Fibre loss and distribution in skeletal muscle from patients with severe peripheral arterial insufficiency

Nuclear receptors as potential therapeutic targets in peripheral arterial disease and related myopathy

Peripheral arterial disease (PAD) is a prevalent cardiovascular complication of limb vascular insufficiency, causing ischemic injury, mitochondrial metabolic damage and functional impairment in the skeletal muscle, and ultimately leading to immobility and mortality. While potential therapies have been mostly focussed on revascularization, none of the currently available pharmacological treatments are fully effective in PAD, often leading to amputations, particularly in chronic metabolic diseases. One major limitation of focussed angiogenesis and revascularization as a therapeutic strategy is a limited effect on metabolic restoration and muscle regeneration in the affected limb. Therefore, additional preclinical investigations are needed to discover novel treatment options for PAD preferably targeting multiple aspects of muscle recovery. In this review, we propose nuclear receptors expressed in the skeletal muscle as potential candidates for ischemic muscle repair in PAD. We review classic steroid and orphan receptors that have been reported to be involved in the regulation of paracrine muscle angiogenesis, oxidative metabolism, mitochondrial biogenesis and muscle regeneration, and discuss how these receptors could be critical for recovery from ischemic muscle damage. Furthermore, we identify existing gaps in our understanding of nuclear receptor signalling in the skeletal muscle and propose future areas of research that could be instrumental in exploring nuclear receptors as therapeutic candidates for treating PAD.

Changes in Gait Variables in Patients with Intermittent Claudication

Objective

Intermittent claudication (IC) is a pathological symptom with a particular effect on human gait patterns. Therefore, analyzing these patterns can facilitate rehabilitation or treatment through comparison of the values of kinematic and kinetic variables of patients with the normal values of healthy people. Therefore, the aim of this study was to find differences in the values of gait variables between patients with IC and healthy people.

Methods

The study included 98 patients diagnosed with peripheral arterial disease with IC. The patients traveled a distance of 6 m at a voluntary gait velocity. Ground reaction forces while the foot contacted the ground and kinematic variables of lower limb movements were recorded. The values of normal gait variables were computed based on the results obtained in a group of 30 healthy people.

Results

Patients used a gait velocity below the norm for healthy people. The velocity during the lower limb swing and the step and stride length in patients with IC were below the norm. Differences were also found in the ranges of motion between patients with IC and healthy people for the pelvic obliquity, pelvic rotation, hip flexion-extension, hip abduction-adduction, hip internal-external rotation, knee flexion-extension, ankle dorsi-plantar flexion, and foot progression angles.

Conclusions

The presented kinematic and kinetic characteristics measured by gait variables suggest differences between patients with IC and healthy people. Considering kinematic and kinetic gait variables during the rehabilitation process would facilitate the development of a more economic gait technique (with increased stride length and range of motion in the lower limb joints) to obtain the desired rehabilitation effects. Patients with IC should receive rehabilitation oriented towards improving mobility and increasing muscle strength in selected lower limb joints to increase gait velocity and stride length.

Heat therapy improves soleus muscle force in a model of ischemia-induced muscle damage

Leg muscle ischemia in patients with peripheral artery disease (PAD) leads to alterations in skeletal muscle morphology and reduced leg strength. We tested the hypothesis that exposure to heat therapy (HT) would improve skeletal muscle function in a mouse model of ischemia-induced muscle damage. Male 42-wk-old C57Bl/6 mice underwent ligation of the femoral artery and were randomly assigned to receive HT (immersion in a water bath at 37°C, 39°C, or 41°C for 30 min) or a control intervention for 3 wk. At the end of the treatment, the animals were anesthetized and the soleus and extensor digitorum longus (EDL) muscles were harvested for the assessment of contractile function and examination of muscle morphology. A subset of animals was used to examine the impact of a single HT session on the expression of genes involved in myogenesis and the regulation of muscle mass. Relative soleus muscle mass was significantly higher in animals exposed to HT at 39°C compared with the control group (control: 0.36 ± 0.01 mg/g versus 39°C: 0.40 ± 0.01 mg/g, P = 0.024). Maximal absolute force of the soleus was also significantly higher in animals treated with HT at 37°C and 39°C (control: 274.7 ± 6.6 mN; 37°C: 300.1 ± 7.7 mN; 39°C: 299.5 ± 10 mN, P < 0.05). In the soleus, but not the EDL muscle, a single session of HT enhanced the mRNA expression of myogenic factors as well as of both positive and negative regulators of muscle mass. These findings suggest that the beneficial effects of HT are muscle specific and dependent on the treatment temperature in a model of PAD. NEW & NOTEWORTHY This is the first study to comprehensively examine the impact of temperature and muscle fiber type composition on the adaptations to repeated heat stress in a model of ischemia-induced muscle damage. Exposure to heat therapy (HT) at 37°C and 39°C, but not at 41°C, improved force development of the isolated soleus muscle. These results suggest that HT may be a practical therapeutic tool to restore muscle mass and strength in patients with peripheral artery disease.

Influence of the Physical Training on Muscle Function and Walking Distance in Symptomatic Peripheral Arterial Disease in Elderly

INTRODUCTION

A typical symptom of chronic lower-limb ischaemia is lower-limb pain, which occurs during walking forcing the patient to stop, intermittent claudication (IC). Exercise rehabilitation is the basic form of treatment for these patients.

