Exercise limitations in heart failure with reduced and preserved ejection fraction

Therapeutic potential of ketone bodies on exercise intolerance in heart failure: looking beyond the heart

Recent evidence suggests that ketone bodies have therapeutic potential in many cardiovascular diseases including heart failure (HF). Accordingly, this has led to multiple clinical trials that use ketone esters (KEs) to treat HF patients highlighting the importance of this ketone therapy. KEs, specifically ketone monoesters, are synthetic compounds which, when consumed, are de-esterified into two β-hydroxybutyrate (βOHB) molecules and increase the circulating βOHB concentration. While many studies have primarily focused on the cardiac benefits of ketone therapy in HF, ketones can have numerous favourable effects in other organs such as the vasculature and skeletal muscle. Importantly, vascular and skeletal muscle dysfunction are also heavily implicated in the reduced exercise tolerance, the hallmark feature in HF with reduced ejection fraction and preserved ejection fraction, suggesting that some of the benefits observed in HF in response to ketone therapy may involve these non-cardiac pathways. Thus, we review the evidence suggesting how ketone therapy may be beneficial in improving cardiovascular and skeletal muscle function in HF and identify various potential mechanisms that may be important in the beneficial non-cardiac effects of ketones in HF.

Correlation of Sit-to-Stand Test and 6-Minute Walk Test to Illustrate Cardiorespiratory Fitness in Systolic Heart Failure Patients

OBJECTIVE

To prove 5-time sit-to-stand (5-STS) and 30-second sit-to-stand (30sSTS) tests in assessing cardiorespiratory fitness in chronic heart failure (HF) patients with systolic dysfunction. Alternative tests, such as 5-STS and 30sSTS, may be used to assess cardiorespiratory fitness in patients with HF but have not been thoroughly evaluated. Thus, this study aimed to prove 5-STS and 30sSTS tests in assessing cardiorespiratory fitness in chronic HF patients with systolic dysfunction.

METHODS

A cross-sectional study was done, evaluating chronic HF patients with systolic dysfunction that have received optimal guideline directed medical treatment for at least 3 months. All patients underwent the same intervention on the same day, starting with an initial 5-STS test, followed by a 30sSTS, and a 6-minute walk test (6MWT).

RESULTS

A total of 34 patients were enrolled in this study. The median left ventricular ejection fraction was 44% (interquartile range=34%-48%). Mean values of 5-STS, 30sSTS, and 6MWT were 13.90±4.72, 13.29±3.38, and 463.65±87.04, respectively. 5-STS showed moderate correlation with 6MWT (r=-0.436, p=0.01). However, the 30sSTS revealed strong correlation with 6MWT (r=0.629, p<0.001).

CONCLUSION

The 30sSTS test had strong correlation with 6MWT. It could be used to illustrate cardiorespiratory fitness in chronic HF patients with systolic dysfunction.

Dose-response relationship between Life's Essential 8 score and COPD risk: the NHANES cohort study 2007-2018

Objective

This study aims to discuss the dose-response relationship between the Life's Essential 8 (LE8) score and chronic obstructive pulmonary disease (COPD).

Methods

We screened data from the National Health and Nutrition Examination Survey (NHANES) database for the years 2007-2018. Logistics regression analysis and subgroup analysis were used to explore the relationship between cardiovascular health (CVH) and COPD based on the LE8 score. Additionally, restricted cubic spline (RCS) plots were drawn to visually display the dose-response relationship.

Results

A total of 12,517 participants were included, of which 835 had COPD. After multivariable adjustment, the LE8 score was found to be linearly and inversely associated with the risk of developing COPD. A similar relationship was observed in the scores for health behavior factors, whereas the relationship was weaker for health factors. The RCS plots visually demonstrated the aforementioned dose-response relationship. Moreover, subgroup analyses showed that this relationship remained robust across different groups.

Conclusion

LE8 scores are inversely and linearly associated with the risk of developing COPD. Higher LE8 scores can reduce the risk of developing COPD in individuals over 40 years old, especially concerning health behavior factors.

Comprehensive Benefits of Sodium-Glucose Cotransporter 2 Inhibitors in Heart Failure With Reduced Ejection Fraction: A Literature Review

Sodium-glucose cotransporter 2 (SGLT2) inhibitors, initially developed for type 2 diabetes, have emerged as a promising treatment for heart failure with reduced ejection fraction (HFrEF). They show significant cardiovascular benefits, including reduced cardiovascular mortality and heart failure hospitalizations. This review consolidates knowledge on the efficacy of SGLT2 inhibitors in HFrEF, focusing on their mechanisms of action, clinical benefits, and patient outcomes. To consolidate existing knowledge on the efficacy of SGLT2 inhibitors in reducing cardiovascular mortality in HFrEF, with an emphasis on pathophysiology, clinical benefits, and patient outcomes, major medical databases such as PubMed, Scopus, and Web of Science were reviewed, prioritizing research published from 2020 to 2024. Key studies and clinical trials, including DAPA-HF and EMPEROR-Reduced, were analyzed to understand the impacts of SGLT2 inhibitors on HFrEF management. The review highlights the multifaceted mechanisms by which SGLT2 inhibitors exert their cardiovascular benefits, including osmotic diuresis, natriuresis, improved myocardial energetics, and anti-inflammatory and antifibrotic effects. Clinical trials have consistently demonstrated significant reductions in cardiovascular mortality and hospitalizations among HFrEF patients treated with SGLT2 inhibitors. These benefits are observed across diverse demographic and clinical subgroups, indicating their broad applicability in clinical practice. SGLT2 inhibitors significantly advance HFrEF management, reducing cardiovascular mortality and hospitalizations. However, gaps remain in long-term outcomes, early diagnostic indicators, and mechanisms of action. Future research should address these gaps and explore personalized medicine to optimize treatment. Integrating SGLT2 inhibitors into standard HFrEF management guidelines, supported by updated policies and educational initiatives for healthcare providers, will be crucial to maximize their therapeutic potential and improve patient outcomes.

Differential impacts of body composition on oxygen kinetics and exercise tolerance of HFrEF and HFpEF patients

This study aims to (1) compare the kinetics of pulmonary oxygen uptake (VO2p), skeletal muscle deoxygenation ([HHb]), and microvascular O2 delivery (QO2mv) between heart failure (HF) patients with reduced ejection fraction (HFrEF) and those with preserved ejection fraction (HFpEF), and (2) explore the correlation between body composition, kinetic parameters, and exercise performance. Twenty-one patients (10 HFpEF and 11 HFrEF) underwent cardiopulmonary exercise testing to assess VO2 kinetics, with near-infrared spectroscopy (NIRS) employed to measure [HHb]. Microvascular O2 delivery (QO2mv) was calculated using the Fick principle. Dual-energy X-ray absorptiometry (DEXA) was performed to evaluate body composition. HFrEF patients exhibited significantly slower VO2 kinetics (time constant [t]: 63 ± 10.8 s vs. 45.4 ± 7.9 s; P < 0.05) and quicker [HHb] response (t: 12.4 ± 9.9 s vs. 25 ± 11.6 s; P < 0.05). Microvascular O2 delivery (QO2mv) was higher in HFrEF patients (3.6 ± 1.2 vs. 1.7 ± 0.8; P < 0.05), who also experienced shorter time to exercise intolerance (281.6 ± 84 s vs. 405.3 ± 96 s; P < 0.05). Correlation analyses revealed a significant negative relationship between time to exercise and both QO2mv (ρ= -0.51; P < 0.05) and VO2 kinetics (ρ= -0.63). Body adiposity was negatively correlated with [HHb] amplitude (ρ= -0.78) and peak VO2 (ρ= -0.54), while a positive correlation was observed between lean muscle percentage, [HHb] amplitude, and tau (ρ= 0.74 and 0.57; P < 0.05), respectively. HFrEF patients demonstrate more severely impaired VO2p kinetics, skeletal muscle deoxygenation, and microvascular O2 delivery compared to HFpEF patients, indicating compromised peripheral function. Additionally, increased adiposity and reduced lean mass are linked to decreased oxygen diffusion capacity and impaired oxygen uptake kinetics in HFrEF patients.

Type 2 diabetes mellitus negatively affects the functional performance of 6-min step test in chronic heart failure: a 3-year follow-up study

BACKGROUND

Type 2 diabetes mellitus (T2DM) and chronic heart failure (CHF) present a decrease in functional capacity due to the intrinsic nature of both pathologies. It is not known about the potential impact of T2DM on functional capacity when assessed by 6-min step test (6MST) and its effect as a prognostic marker for fatal and non-fatal events in patients with CHF.

OBJECTIVE

to evaluate the coexistence of T2DM and CHF in functional capacity through 6MST when compared to CHF non-T2DM, as well as to investigate the different cardiovascular responses to 6MST and the risk of mortality, decompensation of CHF and acute myocardial infarction (AMI) over 36 months.

