Cardiac Vagus and Exercise

Vagal nerve stimulation in myocardial ischemia/reperfusion injury: from bench to bedside

The identification of acute cardioprotective strategies against myocardial ischemia/reperfusion (I/R) injury that can be applied in the catheterization room is currently an unmet clinical need and several interventions evaluated in the past at the pre-clinical level have failed in translation. Autonomic imbalance, sustained by an abnormal afferent signalling, is a key component of I/R injury. Accordingly, there is a strong rationale for neuromodulation strategies, aimed at reducing sympathetic activity and/or increasing vagal tone, in this setting. In this review we focus on cervical vagal nerve stimulation (cVNS) and on transcutaneous auricular vagus nerve stimulation (taVNS); the latest has the potential to overcome several of the issues of invasive cVNS, including the possibility of being used in an acute setting, while retaining its beneficial effects. First, we discuss the pathophysiology of I/R injury, that is mostly a consequence of the overproduction of reactive oxygen species. Second, we describe the functional anatomy of the parasympathetic branch of the autonomic nervous system and the most relevant principles of bioelectronic medicine applied to electrical vagal modulation, with a particular focus on taVNS. Then, we provide a detailed and comprehensive summary of the most relevant pre-clinical studies of invasive and non-invasive VNS that support its strong cardioprotective effect whenever there is an acute or chronic cardiac injury and specifically in the setting of myocardial I/R injury. The potential benefit in the emerging field of post cardiac arrest syndrome (PCAS) is also mentioned. Indeed, electrical cVNS has a strong anti-adrenergic, anti-inflammatory, antioxidants, anti-apoptotic and pro-angiogenic effect; most of the involved molecular pathways were already directly confirmed to take place at the cardiac level for taVNS. Pre-clinical data clearly show that the sooner VNS is applied, the better the outcome, with the possibility of a marked infarct size reduction and almost complete left ventricular reverse remodelling when VNS is applied immediately before and during reperfusion. Finally, we describe in detail the limited but very promising clinical experience of taVNS in I/R injury available so far.

The effect of exercise training on heart rate variability in patients with hypertension: A systematic review and meta-analysis

We aimed to assess the effect of exercise training on heart rate variability (HRV) in hypertensive patients and to provide practical recommendations. We systematically searched seven databases for randomized controlled trials (RCTs) comparing the efficacy of exercise interventions vs. non-exercise control for HRV in adults with hypertension. HRV parameters, blood pressure (BP), and heart rate (HR) from the experimental and control groups were extracted to carry out meta-analysis. To explore the heterogeneity, we performed sensitivity analysis, sub-analysis, and meta-regression. Twelve RCTs were included, and the main results demonstrated exercise produced improvement in root mean square of successive RR-intervals differences (RMSSD) and high frequency (HF), and reductions in LF/HF, resting systolic blood pressure (SBP), and HR. The sub-analysis and meta-regression showed that AE improved more HRV indices and was effective in reducing BP compared with RE. Follow-up duration was also an important factor. Data suggests exercise training has ameliorating effects on HRV parameters, resting SBP, and HR in hypertensive patients, showing enhanced autonomic nervous system function and vagal activity. This effect may be better realized with exercise interventions of 4 weeks or more. Considering our results and the hypertension practice guidelines, we tend to recommend patients choose supervised AE.

Heart Rate Recovery: Up to Date in Heart Failure-A Literature Review

The rising prevalence of cardiovascular disease underscores the growing significance of heart failure (HF). Pathophysiological insights into HF highlight the dysregulation of the autonomic nervous system (ANS), characterized by sympathetic overactivity and diminished vagal tone, impacting cardiovascular function. Heart rate recovery (HRR), a metric measuring the heart's ability to return to its baseline rate post-exertion, plays a crucial role in assessing cardiovascular health. Widely applied across various cardiovascular conditions including HF, coronary artery disease (CAD), and arterial hypertension (HTN), HRR quantifies the difference between peak and recovery heart rates. Given its association with elevated sympathetic tone and exercise, HRR provides valuable insights into the perspective of HF, beyond effort tolerance, reaching toward prognostic and mortality indicators. Incorporating HRR into cardiovascular evaluations enhances our understanding of autonomic regulation in HF, offering potential implications for prognostication and patient management. This review addresses the significance of HRR in HF assessment, analyzing recently conducted studies, and providing a foundation for further research and clinical application.

Myoelectric, Myo-Oxygenation, and Myotonometry Changes during Robot-Assisted Bilateral Arm Exercises with Varying Resistances

Robot-assisted bilateral arm training has demonstrated its effectiveness in improving motor function in individuals post-stroke, showing significant enhancements with increased repetitions. However, prolonged training sessions may lead to both mental and muscle fatigue. We conducted two types of robot-assisted bimanual wrist exercises on 16 healthy adults, separated by one week: long-duration, low-resistance workouts and short-duration, high-resistance exercises. Various measures, including surface electromyograms, near-infrared spectroscopy, heart rate, and the Borg Rating of Perceived Exertion scale, were employed to assess fatigue levels and the impacts of exercise intensity. High-resistance exercise resulted in a more pronounced decline in electromyogram median frequency and recruited a greater amount of hemoglobin, indicating increased muscle fatigue and a higher metabolic demand to cope with the intensified workload. Additionally, high-resistance exercise led to increased sympathetic activation and a greater sense of exertion. Conversely, engaging in low-resistance exercises proved beneficial for reducing post-exercise muscle stiffness and enhancing muscle elasticity. Choosing a low-resistance setting for robot-assisted wrist movements offers advantages by alleviating mental and physiological loads. The reduced training intensity can be further optimized by enabling extended exercise periods while maintaining an approximate dosage compared to high-resistance exercises.

The effects of daily dose of intense exercise on cardiac responses and atrial fibrillation

Atrial fibrillation (AF) is a supraventricular tachyarrhythmia that is strongly associated with cardiovascular (CV) disease and sedentary lifestyles. Despite the benefits of exercise on overall health, AF incidence in high-level endurance athletes rivals that of CV disease patients, suggesting a J-shaped relationship with AF. To investigate the dependence of AF vulnerability on exercise, we varied daily swim durations (120, 180 or 240 min day-1 ) in 7-week-old male CD1 mice. We assessed mice after performing equivalent amounts of cumulative work during swimming (i.e. ∼700 L O2  kg-1 ), as determined from O2 consumption rates (V ̇ O 2 ${\dot V_{{{\mathrm{O}}_2}}}$ ). The meanV ̇ O 2 ${\dot V_{{{\mathrm{O}}_2}}}$ during exercise increased progressively throughout the training period and was indistinguishable between the swim groups. Consistent with similar improvements in aerobic conditioning induced by swimming, skeletal muscle mitochondria content increased (P = 0.027) indistinguishably between exercise groups. Physiological ventricular remodelling, characterized by mild hypertrophy and left ventricular dilatation, was also similar between exercised mice without evidence of ventricular arrhythmia inducibility. By contrast, prolongation of daily swim durations caused progressive and vagal-dependent heart rate reductions (P = 0.008), as well as increased (P = 0.005) AF vulnerability. As expected, vagal inhibition prolonged (P = 0.013) atrial refractoriness, leading to reduced AF vulnerability, although still inducible in the 180 and 240 min swim groups. Accordingly, daily swim dose progressively increased atrial hypertrophy (P = 0.003), fibrosis (P < 0.001) and macrophage accumulation (P = 0.006) without differentially affecting the ventricular tissue properties. Thus, increasing daily exercise duration drives progressively adverse atrial-specific remodelling and vagal-dependent AF vulnerability despite robust and beneficial aerobic conditioning and physiological remodelling of ventricles and skeletal muscle. KEY POINTS: Previous studies have suggested that a J-shaped dose-response relationship exists between physical activity and cardiovascular health outcomes, with moderate exercise providing protection against many cardiovascular disease conditions, whereas chronic endurance exercise can promote atrial fibrillation (AF). We found that AF vulnerability increased alongside elevated atrial hypertrophy, fibrosis and inflammation as daily swim exercise durations in mice were prolonged (i.e. ≥180 min day-1 for 6 weeks). The MET-h week-1 (based on O2  measurements during swimming) needed to induce increased AF vulnerability mirrored the levels linked to AF in athletes. These adverse atria effects associated with excessive daily exercise occurred despite improved aerobic conditioning, skeletal muscle adaptation and physiological ventricular remodelling. We suggest that atrial-specific changes observed with exercise arise from excessive elevations in venous filling pressures during prolonged exercise bouts, which we argue has implications for all AF patients because elevated atrial pressures occur in most cardiovascular disease conditions as well as ageing which are linked to AF.

