% peak power interspersed with 75 s of unloaded cycling. Traditional (triglycerides, cholesterol, glucose, insulin, and blood pressure) and novel [flow-mediated dilation (FMD), heart rate variability (HRV)] CVD risk factors were assessed in a fasted and postprandial state before (PRE), 1 day after (POST-1D), and 3 days after (POST-3D) training. Aerobic fitness was determined PRE and POST-3D. Two weeks of HIIT had no effect on aerobic fitness or traditional CVD risk factors determined in the fasted or postprandial state ( P > 0.15). Compared with PRE, fasted FMD was improved POST-1D [ P = 0.003, effect size (ES) = 0.70] but not POST-3D ( P = 0.32, ES = 0.22). Fasted FMD was greater POST-1D compared with POST-3D ( P = 0.04, ES = 0.48). Compared with PRE, postprandial FMD was greater POST-1D ( P < 0.001, ES = 1.01) and POST-3D ( P = 0.01, ES = 0.60). Fasted HRV was greater POST-1D ( P = 0.001, ES = 0.71) and POST-3D ( P = 0.02, ES = 0.44). The test meal lowered HRV in all laboratory visits ( P < 0.001, ES = 0.59), but there were no differences in postprandial HRV between visits ( P > 0.32 for all). Two weeks of HIIT enhanced endothelial function and HRV without improvements in traditional CVD risk factors. However, most of this favorable adaptation was lost POST-3D, suggesting that regularly performing high-intensity exercise is needed to maintain these benefits.

Identifying Common Genetic Risk Factors of Diabetic Neuropathies

Type 2 diabetes mellitus (T2DM) is a global public health problem of epidemic proportions, with 60-70% of affected individuals suffering from associated neurovascular complications that act on multiple organ systems. The most common and clinically significant neuropathies of T2DM include uremic neuropathy, peripheral neuropathy, and cardiac autonomic neuropathy. These conditions seriously impact an individual's quality of life and significantly increase the risk of morbidity and mortality. Although advances in gene sequencing technologies have identified several genetic variants that may regulate the development and progression of T2DM, little is known about whether or not the variants are involved in disease progression and how these genetic variants are associated with diabetic neuropathy specifically. Significant missing heritability data and complex disease etiologies remain to be explained. This article is the first to provide a review of the genetic risk variants implicated in the diabetic neuropathies and to highlight potential commonalities. We thereby aim to contribute to the creation of a genetic-metabolic model that will help to elucidate the cause of diabetic neuropathies, evaluate a patient's risk profile, and ultimately facilitate preventative and targeted treatment for the individual.

Prolonged postocclusive hyperemia response in patients with normal-tension glaucoma

Background

It is believed that endothelial dysfunction may be a link between systemic and ocular dysregulation in glaucoma. The aim of this study was to evaluate peripheral vascular reactive hyperemia in response to occlusion test and to correlate peripheral vascular findings with retrobulbar hemodynamics parameters in patients with normal-tension glaucoma.

Material/Methods

Forty-eight patients with normal-tension glaucoma (mean age 58.1 years, 38 women) and 40 control subjects (mean age 54.1 years, 36 women) were subjected to a brachial arterial occlusion test and color Doppler imaging (LOGIQ 9, GE Medical Systems) of the retrobulbar arteries. Finger hyperemia was assessed by using a 2-channel laser Doppler flowmeter (MBF-3D, Moor Instruments, Ltd.). Time parameters (time to peak flow, half-time of hyperemia, time of recovery) and amplitude parameters (maximum hyperemia response, biological zero) of the post-occlusive reactive hyperemia signal pattern as well as velocities and resistance index of the ophthalmic, central retinal, and short posterior ciliary arteries were evaluated and compared between study groups.

Results

In glaucoma patients, time to peak flow and half-time of hyperemia were significantly longer (21.4 vs. 12.0 s, p=0.02 and 74.1 vs. 44.2 s, p=0.03, respectively) and biological zero was significantly lower (2.4 vs. 3.2, p=0.01) comparing with healthy subjects. In glaucoma patients, peak-systolic and end-diastolic velocities of central retinal artery were significantly lower (12.8 vs.14.1, p=0.03 and 3.9 vs. 4.7, p=0.01, respectively) and resistance index of this artery was significantly higher (0.69 vs. 0.67, p=0.03) compared to controls. In the glaucoma group, maximum hyperemic response was negatively correlated with the resistance index of temporal short posterior ciliary arteries (r=−0.4, p=0.01), whereas in the control group half-time of hyperemia was negatively correlated with end-diastolic velocity of the central retinal artery (r=−0.3, p=0.03).

Conclusions

Arterial occlusion test elicited a prolonged systemic hyperemia response in patients with glaucoma as compared with healthy subjects. Retrobulbar blood flow alterations in glaucoma patients may be related to systemic vascular dysregulation.