METHODS

This is a prospective cohort study with 36 months of follow-up in individuals with T2DM and CHF. All participants completed a clinical assessment, followed by pulmonary function testing, echocardiography, and 6MST. The 6MST was performed on a 20 cm high step and cardiovascular responses were collected: heart rate, systemic blood pressure, oxygen saturation, BORG dyspnea and fatigue. The risk of mortality, acute myocardial infarction and decompensation of CHF was evaluated.

RESULTS

Eighty-six participants were included. The CHF-T2DM group had a significantly lower functional capacity than the CHF non-T2DM group (p < 0.05). Forced Expiratory Volume in one second (L), ejection fraction (%), gender and T2DM influence and are predictors of functional capacity (p < 0.05; adjusted R squared: 0.419). CHF-T2DM group presented a higher risk of mortality and acute myocardial infarction over the 36 months of follow-up (p < 0.05), but not to the risk of decompensation (p > 0.05).

CONCLUSION

T2DM negatively affects the functional performance of 6MST in patients with CHF. Gender, ejection fraction (%), FEV1 (L) and T2DM itself negatively influence exercise performance.

Unilateral hindlimb ischaemia-induced systemic inflammation is associated with non-ischaemic skeletal muscle inflammation

Skeletal muscle atrophy and dysfunction commonly accompany cardiovascular diseases such as peripheral arterial disease and may be partially attributable to systemic inflammation. We sought to determine whether acute systemic inflammation in a model of hindlimb ischaemia (HLI) could affect skeletal muscle macrophage infiltration, fibre size, or capillarization, independent of the ischaemia. Eight-week-old C57BL/6 male mice underwent either Sham or HLI surgery, and were killed 1, 3, or 7 days post-surgery. Circulating inflammatory cytokine concentrations were measured, as well as immune cell infiltration and morphology of skeletal muscle from both limbs of HLI and Sham mice. In HLI compared with Sham mice at day 1, plasma interleukin-1β levels were 216% higher (0.48 ± 0.10 vs. 0.15 ± 0.01 pg/μL, P = 0.005) and decreased by day 3. This was followed by increased macrophage presence in muscle from both ischaemic and non-ischaemic limbs of HLI mice by day 7 (7.3- and 2.3-fold greater than Sham, respectively, P < 0.0001). In HLI mice, muscle from the ischaemic limb had 21% lower fibre cross-sectional area than the non-ischaemic limb (724 ± 28 vs. 916 ± 46 μm2, P = 0.01), but the non-ischaemic limb of HLI mice was no different from Sham. This shows that HLI induces acute systemic inflammation accompanied by immune infiltration in both ischaemic and remote skeletal muscle; however, this did not induce skeletal muscle atrophy in remote muscle within the 7-day time course of this study. This effect of local skeletal muscle ischaemia on the inflammatory status of remote skeletal muscle may signal a priming of muscle for subsequent atrophy over a longer time course. HIGHLIGHTS: What is the central question of this study? Does hindlimb ischaemia-induced inflammation cause acute immune, inflammatory and morphological alterations in remote non-ischaemic skeletal muscle? What is the main finding and its importance? Hindlimb ischaemia induced systemic inflammation with subsequent neutrophil and macrophage infiltration in both ischaemic and non-ischaemic skeletal muscle; however, morphological changes did not occur in non-ischaemic muscle within 7 days. These immune alterations may have functional implications that take longer than 7 days to manifest, and subsequent or prolonged systemic inflammation and immune infiltration of muscle could lead to morphological changes and functional decline.

Physiological determinants of decreased peak leg oxygen uptake in chronic disease: a systematic review and meta-analysis

This systematic review and meta-analysis examined the physiological mechanisms responsible for lower peak exercise leg oxygen uptake (V̇o2) in patients with chronic disease. Studies measuring peak leg V̇o2 (primary outcome) and its physiological determinants during large (cycle) or small muscle mass exercise (single-leg knee extension, SLKE) in patients with chronic disease were included in this meta-analysis. Pooled estimates for each outcome were reported as a weighted mean difference (WMD) between chronic disease and controls. We included 10 studies that measured peak leg V̇o2 in patients with chronic disease (n = 109, mean age: 45 yr; encompassing chronic obstructive pulmonary disease, COPD, heart failure with reduced ejection fraction, HFrEF, or chronic renal failure, RF) and age-matched controls (n = 88). In pooled analysis, peak leg V̇o2 (WMD; -0.23 L/min, 95% CI: -0.32 to -0.13), leg oxygen (O2) delivery (WMD: -0.27 L/min, 95% CI: -0.37 to -0.17), and muscle O2 diffusive conductance (WMD: -5.2 mL/min/mmHg, 95% CI: -7.1 to -3.2) were all significantly lower during cycle and SLKE exercise in chronic disease versus controls. These results highlight that during large and small muscle mass exercise in patients with COPD, HFrEF, or RF, there is no single factor causing peak V̇o2 limitations. Specifically, the lower peak V̇o2 in these pathologies is due to not only the expected impairments in convective O2 delivery but also impairments in muscle oxygen diffusive transport from capillary to mitochondria. Whether impaired muscle O2 transport is caused solely by inactivity or additional muscle pathology remains in question.NEW & NOTEWORTHY Peripheral (skeletal muscle and vasculature) factors contribute significantly to reduced exercise capacity during both large and small muscle mass exercise in chronic diseases such as COPD, HFrEF, or RF and should be important targets of therapy in addition to the primary organs (lungs, heart, and kidneys) affected by disease.

Phenotyping cardiopulmonary exercise testing measures in heart failure with reduced ejection fraction: A comparison between Italy and Brazil

BACKGROUND

While patients with heart failure (HF) with reduced left ventricular ejection fraction (HFrEF) constitutes a global health crisis the incidence, prevalence and prognosis of the disease may differ depending on the continent and country.

OBJECTIVE

To profile, analyze and compare cardiopulmonary exercise testing (CPET) data of patients with HFrEF between Italian and Brazilian cohorts.

METHODS

In this observational study, a total of 630 patients with clinical and functional diagnosis of HFrEF (315 patients from Brazil and 315 patients from Italy) performed CPET.

RESULTS

Although Brazilian patients were slightly younger (Brazil 60±10 vs Italy 64±11 p<0.001) with a better peak oxygen consumption (V̇O2), circulatory power and left ventricular ejection fraction (LVEF) (p<0.01), ventilatory inefficiency and oscillation ventilation was higher when compared to the Italian cohort. When stratifying patients with LVEF≤30 % and age≥60 years, Brazilian patients presented worse ventilatory efficiency, and lower peak V̇O2 compared to the Italian cohort.

CONCLUSION

Patients with HFrEF from Brazil exhibited higher ventilatory inefficiency and a greater prevalence of oscillatory ventilation during CPET compared to patients with the same diagnosis from Italy.

Comparison of the effects of high and low-moderate load lower limb resistance training on muscle strength and exercise capacity in individuals with COPD: A systematic review and meta-analysis

BACKGROUND

Extrapulmonary changes also occur in COPD. Resistance training can increase muscle strength and exercise capacity.

OBJECTIVE

The objective of this systematic review was to examine and compare the effectiveness of high and low-moderate load lower limb resistance training on muscle strength and exercise capacity in individuals with stable chronic obstructive pulmonary disease (COPD).

METHODS

The PubMed/Medline, Scopus, Cochrane Library, ClinicalTrials.gov, Web of Science, EBSCO, and CINAHL databases were searched to identify the articles published in English between January 1970 and July 2023.

RESULTS

Seven randomized controlled trials with a total of 188 individuals with COPD (RT: 100, CG: 88) met the inclusion criteria. A significant difference was revealed (favoring high load) in the change in knee extensor muscle strength and leg press strength in the high load resistance training group compared to the low-moderate load resistance training group (MD 21.90 Nm, 95 % CI 17.46-26.34 Nm, p < 0.00001; MD 5.80 kg, 95 % CI 3.87-7.73 kg, p < 0.00001). A significant difference was observed in the change in 6 MWT (six minute walk test) distance (favoring low-moderate load) and VO2peak (peak oxygen uptake) (favoring high load) in the high load resistance training group compared to the low-moderate load resistance training group (MD -16.90 m, 95 % CI -29.76- -4.04 m, p < 0.010; MD 3.10 ml/kg/min, 95 % CI 2.65-3.55 ml/kg/min, p < 0.00001).

CONCLUSION

This systematic review and meta-analysis demonstrated that both high-load and low-moderate load resistance training increased muscle strength and might increase exercise capacity.

High-Intensity Small Muscle Mass Training in Patients With Heart Failure: Rationale and Design of a Randomized Controlled Trial

OBJECTIVE

Small muscle mass training localized to the quadriceps femoris muscle group has been proposed as an intervention to reverse heart failure-related skeletal muscle impairments. Although this training paradigm has demonstrated efficacy in heart failure, it remains to be evaluated in a conventional clinical context. Hence, the aim of this proposed study is to determine the effects of integrating high-intensity small muscle mass training (HISMT) isolated to the knee extensor muscles within a standard heart failure rehabilitation program.

