Increase In Baroreflex Sensitivity Research Articles

Impact of exercise training associated with enalapril treatment on blood pressure variability and renal dysfunctions in an experimental model of arterial hypertension and postmenopause.

In this study, we aimed to investigate the effects of the concurrent exercise training (CET) associated with the enalapril maleate on blood pressure variability (BPV) and renal profile in an experimental model of arterial hypertension (AH) and postmenopause. Female ovariectomized spontaneously hypertensive rats (SHR) were distributed into 4 groups (n = 8/group): sedentary (SO), sedentary + enalapril (SOE), trained (TO) and trained + enalapril (TOE). Both enalapril (3mg/kg) and CET (3 days/week) were conducted during 8 weeks. Blood pressure (BP) was directly recorded for BPV analyses. Renal function, morphology, inflammation and oxidative stress were assessed. The SOE, TO e TOE groups presented decreased systolic BP compared with SO. Both trained groups (TO and TOE) presented lower BPV and increased baroreflex sensitivity (TO: 0.76 ± 0.20 and TOE: 1.02 ± 0.40 vs. SO: 0.40 ± 0.07 ms/mmHg) compared with SO group, with additional improvements in TOE group. Creatinine and IL-6 levels were reduced in SOE, TO and TOE compared with SO group, while IL-10 was increased only in TOE group (vs. SO). Enalapril combined with CET promote reduction in lipoperoxidation (TOE: 1.37 ± 0.26 vs. SO: 2.08 ± 0.48 and SOE: 1.84 ± 0.35 μmol/mg protein) and hydrogen peroxide (TOE: 1.89 ± 0.40 vs. SO: 3.70 ± 0.19 and SOE: 2.73 ± 0.70 μM), as well as increase in catalase activity (vs. sedentary groups). The tubulointerstitial injury was lower in interventions groups (SOE, TO and TOE vs. SO), with potentialized benefits in the trained groups. Enalapril combined with CET attenuated BPV and baroreflex dysfunctions, probably impacting on end-organ damage, as demonstrated by attenuation in the AH-induced renal inflammations, oxidative stress and morphofunctional impairments in postmenopausal rats.

Treatment with empagliflozin improves cardiac function in infarcted animals associated with increased baroreflex sensitivity

Abstract Background Several clinical and experimental studies have shown an improvement in cardiac function in infarcted patients and animals (diabetic or not) when treated with empagliflozin, as well as an improvement in outcomes in patients with heart failure with reduced ejection fraction or with preserved ejection fraction. Hypothesis: Treatment with empagliflozin for 14 days (10 mg/kg) improves cardiac function in infarcted rats, secondary to increased baroreflex sensitivity. Methods Wistar rats were divided into 2 groups: AMI - acute myocardial infarction (n=8) and AMI+EMPA - acute myocardial infarction + Empagliflozin (n=8). The animals in both groups were anesthetized and submitted to thoracotomy and ligature of the left coronary artery. The animals in the AMI+EMPA group received daily, through oral gavage, 10 mg/kg of empagliflozin, for 14 days. After this period, an echocardiographic examination was performed, followed by cannulation of the femoral vein and artery, to assess hemodynamic parameters and baroreflex activity. The results were evaluated for normality. Data were compared by Student's t tests. And the relationship between the parameters was tested by Pearson's correlation. Results are presented as mean and standard deviation. Results In the echocardiographic evaluation, an improvement in diastolic function indexes was observed in the AMI+EMPA group in relation to the AMI group: E'/A' ratio (1.584 ± 0.437 vs 0.589 ± 0.129), E/E' ratio (14.11 ± 3.946 vs 29.92 ± 6.878) and systolic function: SF (29.30% ± 7.974 vs 19.20% ± 2.445), EF (53.86% ± 11.78 vs 37.91% ± 4.212), FAC (39.31% ± 7.135 vs 23.51 ± 3.940). There was a reduction in mean blood pressure in the AMI+EMPA group (102.4 mmHg ± 6,408) compared to the AMI group (110.7 mmHg ± 8,514) and in diastolic blood pressure (84.4 mmHg ± 3.889 vs 92.8 mmHg ± 7.664). In the assessment of baroreflex sensitivity, an improvement in tachy and bradycardic indexes was observed in the treated animals: tachycardic index (5.021 bpm/mmHg ± 0.346 vs 3.214 bpm/mmHg ± 0.418) and bradycardic index (1.569 bpm/mmHg ± 0.148 vs 0.73 bpm/ mmHg ± 0.046). In addition, the systolic function expressed by the FAC was positively associated with the reflex tachycardic index (p: 0.008; r: 0.616) and to the E'/A' ratio (p: 0.025; r: 0.576) and negatively with PAD (p: 0.040; r: -0.503). Conclusion Treatment with Empagliflozin in infarcted rats was able to improve left ventricular systolic and diastolic function associated with improved performance of arterial baroreceptors.