AIM

The aim of this study was to compare the effectiveness of three types of physical training programmes conducted over a 12-week period in patients with chronic lower-limb arterial insufficiency.

MATERIALS AND METHODS

Ninety-five people qualified for the 3-month supervised motor rehabilitation programme, conducted three times a week. The respondents were assigned to three types of rehabilitation programmes using a pseudo-randomization method: Group I (TW), subjects undertaking treadmill walking training; Group II (NW), subjects undertaking Nordic walking training; Group III (RES+NW), subjects undertaking resistance and Nordic walking training. Treadmill test, 6 Minute Walk Test (6MWT), and isokinetic test were repeated after 3 months of rehabilitation, which 80 people completed.

RESULTS

Combined training (RES+NW) is more effective than Nordic walking alone and supervised treadmill training alone for improving ankle force-velocity parameters (p<0.05) in patients with intermittent claudication. Each of the proposed exercise rehabilitation programmes increased walking distance of patients with intermittent claudication (p<0.05), especially in 6MWT (p=0.001). Significant relationships of force-velocity parameters are observed in the maximum distance obtained in 6MWT, both in Group III (RES + NW) and in Group II (NW) at the level of moderate and strong correlation strength, which indicates that if the lower limbs are stronger the walking distance achieved in 6MWT is longer.

CONCLUSIONS

Given both the force-velocity parameters and the covered distance, the training RES + NW gives the most beneficial changes compared to training TW alone and NW alone. All types of training increased walking distance, which is an important aspect of the everyday functioning of people with IC.

Exposure of Endothelium to Biomimetic Flow Waveforms Yields Identification of miR-199a-5p as a Potent Regulator of Arteriogenesis

Arteriogenesis, the growth of endogenous collateral arteries bypassing arterial occlusion(s), is a fundamental shear stress-induced adaptation with implications for treating peripheral arterial disease (PAD). Nonetheless, endothelial mechano-signaling during arteriogenesis is incompletely understood. Here we tested the hypothesis that a mechanosensitive microRNA, miR-199a-5p, regulates perfusion recovery and collateral arteriogenesis following femoral arterial ligation (FAL) via control of monocyte recruitment and pro-arteriogenic gene expression. We have previously shown that collateral artery segments exhibit distinctly amplified arteriogenesis if they are exposed to reversed flow following FAL in the mouse. We performed a genome-wide analysis of endothelial cells exposed to a biomimetic reversed flow waveform. From this analysis, we identified mechanosensitive miR-199a-5p as a novel candidate regulator of collateral arteriogenesis. In vitro, miR-199a-5p inhibited pro-arteriogenic gene expression (IKKβ, Cav1) and monocyte adhesion to endothelium. In vivo, following FAL in mice, miR-199a-5p overexpression impaired foot perfusion and arteriogenesis. In contrast, a single intramuscular anti-miR-199a-5p injection elicited a robust therapeutic response, including complete foot perfusion recovery, markedly augmented arteriogenesis (>3.4-fold increase in segment conductance), and improved gastrocnemius tissue composition. Finally, we found plasma miR-199a-5p to be elevated in human PAD patients with intermittent claudication compared to a risk factor control population. Through our transformative analysis of endothelial mechano-signaling in response to a biomimetic amplified arteriogenesis flow waveform, we have identified miR-199a-5p as both a potent regulator of arteriogenesis and a putative target for treating PAD.

Histopathological changes in skeletal muscle associated with chronic ischaemia

Muscle biopsy is an essential part in the diagnostic workup in patients with suspected neuromuscular disorders. It is therefore important to be aware of morphological alterations that can be caused by systemic factors or natural ageing. Chronic limb ischaemia is frequent in elderly individuals. This study was performed to examine histopathological and mitochondrial changes in muscle in patients with chronic critical limb ischaemia. Muscle biopsy of skeletal muscle of the lower limb of patients with chronic ischaemia leading to amputation was performed and compared with muscle biopsies of healthy, age-matched controls. The histopathological abnormalities included fibrosis, necrosis, atrophy, glycogen depletion, internal nuclei, rimmed vacuoles, fibre type grouping, cytochrome c oxidase deficient fibres, MHC-I upregulation, and signs of microangiopathy. The only alteration found in age-matched controls was a few cytochrome c oxidase deficient fibres. There were also increased levels of multiple mitochondrial DNA deletions in ischaemic muscles compared with controls. Critical limb ischaemia is associated with significant histopathological changes in muscle tissue and also increased levels of mitochondrial DNA deletions. Since the alterations mimic different primary myopathic changes, chronic ischaemia is important to consider as a differential diagnosis in elderly individuals, investigated with muscle biopsy for muscle disease.

Computational Network Model Prediction of Hemodynamic Alterations Due to Arteriolar Rarefaction and Estimation of Skeletal Muscle Perfusion in Peripheral Arterial Disease

OBJECTIVE

To estimate the relative influence of input pressure and arteriole rarefaction on gastrocnemius muscle perfusion in patients with PAD after exercise and/or percutaneous interventions.

METHODS

A computational network model of the gastrocnemius muscle microcirculation was adapted to reflect rarefaction based on arteriolar density measurements from PAD patients, with and without exercise. A normalized input pressure was applied at the feeder artery to simulate both reduced and restored ABI in the PAD condition.