Heart rate recovery after orthostatic challenge and cardiopulmonary exercise testing in older individuals: prospective multicentre observational cohort study

Background

Impaired vagal function in older individuals, quantified by the 'gold standard' delayed heart rate recovery after maximal exercise (HRRexercise), is an independent predictor of cardiorespiratory capacity and mortality (particularly when HRR ≤12 beats min-1). Heart rate also often declines after orthostatic challenge (HRRorthostatic), but the mechanism remains unclear. We tested whether HRRorthostatic reflects similar vagal autonomic characteristics as HRRexercise.

Methods

Prospective multicentre cohort study of subjects scheduled for cardiopulmonary exercise testing (CPET) as part of routine care. Before undergoing CPET, heart rate was measured with participants seated for 3 min, before standing for 3 min (HRRorthostatic). HRRexercise 1 min after the end of CPET was recorded. The primary outcome was the correlation between mean heart rate change every 10 s for 1 min after peak heart rate was attained on standing and after exercise for each participant. Secondary outcomes were HRRorthostatic and peak VO2 compared between individuals with HRRexercise <12 beats min-1.

Results

A total of 87 participants (mean age: 64 yr [95%CI: 61-66]; 48 (55%) females) completed both tests. Mean heart rate change every 10 s for 1 min after peak heart rate after standing and exercise was significantly correlated (R2=0.81; P<0.0001). HRRorthostatic was unchanged in individuals with HRRexercise ≤12 beats min-1 (n=27), but was lower when HRRexercise >12 beats min-1 (n=60; mean difference: 3 beats min-1 [95% confidence interval 1-5 beats min-1]; P<0.0001). Slower HRRorthostatic was associated with lower peak VO2 (mean difference: 3.7 ml kg-1 min-1 [95% confidence interval 0.7-6.8 ml kg-1 min-1]; P=0.039).

Conclusion

Prognostically significant heart rate recovery after exhaustive exercise is characterised by quantitative differences in heart rate recovery after orthostatic challenge. These data suggest that orthostatic challenge is a valid, simple test indicating vagal impairment.

Clinical trial registration

researchregistry6550.

Electrical stimulation of the auricular branch of the vagus nerve potentiates analgesia induced by physical exercise in mice with peripheral inflammation

Objective

This study evaluated the antihyperalgesic and anti-inflammatory effects of percutaneous vagus nerve electrical stimulation (pVNS) associated with physical exercise, i.e., swimming, in mice with peripheral inflammation.

Methods

The pain model was induced by intraplantar (i.pl.) injection of Freund's complete adjuvant (CFA). Sixty-four male Swiss mice (35-40 g) received an i.pl. of CFA and underwent behavioral tests, i.e., mechanical hyperalgesia, edema, and paw temperature tests. Additionally, cytokine levels, specifically interleukin-6 (IL-6) and interleukin-10 (IL-10), were determined by enzyme-linked immunosorbent assay. Mice were treated with swimming exercise for 30 min alone or associated with different time protocols (10, 20, or 30 min) of stimulation in the left ear with random frequency during four consecutive days.

Results

pVNS for 20 min prolonged the antihyperalgesic effect for up to 2 h, 24 h after CFA injection. pVNS for 30 min prolonged the antihyperalgesic effect for up to 7 h, 96 h after CFA injection. However, it did not alter the edema or temperature at both analyzed times (24 and 96 h). Furthermore, the combination of pVNS plus swimming exercise, but not swimming exercise alone, reduced IL-6 levels in the paw and spinal cord, as well as IL-10 levels in the spinal cord.

Conclusion

pVNS potentiates the analgesic effect induced by swimming, which may be, at least in part, mediated by the modulation of inflammatory cytokines in the periphery (paw) and central nervous system (spinal cord). Therefore, the combination of these therapies may serve as an important adjunctive treatment for persistent inflammatory pain.

Exercise blood pressure and heart rate responses to graded exercise testing in intermediate versus morning chronotypes with obesity

Exaggerated exercise blood pressure (BP) is linked to cardiovascular disease (CVD). Although evening chronotypes have greater CVD risk than morning (Morn) types, it is unknown if exercise BP differs in intermediate (Int) types. Adults with obesity were classified as either Morn [n = 23 (18 females), Morning-Eveningness Questionnaire (MEQ) = 63.96 ± 1.0, 54.74 ± 1.4 yr, 33.7 ± 0.6 kg/m2] or Int [n = 23 (19 females), MEQ = 51.36 ± 1.1, 55.96 ± 1.8 yr, 37.2 ± 1.2 kg/m2] chronotype per MEQ. A graded, incremental treadmill test to maximal aerobic capacity (V̇o2max) was conducted. Systolic (SBP) and diastolic (DBP) blood pressure and mean arterial pressure (MAP), rate pressure product (RPP), heart rate (HR), and rate of perceived intensity (RPE) were determined at baseline, 4 min, 6 min, and maximal stages. HR recovery (HRR; maximum postexercise) was determined at 1 and 2 min postexercise. Preexercise fasted aortic waveforms (applanation tonometry), plasma leptin, nitrate/nitrite (nitric oxide bioavailability), and body composition (dual X-ray, DXA) were also collected. Int had lower V̇o2max and plasma nitrate (both P ≤ 0.02) than Morn. No difference in preexercise BP, aortic waveforms, or body composition were noted between groups, although higher plasma leptin was seen in Int compared with Morn (P = 0.04). Although Int had higher brachial DBP and MAP across exercise stages (both P ≤ 0.05) and higher HR, RPE, and RPP at 6 min of exercise (all P ≤ 0.05), covarying for V̇o2max nullified the BP, but not HR or RPE, difference. HRR was greater in Morn independent of V̇o2max (P = 0.046). Fasted leptin correlated with HR at exercise stage 4 (r = 0.421, P = 0.041) and 6 min (r = 0.593, P = 0.002). This observational study suggests that Int has exaggerated BP and HR responses to exercise compared with Morn, although fitness abolished BP differences.NEW & NOTEWORTHY This study compares blood pressure and heart rate responses with graded, incremental exercise between morning and intermediate chronotype adults with obesity. Herein, blood pressure responses to exercise were elevated in intermediate compared with morning chronotype, although V̇o2max abolished this observation. However, heart rate responses to exercise were higher in intermediate vs. morning chronotypes independent of fitness. Collectively, this exercise hemodynamic response among intermediate chronotype may be related to reduced aerobic fitness, altered nitric oxide metabolism, and/or elevated aortic waveforms.

Cardiac Vagal Nerve Activity Increases During Exercise to Enhance Coronary Blood Flow

BACKGROUND

The phrase complete vagal withdrawal is often used when discussing autonomic control of the heart during exercise. However, more recent studies have challenged this assumption. We hypothesized that cardiac vagal activity increases during exercise and maintains cardiac function via transmitters other than acetylcholine.

METHODS

Chronic direct recordings of cardiac vagal nerve activity, cardiac output, coronary artery blood flow, and heart rate were recorded in conscious adult sheep during whole-body treadmill exercise. Cardiac innervation of the left cardiac vagal branch was confirmed with lipophilic tracer dyes (DiO). Sheep were exercised with pharmacological blockers of acetylcholine (atropine, 250 mg), VIP (vasoactive intestinal peptide; [4Cl-D-Phe6,Leu17]VIP 25 µg), or saline control, randomized on different days. In a subset of sheep, the left cardiac vagal branch was denervated.

RESULTS

Neural innervation from the cardiac vagal branch is seen at major cardiac ganglionic plexi, and within the fat pads associated with the coronary arteries. Directly recorded cardiac vagal nerve activity increased during exercise. Left cardiac vagal branch denervation attenuated the maximum changes in coronary artery blood flow (maximum exercise, control: 63.5±5.9 mL/min, n=8; cardiac vagal denervated: 32.7±5.6 mL/min, n=6, P=2.5×10-7), cardiac output, and heart rate during exercise. Atropine did not affect any cardiac parameters during exercise, but VIP antagonism significantly reduced coronary artery blood flow during exercise to a similar level to vagal denervation.

CONCLUSIONS

Our study demonstrates that cardiac vagal nerve activity actually increases and is crucial for maintaining cardiac function during exercise. Furthermore, our findings show the dynamic modulation of coronary artery blood flow during exercise is mediated by VIP.

Effects of physical activity/exercise on tear film characteristics and dry eye associated symptoms: A literature review

PURPOSE

To conduct a review of the literature in order to identify the potential association between physical activity or exercise and the objective signs and/or subjective symptoms of dry-eye disease.