Effect Of 12 Weeks Yoga Training And 12 Weeks Detraining on Heart Rate Variability on Subjects with Hypertension

Background: Healthy lifestyle modifications can prevent hypertension, an early predictor of cardiovascular disease. Yoga is an effective way to manage stress-induced disorders, such as hypertension. Objective: This study investigated the effects of yoga training on hypertensive individuals receiving routine treatment over a 12-week period, comparing and analyzing heart rate variability (HRV) parameters at and after the 12-week yoga training period (the 12th week) with hypertensives receiving routine treatment (the non-yoga group). Materials and methods: A total of 132 hypertensive subjects between the ages of 25 and 45 were randomly assigned to control or experimental groups (N=66), and 66 of these subjects were exposed to yoga therapy (N=66). Before, after, and during the study period, HRV parameters were obtained. Results: RM ANOVA was used to compare time domain and frequency domain parameters of HRV of the control group at pre, post, and detrain, and it was found that no significant difference existed between the groups. Test group mean values show a significant increase in time domain parameters compared with pre-training values after training. Test group post-training and detrain values significantly increased when compared to control group post-training and detrain values. Test group detrain values decreased significantly from post-training to test group detrain values. Conclusion: Yoga therapy increases the HRV values in essential hypertension at rest. An increase in vagal modulation, a reduction in sympathetic activity, and an increase in baroreflex sensitivity may be responsible for the harmonization of autonomic cardiovascular rhythms. The results of detraining from yoga did not result in an increase in HRV. As a result, the present study shows that regular yoga practice reduces hypertension, and deep rest keeps the body healthy.

Combined Exercise Training Promotes More Benefits on Cardiovascular Autonomic Modulation in Ovariectomized Rats Than Isolated Aerobic or Resistance Training.

Cardiovascular risk increase after ovarian deprivation has been extensively demonstrated by our research group through cardiovascular autonomic analysis. Interventions involving different types of exercises, such as resistance exercises or combined exercises (aerobic and resistance) have been widely recommended to prevent or minimize neuromuscular decline in postmenopausal women, which is aggravated by a sedentary lifestyle. Experimentally, the cardiovascular effects of resistance or combined training, as well as comparison between aerobic, resistance, and combined training, in ovariectomized animals are scarce. In this study, we hypothesized that the combination of aerobic and resistance training may be more effective in preventing muscle mass loss, as well as improving cardiovascular autonomic modulation and baroreflex sensitivity, than aerobic or resistance training individually in ovariectomized rats. Female rats were divided into 5 groups: sedentary (C); ovariectomized (Ovx); trained ovariectomized submitted to aerobic training (OvxAT); resistance training (OvxRT); combined training (OvxCT). Exercise training lasted 8 weeks, with the combined group alternating between aerobic training and resistance training every other day. At the end of the study, glycemia and insulin tolerance were evaluated. Arterial pressure (AP) was directly recorded. Baroreflex sensitivity was assessed by heart rate response to changes in arterial pressure. Cardiovascular autonomic modulation was evaluated by spectral analysis. Combined training was the only training regime that increased baroreflex sensitivity for tachycardic response and reduced all systolic blood pressure variability parameters. Furthermore, all animals submitted to exercise training on a treadmill (OvxAT and OvxCT) presented lower systolic, diastolic, and mean pressure, as well as improvements in the autonomic modulation for the heart. Combined training showed to be more effective than isolated aerobic and resistance training, mixing the isolated benefits of each modality. It was the only modality able to increase baroreflex sensitivity to tachycardic responses, reduce arterial pressure and all parameters of vascular sympathetic modulation.

Food readjustment plus exercise training improves cardiovascular autonomic control and baroreflex sensitivity in high-fat diet-fed ovariectomized mice.

