The Role of Heart Rate Variability (HRV) in Different Hypertensive Syndromes.

Cardiac innervation by the parasympathetic nervous system (PNS) and the sympathetic nervous system (SNS) modulates the heart rate (HR) (chronotropic activity) and the contraction of the cardiac muscle (inotropic activity). The peripheral vasculature is controlled only by the SNS, which is responsible for peripheral vascular resistance. This also mediates the baroreceptor reflex (BR), which in turn mediates blood pressure (BP). Hypertension (HTN) and the autonomic nervous system (ANS) are closely related, such that derangements can lead to vasomotor impairments and several comorbidities, including obesity, hypertension, resistant hypertension, and chronic kidney disease. Autonomic dysfunction is also associated with functional and structural changes in target organs (heart, brain, kidneys, and blood vessels), increasing cardiovascular risk. Heart rate variability (HRV) is a method of assessing cardiac autonomic modulation. This tool has been used for clinical evaluation and to address the effect of therapeutic interventions. The present review aims (a) to approach the heart rate (HR) as a CV risk factor in hypertensive patients; (b) to analyze the heart rate variability (HRV) as a "tool" to estimate the individual risk stratum for Pre-HTN (P-HTN), Controlled-HTN (C-HTN), Resistant and Refractory HTN (R-HTN and Rf-HTN, respectively), and hypertensive patients with chronic renal disease (HTN+CKD).

Neuromodulação Vagal Auricular e sua Aplicabilidade em Pacientes com Insuficiência Cardíaca e Fração de Ejeção Reduzida / Auricular Vagal Neuromodulation and its Application in Patients with Heart Failure and Reduced Ejection Fraction

Resumo Fundamento O desequilíbrio do sistema nervoso autônomo (SNA) na insuficiência cardíaca (IC) cria um ciclo vicioso, o excesso de atividade simpática e a diminuição da atividade vagal contribuindo para a piora da IC. A estimulação elétrica transcutânea de baixa intensidade do ramo auricular do nervo vago (taVNS) é bem tolerada e abre novas possibilidades terapêuticas. Objetivos Gerar hipótese da aplicabilidade e benefício da taVNS na IC através da comparação intergrupos de parâmetros ecocardiográficos, teste de caminhada de 6 min, variabilidade da frequência cardíaca pelo Holter (SDNN e rMSSD), questionário de qualidade de vida de Minnesota e classe funcional pela New York Heart Association. Métodos Estudo clínico prospectivo, duplo cego, randomizado com metodologia sham, unicêntrico. Avaliados 43 pacientes e alocados em 2 grupos: o Grupo 1 recebeu taVNS (frequências 2/15 Hz) e Grupo 2 recebeu sham. Nas comparações, valores de p<0,05 foram considerados significativos. Resultados Na fase pós-intervenção, observou-se que o Grupo 1 se manteve com melhor rMSSD (31 x 21; p = 0,046) e atingiu melhor SDNN (110 vs. 84, p = 0,033). Ao compararmos os parâmetros intragrupos, antes e após intervenção, observou-se que todos melhoraram significativamente no grupo 1 e não houve diferenças no grupo 2. Conclusão A taVNS é uma intervenção segura, de fácil execução e que sugere provável benefício na IC pela melhora na variabilidade da frequência cardíaca, o que indica melhor equilíbrio autonômico. Novos estudos com maior número de pacientes são necessários para responder às questões levantadas por esse estudo.

Abstract Background The autonomic nervous system (ANS) imbalance in heart failure (HF) creates a vicious cycle, excess sympathetic activity, and decreased vagal activity contributing to the worsening of HF. Low-intensity transcutaneous electrical stimulation of the auricular branch of the vagus nerve (taVNS) is well tolerated and opens new therapeutic possibilities. Objectives To hypothesize the applicability and benefit of taVNS in HF through intergroup comparison of echocardiography parameters, 6-minute walk test, Holter heart rate variability (SDNN and rMSSD), Minnesota quality of life questionnaire, and functional class by the New York Heart Association. In comparisons, p values <0.05 were considered significant. Methods Prospective, double-blind, randomized clinical study with sham methodology, unicentric. Forty-three patients were evaluated and divided into 2 groups: Group 1 received taVNS (frequencies 2/15 Hz), and Group 2 received sham. In comparisons, p values <0.05 were considered significant. Results In the post-intervention phase, it was observed that Group 1 had better rMSSD (31 x 21; p = 0.046) and achieved better SDNN (110 vs. 84, p = 0.033). When comparing intragroup parameters before and after the intervention, it was observed that all of them improved significantly in group 1, and there were no differences in group 2. Conclusion taVNS is a safe to perform and easy intervention and suggests a probable benefit in HF by improving heart rate variability, which indicates better autonomic balance. New studies with more patients are needed to answer the questions raised by this study.

