Soothing the sleeping giant: improving skeletal muscle oxygen kinetics and exercise intolerance in HFpEF

Preventing the adverse cardiovascular consequences of allogeneic stem cell transplantation with a multi-faceted exercise intervention: the ALLO-Active trial protocol

BACKGROUND

Allogeneic stem cell transplantation (allo-SCT) is a potentially lifesaving treatment for high-risk hematological malignancy, but survivors experience markedly elevated rates of cardiovascular disease and associated functional impairment. Mounting evidence suggests regular exercise, combined with a reduction in sedentary time through replacement with light exercise may be a useful therapeutic strategy for the prevention of cardiovascular comorbidities. However, this type of intervention has yet to be evaluated in patients undergoing allo-SCT. The ALLO-Active study will evaluate the efficacy of a ~ 4 month multi-faceted exercise intervention, commenced upon admission for allo-SCT, to preserve peak oxygen uptake (VO2peak) and peak cardiac output, compared with usual care. The study will also evaluate the effect of the intervention on functional independence, quality of life, and symptoms of fatigue.

METHODS

Sixty adults with hematological malignancy scheduled for allo-SCT will be randomly assigned to usual care (n = 30) or the exercise and sedentary behaviour intervention (n = 30). Participants assigned to the intervention will complete a thrice weekly aerobic and progressive resistance training program and concomitantly aim to reduce daily sedentary time by 30 min with short, frequent, light-intensity exercise bouts. Participants will undergo testing prior to, immediately after inpatient discharge, and 12 weeks after discharge. To address aim 1, VO2peak and peak cardiac output (multiple primary outcomes, p < 0.025) will be assessed via cardiopulmonary exercise testing and exercise cardiac magnetic resonance imaging, respectively. Secondary outcomes include functional independence (defined as VO2peak ≥ 18.mL.kg-1.min-1), quality of life, and fatigue (assessed via validated questionnaire). Exploratory outcomes will include indices of resting cardiac, vascular, and skeletal muscle structure and function, cardiovascular biomarkers, anxiety and depression, transplant outcomes (e.g., engraftment, graft-versus-host disease), and habitual physical activity, sedentary time, and sleep.

DISCUSSION

Multi-faceted exercise programs are a promising approach for ameliorating the cardiovascular consequences of allo-SCT. If this intervention proves to be effective, it will contribute to the development of evidence-based exercise guidelines for patients undergoing allo-SCT and assist with optimising the balance between acute cancer management and long-term health.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry (ANZCTR), ID: 12619000741189 . Registered 17 May 2019.

Matching of O2 Utilization and O2 Delivery in Contracting Skeletal Muscle in Health, Aging, and Heart Failure

Skeletal muscle is one of the most dynamic metabolic organs as evidenced by increases in metabolic rate of >150-fold from rest to maximal contractile activity. Because of limited intracellular stores of ATP, activation of metabolic pathways is required to maintain the necessary rates of ATP re-synthesis during sustained contractions. During the very early phase, phosphocreatine hydrolysis and anaerobic glycolysis prevails but as activity extends beyond ∼1 min, oxidative phosphorylation becomes the major ATP-generating pathway. Oxidative metabolism of macronutrients is highly dependent on the cardiovascular system to deliver O₂ to the contracting muscle fibres, which is ensured through a tight coupling between skeletal muscle O₂ utilization and O₂ delivery. However, to what extent O₂ delivery is ideal in terms of enabling optimal metabolic and contractile function is context-dependent and determined by a complex interaction of several regulatory systems. The first part of the review focuses on local and systemic mechanisms involved in the regulation of O₂ delivery and how integration of these influences the matching of skeletal muscle O₂ demand and O₂ delivery. In the second part, alterations in cardiovascular function and structure associated with aging and heart failure, and how these impact metabolic and contractile function, will be addressed. Where applicable, the potential of exercise training to offset/reverse age- and disease-related cardiovascular declines will be highlighted in the context of skeletal muscle metabolic function. The review focuses on human data but also covers animal observations.

Effect of Breathing Oxygen-Enriched Air on Exercise Performance in Patients With Pulmonary Hypertension Due to Heart Failure With Preserved Ejection Fraction: A Randomized, Placebo-Controlled, Crossover Trial

Objective: To evaluate the effects of breathing oxygen-enriched air (oxygen) on exercise performance in patients with pulmonary hypertension due to heart failure with preserved ejection fraction (PH-HFpEF).