Despite consensus on the benefits of food readjustment and/or moderate-intensity continuous exercise in the treatment of cardiometabolic risk factors, there is little evidence of the association between these two cardiovascular risk management strategies after menopause. Thus, the objective of this study was to evaluate the effects of food readjustment and/or exercise training on metabolic, hemodynamic, autonomic, and inflammatory parameters in a model of loss of ovarian function with diet-induced obesity. Forty C57BL/6J ovariectomized mice were divided into the following groups: high-fat diet-fed - 60% lipids throughout the protocol (HF), food readjustment - 60% lipids for 5 weeks, readjusted to 10% for the next 5 weeks (FR), high-fat diet-fed undergoing moderate-intensity exercise training (HFT), and food readjustment associated with moderate-intensity exercise training (FRT). Blood glucose evaluations and oral glucose tolerance tests were performed. Blood pressure was assessed by direct intra-arterial measurement. Baroreflex sensitivity was tested using heart rate phenylephrine and sodium nitroprusside induced blood pressure changes. Cardiovascular autonomic modulation was evaluated in time and frequency domains. Inflammatory profile was evaluated by IL-6, IL-10 cytokines, and TNF-alpha measurements. Only the exercise training associated with food readjustment strategy induced improved functional capacity, body composition, metabolic parameters, inflammatory profile, and resting bradycardia, while positively changing cardiovascular autonomic modulation and increasing baroreflex sensitivity. Our findings demonstrate that the association of these strategies seems to be effective in the management of cardiometabolic risk in a model of loss of ovarian function with diet-induced obesity.

Exploring mechanisms of blood pressure regulation in response to device-guided and non-device-guided slow breathing: A mini review.

Hypertension is a widespread disease that, if persistent, increases the risks of coronary heart disease mortality and morbidity. Slow breathing is a recommended blood pressure-lowering strategy though the mechanisms mediating its effects are unknown. This review aims to evaluate autonomic and vascular function as potential mediators driving BP adaptive responses with slow breathing. We searched EBSCO host, Web of Science, Cochrane Central Register of Controlled Trials, and PubMed using key words for optimized search results. Nineteen studies were included in this review (11 device-guided; 8 non-device-guided breathing). Though some studies showed increased vagally mediated components of heart rate variability during slow breathing, results from acute and long-term studies were incongruent. Increases in baroreflex sensitivity (BRS) following a single device-guided slow breathing bout were noted in normotensive and hypertensive adults. Long-term (4weeks to 3months) effects of slow breathing on BRS were absent. Device-guided breathing resulted in immediate reductions in muscle sympathetic nerve activity (MSNA) in normo- and hyper-tensive adults though results from long-term studies yielded inconsistent findings. Non-device-guided slow breathing posed acute and chronic effects on vascular function with reductions in arterial stiffness in adults with type I diabetes and increases in microvascular endothelial function in adults with irritable bowel syndrome. Non-device guided breathing also reduced pro-inflammatory cytokines in healthy and hypertensive adults in acute and chronic studies. No adverse effects or non-adherence to treatment were noted in these trials. Device-guided slow breathing is a feasible and effective modality in improving BRS, HRV, and arterial stiffness though its long-term effects are obscure. Though less evidence exists supporting the efficacy of non-device-guided slow breathing, acute and chronic studies demonstrate improvements in vascular function and inflammatory cytokines. More studies are needed to further explore the long-term effects of slow breathing in general and non-device-guided breathing in particular.

Cardiac-Gated Neuromodulation Increased Baroreflex Sensitivity and Reduced Pain Sensitivity in Female Fibromyalgia Patients.

The study presents a novel approach of programing pain inhibition in chronic pain patients based on the hypothesis that pain perception is modulated by dysfunctional dorsal medial nucleus tractus solitarii (dmNTS) reflex arcs that produce diminished baroreflex sensitivity (BRS) resulting from a conditioned response. This study tested whether administration of noxious and non-noxious electrical stimuli synchronized with the cardiac cycle resets BRS, reestablishing pain inhibition. A total of 30 pain-free normotensives controls (NC) and 32 normotensives fibromyalgia (FM) patients received two, ≈8 min-epochs of cardiac-gated, peripheral electrical stimuli. Non-painful and painful electrical stimuli were synchronized to the cardiac cycle as the neuromodulation experimental protocol (EP) with two control conditions (CC1, CC2). BRS, heart-rate-variability (HRV), pain threshold and tolerance, and clinical pain intensity were assessed. Reduced BRS in FM at baseline increased by 41% during two, ≈8 min-epochs of stimulation. Thresholds in FM increased significantly during the experimental protocol (all Ps < 0.001) as did HRV. FM levels of clinical pain significantly decreased by 35.52% during the experimental protocol but not during control stimulations (p < 0.001). Baroreceptor training may reduce FM pain by BRS-mediated effects on intrinsic pain regulatory systems and autonomic responses.

Postural orthostatic tachycardia syndrome explained using a baroreflex response model.

