Heart rate variability as a biomarker in patients with Chronic Chagas Cardiomyopathy with or without concomitant digestive involvement and its relationship with the Rassi score.

BACKGROUND: Dysautonomia plays an ancillary role in the pathogenesis of Chronic Chagas Cardiomyopathy (CCC), but is the key factor causing digestive organic involvement. We investigated the ability of heart rate variability (HRV) for death risk stratification in CCC and compared alterations of HRV in patients with isolated CCC and in those with the mixed form (CCC + digestive involvement). Thirty-one patients with CCC were classified into three risk groups (low, intermediate and high) according to their Rassi score. A single-lead ECG was recorded for a period of 10-20 min, RR series were generated and 31 HRV indices were calculated. The HRV was compared among the three risk groups and regarding the associated digestive involvement. Four machine learning models were created to predict the risk class of patients. RESULTS: Phase entropy is decreased and the percentage of inflection points is increased in patients from the high-, compared to the low-risk group. Fourteen patients had the mixed form, showing decreased triangular interpolation of the RR histogram and absolute power at the low-frequency band. The best predictive risk model was obtained by the support vector machine algorithm (overall F1-score of 0.61). CONCLUSIONS: The mixed form of Chagas' disease showed a decrease in the slow HRV components. The worst prognosis in CCC is associated with increased heart rate fragmentation. The combination of HRV indices enhanced the accuracy of risk stratification. In patients with the mixed form of Chagas disease, a higher degree of sympathetic autonomic denervation may be associated with parasympathetic impairment.

Electrocardiographic changes in the acute hyperkalaemia produced by intragastric KCl load in rats.

NEW FINDINGS: What is the central question of this study? This study presents a new model for studying the rapid onset of severe, acute hyperkalaemia in rats with intact kidney function by administering an intragastric KCl load. What is the main finding and its importance? This new model of intragastric KCl load produces a reliable and reproducible model for studying the rapid onset of severe, acute hyperkalaemia in rats with intact kidney function. We report unprecedented rapid changes (30 min) in ECG, blood pressure and various arterial blood analyses with this new model, providing a solid foundation for future experiments in this field. ABSTRACT: A variety of animal models have been proposed to study hyperkalaemia, but most of them have meaningful limitations when the goal is to study the effect of potassium overload on healthy kidneys. In this study, we aimed to introduce a new approach for induction of hyperkalaemia in a reliable and reproducible animal model. We used intragastric administration of potassium chloride [KCl 2.3 M, 10 ml/(kg body weight)] to male Holtzman rats (300-350 g) to induce hyperkalaemia. The results showed that this potassium load can temporarily overwhelm the renal and extrarenal handling of this ion, causing an acute and severe hyperkalaemia that can be useful to study the effect of potassium imbalance in a variety of scenarios. Severe hyperkalaemia (>8 meqiv/l) and very profound ECG alterations, characterized by lengthening waves and intervals, were seen as early as 30 min after intragastric administration of KCl in rats. In addition, a transient increase in arterial blood pressure and time-dependent bradycardia were also seen after the KCl administration. No metabolic acidosis was present in the animals, and the potassium ion did not increase proportionally to chloride ion in the blood, leading to an increased anion gap. In conclusion, the results suggest that intragastric KCl loading is a reliable model to promote rapid and severe hyperkalaemia that can be used for further research on this topic.

Short-term effect of ligature-induced periodontitis on cardiovascular variability and inflammatory response in spontaneously hypertensive rats.

BACKGROUND: We previously reported that periodontal disease (PD) induces high arterial pressure variability (APV) consistent with sympathetic overactivity and elicits myocardial inflammation in Balb/c mice. However, it is unknown whether PD can change APV and heart rate variability (HRV) in spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. This study aimed to evaluate the hemodynamic level, HRV, and APV associating with myocardial inflammation and plasma concentrations of oxide nitric (NO) in SHR and WKY rats with PD. METHODS: Three weeks after bilateral ligation of the first mandibular molar, or Sham operation, the rats received catheters into the femoral artery and had their arterial pressure (AP) recorded the following day. Subsequently, plasma, heart, and jaw were collected. The NO was quantified by the chemiluminescence method in plasma, and the myocardial IL-1ß concentrations were evaluated by ELISA. In the jaw was evaluated linear alveolar bone loss induced by PD. RESULTS: The linear alveolar bone loss in jaws of SHR with PD was higher than in all other groups. AP and heart rate were higher in SHR than in their WKY counterparts. SHR with PD showed lower AP than control SHR. HRV and APV were different between SHR and WKY rats; however, no differences in these parameters were found between the animals with PD and their control counterparts. Plasma NO and myocardial IL-1ß concentrations were higher in SHR with PD as compared to control WKY. A significant correlation was found between linear alveolar bone loss and plasma NO and myocardial IL-1ß concentrations. CONCLUSION: Our results demonstrated that short-term PD lowered the AP in SHR, which might be due to the higher levels of plasma NO. Even though PD did not affect either HRV or APV, it did induce myocardial inflammation, which can determine cardiovascular dysfunction in long-term PD.