METHODS

This single-blind, randomized controlled trial will aim to recruit 70 participants with heart failure. Participants will be randomized to either (1) standard training: combination of upper and lower extremity cardiovascular and resistance-based exercises, or (2) HISMT plus modified standard training: bilateral knee extensor HISMT and a modified version of the standard training, so that the total volume of work will be similar to standard training alone. The training interventions will be undertaken twice weekly for 12 weeks in an outpatient clinical setting. Outcome measurements will be performed at baseline and after the 12-week intervention period. The primary outcome will be exercise capacity (6-Minute Walk Test), with secondary outcomes being physical performance measures, muscle strength, and health-related quality of life. Data will be analyzed using the intention-to-treat principle.

IMPACT

This study will address a gap in the literature regarding the efficacy of small muscle training under routine clinical conditions for individuals with heart failure. The findings will also provide insight into the effects of HISMT within a heart failure rehabilitation program, thus enabling the optimization of exercise prescription for this patient population.

Non-Invasive Assessment of Cardiodynamics by Impedance Cardiography during the Six-Minute Walk Test in Patients with Heart Failure

BACKGROUND

Central Illustration: Non-Invasive Assessment of Cardiodynamics by Impedance Cardiography during the Six-Minute Walk Test in Patients with Heart Failure. The six-minute walk test (6MWT) is commonly used to evaluate heart failure (HF) patients. However, several clinical factors can influence the distance walked in the test. Signal-morphology impedance cardiography (SM-ICG) is a useful tool to noninvasively assess hemodynamics.

OBJECTIVE

This study aimed to compare cardiac output (CO), heart rate (HR), and stroke volume (SV) acceleration and deceleration responses to 6MWT in individuals with HF and reduced ejection fraction (HFrEF) and healthy controls.

METHODS

This is a cross-sectional observational study. CO, HR, SV and cardiac index (CI) were evaluated before, during, and after the 6MWT assessed by SM-ICG. The level of significance adopted in the statistical analysis was 5%.

RESULTS

Twenty-seven participants were included (13 HFrEF and 14 healthy controls). CO and HR acceleration significantly differed between groups (p<0.01; p=0.039, respectively). We found significant differences in SV, CO and CI between groups (p<0.01). Linear regression showed an impaired SV contribution to CO change in HFrEF group (22.9% versus 57.4%).

CONCLUSION

The main finding of the study was that individuals with HFrEF showed lower CO and HR acceleration values during the submaximal exercise test compared to healthy controls. This may indicate an imbalance in the autonomic response to exercise in this condition.

Combined effect of left ventricular ejection fraction and obesity on sedentary behavior in patients with coronary artery disease

Sedentary behavior has been associated with poor adherence to treatment in patients with coronary artery disease. Low left ventricular ejection fraction and obesity have been separately linked to increased sedentary behavior in patients with coronary artery disease. However, the combined effect of low left ventricular ejection fraction and obesity on sedentary behavior in patients with coronary artery disease has not been thoroughly investigated. Therefore, this study aimed to examine the combined influence of left ventricular ejection fraction and obesity on sedentary behavior in patients with coronary artery disease. This descriptive cross-sectional study enrolled 200 inpatients aged ≥ 20 years who were diagnosed with coronary artery disease at a tertiary hospital in Korea between March and August 2022. Data were collected using structured questionnaires, and multivariate logistic regression analysis was performed to determine the combined effect of left ventricular ejection fraction and obesity on sedentary behavior in patients with coronary artery disease. Among the 111 patients with sedentary behavior, 38 (34.2%) had both low left ventricular ejection fraction and obesity, whereas only 11 (12.4%) of the 89 patients without sedentary behavior had both low left ventricular ejection fraction and obesity. In multivariate logistic regression analysis, patients with coronary artery disease who had both low left ventricular ejection fraction and obesity had the highest risk of sedentary behavior compared to those without either low left ventricular ejection fraction or obesity (odds ratio = 13.98, 95% confidence interval = 5.19-37.69, P < .001). The co-existence of low left ventricular ejection fraction and obesity in patients with coronary artery disease may be associated with sedentary behavior. Therefore, evaluating both left ventricular ejection fraction and obesity when assessing sedentary behavior in patients with coronary artery disease may be valuable in implementing patient-centered approaches for the secondary prevention and management of sedentary behavior in patients with coronary artery disease. However, further prospective cohort studies with larger sample sizes are required to establish causal relationships and explore interventions to mitigate sedentary behavior in this population.

Effect of Training on Vascular Function and Repair in Heart Failure With Preserved Ejection Fraction

BACKGROUND

Exercise training improves peak oxygen uptake (V̇O₂peak) in heart failure with preserved ejection fraction (HFpEF). Multiple adaptations have been addressed, but the role of circulating endothelium-repairing cells and vascular function have not been well defined.

OBJECTIVES

The authors investigated effects of moderate-intensity continuous training (MICT) and high-intensity interval training (HIIT) on vascular function and repair in HFpEF.

METHODS

This study is a subanalysis of the OptimEx-Clin Study randomizing patients with HFpEF (n = 180) to HIIT, MICT, or guideline control. At baseline, 3, and 12 months, the authors measured peripheral arterial tonometry (valid baseline measurement in n = 109), flow-mediated dilation (n = 59), augmentation index (n = 94), and flow cytometry (n = 136) for endothelial progenitor cells and angiogenic T cells. Abnormal values were defined as outside 90% of published sex-specific reference values.

RESULTS

At baseline, abnormal values (%) were observed for augmentation index in 66%, peripheral arterial tonometry in 17%, flow-mediated dilation in 25%, endothelial progenitor cells in 42%, and angiogenic T cells in 18%. These parameters did not change significantly after 3 or 12 months of HIIT or MICT. Results remained unchanged when confining analysis to patients with high adherence to training.

CONCLUSIONS

In patients with HFpEF, high augmentation index was common, but endothelial function and levels of endothelium-repairing cells were normal in most patients. Aerobic exercise training did not change vascular function or cellular endothelial repair. Improved vascular function did not significantly contribute to the V̇O₂peak improvement after different training intensities in HFpEF, contrary to previous studies in heart failure with reduced ejection fraction and coronary artery disease. (Optimizing Exercise Training in Prevention and Treatment of Diastolic Heart Failure [OptimEx-Clin]; NCT02078947).

Sympathetic and hemodynamic responses to exercise in heart failure with preserved ejection fraction

Excessive sympathetic activity during exercise causes heightened peripheral vasoconstriction, which can reduce oxygen delivery to active muscles, resulting in exercise intolerance. Although both patients suffering from heart failure with preserved and reduced ejection fraction (HFpEF and HFrEF, respectively) exhibit reduced exercise capacity, accumulating evidence suggests that the underlying pathophysiology may be different between these two conditions. Unlike HFrEF, which is characterized by cardiac dysfunction with lower peak oxygen uptake, exercise intolerance in HFpEF appears to be predominantly attributed to peripheral limitations involving inadequate vasoconstriction rather than cardiac limitations. However, the relationship between systemic hemodynamics and the sympathetic neural response during exercise in HFpEF is less clear. This mini review summarizes the current knowledge on the sympathetic (i.e., muscle sympathetic nerve activity, plasma norepinephrine concentration) and hemodynamic (i.e., blood pressure, limb blood flow) responses to dynamic and static exercise in HFpEF compared to HFrEF, as well as non-HF controls. We also discuss the potential of a relationship between sympathetic over-activation and vasoconstriction leading to exercise intolerance in HFpEF. The limited body of literature indicates that higher peripheral vascular resistance, perhaps secondary to excessive sympathetically mediated vasoconstrictor discharge compared to non-HF and HFrEF, drives exercise in HFpEF. Excessive vasoconstriction also may primarily account for over elevations in blood pressure and concomitant limitations in skeletal muscle blood flow during dynamic exercise, resulting in exercise intolerance. Conversely, during static exercise, HFpEF exhibit relatively normal sympathetic neural reactivity compared to non-HF, suggesting that other mechanisms beyond sympathetic vasoconstriction dictate exercise intolerance in HFpEF.

Does the Addition of Strength Training to a High-Intensity Interval Training Program Benefit More the Patients with Chronic Heart Failure

BACKGROUND

Aerobic exercise, either continuous or high intensity interval training (HIIT), induces important benefits in chronic heart failure (CHF) patients. Resistance training has been also shown to be beneficial in CHF. However, data regarding combined aerobic exercise and muscle strength training is still limited. The aim of this study was to investigate whether adding strength training to a HIIT protocol within a cardiac rehabilitation (CR) program has a cumulative beneficial effect on the functional capacity (FC) and quality of life (QoL) in patients with CHF.

METHODS

Forty-four consecutive patients [35 males, ejection fraction (EF) < 50%] with CHF under medication enrolled in a 36-session CR program and were randomized in two exercise groups; HIIT (HIIT group) or HIIT combined with strength training (high intensity interval training combined with strength training (COM) group). All patients underwent baseline and endpoint outcome measures of a symptom-limited maximal cardiopulmonary exercise testing (CPET), 1 repetition maximum (1RM) test, muscular endurance test, echocardiography, and Minnesota Living with Heart Failure Questionnaire (MLWHFQ).