Patients with postural orthostatic tachycardia syndrome (POTS) experience an excessive increase in heart rate (HR) and low-frequency (∼0.1 Hz) blood pressure (BP) and HR oscillations upon head-up tilt (HUT). These responses are attributed to increased baroreflex (BR) responses modulating sympathetic and parasympathetic signalling. This study uses a closed-loop cardiovascular compartment model controlled by the BR to predict BP and HR dynamics in response to HUT. The cardiovascular model predicts these quantities in the left ventricle, upper and lower body arteries and veins. HUT is simulated by letting gravity shift blood volume (BV) from the upper to the lower body compartments, and the BR control is modelled using set-point functions modulating peripheral vascular resistance, compliance, and cardiac contractility in response to changes in mean carotid BP. We demonstrate that modulation of parameters characterizing BR sensitivity allows us to predict the persistent increase in HR and the low-frequency BP and HR oscillations observed in POTS patients. Moreover, by increasing BR sensitivity, inhibiting BR control of the lower body vasculature, and decreasing central BV, we demonstrate that it is possible to simulate patients with neuropathic and hyperadrenergic POTS.

Evaluation of Heart Rate Variability and Application of Heart Rate Variability Biofeedback: Toward Further Research on Slow-Paced Abdominal Breathing in Zen Meditation.

This review summarizes my own involvement in heart rate variability (HRV) and HRV biofeedback studies, as a tribute to the late Dr. Evgeny Vaschillo. I first review psychophysiological studies on behavioral stress and relaxation performed in my laboratory using an assessment of cardiac parasympathetic activity. Although magnitude of high-frequency (HF) component of HRV corresponding respiratory sinus arrhythmia (RSA) is widely used as an index of cardiac parasympathetic function, a respiratory confound during stress or relaxation may have interfered with the proper assessment of the HF HRV. An enhanced method under frequency-controlled respiration at 0.25Hz provided a reliable assessment of cardiac parasympathetic activity. I then review findings from HRV biofeedback research in my laboratory. Based on the hypothesis that RSA measured as an HF component of HRV represents cardiorespiratory resting function, it was demonstrated that HRV biofeedback before sleep enhanced the magnitude of HF HRV during sleep, a cardiorespiratory resting function. Moreover, by focusing on the spectral peak of the low-frequency (LF) component of HRV, paced breathing at the LF-peak frequency was shown to increase baroreflex sensitivity. Finally, I describe the potential of slow-paced abdominal breathing (i.e., Tanden breathing) performed in Zen meditation. The concept of Tanden breathing as described in a regimen from early modern Japan is introduced, and recent research findings on slow-paced abdominal breathing are summarized. Future research directions of slow-paced abdominal breathing are also discussed.

UPAYA PENURUNAN TEKANAN DARAH DENGAN LATIHAN SLOW DEEP BREATHING PADA PENDERITA HIPERTENSI

Hypertension is an abnormal increase in blood pressure in the arteries continuously over a period. Hypertension has become a public health problem and will become a bigger problem if it is not tackled early on. Slow deep breathing is a non-pharmacological modality that can lead to increased baroreflex sensitivity and reduced sympathetic activity and chemoreflex activation, which shows a potentially beneficial effect in hypertension. The objective of this activity is to improve community skills in hypertension management with slow deep breathing exercises. The methods used in this community service are health education and slow deep breathing exercise demonstrations. The target of this activity is 12 people with hypertension in Pesanggrahan Village. The result of this activity is to increase the knowledge and skills of hypertensive sufferers about hypertension management using slow deep breathing exercises.

3,5-Diiodothyronine protects against cardiac ischaemia-reperfusion injury in male rats.

What is the central question of this study? 3,5-Diiodothyronine (3,5-T2) administration increases resting metabolic rate, prevents or treats liver steatosis in rodent models, and ameliorates insulin resistance: what are its effects on cardiac electrical and contractile properties and autonomic regulation? What is the main finding and its importance? Chronic 3,5-T2 administration has no adverse effects on cardiac function. Remarkably, 3,5-T2 improves the autonomous control of the rat heart and protects against ischaemia-reperfusion injury. The use of 3,5,3'-triiodothyronine (T3) and thyroxine (T4) to treat metabolic diseases has been hindered by potential adverse effects on liver, lipid metabolism and cardiac electrical properties. It is recognized that 3,5-diiodothyronine (3,5-T2) administration increases resting metabolic rate, prevents or treats liver steatosis in rodent models and ameliorates insulin resistance, suggesting 3,5-T2 as a potential therapeutic tool. However, a comprehensive assessment of cardiac electrical and contractile properties has not been made so far. Three-month-old Wistar rats were daily administered vehicle, 3,5-T2 or 3,5-T2+T4 and no signs of atrial or ventricular arrhythmia were detected in non-anaesthetized rats during 90days. Cardiac function was preserved as heart rate, left ventricle diameter and shortening fraction in 3,5-T2-treated rats compared to vehicle and 3,5-T2+T4 groups. Power spectral analysis indicated an amelioration of the heart rate variability only in 3,5-T2-treated rats. An increased baroreflex sensitivity at rest was observed in both 3,5-T2-treated groups. Finally, 3,5-T2 Langendorff-perfused hearts presented a significant recovery of left ventricular function and remarkably smaller infarction area after ischaemia-reperfusion injury. In conclusion, chronic 3,5-T2 administration ameliorates tonic cardiac autonomic control and confers cardioprotection against ischaemia-reperfusion injury in healthy male rats.

