High-intensity interval training attenuates endothelial dysfunction in a Dahl salt-sensitive rat model of heart failure with preserved ejection fraction

Exercise training for patients with heart failure and preserved ejection fraction. A narrative review

Heart failure with preserved ejection fraction (HFpEF) remains a significant global health challenge, accounting for up to 50% of all heart failure cases and predominantly affecting the elderly and women. Despite advancements in therapeutic strategies, HFpEF's complexity poses substantial challenges in management, particularly due to its high comorbidity burden, including renal failure, atrial fibrillation, and obesity, among others. These comorbidities not only complicate the pathophysiology of HFpEF but also exacerbate its symptoms, necessitating a personalized approach to treatment focused on comorbidity management and symptom alleviation. In heart failure with reduced ejection fraction, exercise training (ET) was effective in improving exercise tolerance, quality of life, and reducing hospitalizations. However, the efficacy of ET in HFpEF patients remains less understood, with limited studies showing mixed results. Exercise intolerance is a key symptom in HFpEF patients, and it has a multifactorial origin since both central and peripheral oxygen mechanisms of transport and utilization are often compromised. Recent evidence underscores the potential of supervised ET in enhancing exercise tolerance and quality of life among HFpEF patients; however, the literature remains sparse and predominantly consists of small-scale studies. This review highlights the critical role of exercise intolerance in HFpEF and synthesizes current knowledge on the benefits of ET. It also calls for a deeper understanding and further research into exercise-based interventions and their underlying mechanisms, emphasizing the need for larger, well-designed studies to evaluate the effectiveness of ET in improving outcomes for HFpEF patients.

Heart Failure with Preserved Ejection Fraction: Pathogenesis, Diagnosis, Exercise, and Medical Therapies

Heart failure with preserved ejection fraction (HFpEF) accounts for more than one-half of total heart failure cases, with a high prevalence and poor prognosis, especially in older and female patients. Patients with HFpEF are characterized by hypertension, left ventricular hypertrophy, and diastolic dysfunction, and the main symptoms are dyspnea and exercise intolerance. HFpEF is currently poorly studied, and pharmacological treatment for HFpEF is still underexplored. Accumulating clinical trials have shown that exercise could exert benefits on diastolic dysfunction and quality of life in patients with HFpEF. However, there is a high limitation for applying exercise therapy due to exercise intolerance in patients with HFpEF. Key effectors of exercise-protection could be novel therapeutic targets for developing drugs to prevent and treat HFpEF. In this review article, we provide an overview of the pathogenic factors, diagnostic methods, research animal models, the mechanisms of exercise-mediated cardiac protection, and current treatments for HFpEF.

Endothelial Dysfunction in Heart Failure With Preserved Ejection Fraction: What are the Experimental Proofs?

Heart failure with preserved ejection fraction (HFpEF) has been recognized as the greatest single unmet need in cardiovascular medicine. Indeed, the morbi-mortality of HFpEF is high and as the population ages and the comorbidities increase, so considerably does the prevalence of HFpEF. However, HFpEF pathophysiology is still poorly understood and therapeutic targets are missing. An unifying, but untested, theory of the pathophysiology of HFpEF, proposed in 2013, suggests that cardiovascular risk factors lead to a systemic inflammation, which triggers endothelial cells (EC) and coronary microvascular dysfunction. This cardiac small vessel disease is proposed to be responsible for cardiac wall stiffening and diastolic dysfunction. This paradigm is based on the fact that microvascular dysfunction is highly prevalent in HFpEF patients. More specifically, HFpEF patients have been shown to have decreased cardiac microvascular density, systemic endothelial dysfunction and a lower mean coronary flow reserve. Importantly, impaired coronary microvascular function has been associated with the severity of HF. This review discusses evidence supporting the causal role of endothelial dysfunction in the pathophysiology of HFpEF in human and experimental models.

Animal Models of Exercise From Rodents to Pythons

Acute and chronic animal models of exercise are commonly used in research. Acute exercise testing is used, often in combination with genetic, pharmacological, or other manipulations, to study the impact of these manipulations on the cardiovascular response to exercise and to detect impairments or improvements in cardiovascular function that may not be evident at rest. Chronic exercise conditioning models are used to study the cardiac phenotypic response to regular exercise training and as a platform for discovery of novel pathways mediating cardiovascular benefits conferred by exercise conditioning that could be exploited therapeutically. The cardiovascular benefits of exercise are well established, and, frequently, molecular manipulations that mimic the pathway changes induced by exercise recapitulate at least some of its benefits. This review discusses approaches for assessing cardiovascular function during an acute exercise challenge in rodents, as well as practical and conceptual considerations in the use of common rodent exercise conditioning models. The case for studying feeding in the Burmese python as a model for exercise-like physiological adaptation is also explored.

Reciprocal organ interactions during heart failure: a position paper from the ESC Working Group on Myocardial Function

Heart failure-either with reduced or preserved ejection fraction (HFrEF/HFpEF)-is a clinical syndrome of multifactorial and gender-dependent aetiology, indicating the insufficiency of the heart to pump blood adequately to maintain blood flow to meet the body's needs. Typical symptoms commonly include shortness of breath, excessive fatigue with impaired exercise capacity, and peripheral oedema, thereby alluding to the fact that heart failure is a syndrome that affects multiple organ systems. Patients suffering from progressed heart failure have a very limited life expectancy, lower than that of numerous cancer types. In this position paper, we provide an overview regarding interactions between the heart and other organ systems, the clinical evidence, underlying mechanisms, potential available or yet-to-establish animal models to study such interactions and finally discuss potential new drug interventions to be developed in the future. Our working group suggests that more experimental research is required to understand the individual molecular mechanisms underlying heart failure and reinforces the urgency for tailored therapeutic interventions that target not only the heart but also other related affected organ systems to effectively treat heart failure as a clinical syndrome that affects and involves multiple organs.

Physical exercise prevents age-related heart dysfunction induced by high-salt intake and heart salt-specific overexpression in Drosophila

A long-term high-salt intake (HSI) seems to accelerate cardiac aging and age-related diseases, but the molecular mechanism is still not entirely clear. Exercise is an effective way to delay cardiac aging. However, it remains unclear whether long-term exercise (LTE) can protect heart from aging induced by high-salt stress. In this study, heart CG2196(salt) specific overexpression (HSSO) and RNAi (HSSR) was constructed by using the UAS/hand-Gal4 system in Drosophila. Flies were given exercise and a high-salt diet intervention from 1 to 5 weeks of age. Results showed that HSSR and LTE remarkably prevented heart from accelerated age-related defects caused by HSI and HSSO, and these defects included a marked increase in heart period, arrhythmia index, malondialdehyde (MDA) level, salt expression, and dTOR expression, and a marked decrease in fractional shortening, SOD activity level, dFOXO expression, PGC-1α expression, and the number of mitochondria and myofibrils. The combination of HSSR and LTE could better protect the aging heart from the damage of HSI. Therefore, current evidences suggested that LTE resisted HSI-induced heart presenility via blocking CG2196(salt)/TOR/oxidative stress and activating dFOXO/PGC-1α. LTE also reversed heart presenility induced by cardiac-salt overexpression via activating dFOXO/PGC-1α and blocking TOR/oxidative stress.