RESULTS

Most of the CPET indices, EF, 1RM test, muscular endurance and QoL were improved after the CR program in each exercise training group (p < 0.05). However, COM group demonstrated a further improvement in chest muscle testing and workload at anaerobic threshold (AT) compared to HIIT group.

CONCLUSIONS

An exercise-based CR program, consisted of either HIIT or HIIT combined with strength training, improves FC and QoL of patients with CHF. However, the addition of strength training to HIIT seems to have further beneficial effects on chest muscle strength and endurance, as well as workload at AT.

CLINICAL TRIAL REGISTRATION

The study was registered in ClinicalTrials.gov with number NCT02387411.

Proceedings from the Albert Charitable Trust Inaugural Workshop on 'Understanding the Acute Effects of Exercise on the Brain'

An inaugural workshop supported by "The Leo and Anne Albert Charitable Trust," was held October 4-7, 2019 in Scottsdale, Arizona, to focus on the effects of exercise on the brain and to discuss how physical activity may prevent or delay the onset of aging-related neurodegenerative conditions. The Scientific Program Committee (led by Dr. Jeff Burns) assembled translational, clinical, and basic scientists who research various aspects of the effects of exercise on the body and brain, with the overall goal of gaining a better understanding as to how to delay or prevent neurodegenerative diseases. In particular, research topics included the links between cardiorespiratory fitness, the cerebrovasculature, energy metabolism, peripheral organs, and cognitive function, which are all highly relevant to understanding the effects of acute and chronic exercise on the brain. The Albert Trust workshop participants addressed these and related topics, as well as how other lifestyle interventions, such as diet, affect age-related cognitive decline associated with Alzheimer's and other neurodegenerative diseases. This report provides a synopsis of the presentations and discussions by the participants, and a delineation of the next steps towards advancing our understanding of the effects of exercise on the aging brain.

Excess ventilation and exertional dyspnoea in heart failure and pulmonary hypertension

Increased ventilation relative to metabolic demands, indicating alveolar hyperventilation and/or increased physiological dead space (excess ventilation), is a key cause of exertional dyspnoea. Excess ventilation has assumed a prominent role in the functional assessment of patients with heart failure (HF) with reduced (HFrEF) or preserved (HFpEF) ejection fraction, pulmonary arterial hypertension (PAH) and chronic thromboembolic pulmonary hypertension (CTEPH). We herein provide the key pieces of information to the caring physician to 1) gain unique insights into the seeds of patients' shortness of breath and 2) develop a rationale for therapeutically lessening excess ventilation to mitigate this distressing symptom. Reduced bulk oxygen transfer induced by cardiac output limitation and/or right ventricle-pulmonary arterial uncoupling increase neurochemical afferent stimulation and (largely chemo-) receptor sensitivity, leading to alveolar hyperventilation in HFrEF, PAH and small-vessel, distal CTEPH. As such, interventions geared to improve central haemodynamics and/or reduce chemosensitivity have been particularly effective in lessening their excess ventilation. In contrast, 1) high filling pressures in HFpEF and 2) impaired lung perfusion leading to ventilation/perfusion mismatch in proximal CTEPH conspire to increase physiological dead space. Accordingly, 1) decreasing pulmonary capillary pressures and 2) mechanically unclogging larger pulmonary vessels (pulmonary endarterectomy and balloon pulmonary angioplasty) have been associated with larger decrements in excess ventilation. Exercise training has a strong beneficial effect across diseases. Addressing some major unanswered questions on the link of excess ventilation with exertional dyspnoea under the modulating influence of pharmacological and nonpharmacological interventions might prove instrumental to alleviate the devastating consequences of these prevalent diseases.

Positive airway pressure therapy in heart failure patients comorbid with obstructive sleep apnea: Cardiovascular outcomes and nighttime-duration effect

BACKGROUND

Comorbidity of obstructive sleep apnea (OSA) and heart failure (HF) is becoming increasingly common. This is a global analysis of positive airway pressure (PAP) efficacy for the cardiovascular outcomes in those HF Patients with comorbid OSA.

METHODS

Related randomized controlled trials were included. Analysed indicators covered primary outcomes (cardiac function, motor ability and life quality) and secondary outcomes (blood pressure and OSA-accompanying symptoms). Weighted mean difference was used to analyse the PAP-control difference in different experimental phases and the baseline-post difference in different groups.

RESULTS

Compared with control group, PAP was associated with a 3.48% increase in left ventricle ejection fraction (LVEF) (p < .00001) and little decrease in heart rate (HR) (p = .67). Over 6 h of mean nighttime use was associated with a greater increase in LVEF of 5.21% (p = .0002) and a significant reduction in HR of 3.81 bpm (p = .03). There was no significant difference between PAP and control group in their association with change in motor ability and life quality. Besides, PAP was associated with a 13.08 mm Hg decrease in systolic blood pressure and great improvements in OSA-accompanying symptoms: Apnea-Hypopnea Index, -23.73 e/h; mean oxygen saturation, 1.86%; minimum oxygen saturation, 8.78%; Epworth Sleepiness Scale, -1.39 point; arousal index, -16.41 e/h. There was also no significant difference in diastolic blood pressure.

CONCLUSIONS

Positive airway pressure treatment improves cardiac function in HF patients with comorbid OSA, but the improved magnitude is associated with the duration of nighttime use rather than the duration of treatment.

Regulation of the microvasculature during small muscle mass exercise in chronic obstructive pulmonary disease vs. chronic heart failure

Aim: Skeletal muscle convective and diffusive oxygen (O2) transport are peripheral determinants of exercise capacity in both patients with chronic obstructive pulmonary disease (COPD) and chronic heart failure (CHF). We hypothesised that differences in these peripheral determinants of performance between COPD and CHF patients are revealed during small muscle mass exercise, where the cardiorespiratory limitations to exercise are diminished. Methods: Eight patients with moderate to severe COPD, eight patients with CHF (NYHA II), and eight age- and sex-matched controls were studied. We measured leg blood flow (Q̇leg) by Doppler ultrasound during submaximal one-legged knee-extensor exercise (KEE), while sampling arterio-venous variables across the leg. The capillary oxyhaemoglobin dissociation curve was reconstructed from paired femoral arterial-venous oxygen tensions and saturations, which enabled the estimation of O2 parameters at the microvascular level within skeletal muscle, so that skeletal muscle oxygen conductance (DSMO2) could be calculated and adjusted for flow (DSMO2/Q̇leg) to distinguish convective from diffusive oxygen transport. Results: During KEE, Q̇leg increased to a similar extent in CHF (2.0 (0.4) L/min) and controls (2.3 (0.3) L/min), but less in COPD patients (1.8 (0.3) L/min) (p <0.03). There was no difference in resting DSMO2 between COPD and CHF and when adjusting for flow, the DSMO2 was higher in both groups compared to controls (COPD: 0.97 (0.23) vs. controls 0.63 (0.24) mM/kPa, p= 0.02; CHF 0.98 (0.11) mM/kPa vs. controls, p= 0.001). The Q̇-adjusted DSMO2 was not different in COPD and CHF during KEE (COPD: 1.19 (0.11) vs. CHF: 1.00 (0.18) mM/kPa; p= 0.24) but higher in COPD vs. controls: 0.87 (0.28) mM/kPa (p= 0.02), and only CHF did not increase Q̇-adjusted DSMO2 from rest (p= 0.2). Conclusion: Disease-specific factors may play a role in peripheral exercise limitation in patients with COPD compared with CHF. Thus, low convective O2 transport to contracting muscle seemed to predominate in COPD, whereas muscle diffusive O2 transport was unresponsive in CHF.

Exercise Capacity Is Independent of Respiratory Muscle Strength in Patients with Chronic Heart Failure

Background: Exercise intolerance in patients with chronic heart failure (CHF) is associated with a number of factors, including breathlessness and respiratory muscle weakness. However, many studies reported controversial results, and as yet there is no study on Arabic patients with CHF. This study aimed to examine the impact of breathlessness and respiratory muscle strength on exercise capacity in Arabic patients with CHF. Methods: This was a cross-sectional study, involving 42 stable adult male patients with CHF with a reduced ejection fraction and 42 controls who were free from cardiorespiratory and neuromuscular diseases. Patients with CHF and the controls underwent respiratory muscle strength tests and a six-minute walk test (6MWT), and the measurements were taken. Dyspnea was recorded using the modified Medical Research Council (mMRC) scale, along with the number of comorbidities. Results: Patients with CHF and controls were similar in age and sex. Patients with CHF had a greater number of comorbidities, a higher dyspnea score, a lower 6MWT score, and lower respiratory muscle strength (p < 0.001). Only 7% of patients with CHF had weak inspiratory muscle strength (<60% of that predicted) and 40% terminated the 6MWT due to dyspnea. The 6MWT was associated with mMRC (rs = −0.548, p < 0.001) but not with respiratory muscle strength (p > 0.05). Conclusions: Exercise intolerance in patients with CHF was associated with dyspnea and was independent of respiratory muscle strength.