The Cardiovascular Variability during Transient 6° Head Down Tilt and Slow Breathing in Yoga Experienced Healthy Individuals.

Objective:The intervention of yoga has been shown to improve autonomic conditioning in humans and better adaptability to orthostatic challenges. Similarly, slow breathing at 0.1 Hz akin to pranayama also increases baroreflex sensitivity (BRS). Hence, we intended to investigate whether yoga practitioners have different autonomic responses at rest,during slow deep breathingas well as during 6° head down tilt (HDT) compared to naive group individuals.Aim:The aim of the study was to evaluate the acute effects of slow breathing on cardiovascular variability during HDT in yoga practitioners compared to yoga-naïve individuals.Settings and Design:This was a comparative study with repeated measures design conducted in Autonomic Function Test lab of the Department of Physiology, All India Institute of Medical Sciences, New Delhi, India.Materials and Methods:Time domain and frequency domain parameters of heart rate variability, blood pressure variability (BPV), and BRS were evaluated during 6° HDT and slow breathing at 0.1 Hz on forty yoga-naïve individuals and forty yoga practitioners with an average age of 31.08 ± 7.31 years and 29.93 ± 7.57 years, respectively. All of the participants were healthy.Statistical Analysis Used:General Linear Mixed Model ANOVA was applied with yoga experience as a between-group factor in repeated measures. Independent sample t-test was applied for between group comparison of respiratory rate, demographic, and anthropometric data. P <0.05 is considered statistically significant.Results:Between-group comparison during HDT with spontaneous breathing has shown a significantly lower heart rate (P = 0.004) with higher RR interval (RRI) (P = 0.002) and pNN50% (P = 0.019) in yoga practitioners. The sequence BRS (P < 0.0001) and α low frequency (LF) of spectral BRS (P = 0.035) were also significantly higher in the yoga group compared to the naïve group. Similarly, during HDT with slow breathing, the heart rate was lower (P = 0.01); with higher RRI (P = 0.009); pNN50% (P = 0.048). Standard deviation of successive RR interval difference of systolic BPV was lower (P = 0.024) with higher sequence BRS (P = 0.001) and α LF of spectral BRS (P = 0.002) in yoga group than naïve group.Conclusion:The yoga experienced individuals exhibit higher resting parasympathetic activity, lower systolic BPV, and higher BRS than naïve to yoga individuals. It is inferred from the findings that yoga practitioners were better adapted to transient cephalad fluid shift that happens during 6° HDT. Furthermore, acute slow breathing during 6° HDT reduced the systolic blood pressure in all the participants suggesting the beneficial role of slow breathing during exposure to extreme conditions such as microgravity which might help in the prevention of adverse effects of cephalad fluid shift during long-term weightlessness and maintain the astronaut health. Future mechanistic studies with active yoga intervention are necessary to understand the adaptive mechanisms involving central and vascular modulations contributing to either attenuation or accentuation of the cardiovagal baroreflex during HDT and slow breathing in healthy individuals.

Effects of intracerebroventricular leptin and orexin-A on the baroreflex control of renal sympathetic nerve activity in conscious rats fed a normal or high-fat diet.

This study examined the effect of leptin and orexin-A on autonomic baroreflex control in conscious Wistar rats exposed to high-fat (45% fat) or normal (3.4%) diet for 4weeks. Renal sympathetic nerve activity (RSNA), mean arterial pressure (MAP) and heart rate (HR) were monitored during the generation of baroreflex gain curves and acute volume expansion (VEP). Intracerebroventricular (ICV) leptin (1μg/min) increased RSNA in the normal diet group (0.31±0.04 vs 0.23±0.03mV/s) and MAP in the high-fat diet group (115±5 vs 105±5mm Hg, P<.05). Orexin-A (50ng/min) increased RSNA, HR and MAP in the high-fat diet group (0.26±0.03 vs 0.22±0.02mV/s, 454±8 vs 417±12beats/min, 117±1 vs 108±1mm Hg) and the normal diet group (0.18±0.05 vs 0.17±0.05mV/s, 465±10 vs 426±6beats/min, 116±2 vs 104±3 mmHg). Baroreflex sensitivity for RSNA was increased during ICV leptin by 50% in the normal diet group, compared to 14% in the high-fat diet group (P<.05). Similarly, orexin-A increased baroreflex sensitivity by 56% and 50% in the high-fat and normal diet groups, respectively (all P<.05). During ICV saline, VEP decreased RSNA by 31±5% (P<.05) after 10minutes and the magnitude of this response was blunted during ICV infusion of leptin (17±2%, P<.05) but not orexin-A in the normal diet group. RSNA response to VEP was not changed during ICV leptin or orexin-A in the high-fat diet group. These findings indicate possible central roles for leptin and orexin-A in modulating the baroreflexes under normal or increased fat intake in conscious rats and potential therapeutic approaches for obesity associated hypertension.