Comparison of the autonomic nervous system dysfunction between different chronic spine disorders: neck pain versus low back pain

SUMMARY OBJECTIVE: This study aims to compare heart rate variability (HRV) between patients with chronic neck pain and patients with chronic low back pain and to correlate the chronic pain variables with heart rate variability indices. METHODS: This is a cross-sectional study. We divided the sample into two groups: neck pain (n=30) and low back pain (n=30). We used the Numeric Pain Rating Scale, Neck Disability Index, Roland-Morris Disability Questionnaire, Pain-Related Catastrophizing Thoughts Scale, Tampa Scale of Kinesiophobia, and Pain Self-Efficacy Questionnaire. For heart rate variability analysis, we used the following indices: mean RR, standard deviation of all RR intervals, mean heart rate, root mean square differences of successive RR intervals, triangular index, triangular interpolation of the interval histogram, low-frequency band in arbitrary units and in absolute values, high-frequency band in arbitrary units and in absolute values, standard deviation of the instantaneous beat-to-beat variability (standard deviation 1), long-term standard deviation of continuous RR intervals (standard deviation 2), and Stress Index. We used Student's t-test for comparisons and Spearman's coefficient for correlations. RESULTS: We observe insignificant values in the differences between the groups. Disability and self-efficacy were correlated with heart rate variability only in patients with chronic neck pain, whereas catastrophizing and kinesiophobia showed greater correlations with heart rate variability in patients with chronic low back pain. CONCLUSIONS: Autonomic dysfunction of individuals with chronic neck pain, when compared to patients with chronic low back pain, does present insignificant differences.

Bitter Orange (Citrus aurantium L.) Intake Before Submaximal Aerobic Exercise Is Safe for Cardiovascular and Autonomic Systems in Healthy Males: A Randomized Trial.

Background: There are still no studies of the cardiovascular safety of the isolated use of Citrus aurantium in aerobic submaximal exercise. Objective: To evaluate the effect of C. aurantium supplementation on the recovery of cardiorespiratory and autonomic parameters following a session of submaximal aerobic exercise. Methods: Twelve healthy male adults achieved a crossover, randomized, double-blind, and placebo-controlled trial. C. aurantium (600 mg, p-synephrine at 30% amount [180 mg]) or placebo (600 mg of starch) were ingested 90 min before evaluation in randomized days. We evaluated systolic blood pressure (SBP), diastolic blood pressure (DBP), pulse pressure (PP), mean arterial pressure (MAP), heart rate (HR) and, HR variability indexes at Rest and during 60 min of recovery from exercise. Results: Citrus aurantium ingestion accelerated the reduction in SBP after exercise, anticipated the return of vagal modulation of the heart after exercise via the HF (ms2), pNN50 (%), and 2 UV% indices. Moreover, rushed the output of sympathetic modulation after exercise via the 0V% index. No unfavorable cardiovascular effects were achieved for HR, DBP, PP, and MAP parameters. Conclusions: Citrus aurantium was shown to be safe for the cardiovascular and autonomic systems alongside submaximal aerobic exercise in healthy males.

Individually guided training prescription by heart rate variability and self-reported measure of stress tolerance in recreational runners: Effects on endurance performance.

The aim of this study was to determine the effect of endurance training individually guided by objective (Heart Rate Variability-HRV) or self-report measure of stress (DALDA-questionnaire) in comparison to predefined endurance training prescription for improving endurance performance in recreational runners. After a 2-week preliminary baseline period to establish resting HRV and self-reported measure of stress, thirty-six male recreational runners were randomly assigned to HRV-guided (GHRV; n = 12), DALDA-guided (GD; n = 12) or predefined training (GT; n = 12) prescription groups. Before and after 5-weeks of endurance training, participants performed a track field peak velocity (Vpeak_TF), time limit (Tlim) at 100% of Vpeak_TF and 5 km time-trial (5 km TT) tests. GD lead to higher improvements in Vpeak_TF (8.4 ± 1.8%; ES = 1.41) and 5 km TT (-12.8 ± 4.2%; ES = -1.97), than GHRV (6.6 ± 1.5% and -8.3 ± 2.8%; ES = -1.20; 1.24) and GT (4.9 ± 1.5% and -6.0 ± 3.3%; ES = -0.82; 0.68), respectively, with no differences for Tlim. Self-report measures of stress may be used to individualize endurance training prescription on a daily basis leading to better performance enhancement, which may be used with HRV for a holistic understanding of daily training-induce adaptations.

Benefits of pharmacological and electrical cholinergic stimulation in hypertension and heart failure.