Cardiac sympathetic drive is increased in cafeteria diet-fed rats independent of impairment in peripheral baroreflex and chemoreflex functions.

BACKGROUND AND AIMS: Consumption of a high caloric diet induces autonomic imbalance, which can lead to cardiovascular disease. Impaired arterial baroreflex control is suggested to play an important role in cardiovascular autonomic imbalance, often seen in obesity. We previously demonstrated that cafeteria diets increase the sympathetic drive to white and brown adipose tissue. METHODS AND RESULTS: After feeding a cafeteria diet to rats for 26 days, we evaluated: (i)heart rate (HR) and arterial pressure (AP); (ii)baroreflex and chemoreflex function; and (iii) autonomic modulation of the heart and vessels, measured through pulse interval (PI) and systolic arterial pressure (SAP) variability analyses and following administration of autonomic blockers. The cafeteria diet increased body fat mass and serum insulin, leptin, triacylglycerol and cholesterol levels. Baseline HR (15%) was also increased, accompanied by increased power in the low frequency band (60%) and in the low frequency/high frequency ratio (104%) in the PI spectra. Nonlinear analysis revealed an increased occurrence of 0V (39%) and decreased occurrence of 2UV (18%) patterns. Following administration of autonomic blockers, we observed an increase in cardiac sympathetic tone (425%) in cafeteria diet-fed rats. The cafeteria diet had no effect on AP, SAP variability, baroreflex and chemoreflex control. CONCLUSION: Our findings suggest that consumption of a cafeteria diet increases sympathetic drive to the heart but not to the blood vessels, independent of impairment in baroreflex and chemoreflex functions. Other mechanisms may be involved in the increased cardiac sympathetic drive, and compensatory vascular mechanisms may prevent the development of hypertension in this model of obesity.

Baroreflex control of renal sympathetic nerve activity in early heart failure assessed by the sequence method.

KEY POINTS: The integrity of the baroreflex control of sympathetic activity in heart failure (HF) remains under debate. We proposed the use of the sequence method to assess the baroreflex control of renal sympathetic nerve activity (RSNA). The sequence method assesses the spontaneous arterial pressure (AP) fluctuations and their related changes in heart rate (or other efferent responses), providing the sensitivity and the effectiveness of the baroreflex. Effectiveness refers to the fraction of spontaneous AP changes that elicits baroreflex-mediated variations in the efferent response. Using three different approaches, we showed that the baroreflex sensitivity between AP and RSNA is not altered in early HF rats. However, the sequence method provided evidence that the effectiveness of baroreflex in changing RSNA in response to AP changes is markedly decreased in HF. The results help us better understand the baroreflex control of the sympathetic nerve activity. ABSTRACT: In heart failure (HF), the reflex control of the heart rate is known to be markedly impaired; however, the baroreceptor control of the sympathetic drive remains under debate. Applying the sequence method to a series of arterial pressure (AP) and renal sympathetic nerve activity (RSNA), we demonstrated a clear dysfunction in the baroreflex control of sympathetic activity in rats with early HF. We analysed the baroreflex control of the sympathetic drive using three different approaches: AP vs. RSNA curve, cross-spectral analysis and sequence method between AP and RSNA. The sequence method also provides the baroreflex effectiveness index (BEI), which represents the percentage of AP ramps that actually produce a reflex response. The methods were applied to control rats and rats with HF induced by myocardial infarction. None of the methods employed to assess the sympathetic baroreflex gain were able to detect any differences between the control and the HF group. However, rats with HF exhibited a lower BEI compared to the controls. Moreover, an optimum delay of 1 beat was observed, i.e. 1 beat is required for the RSNA to respond after AP changing, which corroborates with the findings related to the timing between these two variables. For delay 1, the BEI of the controls was 0.45 ± 0.03, whereas the BEI of rats with HF was 0.29 ± 0.09 (P < 0.05). These data demonstrate that while the gain of the baroreflex is not affected in early HF, its effectiveness is markedly decreased. The analysis of the spontaneous changes in AP and RSNA using the sequence method provides novel insights into arterial baroreceptor reflex function.