EFFECTIVENESS OF SLOW BREATHING TRAINING ON DECREASING BLOOD PRESSURE IN PATIENT WITH HYPERTENSION: A SYSTEMATIC REVIEW

Background: Hypertension is recognized as a major health problem throughout the world leading to various life-threatening heart diseases. The higher the level of blood pressure in the long run, the more likely there is a complication of hypertension. Slow breathing exercises are one of the non-pharmacological therapies that can be used to control or reduce blood pressure and strengthening breathing muscles. This systematic review is to analyze the effectiveness of slow breathing training in blood pressure in patients with hypertension.Methods: Literature search is through Scopus, Pubmed, Proquest, Science Direct, and EBSCO. with the last 5 years (2014-2019). Criteria for inclusion in this review are as follows: studies involving hypertension, ages 18 years and over, patients who have received or are still receiving slow breathing exercises. Keyword in this review was Slow Breathing, Blood Pressure, and Hypertension.Results: There are 10 journals chosen. Total respondents in this review were 1757 hypertensive patients who received slow respiratory therapy. Slow breathing training provides many benefits for hypertensive patients. Subjects with hypertension, pre-hypertension, and antihypertensive drugs, were given slow breathing intervention that is inhaling as much as ≤10 breaths/minute carried out for ≥5 minutes. This exercise is carried out at ≥3 days/week; total duration of intervention ≥4 weeks; Slow breathing training reduces blood pressure at rest, the average using this slow breathing exercise, blood pressure drops 10 -15 mmHg in systole and diastole. Overall, slow breathing exercises decreased SBP by -5.62 mmHg [-7.86, -3.38] and DBP by -2.97 mmHg [-4.28, -1.66].Conclusion: Slow breathing training provides many benefits for hypertensive patients. Especially for patients with isolated systolic hypertension. This non-pharmacological therapy can be carried out by individuals independently in controlling the breathing rate so that they can reach breathing speed both during inspiration and expiration. Slow breathing exercises can also help increase baroreflex sensitivity, then affect blood pressure reduction.

Baroreflex gain and time of pressure decay at different body temperatures in the tegu lizard, Salvator merianae.

Ectotherms may experience large body temperature (Tb) variations. Higher Tb have been reported to increase baroreflex sensitivity in ectotherm tetrapods. At lower Tb, pulse interval (PI) increases and diastolic pressure decays for longer, possibly resulting in lower end-diastolic pressures and mean arterial pressures (Pm). Additionally, compensatory baroreflex-related heart rate modulation (i.e. the cardiac branch of the baroreflex response) is delayed due to increased PI. Thus, low Tb is potentially detrimental, leading to cardiovascular malfunctioning. This raises the question on how Pm is regulated in such an adverse condition. We investigated the baroreflex compensations that enables tegu lizards, Salvator merianae, to maintain blood pressure homeostasis in a wide Tb range. Lizards had their femoral artery cannulated and pressure signals recorded at 15°C, 25°C and 35°C. We used the sequence method to analyse the heart rate baroreflex-related corrections to spontaneous pressure fluctuations at each temperature. Vascular adjustments (i.e. the peripheral branch) were assessed by calculating the time constant for arterial pressure decay (τ)—resultant from the action of both vascular resistance and compliance—by fitting the diastolic pressure descent to the two-element Windkessel equation. We observed that at lower Tb, lizards increased baroreflex gain at the operating point (Gop) and τ, indicating that the diastolic pressure decays at a slower rate. Gop normalized to Pm and PI, as well as the ratio τ/PI, did not change, indicating that both baroreflex gain and rate of pressure decay are adjusted according to PI lengthening. Consequently, pressure parameters and the oscillatory power fraction (an index of wasted cardiac energy) were unaltered by Tb, indicating that both Gop and τ modulation are crucial for cardiovascular homeostasis.

A Practical Guide to Resonance Frequency Assessment for Heart Rate Variability Biofeedback.