RESULTS

In simulations of arteriolar rarefaction, resistance increased non-linearly with rarefaction, leading to a disproportionally large drop in perfusion. In addition, perfusion was less sensitive to changes in input pressure as the degree of rarefaction increased. Reduced arteriolar density was observed in PAD patients and improved 33.8% after three months of exercise. In model simulations of PAD, ABI restoration yielded perfusion recovery to only 66% of baseline. When exercise training was simulated by reducing rarefaction, ABI restoration increased perfusion to 80% of baseline.

CONCLUSION

Microvascular resistance increases non-linearly with increasing arteriole rarefaction. Therefore, muscle perfusion becomes disproportionally less sensitive to ABI restoration as arteriole rarefaction increases. These results highlight the importance of restoring both microvascular structure and upstream input pressure in PAD therapy.

Calf muscle perfusion as measured with magnetic resonance imaging to assess peripheral arterial disease

We hypothesized that skeletal muscle perfusion is impaired in peripheral arterial disease (PAD) patients compared to healthy controls and that perfusion patterns exhibit marked differences across five leg muscle compartments including the anterior muscle group (AM), lateral muscle group (LM), deep posterior muscle group (DM), soleus (SM), and the gastrocnemius muscle (GM). A total of 40 individuals (26 PAD patients and 14 healthy controls) underwent contrast-enhanced magnetic resonance imaging (CE-MRI) utilizing a reactive hyperemia protocol. Muscle perfusion maps were developed for AM, LM, DM, SM, and GM. Perfusion maps were analyzed over the course of 2 min, starting at local pre-contrast arrival, to study early-to-intermediate gadolinium enhancement. PAD patients had a higher fraction of hypointense voxels at pre-contrast arrival for all five muscle compartments compared with healthy controls (p < 0.0005). Among PAD patients, the fraction of hypointense voxels of the AM, LM, and GM were inversely correlated with the estimated glomerular filtration rate (eGFR; r = -0.509, p = 0.008; r = -0.441, p = 0.024; and r = -0.431, p = 0.028, respectively). CE-MRI-based skeletal leg muscle perfusion is markedly reduced in PAD patients compared with healthy controls and shows heterogeneous patterns across calf muscle compartments.

Transforming growth factor-beta 1 produced by vascular smooth muscle cells predicts fibrosis in the gastrocnemius of patients with peripheral artery disease

Background

Lower leg ischemia, myopathy, and limb dysfunction are distinguishing features of peripheral artery disease (PAD). The myopathy of PAD is characterized by myofiber degeneration in association with extracellular matrix expansion, and increased expression of transforming growth factor-beta 1 (TGF-β1; a pro-fibrotic cytokine). In this study, we evaluated cellular expression of TGF-β1 in gastrocnemius of control (CTRL) and PAD patients and its relationship to deposited collagen, fibroblast accumulation and limb hemodynamics.

Methods

Gastrocnemius biopsies were collected from PAD patients with claudication (PAD-II; N = 25) and tissue loss (PAD-IV; N = 20) and from CTRL patients (N = 20). TGF-β1 in slide-mounted specimens was labeled with fluorescent antibodies and analyzed by quantitative wide-field, fluorescence microscopy. We evaluated co-localization of TGF-β1 with vascular smooth muscle cells (SMC) (high molecular weight caldesmon), fibroblasts (TE-7 antigen), macrophages (CD163), T cells (CD3) and endothelial cells (CD31). Collagen was stained with Masson Trichrome and collagen density was determined by quantitative bright-field microscopy with multi-spectral imaging.

Results

Collagen density increased from CTRL to PAD-II to PAD-IV specimens (all differences p < 0.05) and was prominent around microvessels. TGF-β1 expression increased with advancing disease (all differences p < 0.05), correlated with collagen density across all specimens (r = 0.864; p < 0.001), associated with fibroblast accumulation, and was observed exclusively in SMC. TGF-β1 expression inversely correlated with ankle-brachial index across PAD patients (r = −0.698; p < 0.001).

Conclusions

Our findings support a progressive fibrosis in the gastrocnemius of PAD patients that is caused by elevated TGF-β1 production in the SMC of microvessels in response to tissue hypoxia.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-016-0790-3) contains supplementary material, which is available to authorized users.

Peripheral arterial disease decreases muscle torque and functional walking capacity in elderly

OBJECTIVES

The aim of this study is to compare values of force-velocity and functional walking capacity in elderly patients with intermittent claudication with respect to the control group.

MATERIALS AND METHODS

The study involved 135 individuals: 85-peripheral arterial disease (PAD) group diagnosed with stage II chronic lower limb ischemia, according to Fontaine's classification, and 50-control group. The studies included an assessment of walking capacity using a six-minute walk test (6MWT) and measurement of force-velocity parameters (peak torque-PTQ, total work-TW, average power-AVGP) of the lower limbs obtained by means of a functional dynamometry under isokinetic conditions.

RESULTS

The peripheral arterial disease group is characterized by significantly lower values of force-velocity parameters compared to the control group (p<0.005). Walking capacity in this group is significantly reduced due to significant differences in the distance covered (p<0.0001), walking speed (p<0.01), and its intensity (p<0.01). Further, a positive correlation was found between the maximum distance specified in the six-minute walk test and lower limb muscle strength in the isokinetic test.