Allopurinol prevents nitroglycerin-induced tolerance in rat thoracic aorta

Xanthine oxidase is an important source of reactive oxygen species; so, it may play a role in the pathogenesis of endothelium dysfunction and its consequences. Allopurinol, a purine analog, is a famous xanthine oxidase inhibitor. This study aimed to investigate possible effects of allopurinol on nitroglycerin tolerance, vasoconstriction, and vasorelaxation in rat aortic ring. Using thoracic aortic rings obtained from male Wistar rats, the effect of allopurinol was examined on nitroglycerin-induced tolerance. In addition, changes of vasoconstriction (by using KCl and phenylephrine) and vasorelaxation (by using carbachol, sodium nitroprusside, and nitroglycerin) were also measured and compared between tissues treated with and without allopurinol. All 3 concentrations of allopurinol (50, 100, and 150 μM) significantly acted against the development of nitroglycerin-induced tolerance in comparison with controls. In terms of vasoconstriction and vasorelaxation, the effect of allopurinol was significant only on carbachol-induced (endothelium related) vasorelaxation in a dose-dependent manner. In conclusion, although allopurinol had no significant effect on the contractile response of the aorta, in accord with the previous data, it significantly intensified endothelium-dependent vasodilation. The inhibitory effect of allopurinol against the development of nitrate-induced tolerance may suggest its clinical benefit and is worth to be studied more extensively.

eNOS gene haplotype is indirectly associated with the recovery of cardiovascular autonomic modulation from exercise

Polymorphisms in the endothelial nitric oxide synthase (eNOS) gene decrease expression and activation of eNOS in vitro, which is associated with lower post-exercise increase in vasodilator reactivity in vivo. However, it is unknown whether such polymorphisms are associated with other eNOS-related phenotypes during recovery from exercise. Therefore, we investigated the impact of an eNOS haplotype containing polymorphic alleles at loci -786 and 894 on the recovery of cardiovascular autonomic function from exercise. Sedentary, non-obese, healthy subjects were enrolled [n = 107, age 32 ± 1 years (mean ± SEM)]. Resting autonomic modulation (heart rate variability, systolic blood pressure variability, and spontaneous baroreflex sensitivity) and vascular reactivity (forearm hyperemic response post-ischemia) were assessed at baseline, 10, 60, and 120 min after a maximal cardiopulmonary exercise test. Besides, autonomic function was assessed by heart rate recovery (HRR) immediately after peak exercise. Haplotype analysis showed that vagal modulation (i.e., HF n.u.) was significantly higher, combined sympathetic and vagal modulation (i.e., LF/HF) was significantly lower and total blood pressure variability was significantly lower post-exercise in a haplotype containing polymorphic alleles (H2) compared to a haplotype with wild type alleles (H1). HRR was similar between groups. Corroborating previous evidence, H2 had significantly lower post-exercise increase in vasodilator reactivity than H1. In conclusion, a haplotype containing polymorphic alleles at loci -786 and 894 had enhanced recovery of autonomic modulation from exercise, along with unchanged HRR, and attenuated vasodilator reactivity. Then, these results suggest an autonomic compensatory response of a direct deleterious effect of eNOS polymorphisms on the vascular function.

Resting high-frequency heart rate variability is related to resting brain perfusion

We examined the neural correlates of resting cardiac vagal activity in a sample of 432 participants (206 male; 61 African American; mean age 42 years). Pulsed arterial spin labeling was used to quantify whole brain and regional cerebral blood flow at rest. High-frequency heart rate variability (HF-HRV) was used to measure cardiac vagal activity at rest. The primary aim was to determine whether brain regions implicated in regulating cardiac vagal reactions were also related to cardiac vagal activity at rest, and whether these associations varied by sex or race. Brain areas previously related to vagal reactivity were related to resting HF-HRV. Directionality of relationships differed between overall and regional flows. Some relationships were only observed in women and African Americans. There appears to be communality between brain regions associated with task-induced vagal reactivity and those associated with resting cardiac vagal activity.

The effects of exercise training on arterial stiffness in coronary artery disease patients: a state-of-the-art review

The purpose of this state-of-the-art review was to examine the effects of exercise training on arterial stiffness (AS) in patients with coronary artery disease (CAD). A PubMed and SCOPUS literature search was conducted up to March of 2013. Two authors performed the selection of the studies and the subsequent data extraction (e.g. information on study design, exercise programme characteristics and outcome measures). Of 34 papers identified, only five studies met the inclusion criteria, with no one being a randomized controlled trial. Within the selected studies, the sample size varied between 28 and 119 patients, with mean ages ranging from 48 to 67 years old in patients with CAD after an acute myocardial infarction, coronary artery bypass graft or percutaneous transluminal coronary angioplasty. Although all studies utilized the aerobic exercise mode, the other characteristics of the exercise programmes varied largely between the studies: programme length (from 6 to 20 weeks), exercise duration (15-20 to 50 min) and exercise intensity, which was based on heart rate reserve (40 to 85%) or heart rate at anaerobic threshold or ventilatory threshold. All the three studies evaluating pulse wave velocity, as well as one of two studies that assessed the augmentation index, reported significant reductions on those variables after exercise training. Results indicated that the majority of the AS and related measures improved after the different exercise training programmes. However, these results need to be confirmed in future randomized clinical studies controlling potential confounders.

