Effect of exercise training on skeletal muscle histology and metabolism in peripheral arterial disease

Medical Optimization of Patients with Symptomatic Peripheral Arterial Disease

Peripheral artery disease (PAD) is a progressive disease associated with the occurrence of major adverse cardiovascular and limb events and elevated mortality rates. Symptoms of PAD, including claudication and chronic limb-threatening ischemia, impair functional capacity and lead to lower quality of life. The focus of current therapies is to minimize symptoms, improve quality of life, and reduce adverse cardiovascular and limb events. Among the medical therapies are antiplatelets, anticoagulants, antihypertensives, lipid lowering therapies, cilostazol and pentoxifylline, and novel blood sugar-lowering therapies, plus exercise therapy and smoking cessation. In this review, we discuss these evidence-based medical therapies that are available for patients with symptomatic PAD.

Objective assessment of functional capacity in patients with peripheral artery disease: a narrative review

INTRODUCTION

Peripheral artery disease (PAD) patients with claudication symptoms exhibit impaired functional capacity, which has been associated with disease severity, worse quality of life and higher risk of cardiovascular events. Different tests have been used to assess functional capacity in PAD patients. Therefore, understanding the characteristics, strengths and limitations of these tests are important to support the choice of tests to be used in clinical practice.

AREAS COVERED

This review summarizes the main methods to assess functional capacity in PAD patients, discussing their psychometric properties, applications, and limitations.

EXPERT OPINION

Robust evidence supports the use of treadmill and six-minute walk tests in PAD patients, as their results are associated with clinically meaningful outcomes, adequate psychometric properties and are sensitive to effects of interventions. On the other hand, other functional tests (Shuttle-walk test, outdoor walking capacity test, timed-up and go, four-meter walk test, heel-rise test, short physical performance battery and modified physical performance battery) are related to activities of daily living and do not require sophisticated equipment and can be easily used in clinical practice. However, these other tests still need evidence regarding their clinical relevance, reliability, and ability to detect long-term intervention changes, providing further investigation directions.

Peripheral arterial disease: A small and large vessel problem

Peripheral arterial disease (PAD) is one clinical manifestation of systemic atherosclerosis and is very common. Despite its prevalence, PAD remains underdiagnosed, undertreated, and understudied. The most common symptom in patients with PAD is intermittent claudication (IC), or pain in the lower extremities with walking or exertion, which is relieved after a short period of rest. Many patients with confirmed PAD are asymptomatic or have symptoms other than IC. Regardless of symptoms, patients with PAD have poor cardiovascular outcomes. PAD has largely been viewed a disease of large vessel atherosclerosis but what is becoming clear is that arterial plaques and occlusions are only one piece of the puzzle. Recent work has shown that abnormalities in the microvasculature contribute to the outcome of patients with PAD. From the perspective of the leg, limitation in blood flow is not the only problem as patients have a myriad of other problems, including muscle fibrosis, neuropathic changes, changes in the cellular respiration machinery and dysfunction of the small vessels that perfuse skeletal muscle and the supporting structures. Supervised exercise training remains one of the most effective tool to treat patients with PAD, however, the mechanisms behind its effectiveness are still being elucidated and use of structured exercise programs is not widespread. Medical therapy to treat systemic atherosclerosis is underutilized in patients with PAD. Invasive therapies are used only when patients with PAD have reached an advanced stage. While invasive strategies are effective in some patients with PAD, these strategies are costly, carry risk, and many patients are not amenable to invasive therapy. Appreciating the complex pathophysiology of PAD will hopefully spur new research and development of effective therapies for PAD.

The forkhead box O3 (FOXO3): a key player in the regulation of ischemia and reperfusion injury

Forkhead box O3 is a protein encoded by the FOXO3 gene expressed throughout the body. FOXO3 could play a crucial role in longevity and many other pathologies, such as Alzheimer's disease, glioblastoma, and stroke. This study is a comprehensive review of the expression of FOXO3 under ischemia and reperfusion (IR) and the molecular mechanisms of its regulation and function. We found that the expression level of FOXO3 under ischemia and IR is tissue-specific. Specifically, the expression level of FOXO3 is increased in the lung and intestinal epithelial cells after IR. However, FOXO3 is downregulated in the kidney after IR and in the skeletal muscles following ischemia. Interestingly, both increased and decreased FOXO3 expression have been reported in the brain, liver, and heart following IR. Nevertheless, these contribute to stimulating ischemia and reperfusion injury via the induction of inflammatory response, apoptosis, autophagy, mitophagy, pyroptosis, and oxidative damage. These results suggest that FOXO3 could play protective effects in some organs and detrimental effects in others against IR injury. Most importantly, these findings indicate that controlling FOXO3 expression, genetically or pharmacologically, could contribute to preventing or treating ischemia and reperfusion damage.

Supervised Exercise Therapy for Symptomatic Peripheral Artery Disease: A REVIEW OF CURRENT EXPERIENCE AND PRACTICE-BASED RECOMMENDATIONS

PURPOSE

This review encompasses several practical components of supervised exercise therapy (SET) for patients with claudication including referral, exercise training, and billing issues. Real-life SET session examples are also provided. SET was approved for reimbursement by the Centers for Medicare & Medicaid Services (CMS) in 2017, and there is continual growth of programs offering SET and in participation. The purpose of this review is to provide useful information for the clinical exercise professionals working with these patients.

REVIEW METHODS

The 2016 ACC/AHA Guideline on the Management of Patients With Lower Extremity Peripheral Artery Disease (PAD) provided a class I (highest level) recommendation for the use of SET in those with symptomatic PAD. Since there has been much growth in the literature about the utility of SET, the literature was reviewed (PubMed) to provide information for this article. Topics reviewed include the benefits of exercise training, exercise prescription, billing, referral and participation, and best practices.

SUMMARY

SET should be offered to all patients with symptomatic PAD who are not at risk of acute limb ischemia. For optimal results, SET should be implemented several times per week and in a progressive process to increase exercise intensity as tolerated. For best results, programs should recommend patients supplement SET with home exercise. Considerations for utilizing reimbursed sessions should also be discussed because patients have a maximum of 72 sessions/lifetime. Referral practices need refinement, and participation rates remain extremely low and may be influenced by demographics. Research on best practices and home or hybrid training must continue to address issues related to common enrollment and participation barriers.

CONDENSED ABSTRACT

Supervised exercise training (SET) for symptomatic peripheral artery disease is a class IA recommendation and reimbursable by most insurances. Improvements in walking performance can be dramatic. However, referral and participation in SET remain very low and thus SET is vastly underutilized.

Temporal analysis of skeletal muscle remodeling post hindlimb ischemia reveals intricate autophagy regulation

Hind limb ischemia (HLI) is the most severe form of peripheral arterial disease, associated with a substantial reduction of limb blood flow that impairs skeletal muscle homeostasis to promote functional disability. The molecular regulators of HLI-induced muscle perturbations remain poorly defined. This study investigated whether changes in the molecular catabolic-autophagy signaling network were linked to temporal remodeling of skeletal muscle in HLI. HLI was induced in mice via hindlimb ischemia (femoral artery ligation) and confirmed by Doppler echocardiography. Experiments were terminated at time points defined as early- (7 days; n = 5) or late- (28 days; n = 5) stage HLI. Ischemic and nonischemic (contralateral) limb muscles were compared. Ischemic versus nonischemic muscles demonstrated overt remodeling at early-HLI but normalized at late-HLI. Early-onset fiber atrophy was associated with excessive autophagy signaling in ischemic muscle; protein expression increased for Beclin-1, LC3, and p62 (P < 0.05) but proteasome-dependent markers were reduced (P < 0.05). Mitophagy signaling increased in early-stage HLI that aligned with an early and sustained loss of mitochondrial content (P < 0.05). Upstream autophagy regulators, Sestrins, showed divergent responses during early-stage HLI (Sestrin2 increased while Sestrin1 decreased; P < 0.05) in parallel to increased AMP-activated protein kinase (AMPK) phosphorylation (P < 0.05) and lower antioxidant enzyme expression. No changes were found in markers for mechanistic target of rapamycin complex 1 signaling. These data indicate that early activation of the sestrin-AMPK signaling axis may regulate autophagy to stimulate rapid and overt muscle atrophy in HLI, which is normalized within weeks and accompanied by recovery of muscle mass. A complex interplay between Sestrins to regulate autophagy signaling during early-to-late muscle remodeling in HLI is likely.