The molecular signature of high-intensity interval training in the human body

High-intensity training is becoming increasingly popular outside of elite sport for health prevention and rehabilitation. This expanded application of high-intensity training in different populations requires a deeper understanding of its molecular signature in the human body. Therefore, in this integrative review, cellular and systemic molecular responses to high-intensity training are described for skeletal muscle, cardiovascular system, and the immune system as major effectors and targets of health and performance. Different kinds of stimuli and resulting homeostatic perturbations (i. e., metabolic, mechanical, neuronal, and hormonal) are reflected, taking into account their role in the local and systemic deflection of molecular sensors and mediators, and their role in tissue and organ adaptations. In skeletal muscle, a high metabolic perturbation induced by high-intensity training is the major stimulus for skeletal muscle adaptation. In the cardio-vascular system, high-intensity training induces haemodynamic stress and deflection of the Ca ²⁺ handling as major stimuli for functional and structural adaptation of the heart and vessels. For the immune system haemodynamic stress, hormones, exosomes, and O ₂ availability are proposed stimuli that mediate their effects by alteration of different signalling processes leading to local and systemic (anti)inflammatory responses. Overall, high-intensity training shows specific molecular signatures that demonstrate its high potential to improve health and physical performance.

Exercise intolerance in volume overload heart failure is associated with low carotid body mediated chemoreflex drive

Mounting an appropriate ventilatory response to exercise is crucial to meeting metabolic demands, and abnormal ventilatory responses may contribute to exercise-intolerance (EX-inT) in heart failure (HF) patients. We sought to determine if abnormal ventilatory chemoreflex control contributes to EX-inT in volume-overload HF rats. Cardiac function, hypercapnic (HCVR) and hypoxic (HVR) ventilatory responses, and exercise tolerance were assessed at the end of a 6 week exercise training program. At the conclusion of the training program, exercise tolerant HF rats (HF + EX-T) exhibited improvements in cardiac systolic function and reductions in HCVR, sympathetic tone, and arrhythmias. In contrast, HF rats that were exercise intolerant (HF + EX-inT) exhibited worse diastolic dysfunction, and showed no improvements in cardiac systolic function, HCVR, sympathetic tone, or arrhythmias at the conclusion of the training program. In addition, HF + EX-inT rats had impaired HVR which was associated with increased arrhythmia susceptibility and mortality during hypoxic challenges (~ 60% survival). Finally, we observed that exercise tolerance in HF rats was related to carotid body (CB) function as CB ablation resulted in impaired exercise capacity in HF + EX-T rats. Our results indicate that: (i) exercise may have detrimental effects on cardiac function in HF-EX-inT, and (ii) loss of CB chemoreflex sensitivity contributes to EX-inT in HF.

Unveiling the role of exercise training in targeting the inflammatory paradigm of heart failure with preserved ejection fraction: a narrative review

Heart failure with preserved ejection fraction (HFpEF) is currently lacking an effective pharmacological treatment with impact on major outcomes such as hospitalization and mortality. Exercise training (EXT) is recognized as an important nonpharmacological tool, capable of improving exercise capacity and quality of life, and has even been associated with a reduction in hospitalization and cardiovascular mortality risk. However, this positive impact largely lacks a physiological explanation. The aim of this narrative review was to provide an overview of the available data supporting the hypothesis that the beneficial role of EXT in HFpEF might be due to its effects on targeting the inflammatory paradigm described for this disease. A comprehensive literature search was conducted using the PubMed-NCBI database. We reviewed the effects of EXT throughout each step of the pathophysiological pathway leading to HFpEF and found clinical and/or preclinical evidence supporting the reduction of systemic inflammation, endothelial dysfunction, microvascular rarefaction, and myocardial stiffness. We also highlighted some gaps in the knowledge or topics that deserve further clarification in future studies. In conclusion, despite the scarcity of clinical studies in this population, there is compelling evidence suggesting that EXT modulates crucial aspects of the inflammatory pathway described for HFpEF and future investigation on cellular and molecular mechanisms are encouraged.

Circulating microRNAs May Serve as Biomarkers for Hypertensive Emergency End-Organ Injuries and Address Underlying Pathways in an Animal Model

There is an incomplete understanding of the underlying pathophysiology in hypertensive emergencies, where severely elevated blood pressure causes acute end-organ injuries, as opposed to the long-term manifestations of chronic hypertension. Furthermore, current biomarkers are unable to detect early end-organ injuries like hypertensive encephalopathy and renal thrombotic microangiopathy. We hypothesized that circulating microRNAs (c-miRs) could identify acute and chronic complications of severe hypertension, and that combinations of c-miRs could elucidate important pathways involved. We studied the diagnostic accuracy of 145 c-miRs in Dahl salt-sensitive rats fed either a low-salt (N = 20: 0.3% NaCl) or a high-salt (N = 60: 8% NaCl) diet. Subclinical hypertensive encephalopathy and thrombotic microangiopathy were diagnosed by histopathology. In addition, heart failure with preserved ejection fraction was evaluated with echocardiography and N-terminal pro-brain natriuretic peptide; and endothelial dysfunction was studied using acetylcholine-induced aorta ring relaxation. Systolic blood pressure increased severely in animals on a high-salt diet (high-salt 205 ± 20 mm Hg vs. low-salt 152 ± 18 mm Hg, p < 0.001). Partial least squares discriminant analysis revealed 68 c-miRs discriminating between animals with and without hypertensive emergency complications. Twenty-nine c-miRs were strongly associated with hypertensive encephalopathy, 24 c-miRs with thrombotic microangiopathy, 30 c-miRs with heart failure with preserved ejection fraction, and 28 c-miRs with endothelial dysfunction. Hypertensive encephalopathy, thrombotic microangiopathy and heart failure with preserved ejection fraction were associated with deviations in many of the same c-miRs, whereas endothelial dysfunction was associated with a different set of c-miRs. Several of these c-miRs demonstrated fair to good diagnostic accuracy for a composite outcome of hypertensive encephalopathy, thrombotic microangiopathy and heart failure with preserved ejection fraction in receiver-operating-curve analyses (area-under-curve 0.75–0.88). Target prediction revealed an enrichment of genes related to several pathways relevant for cardiovascular disease (e.g., mucin type O-glycan biosynthesis, MAPK, Wnt, Hippo, and TGF-beta signaling). C-miRs could potentially serve as biomarkers of severe hypertensive end-organ injuries and elucidate important pathways involved.