NLRP3 Inflammasome Mediates Aldosterone-Induced Vascular Damage.

BACKGROUND: Inflammation is a key feature of aldosterone-induced vascular damage and dysfunction, but molecular mechanisms by which aldosterone triggers inflammation remain unclear. The NLRP3 inflammasome is a pivotal immune sensor that recognizes endogenous danger signals triggering sterile inflammation. METHODS: We analyzed vascular function and inflammatory profile of wild-type (WT), NLRP3 knockout (NLRP3-/-), caspase-1 knockout (Casp-1-/-), and interleukin-1 receptor knockout (IL-1R-/-) mice treated with vehicle or aldosterone (600 µg·kg-1·d-1 for 14 days through osmotic mini-pump) while receiving 1% saline to drink. RESULTS: Here, we show that NLRP3 inflammasome plays a central role in aldosterone-induced vascular dysfunction. Long-term infusion of aldosterone in mice resulted in elevation of plasma interleukin-1ß levels and vascular abnormalities. Mice lacking the IL-1R or the inflammasome components NLRP3 and caspase-1 were protected from aldosterone-induced vascular damage. In vitro, aldosterone stimulated NLRP3-dependent interleukin-1ß secretion by bone marrow-derived macrophages by activating nuclear factor-κB signaling and reactive oxygen species generation. Moreover, chimeric mice reconstituted with NLRP3-deficient hematopoietic cells showed that NLRP3 in immune cells mediates aldosterone-induced vascular damage. In addition, aldosterone increased the expression of NLRP3, active caspase-1, and mature interleukin-1ß in human peripheral blood mononuclear cells. Hypertensive patients with hyperaldosteronism or normal levels of aldosterone exhibited increased activity of NLRP3 inflammasome, suggesting that the effect of hyperaldosteronism on the inflammasome may be mediated through high blood pressure. CONCLUSIONS: Together, these data demonstrate that NLRP3 inflammasome, through activation of IL-1R, is critically involved in the deleterious vascular effects of aldosterone, placing NLRP3 as a potential target for therapeutic interventions in conditions with high aldosterone levels.

The role of sympathetic and vagal cardiac control on complexity of heart rate dynamics.

Analysis of heart rate variability (HRV) by nonlinear approaches has been gaining interest due to their ability to extract additional information from heart rate (HR) dynamics that are not detectable by traditional approaches. Nevertheless, the physiological interpretation of nonlinear approaches remains unclear. Therefore, we propose long-term (60 min) protocols involving selective blockade of cardiac autonomic receptors to investigate the contribution of sympathetic and parasympathetic function upon nonlinear dynamics of HRV. Conscious male Wistar rats had their electrocardiogram (ECG) recorded under three distinct conditions: basal, selective (atenolol or atropine), or combined (atenolol plus atropine) pharmacological blockade of autonomic muscarinic or ß1-adrenergic receptors. Time series of RR interval were assessed by multiscale entropy (MSE) and detrended fluctuation analysis (DFA). Entropy over short (1 to 5, MSE1-5) and long (6 to 30, MSE6-30) time scales was computed, as well as DFA scaling exponents at short (αshort, 5 ≤ n ≤ 15), mid (αmid, 30 ≤ n ≤ 200), and long (αlong, 200 ≤ n ≤ 1,700) window sizes. The results show that MSE1-5 is reduced under atropine blockade and MSE6-30 is reduced under atropine, atenolol, or combined blockade. In addition, while atropine expressed its maximal effect at scale six, the effect of atenolol on MSE increased with scale. For DFA, αshort decreased during atenolol blockade, while the αmid increased under atropine blockade. Double blockade decreased αshort and increased αlong Results with surrogate data show that the dynamics during combined blockade is not random. In summary, sympathetic and vagal control differently affect entropy (MSE) and fractal properties (DFA) of HRV. These findings are important to guide future studies.NEW & NOTEWORTHY Although multiscale entropy (MSE) and detrended fluctuation analysis (DFA) are recognizably useful prognostic/diagnostic methods, their physiological interpretation remains unclear. The present study clarifies the effect of the cardiac autonomic control on MSE and DFA, assessed during long periods (1 h). These findings are important to help the interpretation of future studies.

Electrical stimulation of the aortic depressor nerve in conscious rats overcomes the attenuation of the baroreflex in chronic heart failure.