Systemic arterial hypertension and heart failure are cardiovascular diseases that affect millions of individuals worldwide. They are characterized by a change in the autonomic nervous system balance, highlighted by an increase in sympathetic activity associated with a decrease in parasympathetic activity. Most therapeutic approaches seek to treat these diseases by medications that attenuate sympathetic activity. However, there is a growing number of studies demonstrating that the improvement of parasympathetic function, by means of pharmacological or electrical stimulation, can be an effective tool for the treatment of these cardiovascular diseases. Therefore, this review aims to describe the advances reported by experimental and clinical studies that addressed the potential of cholinergic stimulation to prevent autonomic and cardiovascular imbalance in hypertension and heart failure. Overall, the published data reviewed demonstrate that the use of central or peripheral acetylcholinesterase inhibitors is efficient to improve the autonomic imbalance and hemodynamic changes observed in heart failure and hypertension. Of note, the baroreflex and the vagus nerve activation have been shown to be safe and effective approaches to be used as an alternative treatment for these cardiovascular diseases. In conclusion, pharmacological and electrical stimulation of the parasympathetic nervous system has the potential to be used as a therapeutic tool for the treatment of hypertension and heart failure, deserving to be more explored in the clinical setting.

Baroreflex Modulation During Acute High-Altitude Exposure in Rats.

Baroreflex (BR) control is critically dependent of sympathetic and parasympathetic modulation. It has been documented that during acute hypobaric hypoxia there is a BR control impairment, however, the effect of a natural hypoxic environment on BR function is limited and controversial. Therefore, the aim of this study was to determine the effect of acute High-Altitude exposure on sympathetic/parasympathetic modulation of BR control in normal rats. Male Sprague Dawley rats were randomly allocated into Sea-Level (n = 7) and High-Altitude (n = 5) (3,270 m above sea level) groups. The BR control was studied using phenylephrine (Phe) and sodium nitroprusside (SNP) through sigmoidal analysis. The autonomic control of the heart was estimated using heart rate variability (HRV) analysis in frequency domain. Additionally, to determine the maximum sympathetic and parasympathetic activation of BR, spectral non-stationary method analysis, during Phe (0.05 µg/mL) and SNP administration (0.10 µg/mL) were used. Compared to Sea-Level condition, the High-Altitude group displayed parasympathetic withdrawal (high frequency, 0.6-2.4 Hz) and sympathoexcitation (low frequency, 0.04-0.6 Hz). Regarding to BR modulation, rats showed a significant decrease (p < 0.05) of curvature and parasympathetic bradycardic responses to Phe, without significant differences in sympathetic tachycardic responses to SNP after High-Altitude exposure. In addition, the non-stationary analysis of HRV showed a reduction of parasympathetic activation (Phe) in the High-Altitude group. Our results suggest that acute exposure to High-Altitude produces an autonomic and BR control impairment, characterized by parasympathetic withdrawal after 24 h of high-altitude exposure.

Heart rate variability: are you using it properly? Standardisation checklist of procedures.

BACKGROUND: Heart rate variability is used as an assessment method for cardiac autonomic modulation. Since the Task Force's publication on heart rate variability in 1996, the European Heart Rhythm Association Position Paper in 2015 and a recent publication in 2017, attention has been paid to recommendations on using heart rate variability analysis methods, as well as their applications in different physiological conditions and clinical studies. This analysis has proved to be useful as a complementary tool for clinical evaluation and to assess the effect of non-pharmacological therapeutic interventions, such as physical exercise programmes, on cardiac autonomic modulation. OBJECTIVE: The aim of this article is to make recommendations and to develop a checklist of normalisation procedures regarding the use of heart rate variability data collection and analysis methodology, focusing on the cardiology area and cardiac rehabilitation. METHODS: Based on previous heart rate variability publications, this paper provides a description of the most common shortcomings of using the analysis methods and considers recommendations and suggestions on how to minimise these occurrences by using a specific checklist. CONCLUSIONS: This article includes recommendations and a checklist regarding the use of heart rate variability collection and analysis methods. This work could help improve reporting on clinical evaluation and therapeutic intervention results and consequently, disseminate heart rate variability knowledge.

Anterior subdiaphragmatic vagotomy decreases the IgA antibody response in the small intestines of BALB/c mice.

To assess the impact of vagotomy on the IgA-response, male BALB/c mice underwent anterior vagotomy or a sham procedure were sacrificed on day 14 post-operation and the proximal and distal small-gut segments were dissected. In intestinal lavages IgA/IgM antibodies were analysed by ELISA; in Peyer's-patches and lamina-propria cell suspensions the intracellular IgA-associated interleukins (ILs) and pro-inflammatory cytokines in CD4+ T cells were analysed by cytofluorometry. Vagotomy reduced the IgA or increased the IgM antibody concentration in both segments and reduced or increased the lamina- propria CD4+ T cell pro-inflammatory cytokine responses in the distal or proximal segments, respectively. Data show the role of the vagus nerve on the IgA response.