The role of vascular function on exercise capacity in health and disease

Three sentinel parameters of aerobic performance are the maximal oxygen uptake ( V ̇ O 2 max ), critical power (CP) and speed of the V ̇ O 2 kinetics following exercise onset. Of these, the latter is, perhaps, the cardinal test of integrated function along the O2 transport pathway from lungs to skeletal muscle mitochondria. Fast V ̇ O 2 kinetics demands that the cardiovascular system distributes exercise-induced blood flow elevations among and within those vascular beds subserving the contracting muscle(s). Ideally, this process must occur at least as rapidly as mitochondrial metabolism elevates V ̇ O 2 . Chronic disease and ageing create an O2 delivery (i.e. blood flow × arterial [O2 ], Q ̇ O 2 ) dependency that slows V ̇ O 2 kinetics, decreasing CP and V ̇ O 2 max , increasing the O2 deficit and sowing the seeds of exercise intolerance. Exercise training, in contrast, does the opposite. Within the context of these three parameters (see Graphical Abstract), this brief review examines the training-induced plasticity of key elements in the O2 transport pathway. It asks how structural and functional vascular adaptations accelerate and redistribute muscle Q ̇ O 2 and thus defend microvascular O2 partial pressures and capillary blood-myocyte O2 diffusion across a ∼100-fold range of muscle V ̇ O 2 values. Recent discoveries, especially in the muscle microcirculation and Q ̇ O 2 -to- V ̇ O 2 heterogeneity, are integrated with the O2 transport pathway to appreciate how local and systemic vascular control helps defend V ̇ O 2 kinetics and determine CP and V ̇ O 2 max in health and how vascular dysfunction in disease predicates exercise intolerance. Finally, the latest evidence that nitrate supplementation improves vascular and therefore aerobic function in health and disease is presented.

Muscular changes in animal models of heart failure with preserved ejection fraction: what comes closest to the patient?

AIMS

Heart failure with preserved ejection fraction (HFpEF) is associated with reduced exercise capacity elicited by skeletal muscle (SM) alterations. Up to now, no clear medical treatment advice for HFpEF is available. Identification of the ideal animal model mimicking the human condition is a critical step in developing and testing treatment strategies. Several HFpEF animals have been described, but the most suitable in terms of comparability with SM alterations in HFpEF patients is unclear. The aim of the present study was to investigate molecular changes in SM of three different animal models and to compare them with alterations of muscle biopsies obtained from human HFpEF patients.

METHODS AND RESULTS

Skeletal muscle tissue was obtained from HFpEF and control patients and from three different animal models including the respective controls-ZSF1 rat, Dahl salt-sensitive rat, and transverse aortic constriction surgery/deoxycorticosterone mouse. The development of HFpEF was verified by echocardiography. Protein expression and enzyme activity of selected markers were assessed in SM tissue homogenates. Protein expression between SM tissue obtained from HFpEF patients and the ZSF1 rats revealed similarities for protein markers involved in muscle atrophy (MuRF1 expression, protein ubiquitinylation, and LC3) and mitochondrial metabolism (succinate dehydrogenase and malate dehydrogenase activity, porin expression). The other two animal models exhibited far less similarities to the human samples.

CONCLUSIONS

None of the three tested animal models mimics the condition in HFpEF patients completely, but among the animal models tested, the ZSF1 rat (ZSF1-lean vs. ZSF1-obese) shows the highest overlap to the human condition. Therefore, when studying therapeutic interventions to treat HFpEF and especially alterations in the SM, we suggest that the ZSF1 rat is a suitable model.

ZSF1 rat as animal model for HFpEF: Development of reduced diastolic function and skeletal muscle dysfunction

AIMS

The prevalence of heart failure with preserved ejection fraction (HFpEF) is still increasing, and so far, no pharmaceutical treatment has proven to be effective. A key obstacle for testing new pharmaceutical substances is the availability of suitable animal models for HFpEF, which realistically reflect the clinical picture. The aim of the present study was to characterize the development of HFpEF and skeletal muscle (SM) dysfunction in ZSF1 rats over time.

METHODS AND RESULTS

Echocardiography and functional analyses of the SM were performed in 6-, 10-, 15-, 20-, and 32-week-old ZSF1-lean and ZSF1-obese. Furthermore, myocardial and SM tissue was collected for molecular and histological analyses. HFpEF markers were evident as early as 10 weeks of age. Diastolic dysfunction, confirmed by a significant increase in E/e', was detectable at 10 weeks. Increased left ventricular mRNA expression of collagen and BNP was detected in ZSF1-obese animals as early as 15 and 20 weeks, respectively. The loss of muscle force was measurable in the extensor digitorum longus starting at 15 weeks, whereas the soleus muscle function was impaired at Week 32. In addition, at Week 20, markers for aortic valve sclerosis were increased.

CONCLUSIONS

Our measurements confirmed the appearance of HFpEF in ZSF1-obese rats as early as 10 weeks of age, most likely as a result of the pre-existing co-morbidities. In addition, SM function was reduced after the manifestation of HFpEF. In conclusion, the ZSF1 rat may serve as a suitable animal model to study pharmaceutical strategies for the treatment of HFpEF.

Guidelines for animal exercise and training protocols for cardiovascular studies

Whole body exercise tolerance is the consummate example of integrative physiological function among the metabolic, neuromuscular, cardiovascular, and respiratory systems. Depending on the animal selected, the energetic demands and flux through the oxygen transport system can increase two orders of magnitude from rest to maximal exercise. Thus, animal models in health and disease present the scientist with flexible, powerful, and, in some instances, purpose-built tools to explore the mechanistic bases for physiological function and help unveil the causes for pathological or age-related exercise intolerance. Elegant experimental designs and analyses of kinetic parameters and steady-state responses permit acute and chronic exercise paradigms to identify therapeutic targets for drug development in disease and also present the opportunity to test the efficacy of pharmacological and behavioral countermeasures during aging, for example. However, for this promise to be fully realized, the correct or optimal animal model must be selected in conjunction with reproducible tests of physiological function (e.g., exercise capacity and maximal oxygen uptake) that can be compared equitably across laboratories, clinics, and other proving grounds. Rigorously controlled animal exercise and training studies constitute the foundation of translational research. This review presents the most commonly selected animal models with guidelines for their use and obtaining reproducible results and, crucially, translates state-of-the-art techniques and procedures developed on humans to those animal models.