Methods: Ten patients with PH-HFpEF (five women, age 60 ± 9 y, mPAP 37 ± 14 mmHg, PAWP 18 ± 2 mmHg, PVR 3 ± 3 WU, resting SpO₂ 98 ± 2%) performed two-cycle incremental exercise tests (IET) and two constant-work-rate exercise test (CWRET) at 75% maximal work-rate (W_max), each with ambient air (FiO₂ 0.21) and oxygen (FiO₂ 0.5) in a randomized, single-blinded, cross-over design. The main outcomes were the change in W_max (IET) and cycling time (CWRET) with oxygen vs. air. Blood gases at rest and end-exercise, dyspnea by Borg CR10 score at end-exercise; continuous SpO₂, minute ventilation (V'E), carbon dioxide output (V'CO₂), and cerebral and quadricep muscle tissue oxygenation (CTO and QMTO) were measured.

Results: With oxygen vs. air, W_max (IET) increased from 94 ± 36 to 99 ± 36 W, mean difference (95% CI) 5.4 (0.9–9.8) W, p = 0.025, and cycling time (CWRET) from 532 ± 203 to 680 ± 76 s, +148 (31.8–264) s, p = 0.018. At end-exercise with oxygen, Borg dyspnea score and V'E/V'CO₂ were lower, whereas PaO₂ and end-tidal PaCO₂ were higher. Other parameters were unchanged.

Conclusion: Patients with PH-HFpEF not revealing resting hypoxemia significantly improved their exercise performance while breathing oxygen-enriched air along with less subjective dyspnea sensation, a better blood oxygenation, and an enhanced ventilatory efficiency. Future studies should investigate whether prolonged training with supplemental oxygen would increase the training effect and, potentially, daily activity for PH-HFpEF patients.

Clinical Trial Registration: [clinicaltrials.gov], identifier [NCT04157660].

The effect of protein and essential amino acid supplementation on muscle strength and performance in patients with chronic heart failure: a systematic review

PURPOSE

Critically low skeletal muscle mass and strength, observed in 20% of people with chronic heart failure (CHF), reduces functional capacity, quality of life (QoL) and survival. Protein and essential amino acid (EAA) supplementation could be a viable treatment strategy to prevent declines in muscle strength and performance, and subsequently improve QoL and survival. This systematic review (PROSPERO: CRD42018103649) aimed to assess the effect of dietary protein and/or EAA supplementation on muscle strength and performance in people with CHF.

METHODS

Searches of PubMed, MEDLINE and Embase identified studies that reported changes in strength or muscle performance following protein and/or EAA supplementation in patients with CHF. Following PRISMA guidelines and using predefined inclusion/exclusion criteria relating to participants, intervention, control, outcome and study design, two reviewers independently screened titles, abstracts and full manuscripts for eligibility. Risk of bias was assessed using Cochrane Risk of Bias Tool (RCTs) or Mixed Methods Appraisal Tool (cohort studies). Data were extracted for analysis using predefined criteria.

RESULTS

Five randomised controlled trials (RCT) and one cohort study met our inclusion criteria. All RCTs had a high risk of bias. The methodological quality of the cohort study was moderate. Heterogeneity of extracted data prevented meta-analyses, qualitative synthesis was therefore performed. Data from 167 patients with CHF suggest that protein and/or EAA supplementation does not improve strength, but may increase six-minute walk test distance, muscle mass and QoL.

CONCLUSIONS

The limited quality of the studies makes firm conclusions difficult, however protein and/or EAA supplementation may improve important outcome measures related to sarcopenia. High-quality randomised controlled studies are needed.

Abnormalities of Skeletal Muscle, Adipocyte Tissue, and Lipid Metabolism in Heart Failure: Practical Therapeutic Targets

Chronic diseases, including heart failure (HF), are often accompanied with skeletal muscle abnormalities in both quality and quantity, which are the major cause of impairment of the activities of daily living and quality of life. We have shown that skeletal muscle abnormalities are a hallmark of HF, in which metabolic pathways involving phosphocreatine and fatty acids are largely affected. Not only in HF, but the dysfunction of fatty acid metabolism may also occur in many chronic diseases, such as arteriosclerosis, as well as through insufficient physical exercise. Decreased fatty acid catabolism affects adenosine triphosphate (ATP) production in mitochondria, via decreased activity of the tricarboxylic acid cycle; and may cause abnormal accumulation of adipose tissue accompanied with hyperoxidation and ectopic lipid deposition. Such impairments of lipid metabolism are in turn detrimental to skeletal muscle, which is hence a chicken-and-egg problem between skeletal muscle and HF. In this review, we first discuss skeletal muscle abnormalities in HF, including sarcopenia; particularly their association with lipid metabolism and adipose tissue. On the other hand, the precise mechanisms involved in metabolic reprogramming and dysfunction are beginning to be understood, and an imbalance of daily nutritional intake of individuals has been found to be a causative factor for the development and worsening of HF. Physical exercise has long been known to be beneficial for the prevention and even treatment of HF. Again, the molecular mechanisms by which exercise promotes skeletal muscle as well as cardiac muscle functions are being clarified by recent studies. We propose that it is now the time to develop more “natural” methods to prevent and treat HF, rather than merely relying on drugs and medical interventions. Further analysis of the basic design of and molecular mechanisms involved in the human body, particularly the inextricable association between physical exercise and the integrity and functional plasticity of skeletal and cardiac muscles is required.