Aerobic exercise and telomere length in patients with systolic heart failure: protocol study for a randomized controlled trial

Background

Heart failure (HF) with reduced ejection fraction (HFrEF) is a syndrome that leads to fatigue and reduced functional capacity due to disease-related pathophysiological mechanisms. Aerobic exercise (AERO) plays a key role in improving HF outcomes, such as an increase in peak oxygen uptake (VO₂peak). In addition, HF promotes cell senescence, which involves reducing telomere length. Several studies have shown that patients with a worse prognosis (i.e., reduced VO₂ peak) also have shorter telomeres. However, the effects of AERO on telomere length in patients with HFrEF are still unknown. In an attempt to fill this gap, we designed a study to determine the effects of 16 weeks of aerobic training (32 sessions) on telomere length in HFrEF patients.

Methods

In this single-center randomized controlled trial, men and women between 50 and 80 years old will be allocated into two different groups: a moderate-intensity aerobic training and a control grouTelomere length, functional capacity, echocardiographic variables, endothelial function, and walking ability will be assessed before and after the 16-week intervention period.

Discussion

Understanding the role of physical exercise in biological aging in HFrEF patients is relevant. Due to cell senescence, these individuals have shown a shorter telomere length. AERO can delay biological aging according to a balance in oxidative stress through antioxidant action. Positive telomere length results are expected for the aerobic training group.

Trial registration

ClinicalTrials.gov NCT03856736. Registered on February 27, 2019

Iron Deficiency Impacts Diastolic Function, Aerobic Exercise Capacity, and Patient Phenotyping in Heart Failure With Preserved Ejection Fraction: A Subanalysis of the OptimEx-Clin Study

Aims

Iron deficiency (ID) is linked to reduced aerobic exercise capacity and poor prognosis in patients with heart failure (HF) with reduced ejection fraction (HFrEF); however, data for HF with preserved ejection fraction (HFpEF) is scarce. We assessed the relationship between iron status and diastolic dysfunction as well as aerobic exercise capacity in HFpEF, and the contribution of iron status to patient phenotyping.

Methods and Results

Among 180 patients with HFpEF (66% women; median age, 71 years) recruited for the Optimizing Exercise Training in Prevention and Treatment of Diastolic HF (OptimEx-Clin) trial, baseline iron status, including iron, ferritin, and transferrin saturation, was analyzed (n = 169) in addition to exercise capacity (peak oxygen uptake [peak V̇O₂]) and diastolic function (E/e′). ID was present in 60% of patients and was more common in women. In multivariable linear regression models, we found that diastolic function and peak V̇O₂ were independently related to iron parameters; however, these relationships were present only in patients with HFpEF and ID [E/e′ and iron: β−0.19 (95% confidence interval −0.32, −0.07), p = 0.003; E/e′ and transferrin saturation: β−0.16 (−0.28, −0.04), p = 0.011; peak V̇O₂ and iron: β 3.76 (1.08, 6.44), p = 0.007; peak V̇O₂ and transferrin saturation: β 3.58 (0.99, 6.16), p = 0.007]. Applying machine learning, patients were classified into three phenogroups. One phenogroup was predominantly characterized by the female sex and few HFpEF risk factors but a high prevalence of ID (86%, p < 0.001 vs. other phenogroups). When excluding ID from the phenotyping analysis, results were negatively influenced.

Conclusion

Iron parameters are independently associated with impaired diastolic function and low aerobic capacity in patients with HFpEF and ID. Patient phenotyping in HFpEF is influenced by including ID.

Clinical Trial Registration

www.ClinicalTrials.gov, identifier NCT02078947.

Role of nitric oxide in convective and diffusive skeletal microvascular oxygen kinetics

Progress in understanding physiological mechanisms often consists of discrete discoveries made across different models and species. Accordingly, understanding the mechanistic bases for how altering nitric oxide (NO) bioavailability impacts exercise tolerance (or not) depends on integrating information from cellular energetics and contractile regulation through microvascular/vascular control of O₂ transport and pulmonary gas exchange. This review adopts state-of-the-art concepts including the intramyocyte power grid, the Wagner conflation of perfusive and diffusive O₂ conductances, and the Critical Power/Critical Speed model of exercise tolerance to address how altered NO bioavailability may, or may not, affect physical performance. This question is germane from the elite athlete to the recreational exerciser and particularly the burgeoning heart failure (and other clinical) populations for whom elevating O₂ transport and/or exercise capacity translates directly to improved life quality and reduced morbidity and mortality. The dearth of studies in females is also highlighted, and areas of uncertainty and questions for future research are identified.

Effect of Interval Training on the Factors Influencing Maximal Oxygen Consumption: A Systematic Review and Meta-Analysis

BACKGROUND

The maximal rate of oxygen consumption (VO_2max) is an important measure in exercise science as it is an indicator of cardiorespiratory fitness. Individual studies have identified central and peripheral adaptions to interval training that may underlie improvements in VO_2max, but there is no compilation of results.

OBJECTIVE

We aimed to systematically review the adaptive responses to high-intensity interval training (HIIT) and sprint interval training (SIT) on the central and peripheral factors influencing VO_2max in healthy individuals.

DATA SOURCES

SPORTDiscus and MEDLINE (up to and including 13 June, 2020) were explored to conduct the literature search.

STUDY SELECTION

Reviewed studies met the following criteria: (1) were in the English language; (2) prospective in nature; (3) included at least three interval sessions or were at least 1 week in duration; (4) contained HIIT or SIT; (5) involved participants between the ages of 18 and 65 years; and (6) included at least one of the following central (blood volume, plasma volume, hemoglobin mass, left ventricular mass, maximal stroke volume, maximal cardiac output) or peripheral factors (capillary density, maximal citrate synthase activity, mitochondrial respiration associated with VO_2max).

RESULTS

Thirty-two studies (369 participants, 49 were female) were included in the quantitative analyses, consisting of both HIIT (n = 18) and SIT (n = 17) interventions. There were only statistically significant changes in hematological measures (plasma volume) following HIIT. There was a significant increase in left ventricular mass following HIIT (7.4%, p < 0.001) and SIT (5.3%, p = 0.007) in inactive individuals, though the change following SIT may be misleading. There was only a significant increase in maximal stroke volume (14.1%, p = 0.015) and maximal cardiac output (12.6%, p = 0.002) following HIIT. In addition to central factors, there was a significant increase in capillary density (13.8%, p < 0.001) following SIT in active individuals. With respect to maximal citrate synthase activity, there were improvements following HIIT (20.8%, p < 0.001) and SIT (15.7%, p < 0.001, I² = 97%) in active individuals. The results for mitochondrial respiration suggested that there was no statistically significant improvement following HIIT (5.0%, p = 0.585).

CONCLUSIONS

Improvements in the central and peripheral factors influencing VO_2max were dependent on the interval type. Only HIIT led to a statistically significant improvement in cardiac function. Both HIIT and SIT increased maximal citrate synthase activity, while changes in other peripheral measures (capillary density, mitochondrial respiration) only occurred with SIT.

Muscle-Skeletal Abnormalities and Muscle Oxygenation during Isokinetic Strength Exercise in Heart Failure with Preserved Ejection Fraction Phenotype: A Cross-Sectional Study

Exercise intolerance, a hallmark of patients with heart failure (HF), is associated with muscle weakness. However, its causative microcirculatory and muscle characteristics among those with preserved or reduced ejection fraction (HFpEF or HFrEF) phenotype is unclear. The musculoskeletal abnormalities that could result in impaired peripheral microcirculation are sarcopenia and muscle strength reduction in HF, implying lowered oxidative capacity and perfusion affect transport and oxygen utilization during exercise, an essential task from the microvascular muscle function. Besides that, skeletal muscle microcirculatory abnormalities have also been associated with exercise intolerance in HF patients who also present skeletal muscle myopathy. This cross-sectional study aimed to compare the muscle microcirculation dynamics via near-infrared spectroscopy (NIRS) response during an isokinetic muscle strength test and ultrasound-derived parameters (echo intensity was rectus femoris muscle, while the muscle thickness parameter was measured on rectus femoris and quadriceps femoris) in heart failure patients with HFpEF and HFrEF phenotypes and different functional severities (Weber Class A, B, and C). Twenty-eight aged-matched patients with HFpEF (n = 16) and HFrEF (n = 12) were assessed. We found phenotype differences among those with Weber C severity, with HFrEF patients reaching lower oxyhemoglobin (O₂Hb, μM) (−10.9 ± 3.8 vs. −23.7 ± 5.7, p = 0.029) during exercise, while HFpEF reached lower O₂Hb during the recovery period (−3.0 ± 3.4 vs. 5.9 ± 2.8, p = 0.007). HFpEF with Weber Class C also presented a higher echo intensity than HFrEF patients (29.7 ± 8.4 vs. 15.1 ± 6.8, p = 0.017) among the ultrasound-derived variables. Our preliminary study revealed more pronounced impairments in local microcirculatory dynamics in HFpEF vs. HFrEF patients during a muscle strength exercise, combined with muscle-skeletal abnormalities detected via ultrasound imaging, which may help explain the commonly observed exercise intolerance in HFpEF patients.