Towards a personalised approach in exercise-based cardiovascular rehabilitation: How can translational research help? A 'call to action' from the Section on Secondary Prevention and Cardiac Rehabilitation of the European Association of Preventive Cardiology

The benefit of regular physical activity and exercise training for the prevention of cardiovascular and metabolic diseases is undisputed. Many molecular mechanisms mediating exercise effects have been deciphered. Personalised exercise prescription can help patients in achieving their individual greatest benefit from an exercise-based cardiovascular rehabilitation programme. Yet, we still struggle to provide truly personalised exercise prescriptions to our patients. In this position paper, we address novel basic and translational research concepts that can help us understand the principles underlying the inter-individual differences in the response to exercise, and identify early on who would most likely benefit from which exercise intervention. This includes hereditary, non-hereditary and sex-specific concepts. Recent insights have helped us to take on a more holistic view, integrating exercise-mediated molecular mechanisms with those influenced by metabolism and immunity. Unfortunately, while the outline is recognisable, many details are still lacking to turn the understanding of a concept into a roadmap ready to be used in clinical routine. This position paper therefore also investigates perspectives on how the advent of 'big data' and the use of animal models could help unravel inter-individual responses to exercise parameters and thus influence hypothesis-building for translational research in exercise-based cardiovascular rehabilitation.

Feasibility of high intensity interval training in patients with breast Cancer undergoing anthracycline chemotherapy: a randomized pilot trial

BACKGROUND

Anthracycline-based chemotherapy is associated with reduced cardiorespiratory fitness in breast cancer patients. High intensity interval training (HIIT) induces greater benefits on cardiorespiratory fitness than moderate continuous aerobic exercise in patients with heart failure. The study purpose was to determine whether a HIIT intervention is a feasible exercise strategy for breast cancer patients undergoing anthracycline-based chemotherapy.

METHODS

Thirty women were randomized to either HIIT or non-exercise control group (CON). Participants performed a maximal cycling fitness test to measure peak power output during maximal oxygen uptake (VO2max). The HIIT group participated in an 8-week HIIT intervention occurring 3 times weekly. Feasibility was calculated by computing (1) the average weekly minutes of HIIT over 8 weeks and (2) the number of sessions attended and multiplied by 100 (percentage of sessions). The intervention was considered feasible if more than 50% of participants completed both an average of 70% of weekly minutes (63/90 min) and attended 70% exercise sessions (17/24 sessions).

RESULTS

Participants were 46.9 ± 9.8 (mean ± SD) years old, diagnosed with clinical stage II (30%) or III (63%) breast cancer. The average weekly minutes of exercise completed was 78 ± 5.1 out of 90 min. Twelve of 15 participants met both feasibility criteria, attending 19.2 ± 2.1 out of 24 sessions (82.3%). VO2max was maintained (19.7 ± 8.7 to 19.4 ± 6.6 ml/kg/min) in HIIT group (p = 0.94) while there was a significant decrease in VO2max (18.7 ± 7.1 to 16.1 ± 6.0 ml/kg/min) in CON group from baseline to 8 weeks (p = 0.001).

CONCLUSIONS

HIIT is a feasible exercise intervention to maintain VO2max in breast cancer patients receiving anthracycline-based chemotherapy.

TRIAL REGISTRATION

The protocol and informed consent were approved by the institutional IRB (HS-12-00227) and registered ( ClinicalTrials.gov NCT02454777; date of registration: May 272,015).

Heart Failure With Preserved Ejection Fraction: A Review of Cardiac and Noncardiac Pathophysiology

Heart failure with preserved ejection fraction (HFpEF) is one of the largest unmet clinical needs in 21st-century cardiology. It is a complex disorder resulting from the influence of several comorbidities on the endothelium. A derangement in nitric oxide bioavailability leads to an intricate web of physiological abnormalities in the heart, blood vessels, and other organs. In this review, we examine the contribution of cardiac and noncardiac factors to the development of HFpEF. We zoom in on recent insights on the role of comorbidities and microRNAs in HFpEF. Finally, we address the potential of exercise training, which is currently the only available therapy to improve aerobic capacity and quality of life in HFpEF patients. Unraveling the underlying mechanisms responsible for this improvement could lead to new biomarkers and therapeutic targets for HFpEF.

Effects of Endurance Training on Detrimental Structural, Cellular, and Functional Alterations in Skeletal Muscles of Heart Failure With Preserved Ejection Fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is underpinned by detrimental skeletal muscle alterations that contribute to disease severity, yet underlying mechanisms and therapeutic treatments remain poorly established. This study used a nonhuman animal model of HFpEF to better understand whether skeletal muscle abnormalities were (1) fiber-type specific and (2) reversible by various exercise training regimes.

METHODS AND RESULTS

Lean control rats were compared with obese ZSF1 rats at 20 weeks and then 8 weeks after sedentary, high-intensity interval training, or moderate continuous treadmill exercise. Oxidative soleus and glycolytic extensor digitorum longus (EDL) muscles were assessed for fiber size, capillarity, glycolytic metabolism, autophagy, and contractile function. HFpEF reduced fiber size and capillarity by 20%-50% (P < .05) in both soleus and EDL, but these effects were not reversed by endurance training. In contrast, both endurance training regimes in HFpEF attenuated the elevated lactate dehydrogenase activity observed in the soleus. Autophagy was down-regulated in EDL and up-regulated in soleus (P < .05), with no influence of endurance training. HFpEF impaired contractile forces of both muscles by ∼20% (P < .05), and these were not reversed by training.

CONCLUSIONS

Obesity-related HFpEF was associated with detrimental structural, cellular, and functional alterations to both slow-oxidative and fast-glycolytic skeletal muscles that could not be reversed by endurance training.

Endothelial function is disturbed in a hypertensive diabetic animal model of HFpEF: Moderate continuous vs. high intensity interval training

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is associated with endothelial dysfunction, but the molecular mechanisms still remain unclear. Whether exercise training (ET) along with which optimal modality can improve endothelial function is controversial. The present study used a hypertensive, diabetic-driven HFpEF animal model (ZSF1 rats) to determine whether different training modalities (moderate-continuous (MCT) and high-intensity interval training (HIIT)) could reverse endothelial dysfunction and to understand the underlying molecular mechanisms.

METHODS AND RESULTS

The development of HFpEF in ZSF1 obese animals was confirmed by echocardiography and hemodynamic measurements. Thereafter, animals were randomized into following groups: 1) sedentary, 2) 8 weeks of MCT, 3) 8 weeks of HIIT. ZSF1 lean animals served as control. In vitro measurement of endothelial function in aortic rings revealed significantly impaired endothelial-dependent and -independent vasodilation in HFpEF, which was reversed by MCT and HIIT. At the molecular level, the development of endothelial dysfunction was associated with a reduced expression / activation of endothelial nitric oxide synthase (eNOS), an increase in NADPH and activation of c-Jun N-terminal protein kinase (JNK), a reduced collagen I/III ratio and a reduced lining of the vessel wall by endothelial cells. ET primarily decreased NADPH oxidase expression, and JNK activation, elevated collagen I/III ratio while further improving aortic endothelial cell coverage.