Dopamine stimulation of the septum enhances exercise efficiency during complicated treadmill running in mice

We aimed to identify the neurotransmitters and brain regions involved in exercise efficiency in mice during continuous complicated exercises. Male C57BL/6J mice practiced treadmill running with intermittent obstacles on a treadmill for 8 days. Oxygen uptake (VO2) during treadmill running was measured as exercise efficiency. After obstacle exercise training, the VO2 measured during treadmill running with obstacles decreased significantly. Obstacle exercise-induced c-Fos expressions and dopamine turnover (DOPAC/dopamine) in the septum after obstacle exercise training were significantly higher than that before training. The dopamine turnover was correlated with exercise efficiency on the 3rd day after exercise training. Furthermore, the training effect on exercise efficiency was significantly decreased by injection of dopamine receptor antagonists into the septum and was associated with decreased c-Fos expressions in the septum and hippocampus of the mice. These results suggest that dopaminergic function in the septum is involved in exercise efficiency during continuous complicated exercises.

Effects of heavy-intensity priming exercise on pulmonary oxygen uptake kinetics and muscle oxygenation in heart failure with preserved ejection fraction

Exercise intolerance is a hallmark feature in heart failure with preserved ejection fraction (HFpEF). Prior heavy exercise ("priming exercise") speeds pulmonary oxygen uptake (V̇o_2p) kinetics in older adults through increased muscle oxygen delivery and/or alterations in mitochondrial metabolic activity. We tested the hypothesis that priming exercise would speed V̇o_2p on-kinetics in patients with HFpEF because of acute improvements in muscle oxygen delivery. Seven patients with HFpEF performed three bouts of two exercise transitions: MOD1, rest to 4-min moderate-intensity cycling and MOD2, MOD1 preceded by heavy-intensity cycling. V̇o_2p, heart rate (HR), total peripheral resistance (TPR), and vastus lateralis tissue oxygenation index (TOI; near-infrared spectroscopy) were measured, interpolated, time-aligned, and averaged. V̇o_2p and HR were monoexponentially curve-fitted. TPR and TOI levels were analyzed as repeated measures between pretransition baseline, minimum value, and steady state. Significance was P < 0.05. Time constant (τ; tau) V̇o_2p (MOD1 49 ± 16 s) was significantly faster after priming (41 ± 14 s; P = 0.002), and the effective HR τ was slower following priming (41 ± 27 vs. 51 ± 32 s; P = 0.025). TPR in both conditions decreased from baseline to minimum TPR ( P < 0.001), increased from minimum to steady state ( P = 0.041) but remained below baseline throughout ( P = 0.001). Priming increased baseline ( P = 0.003) and minimum TOI ( P = 0.002) and decreased the TOI muscle deoxygenation overshoot ( P = 0.041). Priming may speed the slow V̇o_2p on-kinetics in HFpEF and increase muscle oxygen delivery (TOI) at the onset of and throughout exercise. Microvascular muscle oxygen delivery may limit exercise tolerance in HFpEF.

Skeletal Muscle Myopathy in Heart Failure: the Role of Ejection Fraction

PURPOSE OF REVIEW

This review summarizes: (1) the structural and functional features coupled with pathophysiological factors responsible of skeletal muscle myopathy (SMM) in both heart failure with reduced (HFrEF) and preserved (HFpEF) ejection fraction and (2) the role of exercise as treatment of SMM in these HF-related phenotypes.

RECENT FINDINGS

The recent literature showed two main phenotypes of heart failure (HF): (1) HFrEF primarily due to a systolic dysfunction of the left ventricle and (2) HFpEF, mainly related to a diastolic dysfunction. Exercise intolerance is one of most disabling symptoms of HF and it is shown that persists after the normalization of the central hemodynamic impairments by therapy and/or cardiac surgery including heart transplant. A specific skeletal muscle myopathy (SMM) has been defined as one of the main causes of exercise intolerance in HF. The SMM has been well described in the last 20 years in the HFrEF; on the contrary, few studies are available in HFpEF. Recent evidences have revealed that exercise training counteracts HF-related SMM and in turn ameliorates exercise intolerance.

Hemodynamic Profile of Patients With Heart Failure and Preserved Ejection Fraction Vary by Age

Background

Patients with heart failure with preserved ejection fraction (HFpEF) exhibit a range of cardiovascular phenotypic profiles modified by several common comorbidities. In particular, patients with HFpEF tend to be older; however, it is unclear whether the effects of cardiovascular aging per se modify the expression of HFpEF. We therefore sought to investigate the interaction between age and physiologic profile in patients with HFpEF.