Heart rate variability (HRV) represents fluctuations in the time intervals between successive heartbeats, which are termed interbeat intervals. HRV is an emergent property of complex cardiac-brain interactions and non-linear autonomic nervous system (ANS) processes. A healthy heart is not a metronome because it exhibits complex non-linear oscillations characterized by mathematical chaos. HRV biofeedback displays both heart rate and frequently, respiration, to individuals who can then adjust their physiology to improve affective, cognitive, and cardiovascular functioning. The central premise of the HRV biofeedback resonance frequency model is that the adult cardiorespiratory system has a fixed resonance frequency. Stimulation at rates near the resonance frequency produces large-amplitude blood pressure oscillations that can increase baroreflex sensitivity over time. The authors explain the rationale for the resonance frequency model and provide detailed instructions on how to monitor and assess the resonance frequency. They caution that patterns of physiological change must be compared across several breathing rates to evaluate candidate resonance frequencies. They describe how to fine-tune the resonance frequency following an initial assessment. Furthermore, the authors critically assess the minimum epochs required to measure key HRV indices, resonance frequency test-retest reliability, and whether rhythmic skeletal muscle tension can replace slow paced breathing in resonance frequency assessment.

Blockade of adenosine A1 receptor in nucleus tractus solitarius attenuates baroreflex sensitivity response to dexmedetomidine in rats

The α2-adrenergic receptor (α2-AR) agonist dexmedetomidine increases baroreflex sensitivity (BRS). In the current study, we examined the potential role of adenosine A1 receptor (A1R) within the nucleus tractus solitaries (NTS) in such a response. Briefly, adult male Sprague-Dawley rats were anesthetized and randomly received microinjection of selective A1R antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX; 0.1 pmol/1 μl) or saline vehicle into the right NTS. Ten min after the microinjection, dexmedetomidine infusion started at a rate of 30 μg/kg over 15 min followed by infusion at 15 μg·kg−1·h−1 for 105 min, or 100 μg/kg over 15 min followed by infusion at 50 μg·kg−1·h−1 for 105 min. BRS was examined using a standard phenylephrine method prior to infusion (T0), 60 min (T1) and 120 min (T2) after dexmedetomidine infusion started. Adenosine concentration in plasma and brainstem was measured with high-performance liquid chromatography with vs. without α2-AR antagonist atipamezole pretreatment (0.5 mg/kg, i.p.). Dexmedetomidine increased BRS at both 30 (T0: 0.55 ± 0.25 vs. T1: 2.45 ± 0.37, T2: 2.26 ± 0.56 ms/mmHg, P < 0.05) and 100 μg/kg (T0: 0.63 ± 0.24 vs. T1: 6.21 ± 1.87, T2: 6.30 ± 2.12 ms/mmHg, P < 0.05). DPCPX pretreatment obliterated BRS response to 100-μg/kg dexmedetomidine. At 100 μg/kg, dexmedetomidine increased adenosine concentration in plasma (0.23 ± 0.11 to 0.45 ± 0.07 μg/ml, P < 0.05) and brainstem (1.46 ± 0.30 to 2.52 ± 0.22 μg/ml, P < 0.05); such effect was blocked by atipamezole pretreatment. Western blot analysis showed α2-AR up-regulation by 100-μg/kg dexmedetomidine, which can be prevented by DPCPX. Double-labeling with glial fibrillary acidic protein showed α2-AR up-regulation in astrocytes in the NTS. These results suggest that dexmedetomidine enhances baroreflex sensitivity, possibly by increasing adenosine in NTS and α2-AR expression in astrocytes.

Hyperoxia improves autonomic function in individuals with long-duration type 1 diabetes and macroalbuminuria.

Acute oxygen inhalation and slow deep breathing improve measures of autonomic function transiently in individuals with short-duration type 1 diabetes. Our aims were to examine these interventions and changes in autonomic function in individuals with long-duration type 1 diabetes and to explore interactions with the presence of macroalbuminuria or existing cardiovascular autonomic neuropathy. Individuals with type 1 diabetes (n=54) were exposed to acute oxygen inhalation, slow deep breathing and a combination of both (hereafter 'the combination'). Primary outcomes were change in baroreflex sensitivity and heart rate variability. Associations between changes in outcomes were evaluated using mixed effects models. Mean age±sd was 60±10years and diabetes duration was 38±14 years. Changes are presented as per cent difference from baseline with 95% confidence intervals. Acute oxygen inhalation, slow deep breathing and the combination increased baroreflex sensitivity by 21 (10, 34)%, 32 (13, 53)% and 30 (10, 54)%, respectively. Acute oxygen inhalation trended towards increasing heart rate variability 8 (-1, 17)% (P=0.056), and slow deep breathing and the combination increased heart rate variability by 33 (18, 49)% and 44 (27, 64)% respectively. Macroalbuminuria or cardiovascular autonomic neuropathy did not modify results. Autonomic function is improved transiently in individuals with long-duration type 1 diabetes and normoalbuminuria or macroalbuminuria by acute oxygen inhalation and slow deep breathing. There is a risk of survival bias. Autonomic dysfunction might be a reversible condition, and hypoxia might represent a target of intervention.