METHODS

A review of PubMed and Web of Science databases was performed, according to the PRISMA guidelines. The papers included in the review addressed the relationship of physical activity or exercise with dry-eye associated signs (changes in tear volume, osmolarity or biochemical composition) and/or subjective symptoms.

RESULTS

A total of 16 papers were included. In eight, the changes in tear film volume, osmolarity and/or biochemical composition were studied after a single, acute bout of aerobic exercise. In another eight, changes in dry-eye associated symptoms were studied in relation to the habitual practice of physical activity or to prescribed exercise programmes. Acute responses of the tear film to exercise included: a) an increase of tear volume, without an increase of the tear break-up time; b) a trend to increase tear osmolarity, although within its physiological range; and c) a reduced concentration of several cytokines, and other molecular markers of inflammation or oxidative stress. Long-term exposure to physical activity or exercise programmes was associated with relief of dry-eye associated symptoms and a trend to increased tear break-up time.

CONCLUSIONS

Despite a high heterogeneity in the studied population, study designs and methods, the current body of evidence suggests a potential role for physical activity as a modulatory stimulus for the proper functioning of the tear film and/or the relief of dry-eye symptoms.

Correlates of Autonomic Function, Hemodynamics, and Physical Activity Performance During Exercise Stress Testing Among Firefighters

BACKGROUND

Autonomic dysfunction is an important propagator of cardiometabolic disease and can be measured using multiple metrics such as heart rate variability (HRV) and heart rate recovery (HRR). The relationships between HRV and HRR have not been fully examined, nor have the relationships between HRV, HRR, and other physiological measures linked to cardiometabolic disease (e.g., blood pressure recovery). Evaluation of these additional relationships may provide new insights into the association between autonomic function and cardiometabolic disease especially among high-risk groups like firefighters.

METHODS

92 firefighters (96% male, 81% white) without overt cardiovascular disease underwent exercise testing with continuous heart rate (HR) and blood pressure (BP) monitoring. HRR was the difference between maximal HR and HR 1-minute post-exercise; BP recovery (BPR) was the difference between maximal BP and BP 2-minute post-exercise. Afterwards, participants underwent 24-hour electrocardiographic monitoring to measure HRV. Unadjusted Spearman correlations and adjusted partial Spearman correlations were computed. Between group analyses were also conducted with Kruskal-Wallis test.

RESULTS

Associations between HRV and HRR poorly converged (RMSSD and HRR, unadjusted = 0.235; adjusted = 0.144). SDNN Index exhibited the strongest association with parasympathetic tone exhibited by overall lower HRs (unadjusted = -0.600; adjusted = -0.631). HRR demonstrated stronger associations with systolic and diastolic BP responses during exercise (SBP Recovery unadjusted = 0.267; adjusted = 0.297; DBP Recovery unadjusted = -0.276; adjusted = -0.232).

CONCLUSIONS

Overall, while HRV metrics converged and were associated with lower resting heart rates, HRV and HRR poorly converged. Interestingly, HRR was related with measures of hemodynamics indicating a potential relationship with vascular function during both maximal exercise and exercise recovery.

Physics-informed neural networks for modeling physiological time series for cuffless blood pressure estimation

The bold vision of AI-driven pervasive physiological monitoring, through the proliferation of off-the-shelf wearables that began a decade ago, has created immense opportunities to extract actionable information for precision medicine. These AI algorithms model input-output relationships of a system that, in many cases, exhibits complex nature and personalization requirements. A particular example is cuffless blood pressure estimation using wearable bioimpedance. However, these algorithms need training over significant amount of ground truth data. In the context of biomedical applications, collecting ground truth data, particularly at the personalized level is challenging, burdensome, and in some cases infeasible. Our objective is to establish physics-informed neural network (PINN) models for physiological time series data that would use minimal ground truth information to extract complex cardiovascular information. We achieve this by building Taylor's approximation for gradually changing known cardiovascular relationships between input and output (e.g., sensor measurements to blood pressure) and incorporating this approximation into our proposed neural network training. The effectiveness of the framework is demonstrated through a case study: continuous cuffless BP estimation from time series bioimpedance data. We show that by using PINNs over the state-of-the-art time series models tested on the same datasets, we retain high correlations (systolic: 0.90, diastolic: 0.89) and low error (systolic: 1.3 ± 7.6 mmHg, diastolic: 0.6 ± 6.4 mmHg) while reducing the amount of ground truth training data on average by a factor of 15. This could be helpful in developing future AI algorithms to help interpret pervasive physiologic data using minimal amount of training data.

Exercise in the Prevention and Treatment of Type 2 Diabetes

Type 2 diabetes is a systemic, multifactorial disease that is a leading cause of morbidity and mortality globally. Despite a rise in the number of available medications and treatments available for management, exercise remains a first-line prevention and intervention strategy due to established safety, efficacy, and tolerability in the general population. Herein we review the predisposing risk factors for, prevention, pathophysiology, and treatment of type 2 diabetes. We emphasize key cellular and molecular adaptive processes that provide insight into our evolving understanding of how, when, and what types of exercise may improve glycemic control. © 2023 American Physiological Society. Compr Physiol 13:1-27, 2023.

Cardiac electrophysiological remodeling associated with enhanced arrhythmia susceptibility in a canine model of elite exercise

The health benefits of regular physical exercise are well known. Even so, there is increasing evidence that the exercise regimes of elite athletes can evoke cardiac arrhythmias including ventricular fibrillation and even sudden cardiac death (SCD). The mechanism of exercise-induced arrhythmia and SCD is poorly understood. Here, we show that chronic training in a canine model (12 sedentary and 12 trained dogs) that mimics the regime of elite athletes induces electrophysiological remodeling (measured by ECG, patch-clamp, and immunocytochemical techniques) resulting in increases of both the trigger and the substrate for ventricular arrhythmias. Thus, 4 months sustained training lengthened ventricular repolarization (QTc: 237.1±3.4 ms vs. 213.6±2.8 ms, n=12; APD90: 472.8±29.6 ms vs. 370.1±32.7 ms, n=29 vs. 25), decreased transient outward potassium current (6.4±0.5 pA/pF vs. 8.8±0.9 pA/pF at 50 mV, n=54 vs. 42), and increased the short-term variability of repolarization (29.5±3.8 ms vs. 17.5±4.0 ms, n=27 vs. 18). Left ventricular fibrosis and HCN4 protein expression were also enhanced. These changes were associated with enhanced ectopic activity (number of escape beats from 0/hr to 29.7±20.3/hr) in vivo and arrhythmia susceptibility (elicited ventricular fibrillation: 3 of 10 sedentary dogs vs. 6 of 10 trained dogs). Our findings provide in vivo, cellular electrophysiological and molecular biological evidence for the enhanced susceptibility to ventricular arrhythmia in an experimental large animal model of endurance training.

Physics-Informed Neural Networks for Modeling Physiological Time Series: A Case Study with Continuous Blood Pressure

The bold vision of AI-driven pervasive physiological monitoring, through the proliferation of off-the-shelf wearables that began a decade ago, has created immense opportunities to extract actionable information for precision medicine. These AI algorithms model the input-output relationships of a system that, in many cases, exhibits complex nature and personalization requirements. A particular example is cuffless blood pressure estimation using wearable bioimpedance. However, these algorithms need to be trained with a significant amount of ground truth data. In the context of biomedical applications, collecting ground truth data, particularly at the personalized level is challenging, burdensome, and in some cases infeasible. Our objective is to establish physics-informed neural network (PINN) models for physiological time series data that would reduce reliance on ground truth information. We achieve this by building Taylor's approximation for the gradually changing known cardiovascular relationships between input and output (e.g., sensor measurements to blood pressure) and incorporating this approximation into our proposed neural network training. The effectiveness of the framework is demonstrated through a case study: continuous cuffless BP estimation from time series bioimpedance data. We show that by using PINNs over the state-of-the-art time series regression models tested on the same datasets, we retain a high correlation (systolic: 0.90, diastolic: 0.89) and low error (systolic: 1.3 ± 7.6 mmHg, diastolic: 0.6 ± 6.4 mmHg) while reducing the amount of ground truth training data on average by a factor of 15. This could be helpful in developing future AI algorithms to help interpret pervasive physiologic data using minimal amount of training data.