Chronic heart failure (CHF) is characterized by autonomic dysfunction combined with baroreflex attenuation. The hypotensive and bradycardic responses produced by electrical stimulation of the aortic depressor nerve (ADN) were examined in conscious CHF and control male Wistar rats (12-13 wk old). Furthermore, the role of parasympathetic and sympathetic nervous system in mediating the cardiovascular responses to baroreflex activation was evaluated by selective ß1-adrenergic and muscarinic receptor antagonists. CHF was induced by myocardial infarction. After 6 wk, the subjects were implanted with electrodes for ADN stimulation. Twenty-four hours later, electrical stimulation of the ADN was applied for 20 s using five different frequencies (5, 15, 30, 60, and 90 Hz), while the arterial pressure was recorded by a catheter implanted into the femoral artery. Electrical stimulation of the ADN elicited progressive and similar hypotensive and bradycardic responses in control (n = 12) and CHF (n = 11) rats, while the hypotensive response was not affected by methylatropine. Nevertheless, the reflex bradycardia was attenuated by methylatropine in control, but not in CHF rats. Atenolol did not affect the hypotensive or bradycardic response in either group. The ADN function was examined under anesthesia through electroneurographic recordings. The arterial pressure-ADN activity relationship was attenuated in CHF rats. In conclusion, despite the attenuation of baroreceptor function in CHF rats, the electrical stimulation of the ADN elicited a stimulus-dependent hypotension and bradycardia of similar magnitude as observed in control rats. Therefore, electrical activation of the aortic baroreflex overcomes both the attenuation of parasympathetic function and the sympathetic overdrive.

Multiscale entropy analysis of heart rate variability in heart failure, hypertensive, and sinoaortic-denervated rats: classical and refined approaches.

The analysis of heart rate variability (HRV) by nonlinear methods has been gaining increasing interest due to their ability to quantify the complexity of cardiovascular regulation. In this study, multiscale entropy (MSE) and refined MSE (RMSE) were applied to track the complexity of HRV as a function of time scale in three pathological conscious animal models: rats with heart failure (HF), spontaneously hypertensive rats (SHR), and rats with sinoaortic denervation (SAD). Results showed that HF did not change HRV complexity, although there was a tendency to decrease the entropy in HF animals. On the other hand, SHR group was characterized by reduced complexity at long time scales, whereas SAD animals exhibited a smaller short- and long-term irregularity. We propose that short time scales (1 to 4), accounting for fast oscillations, are more related to vagal and respiratory control, whereas long time scales (5 to 20), accounting for slow oscillations, are more related to sympathetic control. The increased sympathetic modulation is probably the main reason for the lower entropy observed at high scales for both SHR and SAD groups, acting as a negative factor for the cardiovascular complexity. This study highlights the contribution of the multiscale complexity analysis of HRV for understanding the physiological mechanisms involved in cardiovascular regulation.

Reduced expression of adherens and gap junction proteins can have a fundamental role in the development of heart failure following cardiac hypertrophy in rats.

Hypertension causes cardiac hypertrophy, cardiac dysfunction and heart failure (HF). The mechanisms implicated in the transition from compensated to decompensated cardiac hypertrophy are not fully understood. This study was aimed to investigate whether alterations in the expression of intercalated disk proteins could contribute to the transition of compensated cardiac hypertrophy to dilated heart development that culminates in HF. Male rats were submitted to abdominal aortic constriction and at 90 days post surgery (dps), three groups were observed: sham-operated animals (controls), animals with hypertrophic hearts (HH) and animals with hypertrophic + dilated hearts (HD). Blood pressure was evaluated. The hearts were collected and Western blot and immunofluorescence were performed to desmoglein-2, desmocollin-2, N-cadherin, plakoglobin, Bcatenin, and connexin-43. Cardiac systolic function was evaluated using the Vevo 2100 ultrasound system. Data were considered significant when p b 0.05. Seventy percent of the animals presented with HH and 30% were HD at 90 dps. The blood pressure increased in both groups. The amount of desmoglein-2 and desmocollin-2 expression was increased in both groups and no difference was observed in either group. The expression of N-cadherin, plakoglobin and B-catenin increased in the HHgroup and decreased in the HDgroup; and connexin-43 decreased only in theHDgroup. Therewas no difference between the ejection fraction and fractional shortening at 30 and 60 dps; however, they were decreased in the HD group at 90 dps. We found that while some proteins have increased expression accompanied by the increase in the cell volume associated with preserved systolic cardiac function in theHHgroup, these same proteins had decreased expression evenwithout significant reduction in the cell volume associated with decreased systolic cardiac function in HD group. The increased expression of desmoglein-2 and desmocollin-2 in both the HH and HD groups could work as a protective compensatory mechanism, helping tomaintain the dilated heart.We can hypothesize that inappropriate intercellular mechanical and electrical coupling associated with necrosis and/or apoptosis are important factors contributing to the transition to HF.