Comparison of Cardiorespiratory Fitness in Black or African American Versus Caucasian Patients With Heart Failure

PURPOSE

Cardiopulmonary exercise testing (CPX) is a well-established assessment with important insight into prognosis and therapeutic efficacy in patients with heart failure (HF). Prior studies have identified several clinical differences between Black or African American (B-AA) and Caucasian patients with HF. Differences in key CPX responses between these two groups require further investigation.

METHODS

Using a database consisting of subjects with symptomatic HF who had undergone CPX for inclusion in various prospective randomized clinical trials, we identified 198 (n = 94 [47%] B-AA; n = 105 [53%] Caucasian) patients with a qualifying baseline CPX. Significant univariate predictors of peak oxygen uptake (V˙o2peak) were included in a multivariate linear regression model.

RESULTS

When compared with Caucasian patients, B-AA were younger (mean ± SD = 54.8 ± 10.0 vs 57.9 ± 9.6 yr, P = .03), had higher C-reactive protein (CRP) (median [IQR] = 4.9 [2.3, 8.8] vs 1.9 [0.6, 5.5] mg/L, P < .0001), lower hemoglobin (13.0 ± 1.8 vs 13.8 ± 1.6 g/dL, P = .003), and lower left ventricular ejection fraction (LVEF) (40 [32, 51] vs 53 [43, 59]%, P < .00010). During CPX, B-AA patients also had lower V˙o2peak (14.6 ± 3.9 vs 17.6 ± 4.8 mL·kg-1·min-1, P < .0001). No differences were observed between B-AA and Caucasian in the minute ventilation/carbon dioxide production (V˙e/V˙co2) slope (P = .14). The difference in V˙o2peak between B-AA and Caucasian was largely attenuated after adjusting for age, body mass index, CRP, N-terminal pro-brain natriuretic peptide, hemoglobin, LVEF, and peak HR (14.1: 95% CI, 13.2-14.9 vs 15.6: 95% CI, 14.4-16.8 mL·kg-1·min-1, P = .053).

CONCLUSIONS

Directly measured V˙o2peak was significantly lower in B-AA than in Caucasians with HF. This is largely explained by differences in clinical characteristics, whereas no significant differences were observed in the V˙e/V˙co2 slope.

Oxygen flux from capillary to mitochondria: integration of contemporary discoveries

Resting humans transport ~ 100 quintillion (10¹⁸) oxygen (O₂) molecules every second to tissues for consumption. The final, short distance (< 50 µm) from capillary to the most distant mitochondria, in skeletal muscle where exercising O₂ demands may increase 100-fold, challenges our understanding of O₂ transport. To power cellular energetics O₂ reaches its muscle mitochondrial target by dissociating from hemoglobin, crossing the red cell membrane, plasma, endothelial surface layer, endothelial cell, interstitial space, myocyte sarcolemma and a variable expanse of cytoplasm before traversing the mitochondrial outer/inner membranes and reacting with reduced cytochrome c and protons. This past century our understanding of O₂'s passage across the body's final O₂ frontier has been completely revised. This review considers the latest structural and functional data, challenging the following entrenched notions: (1) That O₂ moves freely across blood cell membranes. (2) The Krogh-Erlang model whereby O₂ pressure decreases systematically from capillary to mitochondria. (3) Whether intramyocyte diffusion distances matter. (4) That mitochondria are separate organelles rather than coordinated and highly plastic syncytia. (5) The roles of free versus myoglobin-facilitated O₂ diffusion. (6) That myocytes develop anoxic loci. These questions, and the intriguing notions that (1) cellular membranes, including interconnected mitochondrial membranes, act as low resistance conduits for O₂, lipids and H⁺-electrochemical transport and (2) that myoglobin oxy/deoxygenation state controls mitochondrial oxidative function via nitric oxide, challenge established tenets of muscle metabolic control. These elements redefine muscle O₂ transport models essential for the development of effective therapeutic countermeasures to pathological decrements in O₂ supply and physical performance.

Brown adipose tissue prevents glucose intolerance and cardiac remodeling in high-fat-fed mice after a mild myocardial infarction

BACKGROUND

Obesity increases the risk of developing impaired glucose tolerance (IGT) and type 2 diabetes (T2D) after myocardial infarction (MI). Brown adipose tissue (BAT) is important to combat obesity and T2D, and increasing BAT mass by transplantation improves glucose metabolism and cardiac function. The objective of this study was to determine if BAT had a protective effect on glucose tolerance and cardiac function in high-fat diet (HFD) fed mice subjected to a mild MI.

METHODS

Male C57BL/6 mice were fed a HFD for eight weeks and then divided into Sham (Sham-operated) and +BAT (mice receiving 0.1 g BAT into their visceral cavity). Sixteen weeks post-transplantation, mice were further subdivided into ±MI (Sham; Sham-MI; +BAT; +BAT-MI) and maintained on a HFD. Cardiac (echocardiography) and metabolic function (glucose and insulin tolerance tests, body composition and exercise tolerance) were assessed throughout 22 weeks post-MI. Quantitative PCR (qPCR) was performed to determine the expression of genes related to metabolic function of perigonadal adipose tissue (pgWAT), subcutaneous white adipose tissue (scWAT), liver, heart, tibialis anterior skeletal muscle (TA); and BAT.

RESULTS

+BAT prevented the increase in left ventricle mass (LVM) and exercise intolerance in response to MI. Similar to what is observed in humans, Sham-MI mice developed IGT post-MI, but this was negated in +BAT-MI mice. IGT was independent of changes in body composition. Genes involved in inflammation, insulin resistance, and metabolism were significantly altered in pgWAT, scWAT, and liver in Sham-MI mice compared to all other groups.

CONCLUSIONS

BAT transplantation prevents IGT, the increase in LVM, and exercise intolerance following MI. MI alters the expression of several metabolic-related genes in WAT and liver in Sham-MI mice, suggesting that these tissues may contribute to the impaired metabolic response. Increasing BAT may be an important intervention to prevent the development of IGT or T2D and cardiac remodeling in obese patients post-MI.

Skeletal myopathy in a rat model of postmenopausal heart failure with preserved ejection fraction

Heart failure with preserved ejection fraction (HFpEF) accounts for ∼50% of all patients with heart failure and frequently affects postmenopausal women. The HFpEF condition is phenotype-specific, with skeletal myopathy that is crucial for disease development and progression. However, most of the current preclinical models of HFpEF have not addressed the postmenopausal phenotype. We sought to advance a rodent model of postmenopausal HFpEF and examine skeletal muscle abnormalities therein. Female, ovariectomized, spontaneously hypertensive rats (SHRs) were fed a high-fat, high-sucrose diet to induce HFpEF. Controls were female sham-operated Wistar-Kyoto rats on a lean diet. In a complementary, longer-term cohort, controls were female sham-operated SHRs on a lean diet to evaluate the effect of strain difference in the model. Our model developed key features of HFpEF that included increased body weight, glucose intolerance, hypertension, cardiac hypertrophy, diastolic dysfunction, exercise intolerance, and elevated plasma cytokines. In limb skeletal muscle, HFpEF decreased specific force by 15%-30% (P < 0.05) and maximal mitochondrial respiration by 40%-55% (P < 0.05), increased oxidized glutathione by approximately twofold (P < 0.05), and tended to increase mitochondrial H2O2 emission (P = 0.10). Muscle fiber cross-sectional area, markers of mitochondrial content, and indices of capillarity were not different between control and HFpEF in our short-term cohort. Overall, our preclinical model of postmenopausal HFpEF recapitulates several key features of the disease. This new model reveals contractile and mitochondrial dysfunction and redox imbalance that are potential contributors to abnormal metabolism, exercise intolerance, and diminished quality of life in patients with postmenopausal HFpEF.NEW & NOTEWORTHY Heart failure with preserved ejection fraction (HFpEF) is a condition with phenotype-specific features highly prevalent in postmenopausal women and skeletal myopathy contributing to disease development and progression. We advanced a rat model of postmenopausal HFpEF with key cardiovascular and systemic features of the disease. Our study shows that the skeletal myopathy of postmenopausal HFpEF includes loss of limb muscle-specific force independent of atrophy, mitochondrial dysfunction, and oxidized shift in redox balance.