Effects of Home-Based Exercise Training on Cardiac Autonomic Neuropathy and Metabolic Profile in Diabetic Hemodialysis Patients

Background: This study aimed to investigate the effects of a home-based exercise training program on Cardiac Autonomic Neuropathy (CAN) and metabolic profile in Diabetic Kidney Disease (DKD) patients undergoing maintenance hemodialysis (HD). Method: Twenty-eight DKD patients undergoing hemodialysis were randomly assigned into two groups. The exercise (EX) group followed a 6-month combined exercise training program at home, while the control (CO) group remained untrained. All participants at baseline and the end of the study underwent cardiopulmonary exercise testing (CPET), biochemical tests for glucose and lipid profile, and 24-h electrocardiographic monitoring for heart rate variability (HRV) analysis and heart rate turbulence (HRT). Results: At the end of the study, compared to the CO, the EX group showed a significant increase in serum high-density lipoprotein (HDL) by 27.7% (p = 0.01), peak oxygen uptake (VO2peak) by 9.3% (p < 0.05), the standard deviation of R-R intervals (SDNN) by 34.3% (p = 0.03), percentage of successive RR intervals higher than 50ms (pNN50) by 51.1% (p = 0.02), turbulence slope (TS) index by 18.4% (p = 0.01), and decrease in (glycated hemoglobin) HbA1c by 12.5% (p = 0.04) and low-frequency power LF (ms2) by 29.7% (p = 0.01). Linear regression analysis after training showed that VO2peak was correlated with SDNN (r = 0.55, p = 0.03) and HF (r = 0.72, p = 0.02). Multiple regression analysis indicated that the improvement of sympathovagal balance and aerobic capacity depended on patients’ participation in exercise training. Conclusion: In conclusion, a 6-month home-based mixed-type exercise program can improve cardiac autonomic function and metabolic profile in DKD patients on HD.

PE augmented mindfulness: A neurocognitive framework for research and future healthcare

Various well-controlled studies have suggested that practitioners in mindfulness can be prone to patient drop-out (e.g., due to chronic stress, pathology, cognitive reactivity), despite researchers having identified the underlying mechanisms that link mindfulness to mental health. In this article, a framework for physical exercise (PE) augmented mindfulness is proposed, which posits that consistently practiced PE before meditation can support (early-stage) mindfulness. Neurocognitive research shows PE (aerobic exercises or yoga) and mindfulness to impact similar pathways of stress regulation that involve cognitive control and stress regulation, thereby supporting the proposed synergistic potential of PE augmented mindfulness. Research focused on the psychophysiological impact of PE, showed its practice to promote short-term neurocognitive changes that can promote both cognitive control and the attainment of mindful awareness (MA). In order to chart dose responses required for protocol development, further research will be presented. Together these findings are discussed in light of future research on this multidisciplinary topic, protocol development, mindful walking, and further application in healthcare and beyond.

Training History, Cardiac Autonomic Recovery from Submaximal Exercise and Associated Performance in Recreational Runners

This study investigated the effect of prolonged exertion on cardiac parasympathetic (cPS) reorganization and associated aerobic performance in response to repeated short-lasting submaximal exercise bouts (SSE) performed for 7 days following prolonged exertion. In 19 recreational runners, heart rate (HR) and HR variability (HRV) indices (lnRMSSD, lnHF, and lnLF/HF) were monitored pre- and post-submaximal graded cycling performed on consecutive days following a half-marathon (HM) and compared with the baseline, pre-HM values. Additionally, HR recovery (HRR), aerobic performance, and rate of perceived exertion (RPE) were determined. HR, HRV indices, and HRR were tested for correlation with exercise performance. A significant time effect was found in HR, HRR, and HRV indices as well as in aerobic performance and RPE during the study period. Most of the measured parameters differed from their baseline values only on the same day following HM. However, HRR and HR measured in recovery after SSE were additionally affected one day following the half-marathon yet in opposite directions to those recorded on the same day as the HM. Thus, postSSE HR and HRR exhibited a bivariate time response (postSSE HR: 102 ± 14 bpm; p < 0.001; 82 ± 11 bpm; p = 0.007 vs. 88 ± 11 bpm; HRR in 30 s after SSE cessation: 14.9 ± 4.9 bpm; p < 0.001; 30.1 ± 13.3 bpm; p = 0.006 vs. 24.4 ± 10.8 bpm), potentially indicating a cPS dysfunction phase on the same day and cPS rebound phase one day following HM reflected also in consecutive changes in aerobic power. Correlations were found between the changes in measured cardiac indices with respect to baseline and the changes in aerobic performance indices throughout the study period. The effect of exercise history on cPS reorganization is more pronounced in response to SSE than at rest. Accordingly, we conclude that SSE performed repeatedly on a daily basis following prolonged exertion offers a noninvasive tool to evaluate the impact of training history on cPS recovery and associated aerobic power output in recreational athletes.

Overnight sleeping heart rate variability of Army recruits during a 12-week basic military training course

Purpose

This study aimed to quantify sleeping heart rate (HR) and HR variability (HRV) alongside circulating tumor necrosis factor alpha (TNFα) concentrations during 12-week Basic Military Training (BMT). We hypothesised that, despite a high allostatic load, BMT would increase cardiorespiratory fitness and HRV, while lowering both sleeping HR and TNFα in young healthy recruits.

Methods

Sixty-three recruits (18–43 years) undertook ≥ 2 overnight cardiac frequency recordings in weeks 1, 8 and 12 of BMT with 4 h of beat-to-beat HR collected between 00:00 and 06:00 h on each night. Beat-to-beat data were used to derive HR and HRV metrics which were analysed as weekly averages (totalling 8 h). A fasted morning blood sample was collected in the equivalent weeks for the measurement of circulating TNFα concentrations and predicted VO₂max was assessed in weeks 2 and 8.

Results

Predicted VO₂max was significantly increased at week 8 (+ 3.3 ± 2.6 mL kg⁻¹ min⁻¹; p < 0.001). Sleeping HR (wk1, 63 ± 7 b min⁻¹) was progressively reduced throughout BMT (wk8, 58 ± 6; wk12, 55 ± 6 b min⁻¹; p < 0.01). Sleeping HRV reflected by the root mean square of successive differences (RMSSD; wk1, 86 ± 50 ms) was progressively increased (wk8, 98 ± 50; wk12, 106 ± 52 ms; p < 0.01). Fasted circulating TNFα (wk1, 9.1 ± 2.8 pg/mL) remained unchanged at wk8 (8.9 ± 2.5 pg/mL; p = 0.79) but were significantly reduced at wk12 (8.0 ± 2.4 pg/mL; p < 0.01).

Conclusion

Increased predicted VO₂max, HRV and reduced HR during overnight sleep are reflective of typical cardiorespiratory endurance training responses. These results indicate that recruits are achieving cardiovascular health benefits despite the high allostatic load associated with the 12-week BMT.

Chronotropic Response and Heart Rate Variability before and after a 160 m Walking Test in Young, Middle-Aged, Frail, and Non-Frail Older Adults

The frailty syndrome is characterized by a decreased capacity to adequately respond to stressors. One of the most impaired physiological systems is the autonomous nervous system, which can be assessed through heart rate (HR) variability (HRV) analysis. In this article, we studied the chronotropic response (HR and HRV) to a walking test. We also analyzed HRV indices in rest as potential biomarkers of frailty. For this, a 160 m-walking test and two standing rest tests (before and after the walking) were performed by young (19−29 years old, n = 21, 57% women), middle-aged (30−59 years old, n = 16, 62% women), and frail older adults (>60 years old, n = 28, 40% women) and non-frail older adults (>60 years old, n = 15, 71% women), classified with the FRAIL scale and the Clinical Frailty Scale (CFS). Frequency domain parameters better allowed to distinguish between frail and non-frail older adults (low-frequency power LF, high-frequency power HF (nu), LF/HF ratio, and ECG-derived respiration rate EDR). Frail older adults showed an increased HF (nu) and EDR and a reduced LF (nu) and LF/HF compared to non-frail older adults. The increase in HF (nu) could be due to a higher breathing effort. Our results showed that a walk of 160 m is a sufficient cardiovascular stressor to exhibit an attenuated autonomic response in frail older adults. Several HRV indices showed to be potential biomarkers of frailty, being LF (nu) and the time required to reach the maximum HR the best candidates.

Analysis of Short-Term Heart Rate Asymmetry in High-Performance Athletes and Non-Athletes

Heart rate asymmetry (HRA) refers to how asymmetrically the acceleration and deceleration patterns in heartbeat fluctuations are distributed. There is limited evidence regarding HRA changes in athletes and their association with autonomic regulation. This study aimed to compare the short-term HRA of high-performance athletes and non-athletes during an autonomic function test by calculating relevant HRA measures. This exploratory study obtained beat-to-beat RR interval time series from 15 high-performance athletes and 12 non-athletes during a standardized autonomic function test. This test includes rest, postural change, controlled respiration, prolonged orthostatism, exercise, and recovery phases. The following HRA parameters were computed from the RR time series for both groups: asymmetric spread index (ASI), slope index (SI), Porta’s index (PI), Guzik’s index (GI), and Ehlers’ index (EI). We found significant differences (p < 0.01) in the mean value of several HRA parameters between athletes and non-athletes and across the autonomic function test phases, mainly in postural change and recovery phases. Our results indicate that high-performance athletes manifest a higher number and magnitude of cardiac decelerations than non-athletes after an orthostatic challenge, as indicated by GI and EI. In addition, lower HRA was found in athletes in the recovery phase than in non-athletes, as indicated by ASI.