Methods and Results

We assessed the hemodynamic and metabolic profile of 40 patients with HFpEF. Patients underwent right heart catheterization at rest and during supine cycle ergometry, and were segregated into 2 groups by the median age of the cohort. Older patients with HFpEF demonstrated reduced resting cardiac output (4.8±1.2 L/min versus 5.7±1.1 L/min). With exercise, older patients demonstrated a marked rise in arteriovenous oxygen content difference (10.8±1.8 versus 7.9±2.4 mL, P≤0.001), driven by enhanced oxygen extraction. There was no significant difference in peak pulmonary capillary wedge pressure (30±7 mm Hg versus 27±6, P=0.135), including when indexed to workload (pulmonary capillary wedge pressure/W, 0.88 mm Hg/W versus 0.92; P=0.83).

Conclusions

Older patients with HFpEF display a different physiological phenotype compared with younger patients, with enhanced oxygen extraction and lower increment in cardiac output to increase oxygen consumption from rest to peak supine exercise. This finding highlights the importance in considering age when considering therapeutic options in patients with HFpEF.

Mechanisms of the Improvement in Peak VO2 With Exercise Training in Heart Failure With Reduced or Preserved Ejection Fraction

Heart failure (HF) is a major health care burden associated with high morbidity and mortality. Approximately 50% of HF patients have reduced ejection fraction (HFrEF) while the remainder of patients have preserved ejection fraction (HFpEF). A hallmark of both HF phenotypes is dyspnoea upon exertion and severe exercise intolerance secondary to impaired oxygen delivery and/or use by exercising skeletal muscle. Exercise training is a safe and effective intervention to improve peak oxygen uptake (VO_2peak) and quality of life in clinically stable HF patients, however, evidence to date suggests that the mechanism of this improvement appears to be related to underlying HF phenotype. The purpose of this review is to discuss the role of exercise training to improve VO_2peak, and how the central and peripheral adaptations that mediate the improvements in exercise tolerance may be similar or differ by HF phenotype (HFrEF or HFpEF).

Impact of Exercise Training on Peak Oxygen Uptake and its Determinants in Heart Failure with Preserved Ejection Fraction

Heart failure with preserved ejection (HFpEF) accounts for over 50 % of all HF cases, and the proportion is higher among women and older individuals. A hallmark feature of HFpEF is dyspnoea on exertion and reduced peak aerobic power (VO_2peak) secondary to central and peripheral abnormalities that result in reduced oxygen delivery to and/or utilisation by exercising skeletal muscle. The purpose of this brief review is to discuss the role of exercise training to improve VO_2peak and the central and peripheral adaptations that reduce symptoms following physical conditioning in patients with HFpEF.

Exercise training in chronic heart failure: improving skeletal muscle O2 transport and utilization

Chronic heart failure (CHF) impairs critical structural and functional components of the O2 transport pathway resulting in exercise intolerance and, consequently, reduced quality of life. In contrast, exercise training is capable of combating many of the CHF-induced impairments and enhancing the matching between skeletal muscle O2 delivery and utilization (Q̇mO2 and V̇mO2 , respectively). The Q̇mO2 /V̇mO2 ratio determines the microvascular O2 partial pressure (PmvO2 ), which represents the ultimate force driving blood-myocyte O2 flux (see Fig. 1). Improvements in perfusive and diffusive O2 conductances are essential to support faster rates of oxidative phosphorylation (reflected as faster V̇mO2 kinetics during transitions in metabolic demand) and reduce the reliance on anaerobic glycolysis and utilization of finite energy sources (thus lowering the magnitude of the O2 deficit) in trained CHF muscle. These adaptations contribute to attenuated muscle metabolic perturbations (e.g., changes in [PCr], [Cr], [ADP], and pH) and improved physical capacity (i.e., elevated critical power and maximal V̇mO2 ). Preservation of such plasticity in response to exercise training is crucial considering the dominant role of skeletal muscle dysfunction in the pathophysiology and increased morbidity/mortality of the CHF patient. This brief review focuses on the mechanistic bases for improved Q̇mO2 /V̇mO2 matching (and enhanced PmvO2 ) with exercise training in CHF with both preserved and reduced ejection fraction (HFpEF and HFrEF, respectively). Specifically, O2 convection within the skeletal muscle microcirculation, O2 diffusion from the red blood cell to the mitochondria, and muscle metabolic control are particularly susceptive to exercise training adaptations in CHF. Alternatives to traditional whole body endurance exercise training programs such as small muscle mass and inspiratory muscle training, pharmacological treatment (e.g., sildenafil and pentoxifylline), and dietary nitrate supplementation are also presented in light of their therapeutic potential. Adaptations within the skeletal muscle O2 transport and utilization system underlie improvements in physical capacity and quality of life in CHF and thus take center stage in the therapeutic management of these patients.