Introduction of Application of Gini Coefficient to Heart Rate Variability Spectrum for Mental Stress Evaluation / Introdução da Aplicação do Coeficiente de Gini ao Espectro de Variabilidade da Frequência Cardíaca para Avaliação do Estresse Mental

Abstract Background: The Gini coefficient is a statistical tool generally used by economists to quantify income inequality. However, it can be applied to any kind of data with unequal distribution, including heart rate variability (HRV). Objectives: To assess the application of the Gini coefficient to measure inequality in power spectral density of RR intervals, and to use this application as a psychophysiological indicator of mental stress. Methods: Thirteen healthy subjects (19 ± 1.5 years) participated in this study, and their RR intervals were obtained by electrocardiogram during rest (five minutes) and during mental stress (arithmetic challenge; five minutes). These RR intervals were used to obtain the estimates of power spectral densities (PSD). The limits for the PSD bands were defined from 0.15 to 0.40 Hz for high frequency band (HF), from 0.04 to 0.15 Hz for low frequency band (LF), from 0.04 to 0.085 Hz for first low frequency sub-band (LF1) and from 0.085 to 0.15 Hz for second low frequency sub-band (LF2). The spectral Gini coefficient (SpG) was proposed to measure the inequality in the power distribution of the RR intervals in each of above-mentioned HRV bands. SpG from each band was compared with its respective traditional index of HRV during the conditions of rest and mental stress. All the differences were considered statistically significant for p < 0.05. Results: There was a significant decrease in HF power (p = 0.046), as well as significant increases in heart rate (p = 0.004), LF power (p = 0.033), LF2 power (p = 0.019) and LF/HF (p = 0.002) during mental stress. There was also a significant increase in SpG(LF) (p = 0.009) and SpG(LF2) (p = 0.033) during mental stress. Coefficient of variation showed SpG has more homogeneity compared to the traditional index of HRV during mental stress. Conclusions: This pilot study suggested that spectral inequality of Heart Rate Variability analyzed using the Gini coefficient seems to be an independent and homogeneous psychophysiological indicator of mental stress. Also, HR, LF/HF, SpG(LF) of HRV are possibly important, reliable and valid indicators of mental stress.

Resumo Fundamento: O coeficiente de Gini é um instrumento estatístico geralmente usado por economistas para quantificar a desigualdade de renda. No entanto, ele pode ser aplicado a qualquer tipo de dados com distribuição desigual, incluindo a variabilidade da frequência cardíaca (VFC). Objetivos: Avaliar a aplicação do coeficiente de Gini para medir a desigualdade na densidade espectral de potência de intervalos RR, e usar esta aplicação como um indicador psicofisiológico do estresse mental. Métodos: Treze indivíduos saudáveis (19 ± 1,5 anos) participaram deste estudo, e seus intervalos RR foram obtidos por eletrocardiograma durante repouso (cinco minutos) e durante estresse mental (desafio aritmético; cinco minutos). Esses intervalos RR foram utilizados para obter as estimativas de densidades espectrais de potência (PSD). Os limites para as bandas PSD foram definidos de 0,15 a 0,40 Hz para banda de alta frequência (HF), de 0,04 a 0,15 Hz para banda de baixa frequência (LF), de 0,04 a 0,085 Hz para a primeira sub-banda de baixa frequência (LF1) e de 0,085 a 0,15 Hz para a segunda sub-banda de baixa frequência (LF2). O coeficiente de Gini espectral (SpG) foi proposto para medir a desigualdade na distribuição de potência dos intervalos RR em cada uma das bandas de VFC mencionadas acima. O SpG de cada banda foi comparado com seu respectivo índice tradicional de VFC durante as condições de repouso e de estresse mental. Todas as diferenças foram consideradas estatisticamente significativas para p < 0,05. Resultados: Houve uma diminuição significativa no poder de FC (p=0,046), bem como aumentos significativos na frequência cardíaca (p = 0,004), potência da LF (p = 0,033), potência da LF2 (p = 0,019) e LF/HF (p = 0,002) durante estresse mental. Houve também um aumento significativo de SpG(LF) (p = 0,009) e SpG(LF2) (p = 0,033) durante estresse mental. O coeficiente de variação mostrou que o SpG tem mais homogeneidade em comparação com o índice tradicional de VFC durante o estresse mental. Conclusões: Este estudo piloto sugeriu que a desigualdade espectral da VFC analisada pelo coeficiente de Gini parece ser um indicador psicofisiológico independente e homogêneo de estresse mental. Além disso, FC, LF/HF, SpG(LF) da VFC são possivelmente indicadores importantes, confiáveis e válidos de estresse mental.