Heart rate variability in myocardial infarction patients: effects of exercise training

Heart rate variability (HRV) is a simple and noninvasive measure that estimates cardiac autonomic modulation, mainly the parasympathetic contribution. Increased sympathetic and/or decreased parasympathetic nervous activity is seen in post-myocardial infarction (MI) patients. Consequently, these patients present reduced HRV, which has been associated with increased risk of adverse events and mortality. Exercise training, recommended as a complementary therapy for patients with cardiovascular disease, has shown numerous beneficial effects. The main aim of the present manuscript was to provide a critical review of studies investigating the effects of exercise training on cardiac autonomic modulation, through HRV, in MI patients and the possible mechanisms involved. Despite conflicting evidence, exercise training appears to be a useful therapeutic intervention to improve the unbalanced autonomic function of MI patients. Finally, the mechanisms involved are not yet well understood, but nitric oxide bioavailability and angiotensin II levels seem to play an important role.

Influence of heart rate at rest for predicting the metabolic syndrome in older Chinese adults

The aim of this study was to examine the relationship between seated resting heart rate and the metabolic syndrome (MetS) among older residents of Guangzhou, South China. A total of 30,519 older participants (≥50 years) from the Guangzhou Biobank Cohort Study were stratified into quartiles based on seated resting heart rate. The associations between each quartile and the MetS were assessed using multivariable logistic regression. A total of 6,907 (22.8 %) individuals were diagnosed as having the MetS, which was significantly associated with increasing heart rate quartiles (P < 0.001). Participants in the uppermost quartile (mean resting heart rate 91 ± 8 beats/min) of this cardiovascular proxy had an almost twofold increased adjusted risk (odds ratio (95 % CI) = 1.94 (1.79, 2.11), P < 0.001) for the MetS, as compared to those in the lowest quartile (mean resting heart rate, 63 ± 4 beats/min). Heart rate, which is an inexpensive and simple clinical measure, was independently associated with the MetS in older Chinese adults. We hope these observations will spur further studies to examine the usefulness of resting heart rate as a means of risk stratification in such populations, for which targeted interventions should be implemented.

Nitric oxide and regulation of heart rate in patients with postural tachycardia syndrome and healthy subjects

The objective is to study the role of nitric oxide (NO) on cardiovascular regulation in healthy subjects and postural tachycardia syndrome (POTS) patients. Reduced neuronal NO function, which could contribute to a hyperadrenergic state, and increased NO-induced vasodilation, which could contribute to orthostatic intolerance, have been reported in POTS. In protocol 1, 13 healthy volunteers (33 ± 3 years) underwent autonomic blockade with trimethaphan and were administered equipressor doses of Nω-monomethyl-L-arginine (L-NMMA, a NO synthase inhibitor) and phenylephrine to determine the direct chronotropic effects of NO (independent of baroreflex modulation). In protocol 2, we compared the effects of L-NMMA in 9 POTS patients (31 ± 3 years) and 14 healthy (32 ± 2 years) volunteers, during autonomic blockade. During autonomic blockade, L-NMMA and phenylephrine produced similar increases in systolic blood pressure (27 ± 2 versus 27 ± 3 mm Hg). Phenylephrine produced only minimal heart rate changes, whereas L-NMMA produced a modest, but significant, bradycardia (-0.8 ± 0.4 versus -4.8 ± 1.2 bpm; P=0.011). There were no differences between POTS and healthy volunteers in the systolic blood pressure increase (22 ± 2 and 28 ± 5 mm Hg) or heart rate decrease (-6 ± 2 and -4 ± 1 bpm for POTS and controls, respectively) produced by L-NMMA. In the absence of baroreflex buffering, inhibition of endogenous NO synthesis results in a significant bradycardia, reflecting direct tonic modulation of heart rate by NO in healthy individuals. We found no evidence of a primary alteration in NO function in POTS. If NO dysfunction plays a role in POTS, it is through its interaction with the autonomic nervous system.

Increasing peripheral insulin sensitivity by protein tyrosine phosphatase 1B deletion improves control of blood pressure in obesity

Obesity is a major risk factor for hypertension. The copresentation of hypertension and insulin resistance (IR) suggests a role for IR in blood pressure (BP) dysregulation. To test this hypothesis, peripheral IR has been genetically subtracted in a model of obesity by crossing leptin receptor mutant mice (K(db)H(PTP)) with mice lacking protein tyrosine phosphatase 1B (insulin desensitizer, H(db)K(PTP)) to generate obese insulin-sensitive mice (K(db)K(PTP)). BP was recorded in lean (H(db)H(PTP), H(db)K(PTP)) and obese (K(db)H(PTP), K(db)K(PTP)) mice via telemetry, and a frequency analysis of the recording was performed to determine BP variability. Correction of IR in obese mice normalized BP values to baseline levels (H(db)H(PTP): 116 ± 2 mm Hg; K(db)H(PTP): 129 ± 4 mm Hg; K(db)K(PTP): 114 ± 5 mm Hg) and restored BP variability by decreasing its standard deviation and the frequency of BP values over the upper autoregulatory limit of the kidneys. However, although IR-induced increases in proteinuria (versus 53 ± 13 μg/d, H(db)H(PTP)) were corrected in K(db)K(PTP) (112 ± 39 versus 422 ± 159 μg/d, K(db)H(PTP)), glomerular hypertrophy was not. IR reduced plasma aldosterone levels ruling out a role for mineralocorticoids in the development of hypertension. Taken together, these data indicate that correction of IR prevents hypertension, BP variability, and microalbuminuria in obese mice. Although the mechanism remains to be fully determined, increases in aldosterone or sympathoactivation of the cardiovascular system seem to be less likely contributors.