Dysregulated Genes, MicroRNAs, Biological Pathways, and Gastrocnemius Muscle Fiber Types Associated With Progression of Peripheral Artery Disease: A Preliminary Analysis

Background Peripheral artery disease (PAD) is associated with gastrocnemius muscle abnormalities. However, the biological pathways associated with gastrocnemius muscle dysfunction and their associations with progression of PAD are largely unknown. This study characterized differential gene and microRNA (miRNA) expression in gastrocnemius biopsies from people without PAD compared with those with PAD. Participants with PAD included those with and without PAD progression. Methods and Results mRNA and miRNA sequencing were performed to identify differentially expressed genes, differentially expressed miRNAs, mRNA-miRNA interactions, and associated biological pathways for 3 sets of comparisons: (1) PAD progression (n=7) versus non-PAD (n=7); (2) PAD no progression (n=6) versus non-PAD; and (3) PAD progression versus PAD no progression. Immunohistochemistry was performed to determine gastrocnemius muscle fiber types and muscle fiber size. Differentially expressed genes and differentially expressed miRNAs were more abundant in the comparison of PAD progression versus non-PAD compared with PAD with versus without progression. Among the top significant cellular pathways in subjects with PAD progression were muscle contraction or development, transforming growth factor-beta, growth/differentiation factor, and activin signaling, inflammation, cellular senescence, and notch signaling. Subjects with PAD progression had increased frequency of smaller Type 2a gastrocnemius muscle fibers in exploratory analyses. Conclusions Humans with PAD progression exhibited greater differences in the number of gene and miRNA expression, biological pathways, and Type 2a muscle fiber size compared with those without PAD. Fewer differences were observed between people with PAD without progression and control patients without PAD. Further study is needed to confirm whether the identified transcripts may serve as potential biomarkers for diagnosis and progression of PAD.

Metabolite patterns associated with individual response to supervised exercise therapy in patients with intermittent claudication

Objective

Supervised exercise therapy (SET) is the first line treatment for intermittent claudication owing to peripheral arterial disease. Despite multiple randomized controlled trials proving the efficacy of SET, there are large differences in individual patient's responses. We used plasma metabolomics to identify potential metabolic influences on the individual response to SET.

Methods

Primary metabolites, complex lipids, and lipid mediators were measured on plasma samples taken at before and after Gardner graded treadmill walking tests that were administered before and after 12 weeks of SET. We used an ensemble modeling approach to identify metabolites or changes in metabolites at specific time points that associated with interindividual variability in the functional response to SET. Specific time points analyzed included baseline metabolite levels before SET, dynamic metabolomics changes before SET, the difference in pre- and post-SET baseline metabolomics, and the difference (pre- and post-SET) of the dynamic (pre- and post-treadmill).

Results

High levels of baseline anandamide levels pre- and post-SET were associated with a worse response to SET. Increased arachidonic acid (AA) and decreased levels of the AA precursor dihomo-γ-linolenic acid across SET were associated with a worse response to SET. Participants who were able to tolerate large increases in AA during acute exercise had longer, or better, walking times both before and after SET.

Conclusions

We identified two pathways of relevance to individual response to SET that warrant further study: anandamide synthesis may activate endocannabinoid receptors, resulting in worse treadmill test performance. SET may train patients to withstand higher levels of AA, and inflammatory signaling, resulting in longer walking times.

Clinical Relevance

This manuscript describes the use of metabolomic techniques to measure the interindividual effects of SET in patients with peripheral artery disease (PAD). We identified high levels of AEA are linked to CB1 signaling and activation of inflammatory pathways. This alters energy expenditure in myoblasts by decreasing glucose uptake and may induce an acquired skeletal muscle myopathy. SET may also help participants tolerate increased levels of AA and inflammation produced during exercise, resulting in longer walking times. This data will enhance understanding of the pathophysiology of PAD and the mechanism by which SET improves walking intolerance.

The Effects of Exercise Training on Mitochondrial Function in Cardiovascular Diseases: A Systematic Review and Meta-Analysis

Mitochondria dysfunction is implicated in the pathogenesis of cardiovascular diseases (CVD). Exercise training is potentially an effective non-pharmacological strategy to restore mitochondrial health in CVD. However, how exercise modifies mitochondrial functionality is inconclusive. We conducted a systematic review using the PubMed; Scopus and Web of Science databases to investigate the effect of exercise training on mitochondrial function in CVD patients. Search terms included “mitochondria”, “exercise”, “aerobic capacity”, and “cardiovascular disease” in varied combination. The search yielded 821 records for abstract screening, of which 20 articles met the inclusion criteria. We summarized the effect of exercise training on mitochondrial morphology, biogenesis, dynamics, oxidative capacity, antioxidant capacity, and quality. Amongst these parameters, only oxidative capacity was suitable for a meta-analysis, which demonstrated a significant effect size of exercise in improving mitochondrial oxidative capacity in CVD patients (SMD = 4.78; CI = 2.99 to 6.57; p < 0.01), but with high heterogeneity among the studies (I2 = 75%, p = 0.003). Notably, aerobic exercise enhanced succinate-involved oxidative phosphorylation. The majority of the results suggested that exercise improves morphology and biogenesis, whereas findings on dynamic, antioxidant capacity, and quality, were inadequate or inconclusive. A further randomized controlled trial is clearly required to explain how exercise modifies the pathway of mitochondrial quantity and quality in CVD patients.

Impact of supervised exercise on skeletal muscle blood flow and vascular function measured with MRI in patients with peripheral artery disease

Supervised exercise is a common therapeutic intervention for patients with peripheral artery disease (PAD), however, the mechanism underlying the improvement in claudication symptomatology is not completely understood. The hypothesis that exercise improves microvascular blood flow is herein tested via temporally resolved magnetic resonance imaging (MRI) measurement of blood flow and oxygenation dynamics during reactive hyperemia in the leg with the lower ankle-brachial index. One hundred and forty-eight subjects with PAD were prospectively assigned to standard medical care or 3 mo of supervised exercise therapy. Before and after the intervention period, subjects performed a graded treadmill walking test, and MRI data were collected with Perfusion, Intravascular Venous Oxygen saturation, and T2* (PIVOT), a method that simultaneously quantifies microvascular perfusion, as well as relative oxygenation changes in skeletal muscle and venous oxygen saturation in a large draining vein. The 3-mo exercise intervention was associated with an improvement in peak walking time (64% greater in those randomized to the exercise group at follow-up, P < 0.001). Significant differences were not observed in the MRI measures between the subjects randomized to exercise therapy versus standard medical care based on an intention-to-treat analysis. However, the peak postischemia perfusion averaged across the leg between baseline and follow-up visits increased by 10% (P = 0.021) in participants that were adherent to the exercise protocol (completed >80% of prescribed exercise visits). In this cohort of adherent exercisers, there was no difference in the time to peak perfusion or oxygenation metrics, suggesting that there was no improvement in microvascular function nor changes in tissue metabolism in response to the 3-mo exercise intervention.NEW & NOTEWORTHY Supervised exercise interventions can improve symptomatology in patients with peripheral artery disease, but the underlying mechanism remains unclear. Here, MRI was used to evaluate perfusion, relative tissue oxygenation, and venous oxygen saturation in response to cuff-induced ischemia. Reactive hyperemia responses were measured before and after 3 mo of randomized supervised exercise therapy or standard medical care. Those participants who were adherent to the exercise regimen had a significant improvement in peak perfusion.

Connecting the past to the present: A historical review of exercise training for peripheral artery disease

Peripheral artery disease (PAD), a prevalent manifestation of atherosclerosis, is associated with increased cardiovascular morbidity and mortality as well as decreased functional ability. Exercise training for PAD is acknowledged to be a highly effective treatment, which improves walking ability and cardiovascular risk. The historical development of this treatment has not been the focus of a report. Therefore, we present a historical review of research on exercise training for PAD. Overall, this body of knowledge has provided strong evidence of the efficacy of supervised exercise training (SET) to improve walking ability for patients with claudication due to PAD. SET, using intermittent bouts of walking exercise to moderate claudication pain on a treadmill, is considered the most efficacious mode of exercise to improve walking ability in patients with claudication. This compelling evidence published over the past 60 years was evaluated by the Centers for Medicare & Medicaid Services in 2017, which culminated in a national coverage determination for SET to improve symptomatic PAD. Future directions include determining optimal delivery strategies for SET and further elucidation of the mechanisms of improvement in walking ability resulting from SET. In addition, alternative forms of exercise should be evaluated and effective home- and community-based exercise interventions should be assessed. There is an enormous need to increase the inclusion of women and racial and ethnic minority groups in studies. It is to be hoped that researchers will continue with new innovative research and persistence in the treatment of claudication due to PAD.

Exercise Training Increases Resting Calf Muscle Oxygen Metabolism in Patients with Peripheral Artery Disease

Exercise training can mitigate symptoms of claudication (walking-induced muscle pain) in patients with peripheral artery disease (PAD). One adaptive response enabling this improvement is enhanced muscle oxygen metabolism. To explore this issue, we used arterial-occlusion diffuse optical spectroscopy (AO-DOS) to measure the effects of exercise training on the metabolic rate of oxygen (MRO₂) in resting calf muscle. Additionally, venous-occlusion DOS (VO-DOS) and frequency-domain DOS (FD-DOS) were used to measure muscle blood flow (F) and tissue oxygen saturation (StO₂), and resting calf muscle oxygen extraction fraction (OEF) was calculated from MRO₂, F, and blood hemoglobin. Lastly, the venous/arterial ratio (γ) of blood monitored by FD-DOS was calculated from OEF and StO₂. PAD patients who experience claudication (n = 28) were randomly assigned to exercise and control groups. Patients in the exercise group received 3 months of supervised exercise training. Optical measurements were obtained at baseline and at 3 months in both groups. Resting MRO₂, OEF, and F, respectively, increased by 30% (12%, 44%) (p < 0.001), 17% (6%, 45%) (p = 0.003), and 7% (0%, 16%) (p = 0.11), after exercise training (median (interquartile range)). The pre-exercise γ was 0.76 (0.61, 0.89); it decreased by 12% (35%, 6%) after exercise training (p = 0.011). Improvement in exercise performance was associated with a correlative increase in resting OEF (R = 0.45, p = 0.02).