CONCLUSIONS

The present study provides evidence that endothelial dysfunction occurs in experimental HFpEF and that ET, independent of the studied training modality, reverses endothelial dysfunction and specific molecular alterations. ET may therefore provide an important therapeutic intervention for HFpEF patients.

Effects of high-intensity interval training on vascular function in breast cancer survivors undergoing anthracycline chemotherapy: design of a pilot study

INTRODUCTION

Cardiovascular disease (CVD) mortality is higher among breast cancer survivors (BCS) who receive chemotherapy compared with those not receiving chemotherapy. Anthracycline chemotherapy is of particular concern due to anthracycline-related impairment of vascular endothelial cells and dysregulation of the extracellular matrix. One strategy proven to offset these impairments is a form of exercise known as high-intensity interval training (HIIT). HIIT improves endothelial function in non-cancer populations by decreasing oxidative stress, the main contributor to anthracycline-induced vascular dysfunction. The purpose of this pilot study is to assess the feasibility of an 8-week HIIT, as well as the HIIT effects on endothelial function and extracellular matrix remodelling, in BCS undergoing anthracycline chemotherapy.

METHODS AND ANALYSIS

Thirty BCS are randomised to either HIIT, an 8-week HIIT intervention occurring three times per week (seven alternating bouts of 90% of peak power output followed by 10% peak power output), or delayed group (DEL). Feasibility of HIIT is assessed by (1) the percentage of completed exercise sessions and (2) the number of minutes of exercise completed over the course of the study. Vascular function is assessed using brachial artery flow-mediated dilation and carotid intima media thickness. Extracellular matrix remodelling is assessed by the level of matrix metalloproteinases in the plasma. A repeated-measures analysis of covariance model will be performed with group (HIIT and DEL group) and time (pre/post assessment) as independent factors. We hypothesise that HIIT will be feasible in BCS undergoing anthracycline chemotherapy, and that HIIT will improve endothelial function and extracellular matrix remodelling, compared with the DEL group. Success of this study will provide evidence of feasibility and efficacy to support a larger definitive trial which will impact cancer survivorship by decreasing anthracycline-induced vascular dysfunction, thereby benefiting cardiovascular markers that are related to CVD risk.

ETHICS AND DISSEMINATION

This trial was approved by the University of Southern California Institutional Review Board (HS-15-00227).

TRIAL REGISTRATION NUMBER

NCT02454777; Pre-results.

Coronary microvascular dysfunction in patients with heart failure with preserved ejection fraction

There are multiple proposed mechanisms for the pathophysiology of heart failure (HF) with preserved ejection fraction (HFpEF). We hypothesized that coronary microvascular dysfunction is common in these patients. In a prospective, observational study, patients undergoing cardiac catheterization with HFpEF [left ventricular (LV) ejection fraction ≥ 50% and with clinical HF] were compared with similar patients without HFpEF. Patients with ≥50% stenosis were excluded, and coronary flow reserve (CFR) and the index of microvascular resistance (IMR) were measured after adenosine administration using a guidewire, with CFR ≤ 2 and IMR ≥ 23 being abnormal. Baseline characteristics and CFR and IMR were compared in 30 HFpEF patients and 14 control subjects. Compared with control subjects, HFpEF patients were older (65.4 ± 9.6 vs. 55.1 ± 3.1 yr, P < 0.01), had higher numbers of comorbidities (4.4 ± 1.5 vs. 2.6 ± 1.9, P = 0.002), had higher median B-type natriuretic peptide [161 (interquartile range: 75-511) pg/dl vs. 37 (interquartile range: 18.5-111) pg/dl, P < 0.01], and had higher LV end-diastolic pressure (17.8 ± 4.2 vs. 8.4 ± 4.2, P < 0.01). HFpEF patients had lower CFR (2.55 ± 1.60 vs. 3.84 ± 1.89, P = 0.024) and higher IMR (26.7 ± 10.3 vs. 19.7 ± 9.7 units, P = 0.037) than control subjects. Most (71.4%) control subjects had normal coronary physiology, whereas 36.7% of HFpEF patients had both abnormal CFR and IMR and another 36.7% had either abnormal CFR or IMR. In conclusion, this is the first study that has reported invasively determined CFR and IMR in HFpEF patients. We demonstrated the presence of four distinct coronary physiology groups in HFpEF patients. Investigation into the potential mechanisms for these findings is needed. NEW & NOTEWORTHY In this prospective observational study of patients with heart failure with preserved ejection fraction (HFpEF), we found that patients with HFpEF had more abnormalities of coronary flow and resistance than asymptomatic control patients, indicating that coronary microvascular dysfunction may play a role in the HFpEF disease process.

Cardiac adaptation to hypertension in adult female Dahl salt-sensitive rats is dependent on ovarian function, but loss of ovarian function does not predict early maladaptation

Aim of study was to examine experimentally the adult female hypertensive heart in order to determine the role of ovary function in the response of the heart to salt-dependent hypertension. Dahl salt-sensitive rats, age 12 weeks, with/without ovariectomy were fed a standard (0.3% NaCl) or high-salt diet (8%) for 16 weeks. Mean arterial blood pressure monitored noninvasively in conscious state increased significantly by high salt. Echocardiography was performed at baseline and endpoint. Heart function and molecular changes were evaluated at endpoint by left ventricle catheterization, by sirius red staining for collagen and by gene expression using quantitative RT-PCR for selected genes. At endpoint, significant concentric hypertrophy was present with high salt. Increase in relative wall thickening with high salt compared to normal diet was more pronounced with intact ovaries (0.33 ± 0.02 and 0.57 ± 0.04 vs. 0.29 ± 0.00 and 0.46 ± 0.03) as was the reduction in midwall fractional shortening (20 ± 0.6 and 14 ± 2 vs. 19 ± 0.9 and 18 ± 1). Ovariectomy increased stroke volume and decreased the ratio of mitral peak velocity of early filling (E) to early diastolic mitral annular velocity (E') (E/E' ratio) when compared to hearts from intact rats. High salt increased expression of collagen I and III genes and perivascular collagen in the heart slightly, but % interstitial collagen by sirius red staining remained unchanged in intact rats and decreased significantly by ovariectomy. Added volume load but not deterioration of function or structure characterized the nonfailing hypertensive heart of salt-sensitive females ovariectomized at mature age when compared to corresponding intact females.