Relationship between heart rate variability and endothelial function in healthy subjects

In various diseased states reduced cardiac vagal activity is accompanied by impaired endothelial function. Evidence from animal studies indicates interaction between the two systems, but such data from human studies is limited. The aim of this study was to test the hypothesis that cardiac vagal activity and endothelial function are related in healthy individuals. 46 young males were studied. From 10 minute long ECG recordings mean RR-interval and time and frequency domain vagal heart rate variability indices (RMSSD; pNN50 and HF, respectively) were determined. Heart rate variability indices were used to define cardiac vagal activity. Endothelial function was assessed by measuring brachial artery flow mediated dilation. Hyperemic, diastolic shear rate was used to normalize flow mediated dilation. All three vagal heart rate variability indices correlated significantly and positively with flow mediated dilation across subjects, with r values within the range of 0.43-0.52, p<0.01 for all relations. After adjusting for potential confounders, vagal heart rate variability indices remained significantly associated with normalized flow mediated dilation. RR-interval was related to most heart rate variability indices, but was not related to flow mediated dilation. Our data demonstrate that vagal heart rate variability indices are related to flow mediated dilation across healthy male subjects. The results cannot serve as evidence of a causal relationship, but are of interest and render for further investigation into underlying mechanisms.

Endothelial nitric oxide synthase polymorphisms and adaptation of parasympathetic modulation to exercise training

PURPOSE

There is a large interindividual variation in the parasympathetic adaptation induced by aerobic exercise training, which may be partially attributed to genetic polymorphisms. Therefore, we investigated the association among three polymorphisms in the endothelial nitric oxide gene (-786T>C, 4b4a, and 894G>T), analyzed individually and as haplotypes, and the parasympathetic adaptation induced by exercise training.

METHODS

Eighty healthy males, age 20-35 yr, were genotyped by polymerase chain reaction-restriction fragment length polymorphism analysis, and haplotypes were inferred using the software PHASE 2.1. Autonomic modulation (i.e., HR variability and spontaneous baroreflex sensitivity) and peak oxygen consumption (VO(2peak)) were measured before and after training (running, moderate to severe intensity, three times per week, 60 min·day(-1), during 18 wk).

RESULTS

Training increased VO(2peak) (P < 0.05) and decreased mean arterial pressure (P < 0.05) in the whole sample. Subjects with the -786C polymorphic allele had a significant reduction in baroreflex sensitivity after training (change: wild type (-786TT) = 2% ± 89% vs polymorphic (-786TC/CC) = -28% ± 60%, median ± quartile range, P = 0.03), and parasympathetic modulation was marginally reduced in subjects with the 894T polymorphic allele (change: wild type (894GG) = 8% ± 67% vs polymorphic (894GT/TT) = -18% ± 59%, median ± quartile range, P = 0.06). Furthermore, parasympathetic modulation percent change was different between the haplotypes containing wild-type alleles (-786T/4b/894G) and polymorphic alleles at positions -786 and 894 (-786C/4b/894T) (-6% ± 56% vs -41% ± 50%, median ± quartile range, P = 0.04).

CONCLUSIONS

The polymorphic allele at position -786 and the haplotype containing polymorphic alleles at positions -786 and 894 in the endothelial nitric oxide gene were associated with decreased parasympathetic modulation after exercise training.

Effect of pioglitazone on cardiac sympathovagal modulation in patients with type 2 diabetes

This study aims to examine the effect of pioglitazone on potential progression of autonomic damage in addition to changes in control of cardiovascular function in patients with type 2 diabetes (T2DM). Thirty patients with T2DM and 32 healthy subjects participated in the study. Sympathovagal activity, assessed by power spectral analysis (PSA) of R-R intervals variability, and blood pressure (BP) were studied during clinostatism and orthostatism in controls and patients. We have assessed blood pressure control by 24-hour monitoring of ambulatory blood pressure. Patients were treated with pioglitazone (30 mg/day) for 6 months, and then re-evaluated by PSA for heart rate variability (HRV). Reduced levels of HbA1c (P < 0.0001) and urinary albumin (P = 0.008) were observed in pioglitazone-treated patients compared to untreated baseline levels. Arterial BP remained unchanged following pioglitazone treatment. T2DM patients had reduced HRV (low-frequency power; LF; P < 0.0001 and LF/HF; LF/HF; P < 0.0001) at baseline (clinostatism) compared to controls. Baseline clinostatic differences between groups persisted after pioglitazone treatment and no effect of treatment on basal HRV variables was observed. In controls, HF decreased and LF and LF/HF ratio increased in the orthostatic position. A similar effect for HF was observed in patients, but LF and LF/HF did not increase. The normal difference between HF-power in clinostatism versus orthostatism observed for controls (P < 0.0001) was restored in patients following pioglitazone treatment (P = 0.028). A significant decrease from lying to standing position in orthostatic LF-power (P < 0.0001) and LF/HF (P < 0.0001) was also observed between patients and controls. Although no differences in autonomic control of HRV were observed between controls and patients with T2DM, significant differences were observed in sympathovagal balance following either clinostatic or orthostatic challenge. These findings provide initial evidence of a potential additional benefit afforded by pioglitazone for the improvement of cardiac sympathovagal balance in T2DM.