Regional Differences in Sympathetic Nerve Activity Are Generated by Multiple Arterial Baroreflex Loops Arranged in Parallel

In this review, by evaluating the responses during freezing, rapid eye movement (REM) sleep, and treadmill exercise, we discuss how multiple baroreflex loops arranged in parallel act on different organs to modulate sympathetic nerve activity (SNA) in a region-specific and coordinated manner throughout the body. During freezing behaviors, arterial pressure (AP) remains unchanged, heart rate (HR) persistently decreases, renal SNA (RSNA) increases, and lumbar SNA (LSNA) remains unchanged. The baroreflex curve for RSNA shifts upward; that for LSNA remains unchanged; and that for HR shifts to the left. These region-specific changes in baroreflex curves are responsible for the region-specific changes in RSNA, LSNA, and HR during freezing. The decreased HR could allow the heart to conserve energy, which is offset by the increased RSNA caused by decreased vascular conductance, resulting in an unchanged AP. In contrast, the unchanged LSNA leaves the muscles in readiness for fight or flight. During REM sleep, AP increases, RSNA and HR decrease, while LSNA is elevated. The baroreflex curve for RSNA during REM sleep is vertically compressed in comparison with that during non-REM sleep. Cerebral blood flow is elevated while cardiac output is decreased during REM sleep. To address this situation, the brain activates the LSNA selectively, causing muscle vasoconstriction, which overcomes vasodilation of the kidneys as a result of the decreased RSNA and cardiac output. Accordingly, AP can be maintained during REM sleep. During treadmill exercise, AP, HR, and RSNA increase simultaneously. The baroreflex curve for RSNA shifts right-upward with the increased feedback gain, allowing maintenance of a stable AP with significant fluctuations in the vascular conductance of working muscles. Thus, the central nervous system may employ behavior-specific scenarios for modulating baroreflex loops for differential control of SNA, changing the SNA in a region-specific and coordinated manner, and then optimizing circulatory regulation corresponding to different behaviors.

Effects of sex and wet-bulb globe temperature on heart rate variability during prolonged moderate-intensity exercise: A secondary analysis

Sex-differences in heart rate (HR) and heart rate variability (HRV), a surrogate of cardiac autonomic modulation, are evident during rest and exercise in young healthy individuals. However, it remains unclear whether sex impacts HRV during prolonged exercise at differing levels of environmental heat stress. Therefore, we completed a secondary analysis upon the effects of sex and wet-bulb globe temperature (WBGT) on HR and HRV during prolonged exercise. To achieve this, HR and HRV were assessed in non-endurance-trained and non-heat-acclimatized healthy men (n=19) and women (n=15) aged 18-45 years during 180-min treadmill walking at a moderate metabolic rate (200 W/m2: equivalent to ~35% peak aerobic power) in 16, 24, 28, and 32°C WBGT. In the final 5 min prior to exercise termination, HR was observed to be higher in women relative to men in all but the 32°C WBGT. Although no sex-differences were observed for the HRV metric of root-mean-square of successive differences, high frequency power was higher in women relative to men across WBGT conditions. These findings indicate that, in healthy non-heat-acclimatized individuals, women respond to prolonged exercise-heat stress with a greater increase in HR despite cardiac vagal autonomic modulation remaining equal or increasing compared to men. Novelty points. • Prior to exercise termination, females respond with a greater increase in heart rate under all wet-bulb globe temperatures except the hottest (32°C). • Sex influenced heart rate variability (HRV) metrics during all wet-bulb globe temperatures, but results were mixed. • Further characterisation of HRV sex differences remains an important area of research.

Autonomic dysfunction in adults following mild traumatic brain injury: A systematic review

BACKGROUND

Increasing evidence suggests autonomic nervous system (ANS) dysfunction may occur following mild traumatic brain injury (mTBI). Measures of heart rate, heart rate variability, blood pressure and baroreceptor sensitivity can be used to evaluate ANS dysfunction following mTBI.

OBJECTIVE

Summarize the evidence for ANS dysfunction in adults following mTBI.

METHODS

A search of Embase, MEDLINE, Cochrane Central Register, PsycINFO, CINAHL and SPORTDiscus databases was conducted. Search topics included: mTBI and ANS. Identified abstracts were independently reviewed by 2 reviewers followed by full text screening. Risk of bias was assessed using a modified SIGN checklist. A structured synthesis was performed.

RESULTS

Thirty-nine studies (combined 1,467 participants diagnosed with mTBI) evaluating ANS function were included. ANS function was evaluated under various conditions including: rest, during exertion, cold pressor test, Valsalva maneuver, using face cooling and eyeball pressure paradigms. Short-term or ultra-short-term recordings were most common. The majority of studies (28/39) were rated as "unacceptable" for quality of evidence.

CONCLUSIONS

Altered parameters of ANS function have been reported in multiple conditions following mTBI, both acutely and in the post-acute/chronic stages of recovery. However, due to methodological limitations, conclusions regarding the severity and timing of ANS dysfunction following mTBI cannot be drawn.

Dysautonomia following COVID-19 is not associated with subjective limitations or symptoms but is associated with objective functional limitations

Background

Individuals who contract coronavirus disease 2019 (COVID-19) can suffer with persistent and debilitating symptoms long after the initial acute illness. Heart rate (HR) profiles determined during cardiopulmonary exercise testing (CPET) and delivered as part of a post-COVID recovery service may provide insight into the presence and impact of dysautonomia on functional ability.

Objective

Using an active, working-age, post–COVID-19 population, the purpose of this study was to (1) determine and characterize any association between subjective symptoms and dysautonomia; and (2) identify objective exercise capacity differences between patients classified “with” and those “without” dysautonomia.

Methods

Patients referred to a post–COVID-19 service underwent comprehensive clinical assessment, including self-reported symptoms, CPET, and secondary care investigations when indicated. Resting HR >75 bpm, HR increase with exercise <89 bpm, and HR recovery <25 bpm 1 minute after exercise were used to define dysautonomia. Anonymized data were analyzed and associations with symptoms, and CPET outcomes were determined.

Results

Fifty-one of the 205 patients (25%) reviewed as part of this service evaluation had dysautonomia. There were no associations between symptoms or perceived functional limitation and dysautonomia (P >.05). Patients with dysautonomia demonstrated objective functional limitations with significantly reduced work rate (219 ± 37 W vs 253 ± 52 W; P <.001) and peak oxygen consumption (V̇o₂: 30.6 ± 5.5 mL/kg/min vs 35.8 ± 7.6 mL/kg/min; P <.001); and a steeper (less efficient) V̇e/V̇co₂ slope (29.9 ± 4.9 vs 27.7 ± 4.7; P = .005).

Conclusion

Dysautonomia is associated with objective functional limitations but is not associated with subjective symptoms or limitation.

The ratio of heart rate to heart rate variability reflects sympathetic activity during incremental cycling exercise

A low-frequency to a high-frequency component ratio (LF/HF) in heart rate variability (HRV) may not accurately reflect sympathetic nervous activity during exercise. Thus, a valid HRV-based index of sympathetic nervous activity is needed. Therefore, the heart rate to LF ratio (Heart rate/LF) was evaluated as sympathetic nervous activity index which is reflected by catecholamine levels during incremental exercise. In this study, 15 healthy adults performed an incremental exercise test using a cycle ergometer. HRV was derived from electrocardiography and HRV components related to the autonomic nervous system were obtained using frequency analysis. Heart rate/LF was calculated using the heart rate and LF component produced by HRV analysis. Catecholamine, blood lactate levels and respiratory gas were also measured throughout the exercise test. While LF/HF did not increase with increasing exercise intensity, Heart rate/LF non-linearly increased during the incremental exercise test, as did noradrenaline and blood lactate. Interestingly, Heart rate/LF values were positively correlated with noradrenaline (ρ = 0.788, p < 0.05) and blood lactate (ρ = 0.802, p < 0.05) levels and carbon dioxide production (ρ = 0.903, p < 0.05) from at rest through the exercise stages. Heart rate/LF reflects sympathetic nervous activity and metabolic responses during incremental cycling exercise and has potential as an HRV index of sympathetic nervous activity during exercise.Trial registration: UMIN Japan identifier: UMIN000039639..