Posterior Subdiaphragmatic Vagotomy Downmodulates the IgA Levels in the Small Intestine of BALB/c Mice.

OBJECTIVE: The posterior vagus nerve trunk innervates the entire small intestine, and elucidating its modulatory role in the IgA response was the aim of this study. METHODS: Two groups of six male BALB/c mice underwent sham or posterior subdiaphragmatic vagotomy and were euthanized on the 14th postoperative day; then, the small intestines were dissected. The intestinal fluid was harvested for antibody analysis by ELISA, and cell suspensions from Peyer's patches and lamina propria were prepared for cytofluorometric analysis of plasma cells and T lymphocytes. The CD4+ T cells were labeled for the intracellular IgA-producing interleukins (ILs)-4, -5, -6, and -10; transforming growth factor (TGF)-ß; and the inflammatory cytokines tumor necrosis factor (TNF)-α, interferon (IFN)-γ, and IL-12. In the intestinal tissue samples, myeloperoxidase (MPO) visualization and the enzymatic activity were assessed by immunohistochemistry and ELISA, respectively. The data were analyzed by Student's t test, and the differences were considered significant at p < 0.05. RESULTS: In the vagotomy group, the IgA levels and the CD4+ T cells labeled with mediators that promote IgA secretion, including IL-4 (only at lamina propria), TNF-α, and IFN-γ, were decreased, whereas the lamina propria IgA+ plasma cells and MPO presence/activity were increased; changes in the IgM levels, IgM+ plasma cells, and CD4+ T cells labeled with TGF-ß, which have a role in class switch recombination, were not observed. CONCLUSION: The downmodulating impact of vagotomy on IgA levels may result from defective IgA secretion without affecting class switch recombination, whereas vagotomy evoked a proinflammatory response regarding MPO. These findings may reflect the role of the vagus nerve on the control of the IgA response in the small intestine.

Ischemic preconditioning boosts post-exercise but not resting cardiac vagal control in endurance runners.

PURPOSE: High cardiac vagal control in endurance athletes has been generally associated with adequate recovery from training and readiness to cope high-intensity training. A method that improves cardiac vagal control in endurance athletes could therefore be advantageous. Accordingly, we sought to test whether ischemic preconditioning (IPC) could enhance cardiac vagal control in endurance runners. METHODS: Fifteen subjects underwent IPC, sham ultrasound (SHAM) or control (CT), in random order. Subjects were informed both IPC and SHAM would be beneficial vs. CT (i.e., similar placebo induction), and IPC would be harmless despite ischemia sensations (i.e., nocebo avoidance). Resting cardiac vagal control was assessed via respiratory sinus arrhythmia (RSA) and heart rate variability (HRV) indexes. Post-exercise cardiac vagal control was assessed via heart rate recovery [HR time constant decay (T30) and absolute HR decay (HRR30s)] during 30-s breaks of a discontinuous incremental test. Capillary blood samples were collected for lactate threshold identification. RESULTS: RSA and HRV were similar among interventions at pre- and post-intervention assessments. Lactate threshold occurred at 85 ± 4% of maximal effort. T30 was similar among interventions, but IPC increased HRR30s at 70% and 75% of maximal effort vs. SHAM and CT (70%: IPC = 31 ± 2 vs. SHAM = 26 ± 3 vs. CT = 26 ± 2 bpm, mean ± SEM, P < 0.01; 75%: IPC = 29 ± 2 vs. SHAM = 25 ± 2 vs. CT = 24 ± 2 bpm, P < 0.01). CONCLUSION: IPC did not change resting cardiac vagal control, but boosted fast post-exercise cardiac vagal reactivation at exercise intensities below lactate threshold in endurance runners.

Is a short-stage protocol during an incremental exercise test reliable for heart rate variability threshold analysis?