Murine Models of Heart Failure with Preserved Ejection Fraction: a "Fishing Expedition"

Heart failure with preserved ejection fraction (HFpEF) is characterized by signs and symptoms of HF in the presence of a normal left ventricular (LV) ejection fraction (EF). Despite accounting for up to 50% of all clinical presentations of HF, the mechanisms implicated in HFpEF are poorly understood, thus precluding effective therapy. The pathophysiological heterogeneity in the HFpEF phenotype also contributes to this disease and likely to the absence of evidence-based therapies. Limited access to human samples and imperfect animal models that completely recapitulate the human HFpEF phenotype have impeded our understanding of the mechanistic underpinnings that exist in this disease. Aging and comorbidities such as atrial fibrillation, hypertension, diabetes and obesity, pulmonary hypertension and renal dysfunction are highly associated with HFpEF. Yet, the relationship and contribution between them remains ill-defined. This review discusses some of the distinctive clinical features of HFpEF in association with these comorbidities and highlights the advantages and disadvantage of commonly used murine models, used to study the HFpEF phenotype.

Revisiting the physiological effects of exercise training on autonomic regulation and chemoreflex control in heart failure: does ejection fraction matter?

Heart failure (HF) is a global public health problem that, independent of its etiology [reduced (HFrEF) or preserved ejection fraction (HFpEF)], is characterized by functional impairments of cardiac function, chemoreflex hypersensitivity, baroreflex sensitivity (BRS) impairment, and abnormal autonomic regulation, all of which contribute to increased morbidity and mortality. Exercise training (ExT) has been identified as a nonpharmacological therapy capable of restoring normal autonomic function and improving survival in patients with HFrEF. Improvements in autonomic function after ExT are correlated with restoration of normal peripheral chemoreflex sensitivity and BRS in HFrEF. To date, few studies have addressed the effects of ExT on chemoreflex control, BRS, and cardiac autonomic control in HFpEF; however, there are some studies that have suggested that ExT has a beneficial effect on cardiac autonomic control. The beneficial effects of ExT on cardiac function and autonomic control in HF may have important implications for functional capacity in addition to their obvious importance to survival. Recent studies have suggested that the peripheral chemoreflex may also play an important role in attenuating exercise intolerance in HFrEF patients. The role of the central/peripheral chemoreflex, if any, in mediating exercise intolerance in HFpEF has not been investigated. The present review focuses on recent studies that address primary pathophysiological mechanisms of HF (HFrEF and HFpEF) and the potential avenues by which ExT exerts its beneficial effects.

Exercise Training Reveals Inflexibility of the Diaphragm in an Animal Model of Patients With Obesity-Driven Heart Failure With a Preserved Ejection Fraction

BACKGROUND

Respiratory muscle weakness contributes to exercise intolerance in patients with heart failure with a preserved ejection fraction (HFpEF)-a condition characterized by multiple comorbidities with few proven treatments. We aimed, therefore, to provide novel insight into the underlying diaphragmatic alterations that occur in HFpEF by using an obese cardiometabolic rat model and further assessed whether exercise training performed only after the development of overt HFpEF could reverse impairments.

METHODS AND RESULTS

Obese ZSF1 rats (n=12) were compared with their lean controls (n=8) at 20 weeks, with 3 additional groups of obese ZSF1 rats compared at 28 weeks following 8 weeks of either sedentary behavior (n=13), high-intensity interval training (n=11), or moderate-continuous training (n=11). Obese rats developed an obvious HFpEF phenotype at 20 and 28 weeks. In the diaphragm at 20 weeks, HFpEF induced a shift towards an oxidative phenotype and a fiber hypertrophy paralleled by a lower protein expression in MuRF1 and MuRF2, yet mitochondrial and contractile functional impairments were observed. At 28 weeks, neither the exercise training regimen of high-intensity interval training or moderate-continuous training reversed any of the diaphragm alterations induced by HFpEF.

CONCLUSIONS

This study, using a well-characterized rat model of HFpEF underpinned by multiple comorbidities and exercise intolerance (ie, one that closely resembles the patient phenotype), provides evidence that diaphragm alterations and dysfunction induced in overt HFpEF are not reversed following 8 weeks of aerobic exercise training. As such, whether alternative therapeutic interventions are required to treat respiratory muscle weakness in HFpEF warrants further investigation.

Exercise limitations in heart failure with reduced and preserved ejection fraction

The hallmark symptom of chronic heart failure (HF) is severe exercise intolerance. Impaired perfusive and diffusive O₂ transport are two of the major determinants of reduced physical capacity and lowered maximal O₂ uptake in patients with HF. It has now become evident that this syndrome manifests at least two different phenotypic variations: heart failure with preserved or reduced ejection fraction (HFpEF and HFrEF, respectively). Unlike HFrEF, however, there is currently limited understanding of HFpEF pathophysiology, leading to a lack of effective pharmacological treatments for this subpopulation. This brief review focuses on the disturbances within the O₂ transport pathway resulting in limited exercise capacity in both HFpEF and HFrEF. Evidence from human and animal research reveals HF-induced impairments in both perfusive and diffusive O₂ conductances identifying potential targets for clinical intervention. Specifically, utilization of different experimental approaches in humans (e.g., small vs. large muscle mass exercise) and animals (e.g., intravital microscopy and phosphorescence quenching) has provided important clues to elucidating these pathophysiological mechanisms. Adaptations within the skeletal muscle O₂ delivery-utilization system following established and emerging therapies (e.g., exercise training and inorganic nitrate supplementation, respectively) are discussed. Resolution of the underlying mechanisms of skeletal muscle dysfunction and exercise intolerance is essential for the development and refinement of the most effective treatments for patients with HF.

Delayed Repolarization Underlies Ventricular Arrhythmias in Rats With Heart Failure and Preserved Ejection Fraction

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) represents approximately half of heart failure, and its incidence continues to increase. The leading cause of mortality in HFpEF is sudden death, but little is known about the underlying mechanisms.

METHODS

Dahl salt-sensitive rats were fed a high-salt diet (8% NaCl) from 7 weeks of age to induce HFpEF (n=38). Rats fed a normal-salt diet (0.3% NaCl) served as controls (n=13). Echocardiograms were performed to assess systolic and diastolic function from 14 weeks of age. HFpEF-verified and control rats underwent programmed electrical stimulation. Corrected QT interval was measured by surface ECG. The mechanisms of ventricular arrhythmias (VA) were probed by optical mapping, whole-cell patch clamp to measure action potential duration and ionic currents, and quantitative polymerase chain reaction and Western blotting to investigate changes in ion channel expression.