The effects of exercise training on hypertensive older adults: an umbrella meta-analysis

Exercise training has been shown to blunt many of the physiological declines and common diseases of the aging process. One such beneficial effect is the reduction of blood pressure (BP) in hypertensive older adults. However, there is no consensus about which benefits of aerobic (AT) or resistance training (RT) may be lost by the use of combined training (CT) or even what benefits could be acquired only by performing CT, considering the extensive health needs of older adults with hypertension. Thus, we performed an umbrella meta-analysis. The benefits conferred by CT are extensive and encompass cardiorespiratory fitness, muscular fitness, and blood lipid profile improvements. CT may be recommended to improve the extensive health needs of hypertensive older adults that go beyond blood pressure reduction.

Athlete's Heart in Asian Military Males: The CHIEF Heart Study

Background: Elite athlete's heart is characterized by a greater left ventricular mass indexed by body surface area (LVMI) and diastolic function; however previous studies are mainly conducted in non-Asian athletes compared to sedentary controls.

Methods: This study included 1,388 male adults, aged 18–34 years, enrolled in the same unified 6-month physical training program in Taiwan. During the midterm exams of 2020, all trainees completed a 3-km run (endurance) test, and 577 were randomly selected to attend a 2-min push-up (muscular strength) test. Elite athletes were defined as the performance of each exercise falling one standard deviation above the mean (16%). Cardiac structure and function were measured by echocardiography and compared between elite and non-elite athletes. Multiple logistic regression analysis was used to determine the independent predictors of elite athlete status at each exercise modality.

Results: As compared to non-elite controls, elite endurance athletes had greater LVMI (84.4 ± 13.6 vs. 80.5 ± 12.9 g/m², p < 0.001) and lateral mitral E'/A' ratio (2.37 ± 0.73 vs. 2.22 ± 0.76, p < 0.01) with lower late diastolic A' (7.77 ± 2.16 vs. 8.30 ± 3.69 cm/s, p = 0.03). Elite strength athletes had greater LVMI (81.8 ± 11.4 vs. 77.5 ± 12.1, p = 0.004) and lateral mitral E'/A' ratio (2.36 ± 0.70 vs. 2.11 ± 0.71, p < 0.01) with a greater early diastolic E' (19.30 ± 4.06 vs. 18.18 ± 4.05 cm/s, p = 0.02). Greater LVMI and lower heart rate were independent predictors of elite endurance athletes [odds ratio (OR) and 95% confidence intervals: 1.03 (1.02, 1.04) and 0.96 (0.95, 0.98), respectively]. Greater LVMI, lateral mitral E'/A' ratio and right ventricular systolic pressure were independent predictors of elite strength athletes [OR: 1.03 (1.01, 1.05), 1.50 (1.06, 2.12), and 1.12 (1.05, 1.19), respectively].

Conclusions: Cardiac structural and functional characteristics differ between endurance and strength elite athletes. While greater LVMI predicts elite status in both groups of Asian athletes, consistent with findings from Western elite athletes, greater diastolic function, and right ventricular systolic pressure characterize strength elite athletes, while lower heart rate at rest predicts endurance elite athletic status.

Proteomic Analysis of Cardiac Adaptation to Exercise by High Resolution Mass Spectrometry

Regular exercise has many health benefits, among which is a significant reduction of cardiovascular risk. Although many beneficial effects of exercise are well described, the exact mechanisms by which exercise confers cardiovascular benefits are yet to be fully understood. In the current study, we have used high resolution mass spectrometry to determine the proteomic responses of the heart to exercise training in mice. The impact of exercise-induced oxidative stress on modifications of cardiomyocyte proteins with lipid peroxidation biomarker 4-hydroxynonenal (4-HNE) was examined as well. Fourteen male mice were randomized into the control (sedentary) group and the exercise group that was subjected to a swim exercise training program for 5 days a week for 5 months. Proteins were isolated from the left ventricular tissue, fractionated and digested for shotgun proteomics. Peptides were separated by nanoliquid chromatography and analyzed on an Orbitrap Fusion mass spectrometer using high-energy collision–induced dissociation and electron transfer dissociation fragmentation. We identified distinct ventricular protein signatures established in response to exercise training. Comparative proteomics identified 23 proteins that were upregulated and 37 proteins that were downregulated with exercise, in addition to 65 proteins that were identified only in ventricular tissue samples of exercised mice. Most of the proteins specific to exercised mice are involved in respiratory electron transport and/or implicated in glutathione conjugation. Additionally, 10 proteins were found to be modified with 4-HNE. This study provides new data on the effects of exercise on the cardiac proteome and contributes to our understanding of the molecular mechanisms underlying the beneficial effects of exercise on the heart.

Burst Exercise Testing Can Unmask Arrhythmias in Patients With Incompletely Penetrant Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is characterized by cardiac arrest during sudden exertion. However, standard exercise stress testing (EST) lacks sensitivity, leading to misdiagnosis and undertreatment. After a nondiagnostic standard gradual EST, we report 6 patients who underwent a novel burst exercise test characterized by sudden high workload at the outset of testing. In 5 of 6 patients, the burst EST induced new and more complex arrhythmias versus standard EST, which compelled medication initiation in 3 patients. We postulate that this simple EST modification better mimics a typical CPVT triggering event and could improve diagnostic sensitivity and therapeutic decision making.

Clinical analysis of cardiac autonomic ganglion plexus ablation for bradyarrhythmia: Research protocol for an intervention study

OBJECTIVE

This study aimed to explore the safety and effectiveness of selective cardiac autonomic ganglion plexus (GP) ablation on patients with bradyarrhythmia. The heart is controlled by its own intrinsic and central autonomic nerves. Increased cardiac vagal tone leads to sinus node dysfunction and atrioventricular conduction disorders, resulting in bradyarrhythmia. Pacemaker implantation can relieve the symptoms of arrhythmia caused by bradycardia, but it is not easy for patients to accept a pacemaker implantation as a form of treatment. Therefore, more and more attention has been paid to cardiac vagus nerve ablation.

METHODS

In this study, 20 patients who met the inclusion criteria of GP ablation in the First Affiliated Hospital of Xinjiang Medical University from November 2019 to June 2020 were enrolled. Biochemical and other related examinations along with electrophysiological examinations were conducted before ablation, and then cardiac GP ablation was performed. The patients were followed up 3 times at 3, 6, and 12 months after the operation.

RESULTS

The minimum HR and mean HR were significantly increased after treatment with cardiac autonomic GP ablation (p<0.01). Moreover, the SDNN (Standard deviation of Normal-to-Normal Intervals) and RMSSD (Root mean square successive differences between successive R-R intervals) was significantly decreased after treatment with cardiac autonomic ganglion plexus ablation for 6 months and 12 months (p<0.01).

CONCLUSION

Cardiac GP ablation is relatively simple and easy to implement in units that have performed radiofrequency ablation for bradyarrhythmias. This procedure can be performed without any new equipment. Some patients with bradycardia may not have a permanent pacemaker implantation and may go in for additional treatment options.

[Contribution of sympathetic activation to antihypertrophic memory after regression of exercise-induced physiological myocardial hypertrophy in mice]

OBJECTIVE

To investigate whether anti-hypertrophic memory exists after regression of exercise-induced physiological myocardial hypertrophy (PMH) and explore the contribution of sympathetic activation to hypertrophic memory formation.

OBJECTIVE

Seventy-two mice were randomized equally into 6 groups, including sedentary sham-operated group, exercise hypertrophic preconditioning (EHP) + sham operation group, bisoprolol (an adrenergic β1 receptor blocker) + EHP + sham operation group (biso+Exe+Sham group), sedentary group with transverse aortic constriction (TAC) (Sed+TAC group), EHP+ TAC group (Exe+TAC group), and bisoprolol+EHP+TAC group (biso+Exe+TAC group). The mice in the EHP groups were subjected to 3 weeks of swimming training, and in the bisoprolol groups, bisoprolol was administered by gavage once daily from two days before till the end of the training. One week after the training, TAC or sham surgery was performed. Echocardiography and hemodynamic measurements were performed to evaluate cardiac function of the mice, and the myocardial tissues were examined histologically to detect cardiac remodeling.