Moderate Intensity Functional Training as Adjuvant Treatment in Patients With Peripheral Arterial Disease: A Case Report

BACKGROUND

Traditional aerobic training and muscle resistance ("strength") training have been shown to be effective for improving functional and health-related quality of life (HRQoL) outcomes in peripheral arterial disease (PAD). However, the transfer of the current resistance exercise modes proposed to other activities of daily living (ADLs) is questionable. Moderate intensity functional training (MIFT) has emerged with the aim of achieving cardiovascular and neuromuscular adaptations simultaneously with functional exercises typical of ADLs. The effect of MIFT in patients with PAD is not yet known. Our purpose is to verify the influence of the combination of intermittent treadmill walking exercise with MIFT on functional capacity and HRQoL in patients with PAD.

METHODS

Three patients with PAD participated in a novel supervised exercise therapy program of 6 weeks duration based on intermittent treadmill walking exercise and MIFT.

RESULTS

After the training period, the 3 patients showed high adherence to the program (95%) and they improved total distance (TD) (25%, 9%, and 21%), claudication onset distance (COD) (56%, 19%, and 151%), total number of repetitions (33%, 24%, and 33%) and total work capacity (80%, 79%, and 72%). Also, physical component in Short Form-36 Health Survey (SF-36) and Vascular Quality of Life Questionnaire-6 (VascuQol-6) showed increases in the patients.

CONCLUSIONS

The 6-week intervention in patients with PAD, based on intermittent treadmill walking exercise and MIFT, seems to improve their functional status and total work capacity in functional exercises as well as their HRQoL.

Phytochemicals as Therapeutic Interventions in Peripheral Artery Disease

Peripheral artery disease (PAD) affects over 200 million people worldwide, resulting in significant morbidity and mortality, yet treatment options remain limited. Among the manifestations of PAD is a severe functional disability and decline, which is thought to be the result of different pathophysiological mechanisms including oxidative stress, skeletal muscle pathology, and reduced nitric oxide bioavailability. Thus, compounds that target these mechanisms may have a therapeutic effect on walking performance in PAD patients. Phytochemicals produced by plants have been widely studied for their potential health effects and role in various diseases including cardiovascular disease and cancer. In this review, we focus on PAD and discuss the evidence related to the clinical utility of different phytochemicals. We discuss phytochemical research in preclinical models of PAD, and we highlight the results of the available clinical trials that have assessed the effects of these compounds on PAD patient functional outcomes.

Walking Exercise Therapy Effects on Lower Extremity Skeletal Muscle in Peripheral Artery Disease

Walking exercise is the most effective noninvasive therapy that improves walking ability in peripheral artery disease (PAD). Biologic mechanisms by which exercise improves walking in PAD are unclear. This review summarizes evidence regarding effects of walking exercise on lower extremity skeletal muscle in PAD. In older people without PAD, aerobic exercise improves mitochondrial activity, muscle mass, capillary density, and insulin sensitivity in skeletal muscle. However, walking exercise increases lower extremity ischemia in people with PAD, and therefore, mechanisms by which this exercise improves walking may differ between people with and without PAD. Compared with people without PAD, gastrocnemius muscle in people with PAD has greater mitochondrial impairment, increased reactive oxygen species, and increased fibrosis. In multiple small trials, walking exercise therapy did not consistently improve mitochondrial activity in people with PAD. In one 12-week randomized trial of people with PAD randomized to supervised exercise or control, supervised treadmill exercise increased treadmill walking time from 9.3 to 15.1 minutes, but simultaneously increased the proportion of angular muscle fibers, consistent with muscle denervation (from 7.6% to 15.6%), while angular myofibers did not change in the control group (from 9.1% to 9.1%). These findings suggest an adaptive response to exercise in PAD that includes denervation and reinnervation, an adaptive process observed in skeletal muscle of people without PAD during aging. Small studies have not shown significant effects of exercise on increased capillary density in lower extremity skeletal muscle of participants with PAD, and there are no data showing that exercise improves microcirculatory delivery of oxygen and nutrients in patients with PAD. However, the effects of supervised exercise on increased plasma nitrite abundance after a treadmill walking test in people with PAD may be associated with improved lower extremity skeletal muscle perfusion and may contribute to improved walking performance in response to exercise in people with PAD. Randomized trials with serial, comprehensive measures of muscle biology, and physiology are needed to clarify mechanisms by which walking exercise interventions improve mobility in PAD.

Supervised Resistance Training on Functional Capacity, Muscle Strength and Vascular Function in Peripheral Artery Disease: An Updated Systematic Review and Meta-Analysis

Supervised resistance training appears to be a promising alternative exercise modality to supervised walking in patients with peripheral artery disease (PAD). This meta-analysis examined the efficacy of supervised RT for improving walking capacity, and whether adaptations occur at the vascular and/or skeletal muscle level in PAD patients. We searched Medline, CINAHL, Scopus, and Cochrane Central Register of Controlled Trials databases for randomized controlled trials (RCTs) in PAD patients testing the effects of supervised RT for ≥4 wk. on walking capacity, vascular function, and muscle strength. Pooled effect estimates were calculated and evaluated using conventional meta-analytic procedures. Six RCTs compared supervised RT to standard care. Overall, supervised RT prolonged claudication onset distance during a 6-min walk test (6-MWT) (101.7 m (59.6, 143.8), p < 0.001) and improved total walking distance during graded treadmill walking (SMD: 0.67 (0.33, 1.01), p < 0.001) and the 6-MWT (49.4 m (3.1, 95.6), p = 0.04). Five RCTS compared supervised RT and supervised intermittent walking, where the differences in functional capacity between the two exercise modalities appear to depend on the intensity of the exercise program. The insufficient evidence on the effects of RT on vascular function and muscle strength permitted only limited exploration. We conclude that RT is effective in prolonging walking performance in PAD patients. Whether RT exerts its influence on functional capacity by promoting blood flow and/or enhancing skeletal muscle strength remains unclear.

Clinical considerations after endovascular therapy of peripheral artery disease

Introduction: Patients with peripheral artery disease (PAD) are at higher risk for all-cause mortality, driven by increased cardiovascular mortality rates. In this manuscript we review the literature on guideline-recommended therapies and discuss the major clinical considerations after endovascular therapy of PAD.Areas covered: Current guidelines recommend smoking cessation, aspirin, statin, and renin-angiotensin system inhibitors in order to reduce the risk of cardiovascular and limb-related adverse events. Nonetheless, studies have shown that patients with PAD are undertreated with these important medical therapies. Additionally, there is lack in evidence regarding the most optimal follow up imaging approach for early detection of disease recurrence and re-intervention among patients undergoing endovascular therapy for PAD. We also describe the benefits of supervised walking exercise for patients with PAD that undergo revascularization procedures and are fit for such interventions.Expert opinion: Adherence to guideline recommended medical therapy is crucial for improved outcomes in PAD management. Systematic assessment of risk-reduction interventions could help increase adherence to clinically beneficial interventions and improve the overall prognosis of patients with PAD undergoing revascularization procedures. Additionally, optimization of current follow up protocols is needed, with the optimal goal to develop standardized cost-effective algorithms regarding early detection of disease recurrence and re-intervention.

SPECT/CT imaging of lower extremity perfusion reserve: A non-invasive correlate to exercise tolerance and cardiovascular fitness in patients undergoing clinically indicated myocardial perfusion imaging

BACKGROUND

Although exercise is often prescribed for the management of cardiovascular diseases, a non-invasive imaging approach that quantifies skeletal muscle physiology and correlates with patients' functional capacity and cardiovascular fitness has been absent. Therefore, we evaluated the potential of lower extremity single photon emission computed tomography (SPECT)/CT perfusion imaging as a non-invasive correlate to exercise tolerance and cardiovascular fitness.

METHODS

Patients (n = 31) undergoing SPECT/CT myocardial perfusion imaging underwent additional stress/rest SPECT/CT imaging of the lower extremities. CT-based image segmentation was used for regional quantification of perfusion reserve within the tibialis anterior, soleus, and gastrocnemius muscles. Metabolic equivalents (METs) at peak exercise and heart rate recovery (HRR) after exercise were recorded.