Effects of Ascorbic Acid Intake on the Intima-Media Thickness and Blood Flow Velocities of the Carotid Artery in Patients With Sickle Cell Anemia

This study aims to investigate and compare the effects of six-week oral vitamin C supplementation on blood velocities, intima-media thickness, and cross-sectional diameter (CSD) of the common carotid artery of sickle cell anemia (SCA) and non–sickle cell anemia (NSCA) subjects using sonography. Results showed that the CSD and end-diastolic velocity were significantly higher ( P < .002 and P < .001, respectively) in the SCA subjects than in the NSCA subjects in the presupplementation phase. Calculated resistivity index (RI) was significantly lower in the SCA subjects ( P < .003). Vitamin C supplementation had a slight effect on all the measured parameters in the NSCA subjects but caused a significant increase in peak systolic velocity (PSV) ( P < .02) and RI ( P < .01) in SCA. A comparison of change in each measured variable between the groups showed significant differences. Oral supplementation with vitamin C should be encouraged in patients with SCA as prophylaxis against endothelial damage, thereby preventing vaso-occlusive crises and their associated morbidity.

Effect of high-dose vitamin C on oxygen free radical production and myocardial enzyme after tourniquet ischaemia-reperfusion injury during bilateral total knee replacement

This study investigated the effects of high-dose vitamin C on oxygen free radical production and cardiac enzymes after tourniquet application and ischaemia-reperfusion injury during bilateral total knee replacement (TKR) in elderly patients. In the vitamin C (VC) group (VC group, n = 16), during surgery, patients received a priming bolus of 0.06 g/kg vitamin C with 100 ml saline followed by 0.02 g/kg vitamin C mixed with 30 ml saline, intravenously. The control group (n = 16) received no intra-operative vitamin C. In the VC group, malondialdehyde levels were lower, and arterial oxygen tension and mean blood pressure were higher, than in controls after post-operative deflation of both knee tourniquets. Troponin I levels were lower in the VC group than in controls 8 h post-operation. Administering high-dose vitamin C during bilateral TKR could prevent oxygen free radical production and a decline in arterial oxygen tension and mean blood pressure induced by ischaemia-reperfusion injury, thereby protecting the myocardium.

Indian Asians have poorer cardiovascular autonomic function than Europeans: this is due to greater hyperglycaemia and may contribute to their greater risk of heart disease

AIMS/HYPOTHESIS

A high prevalence of diabetes contributes to excess CHD in Indian Asians, but the underlying mechanisms are unclear. Heart rate, heart rate variability (HRV) and baroreflex sensitivity (BRS) are measures of cardiac autonomic function that are disturbed by hyperglycaemia and predict CHD. We compared these measures in Indian Asians and Europeans, and sought explanations for the observed differences.

METHODS

A representative sample of 149 Europeans and 151 Indian Asians was recruited from primary care, 66% of them men (aged 35-75 years), 34% women (aged 55-75 years). Heart rate, HRV, BRS and cardio-metabolic profiles were measured over four successive 5 min periods with continuous ECG and blood pressure monitoring.

RESULTS

Indian Asians were hyperglycaemic compared with Europeans (HbA(1c) (mean +/- SD) 6.5 +/- 1.2% vs 5.9 +/- 1.0%, p = 0.001). They had shorter mean RR intervals ((mean +/- SE) 969 +/- 13 vs 1,022 +/- 12 ms, p = 0.002), lower total RR interval power ((geometric mean, 95% CI) 925 [796-1075] vs 1,224 [1,064-1,422] ms(2), p = 0.008) and lower BRS ((mean +/- SE) 5.7 +/- 1.0 vs 6.6 +/- 1.0 ms/mmHg, p = 0.01). All measures of cardiac autonomic dysfunction were significantly associated with hyperglycaemia (mean RR interval vs HbA(1c) r = -0.22; p < 0.001). Ethnic differences in cardiac autonomic function persisted after adjustment for age, blood pressure and medication (mean RR interval 973 vs 1,021 ms, p = 0.004), but were attenuated or abolished by adjusting for HbA(1c) (979 vs 1,014 ms, p = 0.06) or other markers of hyperglycaemia.

CONCLUSIONS/INTERPRETATION

Indian Asians from the general population have impaired cardiovascular autonomic function compared with Europeans. This is due to greater hyperglycaemia in Indian Asians and may determine their increased CHD risk.