OBJECTIVE

Compared with the sedentary group, the mice receiving 3 weeks of swimming training had significantly increased heart weight to body weight ratio (HW/BW), HW to tibia length ratio (HW/TL), and the cross-sectional area of the cardiomyocytes (P < 0.05). One week after the training, exercise-induced PMH rapidly diminished and both HW/BW and HW/TL recovered the baseline levels. Treatment with bisoprolol obviously prevented the occurrence of PMH. Four weeks after TAC, the left ventricular posterior wall thickness, HW/BW, HW/TL, left ventricular end diastolic pressure and cross-sectional area of cardiomyocytes were all significantly lower (P < 0.05) while the left ejection fraction and maximal change rate of left ventricular pressure were significantly higher (P < 0.05) in Exe + TAC group than in Sed + TAC group. No significant difference was found in these parameters between biso + Exe + TAC group and Sed + TAC group.

OBJECTIVE

Anti-hypertrophic memory exists even after the regression of exercise-induced PMH, which may be attributed to the activation of sympathetic nervous system during exercise.

Glucagon-like peptide-1 (GLP-1) receptor activation dilates cerebral arterioles, increases cerebral blood flow, and mediates remote (pre)conditioning neuroprotection against ischaemic stroke

Stroke remains one of the most common causes of death and disability worldwide. Several preclinical studies demonstrated that the brain can be effectively protected against ischaemic stroke by two seemingly distinct treatments: remote ischaemic conditioning (RIC), involving cycles of ischaemia/reperfusion applied to a peripheral organ or tissue, or by systemic administration of glucagon-like-peptide-1 (GLP-1) receptor (GLP-1R) agonists. The mechanisms underlying RIC- and GLP-1-induced neuroprotection are not completely understood. In this study, we tested the hypothesis that GLP-1 mediates neuroprotection induced by RIC and investigated the effect of GLP-1R activation on cerebral blood vessels, as a potential mechanism of GLP-1-induced protection against ischaemic stroke. A rat model of ischaemic stroke (90 min of middle cerebral artery occlusion followed by 24-h reperfusion) was used. RIC was induced by 4 cycles of 5 min left hind limb ischaemia interleaved with 5-min reperfusion periods. RIC markedly (by ~ 80%) reduced the cerebral infarct size and improved the neurological score. The neuroprotection established by RIC was abolished by systemic blockade of GLP-1R with a specific antagonist Exendin(9-39). In the cerebral cortex of GLP-1R reporter mice, ~ 70% of cortical arterioles displayed GLP-1R expression. In acute brain slices of the rat cerebral cortex, activation of GLP-1R with an agonist Exendin-4 had a strong dilatory effect on cortical arterioles and effectively reversed arteriolar constrictions induced by metabolite lactate or oxygen and glucose deprivation, as an ex vivo model of ischaemic stroke. In anaesthetised rats, Exendin-4 induced lasting increases in brain tissue PO2, indicative of increased cerebral blood flow. These results demonstrate that neuroprotection against ischaemic stroke established by remote ischaemic conditioning is mediated by a mechanism involving GLP-1R signalling. Potent dilatory effect of GLP-1R activation on cortical arterioles suggests that the neuroprotection in this model is mediated via modulation of cerebral blood flow and improved brain perfusion.

Does exercise attenuate age- and disease-associated dysfunction in unconventional T cells? Shining a light on overlooked cells in exercise immunology

Unconventional T Cells (UTCs) are a unique population of immune cells that links innate and adaptive immunity. Following activation, UTCs contribute to a host of immunological activities, rapidly responding to microbial and viral infections and playing key roles in tumor suppression. Aging and chronic disease both have been shown to adversely affect UTC numbers and function, with increased inflammation, change in body composition, and physical inactivity potentially contributing to the decline. One possibility to augment circulating UTCs is through increased physical activity. Acute exercise is a potent stimulus leading to the mobilization of immune cells while the benefits of exercise training may include anti-inflammatory effects, reductions in fat mass, and improved fitness. We provide an overview of age-related changes in UTCs, along with chronic diseases that are associated with altered UTC number and function. We summarize how UTCs respond to acute exercise and exercise training and discuss potential mechanisms that may lead to improved frequency and function.

Resistance-induced brain activity changes during cycle ergometer exercises

Background

EEGs are frequently employed to measure cerebral activations during physical exercise or in response to specific physical tasks. However, few studies have attempted to understand how exercise-state brain activity is modulated by exercise intensity.

Methods

Ten healthy subjects were recruited for sustained cycle ergometer exercises at low and high resistance, performed on two separate days a week apart. Exercise-state EEG spectral power and phase-locking values (PLV) are analyzed to assess brain activity modulated by exercise intensity.

Results

The high-resistance exercise produced significant changes in beta-band PLV from early to late pedal stages for electrode pairs F3-Cz, P3-Pz, and P3-P4, and in alpha-band PLV for P3-P4, as well as the significant change rate in alpha-band power for electrodes C3 and P3. On the contrary, the evidence for changes in brain activity during the low-resistance exercise was not found.

Conclusion

These results show that the cortical activation and cortico-cortical coupling are enhanced to take on more workload, maintaining high-resistance pedaling at the required speed, during the late stage of the exercise period.

The Vagal Autonomic Pathway of COVID-19 at the Crossroad of Alzheimer's Disease and Aging: A Review of Knowledge

Coronavirus Disease 2019 (COVID-19) pandemic-triggered mortality is significantly higher in older than in younger populations worldwide. Alzheimer's disease (AD) is related to aging and was recently reported to be among the major risk factors for COVID-19 mortality in older people. The symptomatology of COVID-19 indicates that lethal outcomes of infection rely on neurogenic mechanisms. The present review compiles the available knowledge pointing to the convergence of COVID-19 complications with the mechanisms of autonomic dysfunctions in AD and aging. The severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is prone to neuroinvasion from the lung along the vagus nerve up to the brainstem autonomic nervous centers involved in the coupling of cardiovascular and respiratory rhythms. The brainstem autonomic network allows SARS-CoV-2 to trigger a neurogenic switch to hypertension and hypoventilation, which may act in synergy with aging- and AD-induced dysautonomias, along with an inflammatory "storm". The lethal outcomes of COVID-19, like in AD and unhealthy aging, likely rely on a critical hypoactivity of the efferent vagus nerve cholinergic pathway, which is involved in lowering cardiovascular pressure and systemic inflammation tone. We further discuss the emerging evidence supporting the use of 1) the non-invasive stimulation of vagus nerve as an additional therapeutic approach for severe COVID-19, and 2) the demonstrated vagal tone index, i.e., heart rate variability, via smartphone-based applications as a non-serological low-cost diagnostic of COVID-19. These two well-known medical approaches are already available and now deserve large-scale testing on human cohorts in the context of both AD and COVID-19.

Disordered autonomic function during exposure to moderate heat or exercise in a mouse model of Dravet syndrome

OBJECTIVE

To examine autonomic regulation of core body temperature, heart rate (HR), and breathing rate (BR) in response to moderately elevated ambient temperature or moderate physical exercise in a mouse model of Dravet syndrome (DS).

METHODS

We studied video-EEG, ECG, respiration, and temperature in mice with global heterozygous Scn1a knockout (KO) (DS mice), interneuron specific Scn1a KO, and wildtype (WT) mice during exposure to increased environmental temperature and moderate treadmill exercise.

RESULTS

Core body temperatures of WT and DS mice were similar during baseline. After 15 mins of heat exposure, the peak value was lower in DS than WT mice. In the following mins of heat exposure, the temperature slowly returned close to baseline level in WT, whereas it remained elevated in DS mice. KO of Scn1a in GABAergic neurons caused similar thermoregulatory deficits in mice. During exercise, the HR increase was less prominent in DS than WT mice. After exercise, the HR was significantly more suppressed in DS. The heart rate variability (HRV) was lower in DS than WT mice during baseline and higher in DS during exercise-recovery periods.

SIGNIFICANCE

We found novel abnormalities that expand the spectrum of interictal, ictal, and postictal autonomic dysregulation in DS mice. During mild heat stress, there was a significantly blunted correction of body temperature, and a less suppression of both HR and respiration rate in DS than WT mice. These effects were seen in mice with selective KO of Scn1A in GABAergic neurons. During exercise stress, there was diminished increase in HR, followed by an exaggerated HR suppression and HRV elevation during recovery in DS mice compared to controls. These findings suggest that different environmental stressors can uncover distinct autonomic disturbances in DS mice. Interneurons play an important role in thermoregulation. Understanding the spectrum and mechanisms of autonomic disorders in DS may help develop more effective strategies to prevent seizures and SUDEP.