Cholinergic stimulation with pyridostigmine protects myocardial infarcted rats against ischemic-induced arrhythmias and preserves connexin43 protein.

We investigated the effects of acute pyridostigmine (PYR) treatment, an acetylcholinesterase inhibitor, on arterial pressure (AP), heart rate (HR), cardiac sympathovagal balance, and the incidence of arrhythmias during the first 4 h after myocardial infarction (MI) in anesthetized rats. Male Wistar rats were implanted with catheters into the femoral artery and vein for AP recordings and drug administration. Rats received the autonomic receptor blockers methyl-atropine (1 mg/kg iv) and propranolol (2 mg/kg iv) at intervals of 15 min, 1 h after saline (n=16) or PYR (0.25 mg/kg iv, n=18), to indirectly assess sympathovagal balance. Acute treatment with PYR increased cardiac vagal (86±7 vs. 44±5 beats/min) and decreased sympathetic tone (-31±8 vs. -69±7 beats/min). Different animals were implanted with ECG electrodes and catheters. A large MI was induced via left coronary artery ligation after basal recordings. Rats received PYR (n=14) or saline (n=14) 10-15 min after MI, and the recordings lasted up to 4 h. In part of the animals, hearts were removed for connexin43 quantification after all procedures. MI elicited a fall in AP (-45±5 mmHg), a progressive rise in HR (26±14 beats/min), and an increase in corrected QT interval (33±13 ms). PYR elicited a prompt bradycardia (-50±14 beats/min) that returned to basal levels over time, and it prevented the lengthening of the corrected QT interval. Treatment with PYR increased by ∼20% the occurrence of rats free of arrhythmias after MI. MI markedly decreased connexin43 in left ventricles, and PYR treatment partially prevented this decrease.

Autonomic cardiocirculatory control in mice with reduced expression of the vesicular acetylcholine transporter.

In cardiovascular diseases, sympathetic tone has been comprehensively studied, whereas parasympathetic tone has received minor attention. The vesicular ACh transporter (VAChT) knockdown homozygous (VAChT KD(HOM)) mouse is a useful model for examining the cardiocirculatory sympathovagal balance. Therefore, we investigated whether cholinergic dysfunction caused by reduced VAChT expression could adversely impact hemodynamic parameter [arterial pressure (AP) and heart rate (HR)] daily oscillation, baroreflex sensitivity, hemodynamic variability, sympathovagal balance, and cardiovascular reactivity to restraint stress. Wild-type and VAChT KD(HOM) mice were anesthetized for telemetry transmitter implantation, and APs and HRs were recorded 10 days after surgical recovery. Changes in HR elicited by methylatropine and propranolol provided the indexes of sympathovagal tone. Cardiovascular reactivity in response to a restraint test was examined 24 h after continuous recordings of AP and HR. VAChT KD(HOM) mice exhibited reduced parasympathetic and elevated sympathetic tone. Daily oscillations of AP and HR as well as AP variability were similar between groups. Nevertheless, HR variability, patterns with two dissimilar variations from symbolic analysis, and baroreflex sensitivity were reduced in VAChT KD(HOM) mice. The change in mean AP due to restraint stress was greater in VAChT KD(HOM) mice, whereas the tachycardic response was not. These findings demonstrate that the cholinergic dysfunction present in the VAChT KD(HOM) mouse did not adversely impact basal hemodynamic parameters but promoted autonomic imbalance, an attenuation of baroreflex sensitivity, and a greater pressure response to restraint stress. These results provide a framework for understanding how autonomic imbalance impacts cardiovascular function.

Toll-like receptor 9 plays a key role in the autonomic cardiac and baroreflex control of arterial pressure.

The crosstalk between the immune and the autonomic nervous system may impact the cardiovascular function. Toll-like receptors are components of the innate immune system and play developmental and physiological roles. Toll-like receptor 9 (TLR9) is involved in the pathogenesis of cardiovascular diseases, such as hypertension and heart failure. Since such diseases are commonly accompanied by autonomic imbalance and lower baroreflex sensitivity, we hypothesized that TLR9 modulates cardiac autonomic and baroreflex control of arterial pressure (AP). Toll-like receptor 9 knockout (TLR9 KO) and wild-type (WT) mice were implanted with catheters into carotid artery and jugular vein and allowed to recover for 3 days. After basal recording of AP, mice received methyl-atropine or propranolol. AP and pulse interval (PI) variability were evaluated in the time and frequency domain (spectral analysis), as well as by multiscale entropy. Spontaneous baroreflex was studied by sequence technique. Behavioral and cardiovascular responses to fear-conditioning stress were also evaluated. AP was similar between groups, but TLR9 KO mice exhibited lower basal heart rate (HR). AP variability was not different, but PI variability was increased in TLR9 KO mice. The total entropy was higher in TLR9 KO mice. Moreover, baroreflex function was found higher in TLR9 KO mice. Atropine-induced tachycardia was increased in TLR9 KO mice, whereas the propranolol-induced bradycardia was similar to WT mice. TLR9 KO mice exhibit increased behavioral and decreased tachycardia responses to fear-conditioning stress. In conclusion, our findings suggest that TLR9 may negatively modulate cardiac vagal tone and baroreflex in mice.