Aim: Heart rate variability threshold (HRVT) is a valid method to determine parasympathetic depression during an incremental exercise test (IET). However, HRVT is usually assessed using the last 60s of each 180s stage of an IET, resulting in longer and demotivating tests. This study aimed to evaluate the agreement of HRVT analysis adopting the first and second minute of R-R interval (iRR) segment comparatively to a standard third-minute segment obtained at each 3-min stage on IET. Methods: Seventeen young male subjects (22.2 ± 3.1 years; 23.4 ± 2.3 kg/m2) underwent IET on a cycle ergometer. HRVT was considered the load corresponding to the point of stabilization of the SD1 index (HRVTV), or the first load with SD1 value < 3ms (HRVT<3), both assessed by the 1st (HRVT1V, HRVT1<3), 2nd (HRVT2V, HRVT2<3) and standard 3rd (HRVT3V, HRVT3<3) 60s iRR segment analyzed at each stage of IET. Agreement and reliability were assessed by the Bland-Altman analysis and the intraclass correlation coefficient (ICC), respectively. Results: High reliability and non-significant bias were observed considering HRVT1V vs HRVT3V (ICC = 0.92; p = 0.18) or HRVT2V vs HRVT3V (ICC = 0.94; p = 0.99). However, lower reliability was observed for HRVT1<3 vs HRVT3<3 (ICC = 0.79; p = 0.75) and for HRVT2<3 vs HRVT3<3 (ICC = 0.91; p = 0.33). Conclusion: HRVT can be similarly assessed by the 1st, 2nd or 3rd 60 seconds iRR segment, mainly when assessed by a visual method.(AU)

Impact of heart rate on reproducibility of heart rate variability analysis in the supine and standing positions in healthy men

OBJECTIVE: The reliability of heart rate variability (HRV) analysis is not yet fully understood, especially considering different body positions and the mathematical influence of heart rate. The aim of this study was to evaluate the reliability of HRV in supine and standing positions, with and without mathematical adjustment of HRV by the average R-R interval (iRR). METHODS: We evaluated 37 young males (23.1±4 years; 25.1±3 kg/m2). A 5-min segment of the iRR was collected in the supine and standing positions on three occasions separated by 48-hour intervals. Absolute and relative reliability of temporal and spectral indices were assessed by the coefficient of variation (CV) and the intraclass correlation coefficient (ICC), respectively. RESULTS: We did not observe differences in HRV indices in the three occasions in the supine or standing position (p>0.05). Moderate to good reproducibility was observed for temporal and spectral indices of HRV in the supine position (ICC: 0.65-0.89; CV: 0.9-19.8). In the orthostatic position, low to good reproducibility was observed (ICC: 0.35-0.89; CV: 1.1-34.8), with higher ICCs for temporal indices. After mathematical adjustment, only a small modification in HRV reliability was observed in both positions. CONCLUSIONS: In young adult males, the mathematical adjustment of HRV by the average iRR led to a nonsignificant effect on HRV reliability. Additionally, HRV reliability is dependent on body position and the index analyzed. Promising measures in both supine and standing positions include r-MSSD and the HF band (parasympathetic indices).

Effects of Transcutaneous Electrical Nerve Stimulation in Autonomic Nervous System of Hypertensive Patients: A Randomized Controlled Trial.

BACKGROUND: Patients with hypertension have altered autonomic nervous system function, which are increased sympathetic activity. Transcutaneous Electrical Nerve Stimulation (TENS) is a useful modality for pain control and has also been shown to be effective in the reduction of sympathetic activity in healthy subjects and individuals with cardiovascular diseases. OBJECTIVE: The aim of this study was to verify the effects of transcutaneous electrical nerve stimulation by the evaluation of heart rate variability (HRV) in patients with essential hypertension. METHOD: Twenty-eight patients received an application of low-frequency TENS(4 Hz) n=8, highfrequency TENS (100 Hz) n=10 or placebo TENS n=10 in paravertebral ganglionar region during thirty minutes. RESULTS: After 4 Hz TENS, there was a decrease in the low-frequency (LFn.u.) component (57.71±9.46 vs 45.58±13.51, p<0.026) and an increase in the high-frequency (HFn.u.) component (33.03±13.83 vs 45.83±20.19, p <0.05) of HRV. After 100 Hz TENS and placebo, there were no changes in the LF and HF components. No significant differences were found in systolic blood pressure with low-frequency TENS (129.37± 15.48 vs 126.69 ± 15.21, p<0.490). There was an increase, although not significant, with high-frequency TENS (131.00 ± 15.97 vs 138.75 ± 25.79, p<0.121) and placebo (133.80 ± 29.85 vs 134.80 ± 29.72, p< 0.800). No differences were found in the diastolic blood pressure with low-frequency TENS and placebo, but there was a significant increase in high-frequency TENS (81.00 ± 11.78 vs 85.65 ± 13.68, p< 0.018). CONCLUSION: Low-frequency TENS decreases sympathetic nervous system activity and increases parasympathetic nervous system activity and high-frequency TENS increases diastolic blood pressure, when applied on the paravertebral ganglionar region in the hypertensive patients.

Effects of spinal manipulation and myofascial techniques on heart rate variability: A systematic review.