Mechanism of Dyspnea during Exercise in Children with Corrected Congenital Heart Disease

This study will evaluate cardiorespiratory and peripheral muscle function and their relationship with subjective dyspnea threshold after the surgical correction of congenital heart disease in children. Thirteen children with surgically repaired congenital heart disease were recruited. Each participant performed an incremental exercise test on a cycle ergometer until exhaustion. Gas exchanges were continuously sampled to measure the maximal aerobic parameters and ventilatory thresholds. The functional capacity of the subjects was assessed with a 6 min walk test. At the end of the exercise test, isokinetic Cybex Norm was used to evaluate the strength and endurance of the knee extensor muscle in the leg. Dyspnea was subjectively scored with a visual analog scale during the last 15 s of each exercise step. Oxygen consumption measured at the dyspnea score/VO₂ relationship located at the dyspnea threshold, at which dyspnea suddenly increased. Results: The maximal and submaximal values of the parameters describing the exercise and the peripheral muscular performances were: VO₂ Peak: 33.8 ± 8.9 mL·min^-1·kg^-1; HR: 174 ± 9 b·min^-1; VEmax: 65.68 ± 15.9 L·min^-1; P max: 117 ± 27 W; maximal voluntary isometric force MVIF: 120.8 ± 41.9 N/m; and time to exhaustion Tlim: 53 ± 21 s. Oxygen consumption measured at the dyspnea threshold was related to VO₂ Peak (R² = 0.74; p < 0.01), Tlim (R² = 0.78; p < 0.01), and the distance achieved during the 6MWT (R² = 0.57; p < 0.05). Compared to the theoretical maximal values for the power output, VO₂, and HR, the surgical correction did not repair the exercise performance. After the surgical correction of congenital heart disease, exercise performance was impeded by alterations of the cardiorespiratory function and peripheral local factors. A subjective evaluation of the dyspnea threshold is a reliable criterion that allows the prediction of exercise capacity in subjects suffering from congenital heart disease.

High-intensity interval training versus progressive high-intensity circuit resistance training on endothelial function and cardiorespiratory fitness in heart failure: A preliminary randomized controlled trial

INTRODUCTION

Exercise training is strongly recommended as a therapeutic approach to treat individuals with heart failure. High-intensity exercise training modalities still controversial in this population. The study aims to preliminary assess the consequences of high-intensity exercise training modalities, aerobic interval training (HIIT) and progressive high circuit-resistance training (CRT), on primarily endothelial function and cardiorespiratory fitness, and secondly on muscle strength and physical performance in heart failure patients.

METHODS

This preliminary multicentric randomized controlled trial comprised 23 heart failure patients, aged 56 ± 10 years old, mainly New York Heart Association classification I and II (%), hemodynamically stable, who compromise at least 36 exercise sessions of a randomly assigned intervention (HIIT, CRT or control group). Endothelial function, cardiopulmonary exercise testing, muscle strength and physical performance were completed at baseline and post-intervention.

RESULTS

Although no effects on endothelial function; both HIIT and CRT modalities were able to produce a positive effect on [Formula: see text] peak (HIIT = +2.1±6.5, CRT = +3.0±4.2 and control group = -0.1± 5.3 mL/kg/min, time*group p-value<0,05) and METs (HIIT = +0.6±1.8, CRT = +0.9±1.2 and control group = 0±1.6, time*group p-value<0,05). Only HIIT increased isokinetic torque peak (HIIT = +8.8±55.8, CRT = 0.0±60.7 and control group = 1.6±57.6 Nm) matched p-value<0,05. Regarding the physical performance, the CRT modality reduced chair stand test completion time (HIIT = -0.7±3.1, CRT = -3.3±3.2 and control group = -0.3±2.5 s, matched p-value<0,05 and HIIT improved global physical performance(time*group p<0,05).

CONCLUSION

This preliminary study trends to indicate for the first time that high-intensity interval training promotes a jointly superior effect compared to progressive high intensity circuit-resistance training by improving cardiorespiratory fitness, muscular strength, and physical performance. Further research with larger cohort is necessary.

CLINICAL TRIAL REGISTRATION NUMBER

ReBEC RBR-668c8v.

Reliability and validity of six-minute step test in patients with heart failure

Exercise intolerance is the hallmark consequence of advanced chronic heart failure (HF). The six-minute step test (6MST) has been considered an option for the six-minute walk test because it is safe, inexpensive, and can be applied in small places. However, its reliability and concurrent validity has still not been investigated in participants with HF with reduced ejection fraction (HFrEF). Clinically stable HFrEF participants were included. Reliability and error measurement were calculated by comparing the first with the second 6MST result. Forty-eight hours after participants underwent the 6MST, they were invited to perform a cardiopulmonary exercise test (CPET) on a cycle ergometer. Concurrent validity was assessed by correlation between number of steps and peak oxygen uptake (V̇O2 peak) at CPET. Twenty-seven participants with HFrEF (60±8 years old and left ventricle ejection fraction of 41±6%) undertook a mean of 94±30 steps in the 6MST. Intra-rater reliability was excellent for 6MST (ICC=0.9), with mean error of 4.85 steps and superior and inferior limits of agreement of 30.6 and -20.9 steps, respectively. In addition, strong correlations between number of steps and CPET workload (r=0.76, P<0.01) and peak V̇O2 (r=0.71, P<0.01) were observed. From simple linear regression the following predictive equations were obtained with 6MST results: V̇O2 peak (mL/min) = 350.22 + (7.333 × number of steps), with R2=0.51, and peak workload (W) = 4.044 + (0.772 × number of steps), with R2=0.58. The 6MST was a reliable and valid tool to assess functional capacity in HFrEF participants and may moderately predict peak workload and oxygen uptake of a CPET.

Exercise intolerance in pulmonary arterial hypertension: insight into central and peripheral pathophysiological mechanisms

Exercise intolerance is a cardinal symptom of pulmonary arterial hypertension (PAH) and strongly impacts patients' quality of life (QoL). Although central cardiopulmonary impairments limit peak oxygen consumption (V' O2peak ) in patients with PAH, several peripheral abnormalities have been described over the recent decade as key determinants in exercise intolerance, including impaired skeletal muscle (SKM) morphology, convective O2 transport, capillarity and metabolism indicating that peripheral abnormalities play a greater role in limiting exercise capacity than previously thought. More recently, cerebrovascular alterations potentially contributing to exercise intolerance in patients with PAH were also documented. Currently, only cardiopulmonary rehabilitation has been shown to efficiently improve the peripheral components of exercise intolerance in patients with PAH. However, more extensive studies are needed to identify targeted interventions that would ultimately improve patients' exercise tolerance and QoL. The present review offers a broad and comprehensive analysis of the present literature about the complex mechanisms and their interactions limiting exercise in patients and suggests several gaps in knowledge that need to be addressed in the future for a better understanding of exercise intolerance in patients with PAH.

Relationship of end-tidal oxygen partial pressure to the determinants of anaerobic threshold in post-myocardial infarction patients

The anaerobic threshold (AT), obtained during cardiopulmonary exercise testing (CPET), is an important prognostic measure and can be used to develop an exercise prescription in patients after a myocardial infarction (post-MI). The purpose of this study was to examine the central and peripheral determinants of AT in post-MI patients end-tidal oxygen partial pressure (PETO₂) measures. We performed cardiopulmonary exercise testing (CPET) on 148 consecutively enrolled post-MI patients to determine PETO₂ measured at the AT (AT PETO₂) and ΔPETO₂ (difference between resting PETO₂ and AT PETO₂). We subsequently investigated the relationship between these measures of PETO₂ and the individual AT for each patient. Multivariate linear regression analysis indicated that AT PETO₂ and ΔPETO₂ were independently and significantly associated with the AT (β = -0.344, p < 0.001 and β = 0.228, p < 0.001, respectively). Furthermore, the independent factors of AT PETO₂ were left ventricular ejection fraction (p = 0.005), resting ventilatory equivalent for carbon dioxide (p = 0.002), and resting dead-space gas volume to tidal volume ratio (p < 0.001). However, the independent factors for ΔPETO₂ were history of diabetes (p = 0.047), estimated glomerular filtration rate (p = 0.001), and resting systolic blood pressure (p = 0.017). These findings suggested that AT PETO₂ was associated with central determinants; whereas, and ΔPETO₂ was associated with peripheral determinants, The AT PETO₂ and ΔPETO₂ provide variable insight regarding the cause of exercise intolerance and can be used to determine appropriate therapies.

Effects of inorganic nitrate supplementation on cardiovascular function and exercise tolerance in heart failure

Heart failure (HF) results in a myriad of central and peripheral abnormalities that impair the ability to sustain skeletal muscle contractions and, therefore, limit tolerance to exercise. Chief among these abnormalities is the lowered maximal oxygen uptake, which is brought about by reduced cardiac output and exacerbated by O2 delivery-utilization mismatch within the active skeletal muscle. Impaired nitric oxide (NO) bioavailability is considered to play a vital role in the vascular dysfunction of both reduced and preserved ejection fraction HF (HFrEF and HFpEF, respectively), leading to the pursuit of therapies aimed at restoring NO levels in these patient populations. Considering the complementary role of the nitrate-nitrite-NO pathway in the regulation of enzymatic NO signaling, this review explores the potential utility of inorganic nitrate interventions to increase NO bioavailability in the HFrEF and HFpEF patient population. Although many preclinical investigations have suggested that enhanced reduction of nitrite to NO in low Po2 and pH environments may make a nitrate-based therapy especially efficacious in patients with HF, inconsistent results have been found thus far in clinical settings. This brief review provides a summary of the effectiveness (or lack thereof) of inorganic nitrate interventions on exercise tolerance in patients with HFrEF and HFpEF. Focus is also given to practical considerations and current gaps in the literature to facilitate the development of effective nitrate-based interventions to improve exercise tolerance in patients with HF.