Heart rate complexity in sinoaortic-denervated mice.

NEW FINDINGS: What is the central question of this study? New measurements for cardiovascular complexity, such as detrended fluctuation analysis (DFA) and multiscale entropy (MSE), have been shown to predict cardiovascular outcomes. Given that cardiovascular diseases are accompanied by autonomic imbalance and decreased baroreflex sensitivity, the central question is: do baroreceptors contribute to cardiovascular complexity? What is the main finding and its importance? Sinoaortic denervation altered both DFA scaling exponents and MSE, indicating that both short- and long-term mechanisms of complexity are altered in sinoaortic denervated mice, resulting in a loss of physiological complexity. These results suggest that the baroreflex is a key element in the complex structures involved in heart rate variability regulation. Recently, heart rate (HR) oscillations have been recognized as complex behaviours derived from non-linear processes. Physiological complexity theory is based on the idea that healthy systems present high complexity, i.e. non-linear, fractal variability at multiple scales, with long-range correlations. The loss of complexity in heart rate variability (HRV) has been shown to predict adverse cardiovascular outcomes. Based on the idea that most cardiovascular diseases are accompanied by autonomic imbalance and a decrease in baroreflex sensitivity, we hypothesize that the baroreflex plays an important role in complex cardiovascular behaviour. Mice that had been subjected to sinoaortic denervation (SAD) were implanted with catheters in the femoral artery and jugular vein 5 days prior to the experiment. After recording the baseline arterial pressure (AP), pulse interval time series were generated from the intervals between consecutive values of diastolic pressure. The complexity of the HRV was determined using detrended fluctuation analysis and multiscale entropy. The detrended fluctuation analysis α1 scaling exponent (a short-term index) was remarkably decreased in the SAD mice (0.79 ± 0.06 versus 1.13 ± 0.04 for the control mice), whereas SAD slightly increased the α2 scaling exponent (a long-term index; 1.12 ± 0.03 versus 1.04 ± 0.02 for control mice). In the SAD mice, the total multiscale entropy was decreased (13.2 ± 1.3) compared with the control mice (18.9 ± 1.4). In conclusion, fractal and regularity structures of HRV are altered in SAD mice, affecting both short- and long-term mechanisms of complexity, suggesting that the baroreceptors play a considerable role in the complex structure of HRV.

The hydrogen sulfide donor 4-carboxyphenyl-isothiocyanate decreases blood pressure and promotes cardioprotective effect through reduction of oxidative stress and nuclear factor kappa B/matrix metalloproteinase (MMP)-2 axis in hypertension.

AIMS: Our aim was to evaluate whether the hydrogen sulfide (H2S) donor, 4-carboxyphenyl-isothiocyanate (4-CPI), exerts cardioprotective effect in the two kidney- one clip (2K-1C) rats through oxidative stress and MMP-2 activity attenuation and compare it with the classical H2S donor, Sodium Hydrosulfide (NaHS). MATERIALS AND METHODS: Renovascular hypertension (two kidneys-one clip; 2K-1C) was surgically induced in male Wistar rats. After two weeks, normotensive (2K) and hypertensive rats were intraperitoneally treated with vehicle (0.6 % dimethyl sulfoxide), NaHS (0.24 mg/Kg/day) or with 4-CPI (0.24 mg/Kg/day), for more 4 weeks. Systolic blood pressure (SBP) was evaluated weekly by tail-cuff plethysmography. Heart function was assessed by using the Millar catheter. Cardiac hypertrophy and fibrosis were evaluated by hematoxylin and eosin, and Picrosirius Red staining, respectively. The H2S was analyzed using WSP-1 fluorimetry and the cardiac oxidative stress was measured by lucigenin chemiluminescence and Amplex Red. MMP-2 activity was measured by in-gel gelatin or in situ zymography assays. Nox1, gp91phox, MMP-2 and the phospho-p65 subunit (Serine 279) nuclear factor kappa B (NF-κB) levels were evaluated by Western blotting. KEY FINDINGS: 4-CPI reduced blood pressure in hypertensive rats, decreased cardiac remodeling and promoted cardioprotection through the enhancement of cardiac H2S levels. An attenuation of oxidative stress, with inactivation of the p65-NF-κB/MMP-2 axis was similarly observed after NaHS or 4-CPI treatment in 2K-1C hypertension. SIGNIFICANCE: H2S is a mediator that promotes cardioprotective effects and decreases blood pressure, and 4-CPI seems to be a good candidate to reverse the maladaptive remodeling and cardiac dysfunction in renovascular hypertension.