BACKGROUND: The analysis of heart rate variability is important to the investigation of stimuli from the autonomic nervous system. Osteopathy is a form of treatment that can influence this system in healthy individuals as well as those with a disorder or disease. OBJECTIVES: The aim of the present study was to perform a systematic review of the literature regarding the effect of spinal manipulation and myofascial techniques on heart rate variability. METHODS: Searches were performed of the Pubmed, Scielo, Lilacs, PEDro, Ibesco, Cochrane and Scopus databases for relevant studies. The PEDro scale was used to assess the methodological quality of each study selected. RESULTS: A total of 505 articles were retrieved during the initial search. After an analysis of the abstracts, nine studies were selected for the present review. CONCLUSION: Based on the findings, osteopathy exerts an influence on the autonomic nervous system depending on the stimulation site and type. A greater parasympathetic response was found when stimulation was performed in the cervical and lumbar regions, whereas a greater sympathetic response was found when stimulation was performed in the thoracic region.

Cholinesterase inhibition reduces arrhythmias in asymptomatic Chagas disease.

INTRODUCTION: Parasympathetic dysfunction may play a role in the genesis of arrhythmias in Chagas disease. AIM: This study evaluates the acute effects of pyridostigmine (PYR), a reversible cholinesterase inhibitor, on the occurrence of arrhythmias in patients with Chagas cardiac disease. METHOD: Following a double-blind, randomized, placebo-controlled, cross-over protocol, 17 patients (age 50±2 years) with Chagas cardiac disease type B underwent 24-hour Holter recordings after oral administration of either pyridostigmine bromide (45 mg, 3 times/day) or placebo (PLA). RESULTS: Pyridostigmine reduced the 24-hours incidence (median [25%-75%]) of premature ventricular beats-PLA: 2998 (1920-4870), PYR: 2359 (940-3253), P=.044; ventricular couplets-PLA: 84 (15-159), PYR: 33 (6-94), P=.046. Although the total number of nonsustained ventricular tachycardia in the entire group was not different (P=.19) between PLA (1 [0-8]) and PYR (0 [0-4]), there were fewer episodes under PYR in 72% of the patients presenting this type of arrhythmia (P=.033). CONCLUSION: Acute administration of pyridostigmine reduced the incidence of nonsustained ventricular arrhythmias in patients with Chagas cardiac disease. Further studies that address the use of pyridostigmine by patients with Chagas cardiac disease under a more prolonged follow-up are warranted.

EFEITO DE DIFERENTES PROTOCOLOS DE RECUPERAÇÃO SOBRE A FUNÇÃO AUTONÔMICA CARDÍACA / EFFECT OF DIFFERENT RECOVERY PROTOCOLS ON THE CARDIAC AUTONOMIC FUNCTION / EFECTO DE DIFERENTES PROTOCOLOS DE RECUPERACIÓN SOBRE LA FUNCIÓN AUTONÓMICA CARDIACA

RESUMO Introdução: A avaliação da função autonômica cardíaca (FAC) após o teste de esforço (TE) é considerada um preditor poderoso e independente de risco cardiovascular. É escasso o conhecimento da influência de diferentes protocolos de recuperação sobre a FAC após TE em esteira rolante com os voluntários na posição ortostática. Objetivo: Comparar a reativação vagal e o grau de modulação global da FAC em dois diferentes protocolos de recuperação, passiva (RP) e ativa (RA), imediatamente após TE submáximo em esteira rolante. Métodos: Foram avaliados 24 homens fisicamente ativos com idade (média ± DP) de 27,2 ± 4,4 anos e IMC 24,8 ± 1,8 kg/m2. A ordem dos protocolos de recuperação foi definida de forma aleatória. Os testes foram realizados com intervalo de sete dias. Ambas as recuperações foram realizadas na posição ortostática durante cinco minutos, imediatamente após TE. Os índices temporais da variabilidade da frequência cardíaca foram utilizados para avaliar a reativação vagal e o grau de modulação global de FAC, rMSSD e SDNN, respectivamente, na RP e RA. Após análise da distribuição dos dados, utilizaram-se os testes de Mann-Whitney e de Friedman com post-hoc de Dum, no nível de significância de p ≤ 0,05. Resultados: Verificou-se maior reativação vagal no primeiro minuto de recuperação na RP comparativamente a RA [4,1 (4,9-3,4) ms vs. 3,4 (4,0-2,9) ms, p = 0,03] e maior grau de modulação global da FAC do terceiro ao quinto minuto e tendência a diferença significativa no segundo minuto de RP comparativamente a RA (p = 0,09-0,005). Conclusão: Os achados demonstram que o mínimo esforço físico, como caminhar lentamente sobre a esteira rolante, diminuiu a reativação vagal e o grau de modulação global da FAC após o TE submáximo em homens fisicamente ativos.