CONCLUSIONS

Mean values of all force-velocity parameters and walk distance were significantly higher in the control group than in the peripheral arterial disease group. In the PAD group, in both men and women, the value of the agonist/antagonist ratio of both lower limbs are lower in men and women comparing to the control group. A rehabilitation program for patients with intermittent claudication must consider exercises improving strength, exercise capacity, and endurance in patients with PAD.

Protein concentration and mitochondrial content in the gastrocnemius predicts mortality rates in patients with peripheral arterial disease

OBJECTIVE

This study evaluated the hypothesis that protein concentration and mitochondrial content in gastrocnemius biopsies from patients with peripheral arterial disease (PAD) predict mortality rates.

BACKGROUND

PAD patients experience advancing myopathy characterized by mitochondrial dysfunction, myofiber degradation, and fibrosis in their ischemic legs, along with increased mortality rates.

METHODS

Samples from the gastrocnemius of PAD patients were used for all analyses. Protein concentration was normalized to muscle wet weight, and citrate synthase activity (standard measure of mitochondrial content in cells) was normalized to muscle wet weight and protein concentration. Protein and citrate synthase data were grouped into tertiles and 5-year, all-cause mortality for each tertile was determined with Kaplan-Meier curves and compared by the modified Peto-Peto test. A Cox-regression model for each variable controlled for the effects of clinical characteristics.

RESULTS

Of the 187 study participants, 46 died during a mean follow-up of 23.0 months. Five-year mortality rate was highest for patients in the lowest tertile of protein concentration. Mortality was lowest for patients in the middle tertile of citrate synthase activity when normalized to either muscle wet weight or protein concentration. The mortality hazard ratios (HRs) from the Cox analysis were statistically significant for protein concentration normalized to muscle wet weight (lowest vs middle tertile; HR = 2.93; P = 0.008) and citrate synthase normalized to protein concentration (lowest vs middle tertile; HR = 4.68; P = 0.003; and lowest vs highest tertile; HR = 2.36; P = 0.027).

CONCLUSIONS

Survival analysis of a contemporaneous population of PAD patients identifies protein and mitochondrial content of their gastrocnemius as predictors of mortality rate.

Abnormal myofiber morphology and limb dysfunction in claudication

BACKGROUND

Peripheral artery disease (PAD), which affects an estimated 27 million people in Europe and North America, is caused by atherosclerotic plaques that limit blood flow to the legs. Chronic, repeated ischemia in the lower leg muscles of PAD patients is associated with loss of normal myofiber morphology and myofiber degradation. In this study, we tested the hypothesis that myofiber morphometrics of PAD calf muscle are significantly different from normal calf muscle and correlate with reduced calf muscle strength and walking performance.

METHODS

Gastrocnemius biopsies were collected from 154 PAD patients (Fontaine stage II) and 85 control subjects. Morphometric parameters of gastrocnemius fibers were determined and evaluated for associations with walking distances and calf muscle strength.

RESULTS

Compared with control myofibers, PAD myofiber cross-sectional area, major and minor axes, equivalent diameter, perimeter, solidity, and density were significantly decreased (P < 0.005), whereas roundness was significantly increased (P < 0.005). Myofiber morphometric parameters correlated with walking distances and calf muscle strength. Multiple regression analyses demonstrated myofiber cross-sectional area, roundness, and solidity as the best predictors of calf muscle strength and 6-min walking distance, whereas cross-sectional area was the main predictor of maximum walking distance.

CONCLUSIONS

Myofiber morphometrics of PAD gastrocnemius differ significantly from those of control muscle and predict calf muscle strength and walking distances of the PAD patients. Morphometric parameters of gastrocnemius myofibers may serve as objective criteria for diagnosis, staging, and treatment of PAD.

A review of the relationship between leg power and selected chronic disease in older adults

OBJECTIVE

This review investigates the relationship between leg muscle power and the chronic conditions of osteoarthritis, diabetes mellitus, and cardiovascular disease among older adults. Current literature assessing the impact of chronic disease on leg power has not yet been comprehensively characterized. Importantly, individuals with these conditions have shown improved leg power with training.

METHODS

A search was performed using PubMed to identify original studies published in English from January 1998 to August 2013. Leg power studies, among older adults ≥ 50 years of age, which assessed associations with osteoarthritis, diabetes mellitus, and/or cardiovascular disease were selected. Studies concerning post-surgery rehabilitation, case studies, and articles that did not measure primary results were excluded.

RESULTS

Sixteen studies met inclusion criteria, addressing osteoarthritis (n=5), diabetes mellitus (n=5), and cardiovascular disease (n=6). Studies generally supported associations of lower leg power among older adults with chronic disease, although small sample sizes, cross-sectional data, homogenous populations, varied disease definitions, and inconsistent leg power methods limited conclusions.

CONCLUSIONS

Studies suggest that osteoarthritis, diabetes mellitus, and cardiovascular disease are associated with lower leg power compared to older adults without these conditions. These studies are limited, however, by the heterogeneity in study populations and a lack of standardized measurements of leg power. Future larger studies of more diverse older adults with well-defined chronic disease using standard measures of leg power and interventions to improve leg power in these older adults with chronic disease are needed.