Increase in parasympathetic tone by pyridostigmine prevents ventricular dysfunction during the onset of heart failure.

Heart failure (HF) is characterized by elevated sympathetic activity and reduced parasympathetic control of the heart. Experimental evidence suggests that the increase in parasympathetic function can be a therapeutic alternative to slow HF evolution. The parasympathetic neurotransmission can be improved by acetylcholinesterase inhibition. We investigated the long-term (4 wk) effects of the acetylcholinesterase inhibitor pyridostigmine on sympathovagal balance, cardiac remodeling, and cardiac function in the onset of HF following myocardial infarction. Myocardial infarction was elicited in adult male Wistar rats. After 4 wk of pyridostigmine administration, per os, methylatropine and propranolol were used to evaluate the cardiac sympathovagal balance. The tachycardic response caused by methylatropine was considered to be the vagal tone, whereas the bradycardic response caused by propranolol was considered to be the sympathetic tone. In conscious HF rats, pyridostigmine reduced the basal heart rate, increased vagal, and reduced sympathetic control of heart rate. Pyridostigmine reduced the myocyte diameter and collagen density of the surviving left ventricle. Pyridostigmine also increased vascular endothelial growth factor protein in the left ventricle, suggesting myocardial angiogenesis. Cardiac function was assessed by means of the pressure-volume conductance catheter system. HF rats treated with pyridostigmine exhibited a higher stroke volume, ejection fraction, cardiac output, and contractility of the left ventricle. It was demonstrated that the long-term administration of pyridostigmine started right after coronary artery ligation augmented cardiac vagal and reduced sympathetic tone, attenuating cardiac remodeling and left ventricular dysfunction during the progression of HF in rats.

Heart rate fragmentation is impaired in type 2 diabetes mellitus patients.

AIMS: To evaluate the heart rate fragmentation (HRF) of type 2 diabetes mellitus (T2DM) patients and its relationship with heart rate variability (HRV) indices. METHODS: One hundred sixty-four men, aged 47-57 years were retrospectively analyzed from a database. Participants were T2DM (n = 82) and apparently healthy (n = 82). R-R interval time series recorded by electrocardiogram were collected at the supine position for 10 to 15 min. From HRF, the percentage of inflection points (PIP), percentage of words with zero, one, two, or three inflections points (W0, W1, W2, W3), and percentage with only type hard, soft, or mixed inflections points type (WH, WS, WM) were quantified. RESULTS: T2DM presented higher PIP, WS, WM and W3, while WH and W1 was lower compared with healthy (p < 0.05). Moreover, a positive moderate correlation was found between WH and root mean square of the successive R-R differences (RMSSD) and high frequency (HF) indices. In contrast, a negative moderate correlation was found between WS and WM with RMSSD and HF indices. CONCLUSIONS: T2DM have increased fragmentation patterns, and words grouped by inflection type are more closely related to HRV. The HRF approach might be useful to assess heart rate dynamic abnormalities in males with type 2 diabetes.

Investigating autonomic nervous system dysfunction among patients with post-COVID condition and prolonged cardiovascular symptoms.

Heart Rate Variability (HRV) and arterial pressure (AP) variability and their responses to head-up tilt test (HUTT) were investigated in Post-COVID-19 syndrome (PCS) patients reporting tachycardia and/or postural hypotension. Besides tachycardia, PCS patients also showed attenuation of the following HRV parameters: RMSSD [square root of the mean of the sum of the squares of differences between adjacent normal-to-normal (NN) intervals] from statistical measures; the power of RR (beat-to-beat interval) spectra at HF (high frequency) from the linear method spectral analysis; occurrence of 2UV (two unlike variation) pattern of RR from the nonlinear method symbolic analysis; and the new family of statistics named sample entropy, when compared to control subjects. Basal AP and LF (low frequency) power of systolic AP were similar between PCS patients and control subjects, while 0 V (zero variation) patterns of AP from the nonlinear method symbolic analysis were exacerbated in PCS patients. Despite tachycardia and a decrease in RMSSD, no parameter of HRV changed during HUTT in PCS patients compared to control subjects. PCS patients reassessed after 6 months showed higher HF power of RR spectra and a higher percentage of 2UV pattern of RR. Moreover, the reassessed PCS patients showed a lower occurrence of 0 V patterns of AP, while the HUTT elicited HR (heart rate) and AP responses identical to control subjects. The HRV and AP variability suggest an autonomic dysfunction with sympathetic predominance in PCS patients. In contrast, the lack of responses of HRV and AP variability indices during HUTT indicates a marked impairment of autonomic control. Of note, the reassessment of PCS patients showed that the noxious effect of COVID-19 on autonomic control tended to fade over time.