RESULTS

Peak METs were significantly associated with perfusion reserve of tibialis anterior (p = 0.02), soleus (p = 0.01) and gastrocnemius (p = 0.01). HRR was significantly associated with perfusion reserve of the soleus (p = 0.02) and gastrocnemius (p = 0.04) muscles. Perfusion reserve of the tibialis anterior (40.6 ± 20.2%), soleus (35.4 ± 16.7%), and gastrocnemius (29.7 ± 19.1%) all significantly differed from each other.

CONCLUSIONS

SPECT/CT imaging provides regional quantification of skeletal muscle perfusion reserve which is significantly associated with exercise tolerance and cardiovascular fitness. Future application of SPECT/CT may elucidate the underlying skeletal muscle adapations to exercise therapy in patients with cardiovascular diseases.

Peripheral Artery Disease in Diabetes Mellitus: Focus on Novel Treatment Options

Diabetes mellitus (DM) and peripheral artery disease (PAD) are two clinical entities closely associated. They share many pathophysiological pathways such as inflammation, endothelial dysfunction, oxidative stress and pro-coagulative unbalance. Emerging data focusing on agents targeting these pathways may be promising. Moreover, due to the increased cardiovascular risk, there is a growing interest in cardiovascular and "pleiotropic" effects of novel glucose lowering drugs. This review summarizes the main clinical features of PAD in patients, the diagnostic process and current medical/interventional approaches, ranging from "classical treatment" to novel agents.

Skeletal Muscle Pathology in Peripheral Artery Disease: A Brief Review

This brief review summarizes current evidence regarding lower extremity peripheral artery disease (PAD) and lower extremity skeletal muscle pathology. Lower extremity ischemia is associated with reduced calf skeletal muscle area and increased calf muscle fat infiltration and fibrosis on computed tomography or magnetic resonance imaging. Even within the same individual, the leg with more severe ischemia has more adverse calf muscle characteristics than the leg with less severe ischemia. More adverse computed tomography-measured calf muscle characteristics, such as reduced calf muscle density, are associated with higher rates of mobility loss in people with PAD. Calf muscle in people with PAD may also have reduced mitochondrial activity compared with those without PAD, although evidence is inconsistent. Muscle biopsy document increased oxidative stress in PAD. Reduced calf muscle perfusion, impaired mitochondrial activity, and smaller myofibers are associated with greater walking impairment in PAD. Preliminary evidence suggests that calf muscle pathology in PAD may be reversible. In a small uncontrolled trial, revascularization improved both the ankle-brachial index and mitochondrial activity, measured by calf muscle phosphocreatine recovery time. A pilot clinical trial showed that cocoa flavanols increased measures of myofiber health, mitochondrial activity, and capillary density while simultaneously improving 6-minute walk distance in PAD. Calf muscle pathological changes are associated with impaired walking performance in people with PAD, and interventions that both increase calf perfusion and improve calf muscle health are promising therapies to improve walking performance in PAD.

Modes of exercise training for intermittent claudication

BACKGROUND

According to international guidelines and literature, all patients with intermittent claudication should receive an initial treatment of cardiovascular risk modification, lifestyle coaching, and supervised exercise therapy. In the literature, supervised exercise therapy often consists of treadmill or track walking. However, alternative modes of exercise therapy have been described and yielded similar results to walking. This raises the following question: which exercise mode produces the most favourable results? This is the first update of the original review published in 2014.

OBJECTIVES

To assess the effects of alternative modes of supervised exercise therapy compared to traditional walking exercise in patients with intermittent claudication.

SEARCH METHODS

The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase and CINAHL databases and World Health Organization International Clinical Trials Registry Platform and ClinicalTrials.gov trials registers to 4 March 2019. We also undertook reference checking, citation searching and contact with study authors to identify additional studies. No language restriction was applied.

SELECTION CRITERIA

We included parallel-group randomised controlled trials comparing alternative modes of exercise training or combinations of exercise modes with a control group of supervised walking exercise in patients with clinically determined intermittent claudication. The supervised walking programme needed to be supervised at least twice a week for a consecutive six weeks of training.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected studies, extracted data, and assessed the risk of bias for each study. As we included studies with different treadmill test protocols and different measuring units (metres, minutes, or seconds), the standardised mean difference (SMD) approach was used for summary statistics of mean walking distance (MWD) and pain-free walking distance (PFWD). Summary estimates were obtained for all outcome measures using a random-effects model. We used the GRADE approach to assess the certainty of the evidence.

MAIN RESULTS

For this update, five additional studies were included, making a total of 10 studies that randomised a total of 527 participants with intermittent claudication (IC). The alternative modes of exercise therapy included cycling, lower-extremity resistance training, upper-arm ergometry, Nordic walking, and combinations of exercise modes. Besides randomised controlled trials, two quasi-randomised trials were included. Overall risk of bias in included studies varied from high to low. According to GRADE criteria, the certainty of the evidence was downgraded to low, due to the relatively small sample sizes, clinical inconsistency, and inclusion of three studies with risk of bias concerns. Overall, comparing alternative exercise modes versus walking showed no clear differences for MWD at 12 weeks (standardised mean difference (SMD) -0.01, 95% confidence interval (CI) -0.29 to 0.27; P = 0.95; 6 studies; 274 participants; low-certainty evidence); or at the end of training (SMD -0.11, 95% CI -0.33 to 0.11; P = 0.32; 9 studies; 412 participants; low-certainty evidence). Similarly, no clear differences were detected in PFWD at 12 weeks (SMD -0.01, 95% CI -0.26 to 0.25; P = 0.97; 5 studies; 249 participants; low-certainty evidence); or at the end of training (SMD -0.06, 95% CI -0.30 to 0.17; P = 0.59; 8 studies, 382 participants; low-certainty evidence). Four studies reported on health-related quality of life (HR-QoL) and three studies reported on functional impairment. As the studies used different measurements, meta-analysis was only possible for the walking impairment questionnaire (WIQ) distance score, which demonstrated little or no difference between groups (MD -5.52, 95% CI -17.41 to 6.36; P = 0.36; 2 studies; 96 participants; low-certainty evidence).

AUTHORS' CONCLUSIONS

This review found no clear difference between alternative exercise modes and supervised walking exercise in improving the maximum and pain-free walking distance in patients with intermittent claudication. The certainty of this evidence was judged to be low, due to clinical inconsistency, small sample size and risk of bias concerns. The findings of this review indicate that alternative exercise modes may be useful when supervised walking exercise is not an option. More RCTs with adequate methodological quality and sufficient power are needed to provide solid evidence for comparisons between each alternative exercise mode and the current standard of supervised treadmill walking. Future RCTs should investigate outcome measures on walking behaviour, physical activity, cardiovascular risk, and HR-QoL, using standardised testing methods and reporting of outcomes to allow meaningful comparison across studies.

Sarcopenia and peripheral arterial disease: a systematic review

BACKGROUND

Patients with lower extremity peripheral arterial disease (PAD) and sarcopenia are a population at risk requiring specific and targeted care. The aim of this review is to gather all relevant studies associating sarcopenia and PAD and to identify the underlying pathophysiological mechanisms as well as potential therapeutic strategies to improve skeletal muscle function.

METHODS

A systematic review was carried out following the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA).

RESULTS

Data extraction allowed the evaluation of 140 publications; 87 met the inclusion criteria; of which 79 were included in the final review, reporting sufficient data for epidemiological and diagnostic criteria, mechanical analysis, and therapeutic approaches. Epidemiological analysis and diagnostic criteria were based on 18 studies following 2362 PAD patients [31.39% (SD 7.61) women], aged 72.42 (SD 2.84); sarcopenia was present in 34.63% (SD 12.86) of the patients. Mechanical and pathway analysis were based on five animal studies and 29 clinical reports, showing significantly altered muscle strength and function in 1352 PAD patients [26.49% (SD 17.32) women], aged 67.67 (SD 5.14) years; impaired muscle histology in 192 PAD patients (9.2% (SD 11.22) women), aged 64.3 (SD 0.99) years; +58.63% (SD 25.48) of oxidative stress in 69 PAD patients [16.96% (SD 8.10) women], aged 63.17 (SD 1.43) years; mitochondriopathy in 153 PAD patients [29.39% (SD 28.27) women], aged 63.50 (SD 1.83) years; +15.58% (SD 7.41) of inflammation in 900 PAD patients [40.77% (SD 3.71) women], aged 74.88 (SD 2.76) years; and altered signalling pathways in 51 PAD patients [34.45% (SD 32.23) women], aged 72.25 (SD 5.25) years. Therapeutic approaches analysis was based on seven animal studies and 21 clinical reports. In total, 884 patients followed an exercise therapy, and 18 received an angiogenesis treatment; 30.84% (SD 17.74) were women. Mean ages of patients studied were 66.85 (SD 3.96).