Abnormal accumulation of desmin in gastrocnemius myofibers of patients with peripheral artery disease: associations with altered myofiber morphology and density, mitochondrial dysfunction and impaired limb function

Patients with peripheral artery disease (PAD) develop a myopathy in their ischemic lower extremities, which is characterized by myofiber degeneration, mitochondrial dysfunction and impaired limb function. Desmin, a protein of the cytoskeleton, is central to maintenance of the structure, shape and function of the myofiber and its organelles, especially the mitochondria, and to translation of sarcomere contraction into muscle contraction. In this study, we investigated the hypothesis that disruption of the desmin network occurs in gastrocnemius myofibers of PAD patients and correlates with altered myofiber morphology, mitochondrial dysfunction, and impaired limb function. Using fluorescence microscopy, we evaluated desmin organization and quantified myofiber content in the gastrocnemius of PAD and control patients. Desmin was highly disorganized in PAD but not control muscles and myofiber content was increased significantly in PAD compared to control muscles. By qPCR, we found that desmin gene transcripts were increased in the gastrocnemius of PAD patients as compared with control patients. Increased desmin and desmin gene transcripts in PAD muscles correlated with altered myofiber morphology, decreased mitochondrial respiration, reduced calf muscle strength and decreased walking performance. In conclusion, our studies identified disruption of the desmin system in gastrocnemius myofibers as an index of the myopathy and limitation of muscle function in patients with PAD.

Oxidative damage in the gastrocnemius of patients with peripheral artery disease is myofiber type selective

Background

Peripheral artery disease (PAD), a manifestation of systemic atherosclerosis that produces blockages in the arteries supplying the legs, affects approximately 5% of Americans. We have previously, demonstrated that a myopathy characterized by myofiber oxidative damage and degeneration is central to PAD pathophysiology.

Objectives

In this study, we hypothesized that increased oxidative damage in the myofibers of the gastrocnemius of PAD patients is myofiber-type selective and correlates with reduced myofiber size.

Methods

Needle biopsies were taken from the gastrocnemius of 53 PAD patients (28 with early PAD and 25 with advanced PAD) and 25 controls. Carbonyl groups (marker of oxidative damage), were quantified in myofibers of slide-mounted tissue, by quantitative fluorescence microscopy. Myofiber cross-sectional area was determined from sarcolemma labeled with wheat germ agglutinin. The tissues were also labeled for myosin I and II, permitting quantification of oxidative damage to and relative frequency of the different myofiber Types (Type I, Type II and mixed Type I/II myofibers). We compared PAD patients in early (N=28) vs. advanced (N=25) disease stage for selective, myofiber oxidative damage and altered morphometrics.

Results

The carbonyl content of gastrocnemius myofibers was higher in PAD patients compared to control subjects, for all three myofiber types (p<0.05). In PAD patients carbonyl content was higher (p<0.05) in Type II and I/II fibers compared to Type I fibers. Furthermore, the relative frequency and cross-sectional area of Type II fibers were lower, while the relative frequencies and cross-sectional area of Type I and Type I/II fibers were higher, in PAD compared to control gastrocnemius (p<0.05). Lastly, the type II-selective oxidative damage increased and myofiber size decreased as the disease progressed from the early to advanced stage.

Conclusions

Our data confirm increased myofiber oxidative damage and reduced myofiber size in PAD gastrocnemius and demonstrate that the damage is selective for type II myofibers and is worse in the most advanced stage of PAD.

•

Peripheral artery disease, is characterized by the formation of atherosclerotic plaques that limit blood flow to the legs.

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There was increased myofiber oxidative damage and degeneration in the gastrocnemius of PAD patients compared to controls.

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Myofiber oxidative damage and morphology were worse for Type II myofibers.

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Type II-selective oxidative damage and abnormal morphology worsened as the PAD progressed from the early to advanced stage.

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Myofiber oxidative damage and degeneration is a significant contributors to the pathophysiology of PAD.

Despite normal arteriogenic and angiogenic responses, hind limb perfusion recovery and necrotic and fibroadipose tissue clearance are impaired in matrix metalloproteinase 9-deficient mice

OBJECTIVE

The relative contributions of arteriogenesis, angiogenesis, and ischemic muscle tissue composition toward reperfusion after arterial occlusion are largely unknown. Differential loss of bone marrow-derived cell (BMC) matrix metalloproteinase 9 (MMP9), which has been implicated in all of these processes, was used to assess the relative contributions of these processes during limb reperfusion.

METHODS

We compared collateral growth (arteriogenesis), capillary growth (angiogenesis), and ischemic muscle tissue composition after femoral artery ligation in FVB/NJ mice that had been reconstituted with bone marrow from wild-type or MMP9(-/-) mice.

RESULTS

Laser Doppler perfusion imaging confirmed decreased reperfusion capacity in mice with BMC-specific loss of MMP9; however, collateral arteriogenesis was not affected. Furthermore, when accounting for the fact that muscle tissue composition changes markedly with ischemia (ie, necrotic, fibroadipose, and regenerating tissue regions are present), angiogenesis was also unaffected. Instead, BMC-specific loss of MMP9 caused an increase in the proportion of necrotic and fibroadipose tissue, which showed the strongest correlation with poor perfusion recovery. Similarly, the reciprocal loss of MMP9 from non-BMCs showed similar deficits in perfusion and tissue composition without affecting arteriogenesis.