RESULTS

After 7 weeks of a high-salt diet, 31 of 38 rats showed diastolic dysfunction and preserved ejection fraction along with signs of heart failure and hence were diagnosed with HFpEF. Programmed electric stimulation demonstrated increased susceptibility to VA in HFpEF rats (P<0.001 versus controls). The arrhythmogenicity index was increased (P<0.001) and the corrected QT interval on ECG was prolonged (P<0.001) in HFpEF rats. Optical mapping of HFpEF hearts demonstrated prolonged action potentials (P<0.05) and multiple reentry circuits during induced VA. Single-cell recordings of cardiomyocytes isolated from HFpEF rats confirmed a delay of repolarization (P=0.001) and revealed downregulation of transient outward potassium current (I_to; P<0.05). The rapid components of the delayed rectifier potassium current (I_Kr) and the inward rectifier potassium current (I_K1) were also downregulated (P<0.05), but the current densities were much lower than for I_to. In accordance with the reduction of I_to, both Kcnd3 transcript and Kv4.3 protein levels were decreased in HFpEF rat hearts.

CONCLUSIONS

Susceptibility to VA was markedly increased in rats with HFpEF. Underlying abnormalities include QT prolongation, delayed repolarization from downregulation of potassium currents, and multiple reentry circuits during VA. Our findings are consistent with the hypothesis that potassium current downregulation leads to abnormal repolarization in HFpEF, which in turn predisposes to VA and sudden cardiac death.

Exercise Training Reverses Extrapulmonary Impairments in Smoke-exposed Mice

PURPOSE

Cigarette smoking is the main risk factor for chronic obstructive pulmonary disease and emphysema. However, evidence on the extrapulmonary effects of smoke exposure that precede lung impairments remains unclear at present, as are data on nonpharmacological treatments such as exercise training.

METHODS

Three groups of mice, including control (n = 10), smoking (n = 10), and smoking with 6 wk of high-intensity interval treadmill running (n = 11), were exposed to 20 wk of fresh air or whole-body cigarette smoke. Exercise capacity (peak oxygen uptake) and lung destruction (histology) were subsequently measured, whereas the heart, peripheral endothelium (aorta), and respiratory (diaphragm) and limb (extensor digitorum longus and soleus) skeletal muscles were assessed for in vivo and in vitro function, in situ mitochondrial respiration, and molecular alterations.

RESULTS

Smoking reduced body weight by 26% (P < 0.05) without overt airway destruction (P > 0.05). Smoking impaired exercise capacity by 15% while inducing right ventricular dysfunction by ~20%, endothelial dysfunction by ~20%, and diaphragm muscle weakness by ~15% (all P < 0.05), but these were either attenuated or reversed by exercise training (P < 0.05). Compared with controls, smoking mice had normal limb muscle and mitochondrial function (cardiac and skeletal muscle fibers); however, diaphragm measures of oxidative stress and protein degradation were increased by 111% and 65%, respectively (P < 0.05), but these were attenuated by exercise training (P < 0.05).

CONCLUSIONS

Prolonged cigarette smoking reduced exercise capacity concomitant with functional impairments to the heart, peripheral endothelium, and respiratory muscle that preceded the development of overt emphysema. However, high-intensity exercise training was able to reverse these smoke-induced extrapulmonary impairments.

Endothelial Senescence Contributes to Heart Failure With Preserved Ejection Fraction in an Aging Mouse Model

BACKGROUND

Because of global aging, the prevalence of heart failure with preserved ejection fraction (HFpEF) continues to rise. Although HFpEF pathophysiology remains incompletely understood, endothelial inflammation is stated to play a central role. Cellular senescence is a process of cellular growth arrest linked with aging and inflammation. We used mice with accelerated aging to investigate the role of cellular senescence in HFpEF development.

METHODS AND RESULTS

Senescence-accelerated mice (SAM, n=18) and control mice with normal senescence (n=15) were fed normal chow or a high-fat, high-salt diet (WD). Vascular and cardiac function was assessed at 8, 16, and 24 weeks of age. At 24 weeks, both SAM on WD (SAM-WD) and SAM on regular diet displayed endothelial dysfunction, as evidenced by impaired acetylcholine-induced relaxation of aortic segments and reduced basal nitric oxide. At week 24, SAM-WD had developed HFpEF, characterized by diastolic dysfunction, left ventricular hypertrophy, left atrial dilatation, and interstitial fibrosis. Also, exercise capacity was reduced and lung weight increased. Cardiovascular inflammation and senescence were assessed by immunohistochemical and immunofluorescence staining of hearts and aortas. SAM-WD showed increased endothelial inflammation (intercellular adhesion molecule 1 expression) and increased endothelial senescence (acetyl-p53/CD31 costaining). The latter correlated with diastolic function and intercellular adhesion molecule 1 expression.

CONCLUSIONS

SAM develop endothelial dysfunction. Adding a high-salt, high-fat diet accelerates endothelial senescence and instigates endothelial inflammation. This coincides with hemodynamic and structural changes typical of HFpEF. Targeting endothelial senescence could be a new therapeutic avenue in HFpEF.

Skeletal Muscle Alterations Are Exacerbated in Heart Failure With Reduced Compared With Preserved Ejection Fraction: Mediated by Circulating Cytokines?

BACKGROUND

A greater understanding of the different underlying mechanisms between patients with heart failure with reduced (HFrEF) and with preserved (HFpEF) ejection fraction is urgently needed to better direct future treatment. However, although skeletal muscle impairments, potentially mediated by inflammatory cytokines, are common in both HFrEF and HFpEF, the underlying cellular and molecular alterations that exist between groups are yet to be systematically evaluated. The present study, therefore, used established animal models to compare whether alterations in skeletal muscle (limb and respiratory) were different between HFrEF and HFpEF, while further characterizing inflammatory cytokines.

METHODS AND RESULTS

Rats were assigned to (1) HFrEF (ligation of the left coronary artery; n=8); (2) HFpEF (high-salt diet; n=10); (3) control (con: no intervention; n=7). Heart failure was confirmed by echocardiography and invasive measures. Soleus tissue in HFrEF, but not in HFpEF, showed a significant increase in markers of (1) muscle atrophy (ie, MuRF1, calpain, and ubiquitin proteasome); (2) oxidative stress (ie, higher nicotinamide adenine dinucleotide phosphate oxidase but lower antioxidative enzyme activities); (3) mitochondrial impairments (ie, a lower succinate dehydrogenase/lactate dehydrogenase ratio and peroxisome proliferator-activated receptor-γ coactivator-1α expression). The diaphragm remained largely unaffected between groups. Plasma concentrations of circulating cytokines were significantly increased in HFrEF for tumor necrosis factor-α, whereas interleukin-1β and interleukin-12 were higher in HFpEF.