CONCLUSIONS

Sarcopenia and lower extremity PAD have musculoskeletal consequences that directly impair patients' quality of life and prognosis. Although PAD is primarily a vascular disease, all etiological factors of sarcopenia identified so far are present in PAD. Indeed, both sarcopenia and PAD are accompanied by oxidative stress, skeletal muscle mitochondrial impairments, inflammation, inhibition of specific pathways regulating muscle synthesis or protection (i.e. IGF-1, RISK, and SAFE), and activation of molecules associated with muscle degradation. To date, besides revascularization, the best therapeutic strategy includes exercise, but approaches targeting the underlying mechanisms still deserve further studies.

Preserved Capacity for Adaptations in Strength and Muscle Regulatory Factors in Elderly in Response to Resistance Exercise Training and Deconditioning

Aging is related to an inevitable loss of muscle mass and strength. The mechanisms behind age-related loss of muscle tissue are not fully understood but may, among other things, be induced by age-related differences in myogenic regulatory factors. Resistance exercise training and deconditioning offers a model to investigate differences in myogenic regulatory factors that may be important for age-related loss of muscle mass and strength. Nine elderly (82 ± 7 years old) and nine young, healthy persons (22 ± 2 years old) participated in the study. Exercise consisted of six weeks of resistance training of the quadriceps muscle followed by eight weeks of deconditioning. Muscle biopsy samples before and after training and during the deconditioning period were analyzed for MyoD, myogenin, insulin-like growth-factor I receptor, activin receptor IIB, smad2, porin, and citrate synthase. Muscle strength improved with resistance training by 78% (95.0 ± 22.0 kg) in the elderly to a similar extent as in the young participants (83.5%; 178.2 ± 44.2 kg) and returned to baseline in both groups after eight weeks of deconditioning. No difference was seen in expression of muscle regulatory factors between elderly and young in response to exercise training and deconditioning. In conclusion, the capacity to gain muscle strength with resistance exercise training in elderly was not impaired, highlighting this as a potent tool to combat age-related loss of muscle function, possibly due to preserved regulation of myogenic factors in elderly compared with young muscle.

Exercise-Induced Vascular Adaptations under Artificially Versus Pathologically Reduced Blood Flow: A Focus Review with Special Emphasis on Arteriogenesis

Background: The vascular effects of training under blood flow restriction (BFR) in healthy persons can serve as a model for the exercise mechanism in lower extremity arterial disease (LEAD) patients. Both mechanisms are, inter alia, characterized by lower blood flow in the lower limbs. We aimed to describe and compare the underlying mechanism of exercise-induced effects of disease- and external application-BFR methods. Methods: We completed a narrative focus review after systematic literature research. We included only studies on healthy participants or those with LEAD. Both male and female adults were considered eligible. The target intervention was exercise with a reduced blood flow due to disease or external application. Results: We identified 416 publications. After the application of inclusion and exclusion criteria, 39 manuscripts were included in the vascular adaption part. Major mechanisms involving exercise-mediated benefits in treating LEAD included: inflammatory processes suppression, proinflammatory immune cells, improvement of endothelial function, remodeling of skeletal muscle, and additional vascularization (arteriogenesis). Mechanisms resulting from external BFR application included: increased release of anabolic growth factors, stimulated muscle protein synthesis, higher concentrations of heat shock proteins and nitric oxide synthase, lower levels in myostatin, and stimulation of S6K1. Conclusions: A main difference between the two comparators is the venous blood return, which is restricted in BFR but not in LEAD. Major similarities include the overall ischemic situation, the changes in microRNA (miRNA) expression, and the increased production of NOS with their associated arteriogenesis after training with BFR.

Bicycle exercise training improves ambulation in patients with peripheral artery disease

OBJECTIVE

Exercise training has multiple beneficial effects in patients with arteriosclerotic diseases; however, the exact underlying mechanisms of the effects are not completely understood. This study aimed to evaluate the effectiveness of a supervised exercise program in improving gait parameters, including the variability and walking performance of lower limb movements, in patients with peripheral artery disease (PAD) and intermittent claudication (IC).

METHODS

Sixteen patients with a history of PAD and IC were recruited for this study, and they completed a 3-month supervised bicycle exercise program. The ankle-brachial index and responses to quality of life (QOL) questionnaires were evaluated. Near-infrared spectroscopy was also performed to determine the hemoglobin oxygen saturation in the calf. Patients' kinematics and dynamics, including joint range of motion and muscle tension, were evaluated using an optical motion capture system. Computed tomography images of each muscle were assessed by manual outlining. Data were collected before and after the supervised bicycle exercise program, and differences were analyzed.

RESULTS

Significant differences were not found in step length, ankle-brachial index, and hemoglobin oxygen saturation before and after the supervised bicycle exercise program; however, IC distance (P = .034), maximum walking distance (P = .006), and all QOL questionnaire scores (P < .001) showed significant improvement. Hip range of motion (P = .035), maximum hip joint torque (right, P = .031; left, P = .044), maximum tension of the gluteus maximus muscle (right, P = .044; left, P = .042), and maximum hip joint work (right, P = .048; left, P = .043) also significantly decreased bilaterally. Computed tomography images showed a significant increase in the cross-sectional area of the abdominal, trunk, and thigh muscles but not in that of the lower leg muscles after the supervised exercise program intervention.

CONCLUSIONS

In this study, bicycle exercise training improved the QOL and walking distance and decreased hip movement. The results showed that bicycling might be as useful as walking in patients with PAD.

Oxidative stress and antioxidant treatment in patients with peripheral artery disease

Peripheral artery disease is an atherosclerotic disease of arterial vessels that mostly affects arteries of lower extremities. Effort induced cycles of ischemia and reperfusion lead to increased reactive oxygen species production by mitochondria. Therefore, the pathophysiology of peripheral artery disease is a consequence of metabolic myopathy, and oxidative stress is the putative major operating mechanism behind the structural and metabolic changes that occur in muscle. In this review, we discuss the evidence for oxidative damage in peripheral artery disease and discuss management strategies related to antioxidant supplementation. We also highlight the major pathways governing oxidative stress in the disease and discuss their implications in disease progression. Potential therapeutic targets and diagnostic methods related to these mechanisms are explored, with an emphasis on the Nrf2 pathway.

Extensive skeletal muscle cell mitochondriopathy distinguishes critical limb ischemia patients from claudicants

The most severe manifestation of peripheral arterial disease (PAD) is critical limb ischemia (CLI). CLI patients suffer high rates of amputation and mortality; accordingly, there remains a clear need both to better understand CLI and to develop more effective treatments. Gastrocnemius muscle was obtained from 32 older (51-84 years) non-PAD controls, 27 claudicating PAD patients (ankle-brachial index [ABI] 0.65 ± 0.21 SD), and 19 CLI patients (ABI 0.35 ± 0.30 SD) for whole transcriptome sequencing and comprehensive mitochondrial phenotyping. Comparable permeabilized myofiber mitochondrial function was paralleled by both similar mitochondrial content and related mRNA expression profiles in non-PAD control and claudicating patient tissues. Tissues from CLI patients, despite being histologically intact and harboring equivalent mitochondrial content, presented a unique bioenergetic signature. This signature was defined by deficits in permeabilized myofiber mitochondrial function and a unique pattern of both nuclear and mitochondrial encoded gene suppression. Moreover, isolated muscle progenitor cells retained both mitochondrial functional deficits and gene suppression observed in the tissue. These findings indicate that muscle tissues from claudicating patients and non-PAD controls were similar in both their bioenergetics profile and mitochondrial phenotypes. In contrast, CLI patient limb skeletal muscles harbor a unique skeletal muscle mitochondriopathy that represents a potentially novel therapeutic site for intervention.

Quantitative real-time optical imaging of the tissue metabolic rate of oxygen consumption

The tissue metabolic rate of oxygen consumption (tMRO2) is a clinically relevant marker for a number of pathologies including cancer and arterial occlusive disease. We present and validate a noncontact method for quantitatively mapping tMRO2 over a wide, scalable field of view at 16  frames  /  s. We achieve this by developing a dual-wavelength, near-infrared coherent spatial frequency-domain imaging (cSFDI) system to calculate tissue optical properties (i.e., absorption, μa, and reduced scattering, μs', parameters) as well as the speckle flow index (SFI) at every pixel. Images of tissue oxy- and deoxyhemoglobin concentration (  [  HbO2  ]   and [HHb]) are calculated from optical properties and combined with SFI to calculate tMRO2. We validate the system using a series of yeast-hemoglobin tissue-simulating phantoms and conduct in vivo tests in humans using arterial occlusions that demonstrate sensitivity to tissue metabolic oxygen debt and its repayment. Finally, we image the impact of cyanide exposure and toxicity reversal in an in vivo rabbit model showing clear instances of mitochondrial uncoupling and significantly diminished tMRO2. We conclude that dual-wavelength cSFDI provides rapid, quantitative, wide-field mapping of tMRO2 that can reveal unique spatial and temporal dynamics relevant to tissue pathology and viability.

Dietary nitrate supplementation in cardiovascular health: an ergogenic aid or exercise therapeutic?