Heart rate variability in older men on the day following prolonged work in the heat

Susceptibility to heat illness during physically demanding work in hot environments is greater on the second of two consecutive workdays. While it has been demonstrated that heat storage is exacerbated on the second compared to first workday in older workers (50-65 yr), the effects on heart rate variability (HRV), an established surrogate of cardiac autonomic modulation, remain unclear. This study evaluated HRV in older workers on the day following prolonged work in the heat. Electrocardiogram was recorded in nine older (53-64 yr) males at rest, during three 30-min bouts of semi-recumbent cycling at fixed rates of metabolic heat production (150, 200, 250 W/m²), each separated by 15-min recovery. Experiments were conducted in hot-dry conditions (40 °C, 20% relative humidity), immediately prior to (Day 1), and on the day following (Day 2), a prolonged work simulation (∼7.5 hr) involving moderate intensity intermittent exercise in hot-dry conditions (38 °C, 34% relative humidity). Core temperature, as well as time, frequency, and nonlinear HRV indices were derived for analysis during rest, the final 5-min of exercise at the highest heat production and recovery. The change in core temperature at the end of work (mean ±SD) was significantly greater on Day 2 (1.0 °C ±0.3) relative to Day 1 (0.8 °C ±0.2; p < 0.01). Heart rate, however, did not significantly differ between days 1 and 2 at rest (Day 1, 59 ±11 bpm; Day 2, 62 ±13 bpm), during exercise (Day 1, 113 ±21 bpm; Day 2, 114 ±18 bpm ) and at the end of recovery (Day 1, 75 ±16 bpm; Day 2, 76 ±12 bpm). Likewise, there were no significant differences in any HRV indices derived from time, frequency, and nonlinear domains (all p > 0.05). Prolonged work in the heat did not modulate next-day heart rhythms, as reflected by HRV, despite augmented core temperature. While HRV can reflect physiological aspects of cardiac autonomic stressors, these findings indicate it does not provide a means to identify exacerbated heat strain in older workers over consecutive work shifts in the heat.

Optogenetic Stimulation of Vagal Efferent Activity Preserves Left Ventricular Function in Experimental Heart Failure

•

This study was designed to determine the effect of selective optogenetic simulation of vagal efferent activity on left ventricular function in an animal (rat) model of MI-induced heart failure.

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Optogenetic stimulation of dorsal brainstem vagal pre-ganglionic neurons transduced to express light-sensitive channels preserved LV function and exercise capacity in animals with MI.

•

The data suggest that activation of vagal efferents is critically important to deliver the therapeutic benefit of VNS in chronic heart failure.

Large clinical trials designed to test the efficacy of vagus nerve stimulation (VNS) in patients with heart failure did not demonstrate benefits with respect to the primary endpoints. The nonselective nature of VNS may account for the failure to translate promising results of preclinical and earlier clinical studies. This study showed that optogenetic stimulation of vagal pre-ganglionic neurons transduced to express light-sensitive channels preserved left ventricular function and exercise capacity in a rat model of myocardial infarction−induced heart failure. These data suggested that stimulation of vagal efferent activity is critically important to deliver the therapeutic benefit of VNS in heart failure.

Heart rate recovery and morbidity after noncardiac surgery: Planned secondary analysis of two prospective, multi-centre, blinded observational studies

Background

Impaired cardiac vagal function, quantified preoperatively as slower heart rate recovery (HRR) after exercise, is independently associated with perioperative myocardial injury. Parasympathetic (vagal) dysfunction may also promote (extra-cardiac) multi-organ dysfunction, although perioperative data are lacking. Assuming that cardiac vagal activity, and therefore heart rate recovery response, is a marker of brainstem parasympathetic dysfunction, we hypothesized that impaired HRR would be associated with a higher incidence of morbidity after noncardiac surgery.

Methods

In two prospective, blinded, observational cohort studies, we established the definition of impaired vagal function in terms of the HRR threshold that is associated with perioperative myocardial injury (HRR ≤ 12 beats min^-1 (bpm), 60 seconds after cessation of cardiopulmonary exercise testing. The primary outcome of this secondary analysis was all-cause morbidity three and five days after surgery, defined using the Post-Operative Morbidity Survey. Secondary outcomes of this analysis were type of morbidity and time to become morbidity-free. Logistic regression and Cox regression tested for the association between HRR and morbidity. Results are presented as odds/hazard ratios [OR or HR; (95% confidence intervals).

Results

882/1941 (45.4%) patients had HRR≤12bpm. All-cause morbidity within 5 days of surgery was more common in 585/822 (71.2%) patients with HRR≤12bpm, compared to 718/1119 (64.2%) patients with HRR>12bpm (OR:1.38 (1.14–1.67); p = 0.001). HRR≤12bpm was associated with more frequent episodes of pulmonary (OR:1.31 (1.05–1.62);p = 0.02)), infective (OR:1.38 (1.10–1.72); p = 0.006), renal (OR:1.91 (1.30–2.79); p = 0.02)), cardiovascular (OR:1.39 (1.15–1.69); p<0.001)), neurological (OR:1.73 (1.11–2.70); p = 0.02)) and pain morbidity (OR:1.38 (1.14–1.68); p = 0.001) within 5 days of surgery.

Conclusions

Multi-organ dysfunction is more common in surgical patients with cardiac vagal dysfunction, defined as HRR ≤ 12 bpm after preoperative cardiopulmonary exercise testing.

Clinical trial registry

ISRCTN88456378.

Cardiovascular reactivity to emotional stress: The hidden challenge for pets in the urbanized environment

Emotional stress is currently considered an important risk factor for cardiovascular diseases. Experimental evidence clearly shows robust autonomic cardiovascular effects in animals exposed to stress stimuli. Considering the remarkable variability of stressors, the urban environment can pose a severe challenge to cardiovascular control. Interestingly, pet ownership is indicated as an efficient non-pharmacological therapy to attenuate stress effects that can reduce the risk of cardiovascular disease. However, the risk of cardiovascular diseases in pets themselves living in urban environment has not received attention it deserves. Here, we review the central mechanisms involved in the autonomic cardiovascular response to emotional stress. Next, we discuss experimental evidence showing the cardiovascular effects produced by emotional stressors in animals, aiming to establish a parallel with common urban stressors. Association of additional risk factors such as sedentarism, obesity and ambient temperature are also considered. Our aim is to identify and raise awareness of the risk of cardiovascular disease in pets exposed to quotidian emotional stressors present in the urban environment.

The hypertension advantage and natural selection: Since type 2 diabetes associates with co-morbidities and premature death, why have the genetic variants remained in the human genome?

Type 2 diabetes is a major public health crisis around the world. It is estimated that more than 300 million people worldwide have type 2 diabetes. Furthermore, the World Health Organization estimates that deaths from the complications of diabetes will increase by two thirds between 2008 and 2030. Since type 2 diabetes is a major public health crisis, why have the genetic variants for diabetes not been removed from the genome by natural selection? We hypothesize that insulin resistance, a predisposition to type 2 diabetes, and the associated elevation in sympathetic nervous system activity and arterial blood pressure provided an advantage to humans who lived as hunter-gatherers. Specifically, sympathetic hyperactivity stimulates the renin-angiotensin aldosterone system, promotes sodium reabsorption, and increases blood volume, heart rate, stroke volume and peripheral vascular resistance, thus inducing hypertension. The hypertension in turn provides a hemodynamic advantage for hunter-gatherers. Specifically, sympathetic hyperactivity and increased blood pressure increases blood flow delivery to working muscles by increasing cardiac output and shunting blood from non-active tissue. This natural selection for hypertension occurred during the time in human evolutionary history when the lifespan of most individuals was probably 30-40 years, and morbidity and mortality from cardiovascular disorders was limited. Thus, the selection pressure for elevation in sympathetic nervous system activity and blood pressure provided an advantage for hunting and gathering that would be greater than the selection pressure exerted by the manifestations of cardiovascular disease in aged individuals.

Physiological comparison of hemorrhagic shock and V˙ O2max: A conceptual framework for defining the limitation of oxygen delivery

IMPACT STATEMENT

Disturbance of normal homeostasis occurs when oxygen delivery and energy stores to the body's tissues fail to meet the energy requirement of cells. The work submitted in this review is important because it advances the understanding of inadequate oxygen delivery as it relates to early diagnosis and treatment of circulatory shock and its relationship to disturbance of normal functioning of cellular metabolism in life-threatening conditions of hemorrhage. We explored data from the clinical and exercise literature to construct for the first time a conceptual framework for defining the limitation of inadequate delivery of oxygen by comparing the physiology of hemorrhagic shock caused by severe blood loss to maximal oxygen uptake induced by intense physical exercise. We also provide a translational framework in which understanding the fundamental relationship between the body's reserve to compensate for conditions of inadequate oxygen delivery as a limiting factor to V ˙ O2max helps to re-evaluate paradigms of triage for improved monitoring of accurate resuscitation in patients suffering from hemorrhagic shock.