TIME COURSE CARDIOVASCULAR AND NEUROIMMUNE DYSFUNCTIONS IN A METABOLIC SYNDROME MODEL: IMPACT OF AEROBIC TRAINING

This study analyzed the effects of aerobic exercise training (ET) in the time course of the dysfunctions observed in metabolic syndrome model (SHR + fructose overload). Animals were randomly distributed into two groups: hypertensive + fructose (HF) and hypertensive + fructose + ET (HFT). The fructose overload (100g/l) and the ET (treadmill 1h/d, 5d/wk) was initiated at 30 days of life, and the animals (n=6/group/time) were evaluated after 7, 15, 30 and 60 days. The ET (HFT group) induced an increase in baroreflex sensitivity for bradycardic response at 7 (100%), 15 (86%), 30 (76%) and 60 (74%) days of protocol and for tachycardia response (TR) in 7 (34%), 15 (31%) and 30 (49%) days of protocol as compared to sedentary group (HF). However, the ET did not attenuate the impairment in TR at 60 days of protocol. There was a reduction in the relation of TNF‐a/IL‐10 in fat tissue (40%) and IL‐1β in the spleen (30%) in the HFT group when compared to the HF group in 15 days of protocol. The nitrites in plasma were increased in HFT group as compared to HF group at 7 and 15 days of protocol. Regarding oxidative stress in plasma at 60 days of protocol, there was an increase in SOD activity (74%) and a decrease in lipid peroxidation (46%) and in protein oxidation (60%) in the HFT group when compared to the HF group. The ET reduced blood glucose (15%) and increased insulin sensitivity (31%) at the end of the protocol, although it did not alter blood triglycerides or blood pressure. Fructose consumption increased NFkB and p47 phox protein expression at day 60. However, aerobic exercise training was able to reduce NFkB at day 30 and 60, and p47 phox at day 60. In conclusion, the hemodynamic, autonomic, inflammatory and oxidative stress disorders seem to be time dependent in SHR with fructose overload. On the other hand, aerobic ET is effective in attenuate disorders in this model of metabolic syndrome.Support or Funding InformationFAPESP: 2018/17183‐4

Effect of Suboccipital Release on Pain Perception and Autonomic Reflex Responses to Ischemic and Cold Pain.

To determine the autonomic effects of suboccipital release (SOR) during experimentally induced pain, 16 healthy subjects (eight women, eight men) experienced ischemic (forearm postexercise muscle ischemia [PEMI]) and cold (cold pressor test [CPT]) pain. Beat-to-beat heart rate (electrocardiogram), mean arterial blood pressure (finger photoplethysmography), baroreflex sensitivity (transfer function analysis), and pain perception were measured. SOR or a sham (modified yaw; 30 cycles/min) was performed in minute 2 of pain. PEMI increased blood pressure by 23 ± 2 and 20 ± 2 mmHg; no differences occurred between SOR or yaw. PEMI modestly elevated heart rate during ischemia, followed by significant reduction from baseline with SOR (-3 ± 2 bpm) and yaw (-4 ± 2 bpm); no differences were observed between treatments. CPT increased blood pressure (SOR = 11 ± 1, yaw = 9 ± 2 mmHg) and heart rate (SOR = 10 ± 2, yaw = 8 ± 3 bpm) before SOR and yaw. Neither treatment nor sham blunted blood pressure increases (SOR = 25 ± 2, yaw = 22 ± 2 mmHg) during CPT; both decreased heart rate (SOR = -3 ± 2, yaw = -2 ± 2 bpm) from baseline. PEMI and CPT caused increased pain without treatment modulation. Following pain and manual intervention, SOR increased baroreflex sensitivity in the 0.15-0.35 Hz range and decreased R-R interval power spectral density in the 0.03-0.5 Hz range compared with yaw. To probe potential mechanisms and interactions between manual treatment and a prototypic analgesic, oral aspirin (967 mg) was given 60 minutes before testing to reduce prostaglandin synthesis. Aspirin slightly attenuated pain but neither altered cardiovascular changes to PEMI nor interacted with SOR or yaw. SOR has the capacity to modulate pain-induced autonomic control and regulation.