CONCLUSIONS

By concurrently analyzing arteriogenesis, angiogenesis, and ischemic tissue composition, we determined that the loss of BMC-derived or non-BMC-derived MMP9 impairs necrotic and fibroadipose tissue clearance after femoral artery ligation, despite normal arteriogenic and angiogenic vascular growth. These findings imply that therapeutic revascularization strategies for treating peripheral arterial disease may benefit from additionally targeting necrotic tissue clearance or skeletal muscle regeneration, or both.

A novel stable isotope tracer method to measure muscle protein fractional breakdown rate during a physiological non-steady-state condition

The measurement of the fractional breakdown rate (FBR) of muscle proteins during physiological non-steady state of amino acids (AAs) presents some challenges. Therefore, the goal of the present experiment was to modify the bolus stable isotope tracer injection approach to determine both fractional synthesis rate (FSR) and FBR of leg muscle protein during a physiological non-steady state of AAs. The approach uses the traditional precursor-product principle but is modified with the assumption that inward transport of AAs is proportional to their plasma concentrations. The FBR value calculated from the threonine tracer served as a reference to evaluate the validity of the FBR measurement from the phenylalanine tracer, which was under a non-steady-state condition due to the concomitant injection of unlabeled phenylalanine. Plasma phenylalanine concentration increased more than fourfold after the bolus injection, and thereafter it decreased exponentially, whereas the threonine concentration remained stable. FBR values were similar with the two tracers [0.133 ± 0.003 and 0.148 ± 0.003%/h (means ± SE) for the phenylalanine and threonine tracers, respectively, P > 0.05]. In addition, FSR values for the two tracers were similar (0.069 ± 0.002 and 0.067 ± 0.001%/h for the phenylalanine and threonine tracers, respectively, P > 0.05), indicating that the traditional FSR approach can also be used in the non-steady state. Accordingly, net balance (NB) values were similar (-0.065 ± 0.002 and -0.081 ± 0.002%/h for the phenylalanine and threonine tracers, respectively, P > 0.05). This new method of measuring muscle protein FBR during physiological non-steady state gives reliable results and allows simultaneous measurement of muscle protein FSR and thus a calculation of NB.

Lower extremity nerve function, calf skeletal muscle characteristics, and functional performance in peripheral arterial disease

OBJECTIVES

To determine whether poor lower extremity nerve function is associated with less-favorable calf muscle characteristics and greater functional impairment in people with and without peripheral arterial disease (PAD).

DESIGN

Cross-sectional.

SETTING

Three Chicago-area medical centers.

PARTICIPANTS

Four hundred thirteen participants with PAD (ankle-brachial index (ABI) < 0.90) and 255 without.

MEASUREMENTS

Electrodiagnostic testing of the peroneal nerve was performed. Calf muscle cross-sectional area and percentage fat were measured using computed tomography at 66.7% of the distance between the distal and proximal tibia. Six-minute walk performance was measured.

RESULTS

Adjusting for age, sex, race, ABI, leg symptoms, smoking, physical activity, comorbidities, and other covariates, lower peroneal nerve conduction velocity (NCV) was associated with lower calf muscle area (first quartile 4,770.3 mm(2) , fourth quartile 5,571 mm(2) , P < .001) and poorer 6-minute walk distance (first quartile 989.2 feet, fourth quartile 1,210.8 feet, P < .001) in participants without diabetes mellitus with PAD. Lower peroneal NCV was associated with lower calf muscle area (first quartile 5,166.0 mm(2) , fourth quartile 6,003.8 mm(2) , P = .01) and poorer 6-minute walk distance (first quartile 866.4 feet, fourth quartile 1,082.5 feet, P = .01) in participants with diabetes mellitus and PAD as well. In participants without PAD, lower peroneal NCV was not associated with lower calf muscle area but was associated with poorer 6-minute walk distance only in participants without diabetes mellitus (first quartile 1,317.0 feet, fourth quartile 1,570.4 feet, P-trend < .001).

CONCLUSION

Lower peroneal nerve function is associated with smaller calf muscle area and greater functional impairment in individuals with PAD. Future study is needed to determine whether improving peroneal NCV prevents loss of calf muscle and functional decline in people with PAD.

IκBα degradation is necessary for skeletal muscle atrophy associated with contractile claudication

The arterial blockage in patients with peripheral arterial disease (PAD) restricts oxygen delivery to skeletal muscles distal to the blockage. In advanced-stage PAD patients, this creates a chronic ischemic condition in the affected muscles. However, in the majority of PAD patients, the muscles distal to the blockage only become ischemic during physical activity when the oxygen demands of these muscles are increased. Therefore, the skeletal muscle of most PAD patients undergoes repeated cycles of low-grade ischemia-reperfusion each time the patient is active and then rests. This has been speculated to contribute to the biochemical and morphological myopathies observed in PAD patients. The current study aimed to determine, using a rodent model, whether repeated hind limb muscle contractions during blood flow restriction to the hind limb muscles increases NF-κB activity. We, subsequently, determined whether an increase in NF-κB activity during this condition is required for the increased transcription of specific atrophy-related genes and muscle fiber atrophy. We found that hind limb muscle contractions during blood flow restriction to the limb increased NF-κB activity, the transcription of specific atrophy-related genes, and caused a 35% decrease in muscle fiber cross-sectional area. We further found that inhibition of NF-κB activity, via gene transfer of a dominant-negative inhibitor of κBα (d.n. IκBα), prevented the increase in atrophy gene expression and muscle fiber atrophy. These findings demonstrate that when blood flow to skeletal muscle is restricted, repeated cycles of muscle contraction can cause muscle fiber atrophy that requires NF-κB-IκBα signaling.