Oral consumption of inorganic nitrate, which is abundant in green leafy vegetables and roots, has been shown to increase circulating plasma nitrite concentration, which can be converted to nitric oxide in low oxygen conditions. The associated beneficial physiological effects include a reduction in blood pressure, modification of platelet aggregation, and increases in limb blood flow. There have been numerous studies of nitrate supplementation in healthy recreational and competitive athletes; however, the ergogenic benefits are currently unclear due to a variety of factors including small sample sizes, different dosing regimens, variable nitrate conversion rates, the heterogeneity of participants’ initial fitness levels, and the types of exercise tests used. In clinical populations, the study results seem more promising, particularly in patients with cardiovascular diseases who typically present with disruptions in the ability to transport oxygen from the atmosphere to working tissues and reduced exercise tolerance. Many of these disease-related, physiological maladaptations, including endothelial dysfunction, increased reactive oxygen species, reduced tissue perfusion, and muscle mitochondrial dysfunction, have been previously identified as potential targets for nitric oxide restorative effects. This review is the first of its kind to outline the current evidence for inorganic nitrate supplementation as a therapeutic intervention to restore exercise tolerance and improve quality of life in patients with cardiovascular diseases. We summarize the factors that appear to limit or maximize its effectiveness and present a case for why it may be more effective in patients with cardiovascular disease than as ergogenic aid in healthy populations.

Exercise for intermittent claudication

BACKGROUND

Exercise programmes are a relatively inexpensive, low-risk option compared with other, more invasive therapies for treatment of leg pain on walking (intermittent claudication (IC)). This is the fourth update of a review first published in 1998.

OBJECTIVES

Our goal was to determine whether an exercise programme was effective in alleviating symptoms and increasing walking treadmill distances and walking times in people with intermittent claudication. Secondary objectives were to determine whether exercise was effective in preventing deterioration of underlying disease, reducing cardiovascular events, and improving quality of life.

SEARCH METHODS

For this update, the Cochrane Vascular Information Specialist searched the Specialised Register (last searched 15 November 2016) and the Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 10) via the Cochrane Register of Studies Online, along with trials registries.

SELECTION CRITERIA

Randomised controlled trials of an exercise regimen versus control or versus medical therapy for people with IC due to peripheral arterial disease (PAD). We included any exercise programme or regimen used for treatment of IC, such as walking, skipping, and running. Inclusion of trials was not affected by duration, frequency, or intensity of the exercise programme. Outcome measures collected included treadmill walking distance (time to onset of pain or pain-free walking distance and maximum walking time or maximum walking distance), ankle brachial index (ABI), quality of life, morbidity, or amputation; if none of these was reported, we did not include the trial in this review.

DATA COLLECTION AND ANALYSIS

For this update (2017), RAL and AH selected trials and extracted data independently. We assessed study quality by using the Cochrane 'Risk of bias' tool. We analysed continuous data by determining mean differences (MDs) and 95% confidence intervals (CIs), and dichotomous data by determining risk ratios (RRs) and 95% CIs. We pooled data using a fixed-effect model unless we identified significant heterogeneity, in which case we used a random-effects model. We used the GRADE approach to assess the overall quality of evidence supporting the outcomes assessed in this review.

MAIN RESULTS

We included two new studies in this update and identified additional publications for previously included studies, bringing the total number of studies meeting the inclusion criteria to 32, and involving a total of 1835 participants with stable leg pain. The follow-up period ranged from two weeks to two years. Types of exercise varied from strength training to polestriding and upper or lower limb exercises; supervised sessions were generally held at least twice a week. Most trials used a treadmill walking test for one of the primary outcome measures. The methodological quality of included trials was moderate, mainly owing to absence of relevant information. Most trials were small and included 20 to 49 participants. Twenty-seven trials compared exercise versus usual care or placebo, and the five remaining trials compared exercise versus medication (pentoxifylline, iloprost, antiplatelet agents, and vitamin E) or pneumatic calf compression; we generally excluded people with various medical conditions or other pre-existing limitations to their exercise capacity.Meta-analysis from nine studies with 391 participants showed overall improvement in pain-free walking distance in the exercise group compared with the no exercise group (MD 82.11 m, 95% CI 71.73 to 92.48, P < 0.00001, high-quality evidence). Data also showed benefit from exercise in improved maximum walking distance (MD 120.36 m, 95% CI 50.79 to 189.92, P < 0.0007, high-quality evidence), as revealed by pooling data from 10 studies with 500 participants. Improvements were seen for up to two years.Exercise did not improve the ABI (MD 0.04, 95% CI 0.00 to 0.08, 13 trials, 570 participants, moderate-quality evidence). Limited data were available for the outcomes of mortality and amputation; trials provided no evidence of an effect of exercise, when compared with placebo or usual care, on mortality (RR 0.92, 95% CI 0.39 to 2.17, 5 trials, 540 participants, moderate-quality evidence) or amputation (RR 0.20, 95% CI 0.01 to 4.15, 1 trial, 177 participants, low-quality evidence).Researchers measured quality of life using Short Form (SF)-36 at three and six months. At three months, the domains 'physical function', 'vitality', and 'role physical' improved with exercise; however this was a limited finding, as it was reported by only two trials. At six months, meta-analysis showed improvement in 'physical summary score' (MD 2.15, 95% CI 1.26 to 3.04, P = 0.02, 5 trials, 429 participants, moderate-quality evidence) and in 'mental summary score' (MD 3.76, 95% CI 2.70 to 4.82, P < 0.01, 4 trials, 343 participants, moderate-quality evidence) secondary to exercise. Two trials reported the remaining domains of the SF-36. Data showed improvements secondary to exercise in 'physical function' and 'general health'. The other domains - 'role physical', 'bodily pain', 'vitality', 'social', 'role emotional', and 'mental health' - did not show improvement at six months.Evidence was generally limited in trials comparing exercise versus antiplatelet therapy, pentoxifylline, iloprost, vitamin E, and pneumatic foot and calf compression owing to small numbers of trials and participants.Review authors used GRADE to assess the evidence presented in this review and determined that quality was moderate to high. Although results showed significant heterogeneity between trials, populations and outcomes were comparable overall, with findings relevant to the claudicant population. Results were pooled for large sample sizes - over 300 participants for most outcomes - using reproducible methods.

AUTHORS' CONCLUSIONS

High-quality evidence shows that exercise programmes provided important benefit compared with placebo or usual care in improving both pain-free and maximum walking distance in people with leg pain from IC who were considered to be fit for exercise intervention. Exercise did not improve ABI, and we found no evidence of an effect of exercise on amputation or mortality. Exercise may improve quality of life when compared with placebo or usual care. As time has progressed, the trials undertaken have begun to include exercise versus exercise or other modalities; therefore we can include fewer of the new trials in this update.

Effects of exercise training on calf muscle oxygen extraction and blood flow in patients with peripheral artery disease

We employed near-infrared optical techniques, diffuse correlation spectroscopy (DCS), and frequency-domain near-infrared spectroscopy (FD-NIRS) to test the hypothesis that supervised exercise training increases skeletal muscle microvascular blood flow and oxygen extraction in patients with peripheral artery disease (PAD) who experience claudication. PAD patients ( n = 64) were randomly assigned to exercise and control groups. Patients in the exercise group received 3 mo of supervised exercise training. Calf muscle blood flow and oxygen extraction were optically monitored before, during, and after performance of a graded treadmill protocol at baseline and at 3 mo in both groups. Additionally, measurements of the ankle-brachial index (ABI) and peak walking time (PWT) to maximal claudication were made during each patient visit. Supervised exercise training was found to increase the maximal calf muscle blood flow and oxygen extraction levels during treadmill exercise by 29% (13%, 50%) and 8% (1%, 12%), respectively [ P < 0.001; median (25th percentile, 75th percentile)]. These improvements across the exercise group population were significantly higher than corresponding changes in the control group ( P < 0.004). Exercise training also increased PWT by 49% (18%, 101%) ( P = 0.01). However, within statistical error, the ABI, resting calf muscle blood flow and oxygen extraction, and the recovery half-time for hemoglobin\myoglobin desaturation following cessation of maximal exercise were not altered by exercise training. The concurrent monitoring of both blood flow and oxygen extraction with the hybrid DCS/FD-NIRS instrument revealed enhanced muscle oxidative metabolism during physical activity from exercise training, which could be an underlying mechanism for the observed improvement in PWT. NEW & NOTEWORTHY We report on noninvasive optical measurements of skeletal muscle blood flow and oxygen extraction dynamics before/during/after treadmill exercise in peripheral artery disease patients who experience claudication. The measurements tracked the effects of a 3-mo supervised exercise training protocol and revealed that supervised exercise training improved patient ability to increase microvascular calf muscle blood flow and oxygen extraction during physical activity.