Acute superoxide scavenging restores depressed baroreflex sensitivity in renovascular hypertensive rats

In some pathological conditions such as hypertension, there is an impairment in the autonomic control of blood pressure resulting in changes in baroreflex sensitivity. In the present study we tested the hypothesis that acute superoxide scavenging would restore the reduced baroreflex sensitivity in renovascular hypertension. Male Wistar rats underwent 2-Kidney-1-Clip (2K1C) or sham surgery and were maintained untouched for six weeks to develop hypertension. After six weeks, animals from the 2K1C group were hypertensive when compared to the sham group (165±9 vs. 108±7mm Hg, P<0.05). As a proof of principle for the hypertension model adopted, animals from the 2K1C group presented increased non-clipped kidney and cardiac mass index and reduced clipped kidney mass index. Regarding baroreflex, 2K1C rats presented diminished baroreflex sensitivity when compared to the sham group (2K1C+saline: -1.61±0.15 vs. sham+saline: -2.79±0.24bpm mm Hg(-1), p<0.05). Moreover, acute administration of Vitamin C (150mg/Kg, i.v.) restored baroreflex sensitivity in 2K1C rats (2K1C+Vit C: -3.08±0.37 vs. 2K1C+saline: -1.61±0.15bpm mm Hg(-1), p<0.05). Furthermore, administration of apocynin (30μg/Kg, i.v.), a NADPH oxidase inhibitor, also improved baroreflex sensitivity in the 2K1C group (2K1C+apocynin: -2.81±0.24 vs. 2K1C+saline: -1.61±0.15bpm mm Hg(-1), p<0.05). In addition, autonomic blockade with either methylatropine or propranolol reduced the changes in heart rate to the same extent in all groups suggesting that improved baroreflex sensitivity by antioxidants were mediated by improvement in autonomic function. Taken together, these data suggest that NADPH oxidase-derived reactive oxygen species are involved in the blunted baroreflex sensitivity in renovascular hypertension and that acute scavenging of superoxide restores baroreflex sensitivity.

Role of nitric oxide in young patients with vasovagal syncope

AIMS

Nitric oxide (NO) formed in the vascular endothelium produces, among other effects, a strong vasodilation. In order to evaluate the possible role of NO in hypotension induced by head-up tilt test (HUT), we measured plasma levels of its metabolites, nitrites and nitrates (NOx), during the test.

METHODS AND RESULTS

Twelve patients with vasovagal syncope and positive HUT [HUT(+)] (mean age: 23+/-5 years) and 13 healthy volunteers with negative HUT (controls) (mean age: 24+/-5 years) were included. Venous blood samples were obtained during the baseline stage for biochemical measurements. Plasma values of NOx were obtained under baseline conditions (T0), at the end of the HUT (T1), and 15 min after the end of the HUT (T2). The baseline biochemical values as well as haemodynamic parameters were similar in HUT(+) patients and controls. NOx plasma values (in micromol/L) were as follows [HUT(+) vs. controls]: T0: 5.7+/-1.6 vs. 8.8+/-4.7 (P=0.05), T1: 6.1+/-3.2 vs. 8.5+/-3.6 (P=NS), and T2: 6.1+/-3 vs. 10.2+/-8.9 (P=NS). The NOx levels were directly correlated with the insulin levels (Spearman's R=0.53, P=0.008).

CONCLUSION

Baseline plasma levels of NOx were significantly lower in HUT(+) patients than in controls. However, since the expected increase in NOx values during HUT-induced syncope was not observed, the possible role of NO in vasovagal hypotension is uncertain.

Chronic antioxidant treatment improves arterial renovascular hypertension and oxidative stress markers in the kidney in Wistar rats

BACKGROUND

Sympathetic vasomotor hyperactivity and baroreflex dysfunction are involved in the development and maintenance of renovascular arterial hypertension. We hypothesized that angiotensin (Ang) II-dependent oxidative stress contributes to the pathophysiology of the two-kidney, one-clip (2K-1C) model.

METHODS

The mean arterial pressure (MAP), baroreflex, and renal sympathetic nerve activity (rSNA) were evaluated after chronic administration of an antioxidant, vitamin C (vitC 150 mg/kg/day) in male Wistar 2K-1C rats. Additionally, the mRNA levels of Ang II subtype 1 receptor (AT(1)R), NAD(P)H oxidase subunits (p47phox and gp91phox), and major antioxidant enzymes were evaluated in the renal cortex.

RESULTS

After vitC treatment, the MAP (170 +/- 4 vs. 133 +/- 6 mm Hg; P < 0.05) and rSNA (161 +/- 5 vs. 118 +/- 12 spikes/s; P < 0.05) were significantly reduced only in the 2K-1C group. VitC improved the baroreflex control of heart rate (HR) and rSNA. The expression of AT(1)R, p47phox, and gp91phox was elevated (51, 184, and 132%, respectively) in the clipped kidney of 2K-1C group. VitC downregulated AT(1)R in the clipped kidney (31%). Catalase (CAT) expression was reduced in clipped (70%) and nonclipped (83%) kidneys of 2K-1C rats. VitC treatment augmented the expression of glutathione peroxidase (GPx) in both clipped (185%) and nonclipped (212%) kidneys of the 2K-1C group.