Pathophysiological changes in calf muscle predict mobility loss at 2-year follow-up in men and women with peripheral arterial disease

BACKGROUND

Associations of pathophysiological calf muscle characteristics with functional decline in people with lower extremity peripheral arterial disease are unknown.

METHODS AND RESULTS

Three hundred seventy participants with peripheral arterial disease underwent baseline measurement of calf muscle area, density, and percent fat with the use of computed tomography. Participants were followed up annually for 2 years. The outcome of mobility loss was defined as becoming unable to walk 1/4 mile or walk up and down 1 flight of stairs without assistance among those without baseline mobility limitations. Additional outcomes were > or =20% decline in 6-minute walk distance and becoming unable to walk for 6 minutes continuously among participants who walked continuously for 6 minutes at baseline. With adjustment for age, sex, race, body mass index, the ankle-brachial index, smoking, physical activity, relevant medications, and comorbidities, lower calf muscle density (P for trend <0.001) and lower calf muscle area (P for trend=0.039) were each associated with increased mobility loss rates. Compared with participants in the highest baseline tertiles, participants in the lowest tertile of calf muscle percent fat had a hazard ratio of 0.18 for incident mobility loss (95% confidence interval, 0.06 to 0.55; P=0.003), and participants in the lowest tertile of muscle density had a 3.50 hazard ratio for incident mobility loss (95% confidence interval, 1.28 to 9.57; P=0.015). No significant associations of calf muscle characteristics with 6-minute walk outcomes were observed.

CONCLUSIONS

Our findings suggest that interventions to prevent mobility loss in peripheral arterial disease should focus on reversing pathophysiological findings in calf muscle.

[Muscles of the below-knee amputees]

OBJECTIVE

The objective of this article is to review anatomical, histological and physiological muscle changes following below-knee amputation.

MATERIALS AND METHODS

We searched the PubMed and Reedoc databases for studies evaluating modifications of the below-knee stump and changes over time in its anatomy, volume and histology. We also looked at postamputation modifications in gait and balance.

RESULTS

Below-knee amputees show muscular atrophy on both the amputated side and nonamputated side, with fewer and smaller muscle fibres (particularly slow-twitch fibres). This amyotrophy varies in magnitude and distribution and can reach about 25% for the quadriceps (predominantly on the medial side), but is nonsignificant for the hamstrings. This amyotrophy results from the anatomical consequences of the surgical act. The loss of one or more of a muscle's insertions or reimplantation into a nonphysiological site prompts greater atrophy. Changes in muscle activation patterns also lead to atrophy. The hamstrings replace the triceps as the main muscles for propulsion and the remaining stump muscles contract so as to ensure a good fit with the prosthesis. The below-knee amputee must adapt to a new muscular state: gait symmetry is altered, energy expenditure for walking is higher and training is needed in order to achieve optimal balance control.

Morphological and Immunohistochemical Changes in Muscle Tissue in Association With Mandibular Distraction Osteogenesis

PURPOSE

Studies of changes in the surrounding soft tissue in association with distraction osteogenesis in the maxillofacial region, where various different kinds of tissue are tightly packed, are rare. In this study, we performed morphological and immunohistochemical investigations of muscle tissue during mandibular distraction osteogenesis.

MATERIALS AND METHODS

Japanese white rabbits were divided into 2 groups. In 1 group, the mandibular bone was distracted at a rate of 1 mm/day (DO group), whereas in the other group it was advanced by 10 mm all at once (O group). The cross-section of the anterior belly of the digastric muscle was examined using hematoxylin and eosin, periodic acid-Schiff (PAS), and proliferating cell nuclear antigen (PCNA) staining methods, as well as scanning electronmicroscopy (SEM).

RESULTS

In the DO group, the cross-section of muscle bundle revealed no remarkable changes. In PAS staining, type II fibers gradually disappeared with distraction, but eventually reappeared after a period of consolidation. In the SEM photographs, striation-like laminated structures were evident in the control and the 3-mm distraction, ambiguous in the 6-mm distraction, and not evident in the 10-mm distraction. In contrast, the structure appeared to be restored in the consolidation for 1 week thereafter. In the PCNA immunostaining, the numbers of PCNA-positive nuclei increased during periods of distraction, but subsequently tended to decrease gradually.

CONCLUSIONS

Although minute injuries were induced in muscle fibers in association with distraction osteogenesis, it is suggested that muscle fibers regenerate starting in the distraction period and thus can adapt to the environment.