ABSTRACT Introduction: The evaluation of cardiac autonomic function (CAF) after stress test (ST) is considered a powerful and independent predictor of cardiovascular risk. The knowledge about the influence of different recovery protocols on CAF after ST on treadmill with volunteers in standing position is scarce. Objective: To compare the vagal reactivation and the degree of global CAF modulation in two different recovery protocols, passive (PR) vs. active (AR) immediately after submaximal ST in treadmill. Methods: We evaluated 24 physically active males, aged (mean ± SD) 27.2 ± 4.4 years and BMI 24.8 ± 1.8 kg/m2. The order of the recovery protocol was set at random. The tests were performed in 7-day intervals. Both recovery protocols were performed in standing position for 5 minutes, immediately after ST. The time indices of heart rate variability were used to assess the vagal reactivation and the overall degree of CAF, rMSSD, and SDNN, respectively, in PR and AR. After analysis of the data distribution, the Mann-Whitney and Friedman tests with Dum post-hoc were used at a significance level of p ≤ 0.05. Results: We observed a higher vagal reactivation at first minute of the PR compared to AR [4.1 (4.9-3.4) ms vs. 3.4 (4.0-2.9) ms, p = 0.03], and a higher degree of global CAF modulation from the third to the fifth minute and a tendency to significant difference in the second minute of PR compared to AR (p = 0.09−0.005). Conclusion: The findings demonstrate that minimum physical effort, such as walking slowly on a treadmill, decreased the vagal reactivation and the overall modulation degree of CAF after a submaximal ST in physically active men.

RESUMEN Introducción: La evaluación de la función autonómica cardíaca (FAC) después de la prueba de esfuerzo (PE) se considera un predictor potente e independiente del riesgo cardiovascular. Es escaso el conocimiento de la influencia de los diferentes protocolos de recuperación sobre la FAC después de la PE en la cinta rodante con voluntarios en la posición de pie. Objetivo: Comparar la reactivación vagal y el grado de la modulación general de la FAC en dos diferentes protocolos de recuperación, pasiva (RP) vs. activa (RA) inmediatamente después de la PE submáxima en la cinta rodante. Métodos: Se evaluaron 24 hombres físicamente activos con edades (promedio ± DE) de 27,2 ± 4,4 años y IMC de 24,8 ± 1,8 kg/m2. El orden de los protocolos de recuperación se definió al azar. Las pruebas se realizaron en un intervalo de siete días. Ambas recuperaciones se realizaron en la posición de pie durante cinco minutos inmediatamente después de la PE. Los índices temporales de la variabilidad de la frecuencia cardiaca fueron utilizados para evaluar la reactivación vagal y el grado de modulación general de la FAC, rMSSD y SDNN, respectivamente, en RP y RA. Después del análisis de la distribución de los datos, se utilizaron la prueba de Mann-Whitney y la de Friedman con post-hoc de Dum, a un nivel de significación de p ≤ 0,05. Resultados: Se observó una mayor reactivación vagal en el primer minuto de la PR comparada a la RA [4,1 (4,9-3,4) ms vs. 3,4 (4,0-2,9) ms, p = 0,03] y un mayor grado de modulación general de la FAC del tercer al quinto minuto y una tendencia a la diferencia estadística en el segundo minuto de RP comparada a RA (p = 0,09-0,005). Conclusión: Los resultados muestran que el esfuerzo físico mínimo, como caminar lentamente sobre la cinta rodante, disminuyó la reactivación vagal y el grado de modulación general de la FAC después de la PE submáxima en hombres físicamente activos.

Interaction between the hypothalamus and the immune system.

NEW FINDINGS: What is the topic of this review? Both branches of the autonomic nervous system are involved in the regulation of the inflammatory response. We explore how the hypothalamus may influence this process. What advances does it highlight? We analyse how a lipopolysaccharide signal is transmitted to the brain and which areas participate in the response of the brain to lipopolysaccharide. Recent studies show that the hypothalamus can influence the inflammatory response by modifying the autonomic output. The biological clock, the suprachiasmatic nucleus, is integrated into this circuit, putting a time stamp on the intensity of the inflammatory response. The brain is responsible for maintaining homeostasis of the organism, constantly adjusting its output via hormones and the autonomic nervous system to reach an optimal setting in every compartment of the body. Also, the immune system is under strong control of the brain. Apart from the conventional systemic responses evoked by the brain during inflammation, such as hypothalamic-pituitary-adrenal axis activation and the induction of sickness behaviour, the autonomic nervous system is now recognized to exert regulatory effects on the inflammatory response. Both branches of the autonomic nervous system are proposed to influence the inflammatory process. Here, we focus on those areas of the brain that might be involved in sensing inflammatory stimuli, followed by how that sensing could change the output of the autonomic nervous system in order to regulate the inflammatory response. Finally, we will discuss how the defenses of the body against a lipopolysaccharide challenge are organized by the hypothalamus.