CONCLUSIONS

Our findings suggest, for the first time, that skeletal muscle alterations are exacerbated in HFrEF compared with HFpEF, which predominantly reside in limb, rather than in respiratory, muscle. This disparity may be mediated, in part, by the different circulating inflammatory cytokines that were elevated between HFpEF and HFrEF.

Targeting Endothelial Function to Treat Heart Failure with Preserved Ejection Fraction: The Promise of Exercise Training

Although the burden of heart failure with preserved ejection fraction (HFpEF) is increasing, there is no therapy available that improves prognosis. Clinical trials using beta blockers and angiotensin converting enzyme inhibitors, cardiac-targeting drugs that reduce mortality in heart failure with reduced ejection fraction (HFrEF), have had disappointing results in HFpEF patients. A new “whole-systems” approach has been proposed for designing future HFpEF therapies, moving focus from the cardiomyocyte to the endothelium. Indeed, dysfunction of endothelial cells throughout the entire cardiovascular system is suggested as a central mechanism in HFpEF pathophysiology. The objective of this review is to provide an overview of current knowledge regarding endothelial dysfunction in HFpEF. We discuss the molecular and cellular mechanisms leading to endothelial dysfunction and the extent, presence, and prognostic importance of clinical endothelial dysfunction in different vascular beds. We also consider implications towards exercise training, a promising therapy targeting system-wide endothelial dysfunction in HFpEF.

Exercise training reverses age-induced diastolic dysfunction and restores coronary microvascular function

KEY POINTS

In a rat model of ageing that is free of atherosclerosis or hypertension, E/A, a diagnostic measure of diastolic filling, decreases, and isovolumic relaxation time increases, indicating that both active and passive ventricular relaxation are impaired with advancing age. Resting coronary blood flow and coronary functional hyperaemia are reduced with age, and endothelium-dependent vasodilatation declines with age in coronary resistance arterioles. Exercise training reverses age-induced declines in diastolic and coronary microvascular function. Thus, microvascular dysfunction and inadequate coronary perfusion are likely mechanisms of diastolic dysfunction in aged rats. Exercise training, initiated at an advanced age, reverses age-related diastolic and microvascular dysfunction; these data suggest that late-life exercise training can be implemented to improve coronary perfusion and diastolic function in the elderly.

ABSTRACT

The risk for diastolic dysfunction increases with advancing age. Regular exercise training ameliorates age-related diastolic dysfunction; however, the underlying mechanisms have not been identified. We investigated whether (1) microvascular dysfunction contributes to the development of age-related diastolic dysfunction, and (2) initiation of late-life exercise training reverses age-related diastolic and microvascular dysfunction. Young and old rats underwent 10 weeks of exercise training or remained as sedentary, cage-controls. Isovolumic relaxation time (IVRT), early diastolic filling (E/A), myocardial performance index (MPI) and aortic stiffness (pulse wave velocity; PWV) were evaluated before and after exercise training or cage confinement. Coronary blood flow and vasodilatory responses of coronary arterioles were evaluated in all groups at the end of training. In aged sedentary rats, compared to young sedentary rats, a 42% increase in IVRT, a 64% decrease in E/A, and increased aortic stiffness (PWV: 6.36 ± 0.47 vs.4.89 ± 0.41, OSED vs. YSED, P < 0.05) was accompanied by impaired coronary blood flow at rest and during exercise. Endothelium-dependent vasodilatation was impaired in coronary arterioles from aged rats (maximal relaxation to bradykinin: 56.4 ± 5.1% vs. 75.3 ± 5.2%, OSED vs. YSED, P < 0.05). After exercise training, IVRT, a measure of active ventricular relaxation, did not differ between old and young rats. In old rats, exercise training reversed the reduction in E/A, reduced aortic stiffness, and eliminated impairment of coronary blood flow responses and endothelium-dependent vasodilatation. Thus, age-related diastolic and microvascular dysfunction are reversed by late-life exercise training. The restorative effect of exercise training on coronary microvascular function may result from improved endothelial function.

Molecular effects of exercise training in patients with cardiovascular disease: focus on skeletal muscle, endothelium, and myocardium

For decades, we have known that exercise training exerts beneficial effects on the human body, and clear evidence is available that a higher fitness level is associated with a lower incidence of suffering premature cardiovascular death. Despite this knowledge, it took some time to also incorporate physical exercise training into the treatment plan for patients with cardiovascular disease (CVD). In recent years, in addition to continuous exercise training, further training modalities such as high-intensity interval training and pyramid training have been introduced for coronary artery disease patients. The beneficial effect for patients with CVD is clearly documented, and during the last years, we have also started to understand the molecular mechanisms occurring in the skeletal muscle (limb muscle and diaphragm) and endothelium, two systems contributing to exercise intolerance in these patients. In the present review, we describe the effects of the different training modalities in CVD and summarize the molecular effects mainly in the skeletal muscle and cardiovascular system.

High-intensity interval training prevents oxidant-mediated diaphragm muscle weakness in hypertensive mice

Hypertension is a key risk factor for heart failure, with the latter characterized by diaphragm muscle weakness that is mediated in part by increased oxidative stress. In the present study, we used a deoxycorticosterone acetate (DOCA)-salt mouse model to determine whether hypertension could independently induce diaphragm dysfunction and further investigated the effects of high-intensity interval training (HIIT). Sham-treated (n = 11), DOCA-salt-treated (n = 11), and DOCA-salt+HIIT-treated (n = 15) mice were studied over 4 wk. Diaphragm contractile function, protein expression, enzyme activity, and fiber cross-sectional area and type were subsequently determined. Elevated blood pressure confirmed hypertension in DOCA-salt mice independent of HIIT (P < 0.05). Diaphragm forces were impaired by ∼15-20% in DOCA-salt vs. sham-treated mice (P < 0.05), but this effect was prevented after HIIT. Myosin heavy chain (MyHC) protein expression tended to decrease (∼30%; P = 0.06) in DOCA-salt vs. sham- and DOCA-salt+HIIT mice, whereas oxidative stress increased (P < 0.05). Enzyme activity of NADPH oxidase was higher, but superoxide dismutase was lower, with MyHC oxidation elevated by ∼50%. HIIT further prevented direct oxidant-mediated diaphragm contractile dysfunction (P < 0.05) after a 30 min exposure to H₂O-₂ (1 mM). Our data suggest that hypertension induces diaphragm contractile dysfunction via an oxidant-mediated mechanism that is prevented by HIIT.-Bowen, T. S., Eisenkolb, S., Drobner, J., Fischer, T., Werner, S., Linke, A., Mangner, N., Schuler, G., Adams, V. High-intensity interval training prevents oxidant-mediated diaphragm muscle weakness in hypertensive mice.