Abnormal skeletal muscle blood flow, contractile mechanics and fibre morphology in a rat model of obese-HFpEF

KEY POINTS

Heart failure is characterised by limb and respiratory muscle impairments that limit functional capacity and quality of life. However, compared with heart failure with reduced ejection fraction (HFrEF), skeletal muscle alterations induced by heart failure with preserved ejection fraction (HFpEF) remain poorly explored. Here we report that obese-HFpEF induces multiple skeletal muscle alterations in the rat hindlimb, including impaired muscle mechanics related to shortening velocity, fibre atrophy, capillary loss, and an impaired blood flow response to contractions that implies a perfusive oxygen delivery limitation. We also demonstrate that obese-HFpEF is characterised by diaphragmatic alterations similar to those caused by denervation - atrophy in Type IIb/IIx (fast/glycolytic) fibres and hypertrophy in Type I (slow/oxidative) fibres. These findings extend current knowledge in HFpEF skeletal muscle physiology, potentially underlying exercise intolerance, which may facilitate future therapeutic approaches.

ABSTRACT

Peripheral skeletal muscle and vascular alterations induced by heart failure with preserved ejection fraction (HFpEF) remain poorly identified, with limited therapeutic targets. This study used a cardiometabolic obese-HFpEF rat model to comprehensively phenotype skeletal muscle mechanics, blood flow, microvasculature and fibre atrophy. Lean (n = 8) and obese-HFpEF (n = 8) ZSF1 rats were compared. Skeletal muscles (soleus and diaphragm) were assessed for in vitro contractility (isometric and isotonic properties) alongside indices of fibre-type cross-sectional area, myosin isoform, and capillarity, and estimated muscle PO₂ . In situ extensor digitorum longus (EDL) contractility and femoral blood flow were assessed. HFpEF soleus demonstrated lower absolute maximal force by 22%, fibre atrophy by 24%, a fibre-type shift from I to IIa, and a 17% lower capillary-to-fibre ratio despite increased capillary density (all P < 0.05) with preserved muscle PO₂ (P = 0.115) and isometric specific force (P > 0.05). Soleus isotonic properties (shortening velocity and power) were impaired by up to 17 and 22%, respectively (P < 0.05), while the magnitude of the exercise hyperaemia was attenuated by 73% (P = 0.012) in line with higher muscle fatigue by 26% (P = 0.079). Diaphragm alterations (P < 0.05) included Type IIx fibre atrophy despite Type I/IIa fibre hypertrophy, with increased indices of capillarity alongside preserved contractile properties during isometric, isotonic, and cyclical contractions. In conclusion, obese-HFpEF rats demonstrated blunted skeletal muscle blood flow during contractions in parallel to microvascular structural remodelling, fibre atrophy, and isotonic contractile dysfunction in the locomotor muscles. In contrast, diaphragm phenotype remained well preserved. This study identifies numerous muscle-specific impairments that could exacerbate exercise intolerance in obese-HFpEF.

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.

Heart failure with preserved ejection fraction diminishes peripheral hemodynamics and accelerates exercise-induced neuromuscular fatigue

This study investigated the impact of HFpEF on neuromuscular fatigue and peripheral hemodynamics during small muscle mass exercise not limited by cardiac output. Eight HFpEF patients (NYHA II-III, ejection-fraction: 61 ± 2%) and eight healthy controls performed dynamic knee extension exercise (80% peak workload) to task failure and maximal intermittent quadriceps contractions (8 × 15 s). Controls repeated knee extension at the same absolute intensity as HFpEF. Leg blood flow (Q_L) was quantified using Doppler ultrasound. Pre/postexercise changes in quadriceps twitch torque (ΔQ_tw; peripheral fatigue), voluntary activation (ΔVA; central fatigue), and corticospinal excitability were quantified. At the same relative intensity, HFpEF (24 ± 5 W) and controls (42 ± 6 W) had a similar time-to-task failure (∼10 min), ΔQ_tw (∼50%), and ΔVA (∼6%). This resulted in a greater exercise-induced change in neuromuscular function per unit work in HFpEF, which was significantly correlated with a slower Q_L response time. Knee extension exercise at the same absolute intensity resulted in an ∼40% lower Q_L and greater ΔQ_tw and ΔVA in HFpEF than in controls. Corticospinal excitability remained unaltered during exercise in both groups. Finally, despite a similar ΔVA, ΔQ_tw was larger in HFpEF versus controls during isometric exercise. In conclusion, HFpEF patients are characterized by a similar development of central and peripheral fatigue as healthy controls when tested at the same relative intensity during exercise not limited by cardiac output. However, HFpEF patients have a greater susceptibility to neuromuscular fatigue during exercise at a given absolute intensity, and this impairs functional capacity. The patients' compromised Q_L response to exercise likely accounts, at least partly, for the patients' attenuated fatigue resistance.NEW & NOTEWORTHY The susceptibility to neuromuscular fatigue during exercise is substantially exaggerated in individuals with heart failure with a preserved ejection fraction. The faster rate of fatigue development is associated with the compromised peripheral hemodynamic response characterizing these patients during exercise. Given the role of neuromuscular fatigue as a factor limiting exercise, this impairment likely accounts for a significant portion of the exercise intolerance typical for this population.

Clinical importance of respiratory muscle fatigue in patients with cardiovascular disease

Patients with cardiovascular diseases frequently experience exertional dyspnea. However, the relationship between respiratory muscle strength including its fatigue and cardiovascular dysfunctions remains to be clarified.The maximal inspiratory pressure/maximal expiratory pressure (MIP/MEP) before and after cardiopulmonary exercise testing (CPX) in 44 patients with heart failure and ischemic heart disease were measured. Respiratory muscle fatigue was evaluated by calculating MIP (MIPpost/MIPpre) and MEP (MEPpost/MEPpre) changes.The mean MIPpre and MEPpre values were 67.5 ± 29.0 and 61.6 ± 23.8 cm H2O, respectively. After CPX, MIP decreased in 25 patients, and MEP decreased in 22 patients. We evaluated the correlation relationship between respiratory muscle function including respiratory muscle fatigue and exercise capacity evaluated by CPX such as peak VO2 and VE/VCO2 slope. Among MIP, MEP, change in MIP, and change in MEP, only the value of change in MIP had an association with the value of VE/VCO2 slope (R = -0.36, P = .017). In addition, multivariate analysis for determining factor of change in MIP revealed that the association between the change in MIP and eGFR was independent from other confounding parameters (beta, 0.40, P = .017). The patients were divided into 2 groups, with (MIP change < 0.9) and without respiratory muscle fatigue (MIP change > 0.9), and a significant difference in peak VO2 (14.2 ± 3.4 [with fatigue] vs 17.4 ± 4.7 [without fatigue] mL/kg/min; P = .020) was observed between the groups.Respiratory muscle fatigue demonstrated by the change of MIP before and after CPX significantly correlated with exercise capacity and renal function in patients with cardiovascular disease.

Determinants of Cardiorespiratory Fitness After Bariatric Surgery: Insights From a Randomised Controlled Trial of a Supervised Training Program

BACKGROUND

Severely obese patients have decreased cardiorespiratory fitness (CRF) and poor functional capacity. Bariatric surgery-induced weight loss improves CRF, but the determinants of this improvement are not well known. We aimed to assess the determinants of CRF before and after bariatric surgery and the impact of an exercise training program on CRF after bariatric surgery.

METHODS

Fifty-eight severely obese patients (46.1 ± 6.1 kg/m², 78% women) were randomly assigned to either an exercise group (n = 39) or usual care (n = 19). Exercise training was conducted from the 3rd to the 6th months after surgery. Anthropometric measurements, abdominal and mid-thigh computed tomographic scans, resting echocardiography, and maximal cardiopulmonary exercise testing was performed before bariatric surgery and 3 and 6 months after surgery.

RESULTS

Weight, fat mass, and fat-free mass were reduced significantly at 3 and 6 months, without any additive impact of exercise training in the exercise group. From 3 to 6 months, peak aerobic power (V̇O_2peak) increased significantly (P < 0.0001) in both groups but more importantly in the exercise group (exercise group: from 18.6 ± 4.2 to 23.2 ± 5.7 mL/kg/min; control group: from 17.4 ± 2.3 to 19.7 ± 2.4 mL/kg/min; P value, group × time = 0.01). In the exercise group, determinants of absolute V̇O_2peak (L/min) were peak exercise ventilation, oxygen pulse, and heart rate reserve (r² = 0.92; P < 0.0001), whereas determinants of V̇O_2peak indexed to body mass (mL/kg/min) were peak exercise ventilation and early-to-late filling velocity ratio (r² = 0.70; P < 0.0001).

CONCLUSIONS

A 12-week supervised training program has an additive benefit on cardiorespiratory fitness for patients who undergo bariatric surgery.