Correlation between heart rate variability and polysomnography-derived scores of obstructive sleep apnea.

Obstructive sleep apnea (OSA) is one of the most common sleep disorders and affects nearly a billion people worldwide. Furthermore, it is estimated that many patients with OSA are underdiagnosed, which contributes to the development of comorbidities, such as cardiac autonomic imbalance, leading to high cardiac risk. Heart rate variability (HRV) is a non-invasive, widely used approach to evaluating neural control of the heart. This study evaluates the relationship between HRV indices and the presence and severity of OSA. We hypothesize that HRV, especially the nonlinear methods, can serve as an easy-to-collect marker for OSA early risk stratification. Polysomnography (PSG) exams of 157 patients were classified into four groups: OSA-free (N = 26), OSA-mild (N = 39), OSA-moderate (N = 37), and OSA-severe (N = 55). The electrocardiogram was extracted from the PSG recordings, and a 15-min beat-by-beat series of RR intervals were generated every hour during the first 6 h of sleep. Linear and nonlinear HRV approaches were employed to calculate 32 indices of HRV. Specifically, time- and frequency-domain, symbolic analysis, entropy measures, heart rate fragmentation, acceleration and deceleration capacities, asymmetry measures, and fractal analysis. Results with indices of sympathovagal balance provided support to reinforce previous knowledge that patients with OSA have sympathetic overactivity. Nonlinear indices showed that HRV dynamics of patients with OSA display a loss of physiologic complexity that could contribute to their higher risk of development of cardiovascular disease. Moreover, many HRV indices were found to be linked with clinical scores of PSG. Therefore, a complete set of HRV indices, especially the ones obtained by the nonlinear approaches, can bring valuable information about the presence and severity of OSA, suggesting that HRV can be helpful for in a quick diagnosis of OSA, and supporting early interventions that could potentially reduce the development of comorbidities.

Aryl hydrocarbon receptor (AhR) activation contributes to high-fat diet-induced vascular dysfunction.

BACKGROUND AND PURPOSE: Metabolic and vascular dysfunction are common features of obesity. Aryl hydrocarbon receptor (AhR) regulates lipid metabolism and vascular homeostasis, but whether vascular AhR are activated in obesity or have a protective and/or harmful effects on vascular function in obesity are unknown. Our study addresses whether AhR activation contributes to obesity-associated vascular dysfunction and the mechanisms involved in these AhR effects. EXPERIMENTAL APPROACH: Male AhR KO (Ahr-/- ) and WT mice were fed either control or a HF (high-fat) diet for 10 weeks. Metabolic and inflammatory parameters were measured in serum and adipose tissue. Vascular reactivity (isometric force) was evaluated using a myography. Endothelial NOS (eNOS) and AhR protein expression was determined by western blot, Cyp1A1 and Nos3 gene expression by RT-PCR and.NO production was quantified by DAF fluorescence. KEY RESULTS: HF diet increased total serum HDL and LDL, as well as vascular AhR protein expression and proinflammatory cytokines in the adipose tissue. HF diet decreased endothelium-dependent vasodilation. AhR deletion protected mice from HF diet-induced dyslipidaemia, weight gain and inflammatory processes. HF diet-induced endothelial dysfunction was attenuated in Ahr-/- mice. Vessels from Ahr-/- mice exhibited a greater NO reserve. In cultured endothelial cells, lysophosphatidylcholine (LPC) a major component of LDL and oxidized LDL [oxLDL]) reduced Nos3 gene expression and NO production. Antagonism of the AhR inhibited LPC effects on endothelial cells and induced decreased endothelium-dependent vasodilation. CONCLUSION AND IMPLICATIONS: AhR deletion attenuates HF diet-induced dyslipidaemia and vascular dysfunction by improving eNOS/NO signalling. Targeting AhRs may prevent obesity-associated vascular dysfunction.