The effects of RSR13 on microvascular Po2 kinetics and muscle contractile performance in the rat arterial ligation model of peripheral arterial disease

Exercise intolerance and claudication are symptomatic of peripheral arterial disease. There is a close relationship between muscle O2 delivery, microvascular oxygen partial pressure (P mvO2), and contractile performance. We therefore hypothesized that a reduction of hemoglobin-oxygen affinity via RSR13 would maintain a higher P mvO2 and enhance blood-muscle O2 transport and contractile function. In male Wistar rats (12 wk of age), we created hindlimb ischemia via right-side iliac artery ligation (AL). The contralateral (left) muscle served as control (CONT). Seven days after AL, phosphorescence-quenching techniques were used to measure P mvO2 at rest and during contractions (electrical stimulation; 1 Hz, 300 s) in tibialis anterior muscle (TA) under saline ( n = 10) or RSR13 ( n = 10) conditions. RSR13 at rest increased TA P mvO2 in CONT (13.9 ± 1.6 to 19.3 ± 1.9 Torr, P < 0.05) and AL (9.0 ± 0.5 to 9.9 ± 0.7 Torr, P < 0.05). Furthermore, RSR13 extended maintenance of the initial TA force (i.e., improved contractile performance) such that force was not decreased significantly until contraction 240 vs. 150 in CONT and 80 vs. 20 in AL. This improved muscle endurance with RSR13 was accompanied by a greater ΔP mvO2 (P mvO2 decrease from baseline) (CONT, 7.4 ± 1.0 to 11.2 ± 1.3; AL, 6.9 ± 0.5 to 8.6 ± 0.6 Torr, both P < 0.05). Whereas RSR13 did not alter the kinetics profile of P mvO2 (i.e., mean response time) substantially during contractions, muscle force was elevated, and the ratio of muscle force to P mvO2 increased. In conclusion, reduction of hemoglobin-oxygen affinity via RSR13 in AL increased P mvO2 and improved muscle contractile performance most likely via enhanced blood-muscle O2 diffusion.

NEW & NOTEWORTHY This is the first investigation to examine the effect of RSR13 (erythrocyte allosteric effector) on skeletal muscle microvascular oxygen partial pressure kinetics and contractile function using an arterial ligation model of peripheral arterial disease in experimental animals. The present results provide strong support for the concept that reducing hemoglobin-O2 affinity via RSR13 improved tibialis anterior muscle contractile performance most likely via enhanced blood-muscle O2 diffusion.

A systematic review of muscle morphology and function in intermittent claudication

OBJECTIVE

Intermittent claudication (IC) is frequently associated with deterioration in walking capacity and physical function, and it can often result in an impairment in balance. Whereas supervised exercise is recommended by the National Institute for Health and Care Excellence as the first-line treatment, the mechanism behind walking improvement is poorly understood. The existing literature suggests that there may be some physiologic change to the skeletal muscle contributing to the functional impairment, but these data are conflicting. We therefore sought to undertake a systematic review to clarify the muscle properties of patients with IC.

METHODS

A systematic review of randomized and nonrandomized trials that investigated the role of muscle function in patients diagnosed with IC was undertaken using MEDLINE, Cochrane Central Register of Controlled Trials, and Embase databases. The searches were limited from 1947 to June 2016 in the English language.

RESULTS

The search yielded a total of 506 articles, of which 206 were duplicate articles. Of the remaining 300, a total of 201 were excluded from full-text analysis; 99 full-text articles were assessed for eligibility, with 30 articles deemed appropriate for inclusion in the review. There were four main categories of functional outcome measures: muscle strength, muscle size, muscle fiber type, and muscle metabolism. A total of 2837 patients were included in the study. Nine studies reported on muscle strength, incorporating isometric, concentric, eccentric, and endurance measures. Eight studies reported on muscle size, incorporating circumference, computed tomography scans, and ultrasound imaging techniques. Eleven studies reported on muscle fibers, incorporating fiber type proportions, fiber size, and capillarity measures. Seven papers reported on muscle metabolism, incorporating adenosine diphosphate recovery and phosphocreatine recovery measures.

CONCLUSIONS

Previous literature has found clear evidence that strength (of the calf and thigh musculature) and calf characteristics are related to mortality and functional declines. However, this review has demonstrated the vast array of muscle groups assessed and multiple methods employed to determine strength; therefore, it is unclear exactly what measure of "strength" is impaired. Furthermore, the underlying morphologic causes of potential changes in strength are unclear. This information is essential for designing optimal exercise interventions. The data acquired during this systematic review are heterogeneous, with a substantial lack of high-quality intervention-based studies. Future research should endeavor to establish standardized testing procedures and to implement randomized controlled trials for targeted therapeutic interventions.

Acute and chronic effects of exercise on mRNA expression in the skeletal muscle of two mouse models of peripheral artery disease

Endurance exercise improves walking performance in patients with peripheral artery disease (PAD), which is characterized by skeletal muscle dysfunction caused by lower extremity ischemia. Although transcriptional analyses of exercise-induced changes in normal animals and healthy volunteers have been reported, no detailed study has explored exercise-induced alterations in gene expression in PAD animal models. Here, we determined the acute and chronic effects of exercise on mRNA expression in the skeletal muscles of two mouse models of PAD. Three particular gene categories were investigated: known exercise-responsive genes (Pgc1a, Il6, Nr4a1, Nr4a2, and Nr4a3); myogenic and muscle regeneration-related genes (Myf5, Myogenin, Myomaker, and Myh3); and Gpr56 and its ligand Col3a1. PAD was induced by bilateral femoral artery ligation in normal C57BL/6 and diabetic KK-A^y mice. From 1 week after surgery, repetitive twice-weekly 30-min treadmill endurance exercise sessions were applied. Altered mRNA expression in the soleus muscles was measured in both the acute and chronic phases. In the acute phase, transcript levels of exercise-inducible genes showed significant increases in both C57BL/6 and diabetic KK-A^y PAD mice; levels of regeneration-related genes showed little alteration, and those of Gpr56 increased immediately and significantly after exercise in both models. In the chronic phase, transcript levels of Pgc1a, Myf5, Myogenin, Myomaker, Myh3, Gpr56, and Col3a1 were upregulated significantly in sedentary C57BL/6 PAD mice compared with that in sham-operated mice. Exercise training inhibited the upregulation of Col3a1, Myf5, and Myogenin significantly. In KK-A^y PAD mice, only Gpr56 mRNA levels increased significantly compared with those in sham-operated mice. RNA sequence analysis revealed 33 and 166 differentially upregulated, and 363 and 99 downregulated, genes after exercise training in C57BL/6 PAD and KK-A^y PAD mice, respectively. In summary, we detected significant alterations of skeletal muscle genes after exercise in PAD mouse models and characterized their expression patterns.

Mitochondrial Bioenergetics in the Metabolic Myopathy Accompanying Peripheral Artery Disease

Peripheral artery disease (PAD) is a serious but relatively underdiagnosed and undertreated clinical condition associated with a marked reduction in functional capacity and a heightened risk of morbidity and mortality. The pathophysiology of lower extremity PAD is complex, and extends beyond the atherosclerotic arterial occlusion and subsequent mismatch between oxygen demand and delivery to skeletal muscle mitochondria. In this review, we evaluate and summarize the available evidence implicating mitochondria in the metabolic myopathy that accompanies PAD. Following a short discussion of the available in vivo and in vitro methodologies to quantitate indices of muscle mitochondrial function, we review the current evidence implicating skeletal muscle mitochondrial dysfunction in the pathophysiology of PAD myopathy, while attempting to highlight questions that remain unanswered. Given the rising prevalence of PAD, the detriment in quality of life for patients, and the associated significant healthcare resource utilization, new alternate therapies that ameliorate lower limb symptoms and the functional impairment associated with PAD are needed. A clear understanding of the role of mitochondria in the pathophysiology of PAD may contribute to the development of novel therapeutic interventions.

The effect of supervised exercise therapy for intermittent claudication on lower limb lean mass

OBJECTIVE

Supervised exercise is currently recommended for the first-line treatment of intermittent claudication based on improvement in walking capacity. However, the promotion of skeletal muscle atrophy by repetitive ischemia-reperfusion caused by treadmill-based programs remains a concern. Because preservation of skeletal muscle mass (SMM) and lean mass (LM) is integral to functional capacity and longevity, this study measured the effect of standard treadmill-based supervised exercise on SMM and regional lower limb LM in patients with intermittent claudication.

METHODS

Patients with calf claudication caused by infrainguinal peripheral artery disease underwent whole-body dual-energy X-ray absorptiometry scanning before and after completion of a 12-week supervised treadmill exercise program. Total body SMM and lower limb LM were measured according to anatomical regions of the lower limb (thigh vs calf) and side of symptoms. Walking performance was assessed using pain-free walking distance and 6-minute walking distance tests.

RESULTS

Thirty-six patients with calf claudication completed exercise training and dual-energy X-ray absorptiometry scanning, allowing analysis of 55 symptomatic and 17 asymptomatic lower limbs. No difference in total body SMM (P = .41) or LM of symptomatic (P = .53) or asymptomatic calves (P = .59) was detected after the program. In contrast, a significant decrease in LM was observed in symptomatic (P = .04) and asymptomatic thighs (P = .005). Pain-free walking distance (P = .001) and the 6-minute walking distance both improved significantly (P = .004) but were not associated with changes in LM.