CONCLUSIONS

The present study suggests a role for oxidative stress in the cardiovascular and sympathetic alterations in renovascular hypertension, associated with changes in the expression of AT(1)R, NAD(P)H oxidase subunits, and antioxidant enzymes in the kidney.

Top-down and bottom-up mechanisms in mind-body medicine: development of an integrative framework for psychophysiological research

It has become increasingly evident that bidirectional ("top-down and bottom-up") interactions between the brain and peripheral tissues, including the cardiovascular and immune systems, contribute to both mental and physical health. Therapies directed toward addressing functional links between mind/brain and body may be particularly effective in treating the range of symptoms associated with many chronic diseases. In this paper, we describe the basic components of an integrative psychophysiological framework for research aimed at elucidating the underlying substrates of mind-body therapies. This framework recognizes the multiple levels of the neuraxis at which mind-body interactions occur. We emphasize the role of specific fronto-temporal cortical regions in the representation and control of adverse symptoms, which interact reciprocally with subcortical structures involved in bodily homeostasis and responses to stress. Bidirectional autonomic and neuroendocrine pathways transmit information between the central nervous system and the periphery and facilitate the expression of affective, autonomic, hormonal, and immune responses. We propose that heart rate variability (HRV) and markers of inflammation are important currently available indices of central-peripheral integration and homeostasis within this homeostatic network. Finally, we review current neuroimaging and psychophysiological research from diverse areas of mind-body medicine that supports the framework as a basis for future research on the specific biobehavioral mechanisms of mind-body therapies.

Effects of sildenafil on autonomic nervous function during sleep in obstructive sleep apnea

OBJECTIVE

To evaluate the effects of sildenafil on the autonomic nervous system in patients with severe obstructive sleep apnea.

METHODS

Thirteen male patients with severe obstructive sleep apnea (mean age 43+/-10 years with a mean body mass index of 26.7+/-1.9 kg/m(2)) received a single 50-mg dose of sildenafil or a placebo at bedtime. All-night polysomnography and heart rate variability were recorded. Frequency domain analysis of heart rate variability was performed for the central five-minute sample of the longest uninterrupted interval of slow wave and rapid eye movement sleep, as well as for one-minute samples during apnea and during slow wave and rapid eye movement sleep after resumption of respiration.

RESULTS

Compared to the placebo, sildenafil was associated with an increase in the normalized high-frequency (HF(nu)) components and a decrease in the low/high-frequency components of the heart rate variability ratio (LF/HF) in slow wave sleep (p<0.01 for both). Differences in heart rate variability parameters between one-minute post-apnea and apnea samples (Delta = difference between resumption of respiration and apnea) were assessed. A trend toward a decreasing magnitude of DeltaLF activity was observed during rapid eye movement sleep with sildenafil in comparison to placebo (p=0.046). Additionally, DeltaLF/HF in SWS and rapid eye movement sleep was correlated with mean desaturation (s(R =) -0.72 and -0.51, respectively, p= 0.01 for both), and DeltaHF(nu) in rapid eye movement sleep was correlated with mean desaturation (s(R=) 0.66, p= 0.02) and the desaturation index (s(R=) 0.58, p = 0.047).

CONCLUSIONS

The decrease in arousal response to apnea/hypopnea events along with the increase in HF(nu) components and decrease in LH/HF components of the heart rate variability ratio during slow wave sleep suggest that, in addition to worsening sleep apnea, sildenafil has potentially immediate cardiac effects in patients with severe obstructive sleep apnea.

Associations between plasma homocysteine levels, aortic stiffness and wave reflection in patients with arterial hypertension, isolated office hypertension and normotensive controls

The aim of this study was to evaluate any possible association of homocysteine with arterial stiffness indices in patients with essential arterial hypertension (AH), isolated office hypertension (IOH) and normotensive controls. The final cohort comprised 231 normotensives (NTs, 119 males), 480 patients with IOH (196 males) and 1188 patients with essential AH (713 males). All patients were screened for plasma homocysteine levels and lipidaemic profile and underwent aortic compliance and wave reflection assessment by using carotid-femoral pulse wave velocity (PWVc-f) and aortic augmentation index corrected for heart rate (AIx) accordingly. In the total population, stepwise multiple linear regression analysis showed that homocysteine levels remained a significant determinant of PWV (beta (SE): 0.056 (0.007), P<0.001) and AIx (beta (SE): 0.236 (0.052), P<0.001) independently of the traditional factors affecting arterial stiffness and wave reflection. When the three groups were examined separately, homocysteine levels remained an independent determinant of PWFc-f in all groups (NT: beta (SE): 0.070 (0.022), P=0.002; IOH: beta (SE): 0.109 (0.015), P<0.001; AH: beta (SE): 0.040 (0.009), P<0.001). However, homocysteine levels remained an independent determinant of AIx only in the IOH and AH, but not in the NT group (IOH: beta (SE): 0.302 (0.124), P=0.015; AH: beta (SE): 0.183 (0.057), P=0.001; NT: beta (SE): 0.308 (0.240), P=0.200). This study points to an independent relationship between circulating homocysteine levels, aortic compliance and wave reflection.

Inhibition of nitric oxide synthase evokes central sympatho-excitation in healthy humans

Animal studies have indicated that nitric oxide is a key signalling molecule involved in the tonic restraint of central sympathetic outflow from the brainstem. Extension of these findings to humans has been difficult because systemic infusion of nitric oxide synthase (NOS) inhibitors increases blood pressure due to inhibition of endothelial NOS, resulting in activation of the arterial baroreflex and subsequent inhibition of central sympathetic outflow. To overcome this confounding inhibitory influence of the baroreflex, in the current study we directly measured skin sympathetic nerve activity (SNA), which is not under baroreceptor control. Healthy, normotensive humans were studied before, during a 60 min intravenous infusion of the NOS inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME; 4 mg kg(1)), and for 120 min following the infusion (i.e. 180 min total). Skin SNA and arterial blood pressure (BP) were continuously measured. BP was increased from baseline at the end of the l-NAME infusion (14 +/- 2 mmHg; P < 0.05) and remained significantly elevated for the remainder of the experiment (18 +/- 3 mmHg; P < 0.05). Similarly, systemic NOS inhibition produced time-dependent increases in skin SNA, such that skin SNA was elevated at the end of the l-NAME infusion (total activity, 200 +/- 22% baseline; P = 0.08) and was further increased at the end of the study protocol (total activity, 350 +/- 41% baseline; P < 0.05). Importantly, skin SNA remained unchanged during time and hypertensive (phenylephrine) control experiments. These findings indicate that pharmacological inhibition of NOS causes sympathetic activation and support a role of nitric oxide in central sympathetic control in humans.

Decreased heart rate variability is associated with higher levels of inflammation in middle-aged men

BACKGROUND

Many traditional risk factors for coronary artery disease (CAD) are associated with altered autonomic function. Inflammation may provide a link between risk factors, autonomic dysfunction, and CAD. We examined the association between heart rate variability (HRV), a measure of autonomic function, and inflammation, measured by C-reactive protein (CRP) and interleukin-6 (IL-6).

METHODS

We examined 264 middle-aged male twins free of symptomatic CAD. All underwent ambulatory electrocardiogram monitoring and 24-hour ultra low, very low, low, and high-frequency power were calculated using power spectral analysis. C-reactive protein and IL-6 were measured, and risk factors including age, smoking, hypertension, lipids, diabetes, body mass index (BMI), depression, and physical activity were assessed.

RESULTS

Physical activity, BMI, high-density lipoprotein cholesterol, smoking, depression, and hypertension were directly associated with CRP and IL-6 and inversely associated with one or more HRV variables. There was a graded inverse relationship between all HRV parameters (except high frequency) and CRP and IL-6. After adjustment for age, BMI, activity, high-density lipoprotein, smoking, hypertension, depression, and diabetes, ultra low frequency and very low frequency remained significant predictors of CRP (P < .01).

CONCLUSIONS

C-reactive protein is associated with decreased HRV, even after controlling for traditional CAD risk factors. Autonomic dysregulation leading to inflammation may represent one pathway through which traditional risk factors promote development of CAD.

Effects of glucagon-like peptide-1, yohimbine, and nitrergic modulation on sympathetic and parasympathetic activity in humans

Glucagon-like peptide-1 (GLP-1), an incretin, which is used to treat diabetes mellitus in humans, inhibited vagal activity and activated nitrergic pathways. In rats, GLP-1 also increased sympathetic activity, heart rate, and blood pressure (BP). However, the effects of GLP-1 on sympathetic activity in humans are unknown. Our aims were to assess the effects of a GLP-1 agonist with or without alpha(2)-adrenergic or -nitrergic blockade on autonomic nervous functions in humans. In this double-blind study, 48 healthy volunteers were randomized to GLP-1-(7-36) amide, the nitric oxide synthase (NOS) inhibitor N(G)-monomethyl-l-arginine acetate (l-NMMA), the alpha(2)-adrenergic antagonist yohimbine, or placebo (i.e., saline), alone or in combination. Hemodynamic parameters, plasma catecholamines, and cardiac sympathetic and parasympathetic modulation were measured by spectral analysis of heart rate. Thereafter, the effects of GLP-1-(7-36) amide on muscle sympathetic nerve activity (MSNA) were assessed by microneurography in seven subjects. GLP-1 increased (P = 0.02) MSNA but did not affect cardiac sympathetic or parasympathetic indices, as assessed by spectral analysis. Yohimbine increased plasma catecholamines and the low-frequency (LF) component of heart rate power spectrum, suggesting increased cardiac sympathetic activity. l-NMMA increased the BP and reduced the heart rate but did not affect the balance between sympathetic and parasympathetic activity. GLP-1 increases skeletal muscle sympathetic nerve activity but does not appear to affect cardiac sympathetic or parasympathetic activity in humans.