CONCLUSIONS

Twelve weeks of standard treadmill-training for intermittent calf claudication did not result in loss of calf LM; however, a significant decrease in bilateral thigh LM was observed, even in patients with unilateral symptoms. Further research on optimum exercise modalities and end points are required to determine the pathophysiology and effects of these changes on function and survival.

Skeletal muscle metabolic changes in peripheral arterial disease contribute to exercise intolerance: a point-counterpoint discussion

Patients with claudication have a marked impairment in exercise performance. Several factors contribute to this limitation, including reductions in large vessel blood flow and oxygen delivery as well as metabolic abnormalities in skeletal muscle. The relative contribution of these factors and their role in the pathophysiology of the exercise limitation is discussed using a point-counterpoint approach. Future directions for research conclude the discussion.

Benefits of a Supervised Exercise Program After Lower Limb Bypass Surgery

This study evaluated the efficacy of an exercise program after arterial bypass surgery. Patients undergoing bypass surgery were randomized to a control group (group I), with standard preoperative and postoperative care, or the intervention group (group II) with a supervised exercise program of twice-weekly treadmill assessments from 4 to 10 weeks postoperatively. Ankle-brachial pressure indices and hemodynamic measurements were recorded before and after exercise. The mean increase of maximum walking distance was 3.8% in group I and 175.4% in group II ( P = .001). There was a significant difference between group I and II in the mean ankle-brachial pressure indices increase at the second assessment (0.08 versus 0.23; P = .02). A supervised exercise program leads to better improvement after lower limb bypass surgery for ischemia, but the feasibility of a formal exercise program would be undermined by the reluctance of patients to participate, both in the short-term and long-term.

Peripheral Artery Disease: Evolving Role of Exercise, Medical Therapy, and Endovascular Options

The prevalence of peripheral artery disease (PAD) continues to increase worldwide. It is important to identify patients with PAD because of the increased risk of myocardial infarction, stroke, and cardiovascular death and impaired quality of life because of a profound limitation in exercise performance and the potential to develop critical limb ischemia. Despite effective therapies to lower the cardiovascular risk and prevent progression to critical limb ischemia, patients with PAD continue to be under-recognized and undertreated. The management of PAD patients should include an exercise program, guideline-based medical therapy to lower the cardiovascular risk, and, when revascularization is indicated, an "endovascular first" approach. The indications and strategic choices for endovascular revascularization will vary depending on the clinical severity of the PAD and the anatomic distribution of the disease. In this review, we discuss an evidence-based approach to the management of patients with PAD.

Supervised exercise training combined with ginkgo biloba treatment for patients with peripheral arterial disease

Objectives: To evaluate whether a combination of supervised exercise training and ginkgo biloba treatment is a better treatment than exercise training alone for patients with peripheral arterial disease.

Design: A 24-week double-blind, placebo-controlled ginkgo biloba trial with the first 12-week period as a non-exercise control stage and the second 12-week period as an exercise training stage.

Setting: Exercise physiology laboratory.

Subjects: Twenty-two subjects with peripheral arterial disease.

Interventions: The subjects were randomly allocated into a ginkgo or a placebo group. During the first stage, the ginkgo group ingested standardized ginkgo biloba tablets with a daily dosage of 240 mg, while the placebo group received placebo tablets. During the second stage, all subjects engaged in a supervised treadmill-walking programme while continuing to take the same dosage of ginkgo biloba or placebo tablets.

Main measures: Walking capacity on treadmill, oxygen consumption during exercise, peripheral haemodynamics and blood viscosity were measured at baseline, and after the first and the second stages of treatment.

Results: The ginkgo group did not show significant changes in most of the measured variables after each stage of treatment, except that the maximal walking time was significantly increased after the combined treatment (from 236 ± 112 seconds to 557 ± 130 seconds, P < 0.001). However, similar response was also found in the placebo group after exercise training (from 384 ± 125 seconds to 820 ± 146 seconds, P < 0.001).

Conclusion: Supervised exercise training combined with ginkgo biloba treatment did not produce greater beneficial effects than exercise training alone in patients with peripheral arterial disease.

Limb hemodynamics are not predictive of functional capacity in patients with PAD

To the practicing clinician, it seems obvious that limb hemodynamics would be the primary determinant of walking distance. However, other determinants, such as skeletal muscle metabolism, may play a role. Accordingly, in the current study, we examined the relationship between measures of limb hemodynamics and walking capacity in patients with peripheral arterial disease (PAD). We measured toe and ankle pressures for calculation of toe-(TBI) and ankle (ABI)-brachial indices; basal and hyperemic calf blood flow (CBF; by plethysmography); and initial (ICT) and absolute (ACT) claudication time using the Skinner-Gardner protocol. As expected, PAD patients had impaired limb hemodynamics with reduced TBI, ABI and a reduction in ABI post-exercise. However, there was no relationship between any of the hemodynamic variables (including ABI, ABI reduction post-exercise, TBI, baseline or maximal CBF) and walking distance as assessed by ICT or ACT. A subset of PAD patients with an ACT >750 s (n =16; ‘long claudicators’) were compared with a subset of PAD patients with an ACT <260 s (n = 16; ‘short claudicators’). The average ACT in the long claudicants was over fivefold greater than the short claudicators. Surprisingly, there were no differences between the two groups in any of the hemo-dynamic variables. There was also no relationship between the initial ABI, TBI, toe pressure, baseline or hyperemic CBF, and the improvement in ACT over the 3-month course of the study. This study found little relationship between hemodynamic variables and functional capacity in PAD. Accordingly, to assess the response to therapeutic interventions, exercise performance and functional status need to be directly measured, and cannot be predicted from hemodynamic measurements.

Medical Therapy in Peripheral Artery Disease and Critical Limb Ischemia

OPINION STATEMENT

Peripheral artery disease (PAD) comprises atherosclerosis of the aorta and lower extremities. Many patients with PAD are asymptomatic, while others present with intermittent claudication (IC) or critical limb ischemia (CLI). Defined as rest pain or tissue loss that persists for >2 weeks, CLI represents the most severe clinical manifestation of PAD and is associated with an increased risk of limb loss and death. Patients with PAD, including those with CLI, are underdiagnosed and undertreated. In addition to smoking cessation, medical therapy with an antiplatelet agent and statin is recommended for all patients with PAD. Regular exercise has been shown to improve walking distance and quality of life in patients with symptomatic PAD and should be incorporated into each patient's treatment plan. In patients who have CLI and in those with persistent lifestyle-limiting claudication despite optimal medical therapy and an exercise program, revascularization is indicated for limb salvage and symptom relief, respectively. Consensus guidelines currently support an endovascular first approach to revascularization in the majority of cases. Surgical procedures provide an alternative to endovascular therapy in select cases.

Intensive walking exercise for lower extremity peripheral arterial disease: A systematic review and meta-analysis

BACKGROUND

Supervised treadmill exercise is the recommended therapy for peripheral arterial disease (PAD) patients with intermittent claudication (IC). However, most PAD patients do not exhibit typical symptoms of IC. The aim of the present study was to explore the efficacy and safety of intensive walking exercise in PAD patients with and without IC.

METHODS

The PubMed, Embase and Cochrane Library databases were systematically searched. Randomized controlled trials comparing the effects of intensive walking exercise with usual care in patients with PAD were included for systematic review and meta-analysis.

RESULTS

Eighteen trials with 1200 patients were eligible for the present analysis. Compared with usual care, intensive walking exercise significantly improved the maximal walking distance (MWD), pain-free walking distance, and the 6-min walking distance in patients with PAD (P < 0.00001 for all). Subgroup analyses indicated that a lesser improvement in MWD was observed in the subgroup with more diabetes patients, and that the subgroup with better baseline walking ability exhibited greater improvement in walking performance. In addition, similar improvements in walking performance were observed for exercise programs of different durations and modalities. No significant difference was found in adverse events between the intensive walking and usual care groups (relative risk 0.84; 95% confidence interval 0.51, 1.39; P = 0.50).

CONCLUSIONS

Regardless of exercise length and modality, regularly intensive walking exercise improves walking ability in PAD patients more than usual care. The presence of diabetes may attenuate the improvements in walking performance in patients with PAD following exercise.

The impact of peripheral arterial disease: A proposal for a new classification

Clasically, intermittent claudication, an intermediate stage in peripheral arterial disease, has been considered as a benign condition when considering only the muscular pain on walking. In this paper our aim is to attract attention about the effects linked to ischemic pain and the oxidative injury resulting from episodes of ischemia/reperfusion. Throughout this process alterations in calcium homeostasis as well as uncontrolled generation of reactive oxygen species, in association with the mitochondrial dysfunction and inflammatory phenomena, could lead to accelerate atherosclerosis, with an increased cardiovascular risk stated by means of a reduced ankle-brachial index. Taking this idea into account we propose a possible new classification for the management of the peripheral arterial disease, combining the Fontaine and Rutherford classifications and thinking about the described systemic effects in order to change the traditional management of peripheral arterial disease.