The role of ascorbic acid and exercise in chronic ischemia of skeletal muscle in rats

This study was designed to investigate the effects of peripheral arterial insufficiency, exercise, and vitamin C administration on muscle performance, cross-sectional area, and ultrastructural morphology in extensor digitorum longus (EDL) and soleus (Sol) muscles in rats. Adult Wistar rats were assigned to ischemia alone (isch), ischemia-exercised (exe), ischemia-vitamin C (vit C), and ischemia-exercise-vitamin C (vit C + exe) groups. Ischemia was achieved via unilateral ligation of the right common iliac artery. Contralateral muscles within the same animal served as controls. Exercise protocol consisted of 50-min intermittent level running performed every other day for 5 days. Vitamin C (100 mg/kg body wt) was administered intraperitoneally on a daily basis throughout the 14 days of the experiment. With regard to the EDL muscle, ischemia alone reduced muscle strength, which was not recovered after vitamin C administration. Exercise alone following ischemia induced the most severe structural damage and cross-sectional area decrease in the muscle, yet the reduction in tetanic tension was not significant. Exercise in conjunction with vitamin C administration preserved ischemia-induced EDL muscle tetanic tension. In the Sol muscle, a significant reduction in single twitch tension after vitamin C administration was found, whereas the tetanic force of the ischemic Sol was not significantly decreased compared with the contralateral muscles in any group. Ischemic Sol muscle cross-sectional area was reduced in all but the exe groups. In Sol, muscle strength was reduced in the vit C group, and mean cross-sectional area of ischemic Sol muscles was reduced in all groups except the exe group. These results illustrate that mild exercise, combined with a low dose of vitamin C supplementation, may have beneficial effects on ischemic EDL muscle with a smaller effect on the Sol muscle.

Skeletal muscle phenotype is associated with exercise tolerance in patients with peripheral arterial disease

OBJECTIVE

To better understand the association between skeletal muscle and exercise intolerance in peripheral arterial disease (PAD), we assessed treadmill-walking performance and gastrocnemius muscle phenotype in healthy control subjects and in patients with PAD. We hypothesized that gastrocnemius muscle characteristics would be altered in PAD compared with control subjects and that exercise tolerance in patients PAD would be related to muscle phenotype.

METHODS

Sixteen patients with PAD and intermittent claudication and 13 healthy controls of the same age participated. Each subject completed a graded treadmill-walking test and underwent a resting muscle biopsy. Muscle biopsy samples were obtained from the medial gastrocnemius muscle of the most ischemic limb in PAD and a limb chosen at random in controls. Samples were analyzed for fiber type and cross-sectional area, capillary-to-fiber ratio, the number of capillaries in contact with each fiber type, and the optical density of glycogen within each fiber by using histochemical procedures. Total muscle glycogen content was determined biochemically.

RESULTS

Exercise capacity measured on the incremental walking test in the PAD group was only 30% to 40% of that observed in controls. The PAD group had a lower proportion of type I muscle fibers (P < .05), fewer capillaries per muscle fiber (P < .05), and tended to have smaller fiber areas (P = .08). The relative area of type I fibers, the capillary-to-fiber ratio, capillary contacts with type I and IIa fibers, and the optical density of glycogen in type I fibers were all positively correlated with exercise tolerance in the PAD group (P < .05) but not controls.

CONCLUSIONS

These data suggest that muscle phenotype is altered in PAD and that such alterations are associated with the exercise intolerance in these patients. In light of these findings, therapies such as resistance training or electrical stimulation that target skeletal muscle in PAD may prove beneficial, and further investigation of such therapies is warranted.

Mitochondrial function and oxygen supply in normal and in chronically ischemic muscle: a combined 31P magnetic resonance spectroscopy and near infrared spectroscopy study in vivo

PURPOSE

We used (31)P magnetic resonance spectroscopy (MRS) and near-infrared spectroscopy (NIRS) as a means of quantifying abnormalities in calf muscle oxygenation and adenosine triphosphate (ATP) turnover in peripheral vascular disease (PVD).

METHODS

Eleven male patients with PVD (mean age, 65 years; range, 55-76 years) and nine male control subjects of similar age were observed in a case-control study in vascular outpatients. Inclusion criteria were more than 6 months' calf claudication (median, 1.5 years; range, 0.6-18 years); proven femoropopliteal or iliofemoral occlusive or stenotic disease; maximum treadmill walking distance (2 km/h, 10 degrees gradient) of 50 to 230 m (mean, 112 m); ankle-brachial pressure index of 0.8 or less during exercise (mean, 0.47; range, 0.29-0.60). Exclusion criteria included diabetes mellitus, anemia, and magnet contraindications. Simultaneous (31)P MRS and NIRS of lateral gastrocnemius was conducted during 2 to 4 minutes of voluntary 0.5 Hz isometric plantarflexion at 50% and 75% maximum voluntary contraction force (MVC), followed by 5 minutes recovery. Each subject was studied three times, and the results were combined.

RESULTS

Compared with control subjects, patients with PVD showed (1) normal muscle cross-sectional area, MVC, ATP turnover, and contractile efficiency (ATP turnover per force/area); (2) larger phosphocreatine (PCr) changes during exercise (ie, increased shortfall of oxidative ATP synthesis) and slower PCr recovery (47% +/- 7% [mean +/- SEM] decrease in functional capacity for oxidative ATP synthesis, P = .001); (3) faster deoxygenation during exercise and slower postexercise reoxygenation (59% +/- 7% decrease in rate constant, P = .0009), despite reduced oxidative ATP synthesis; (4) correlation between PCr and NIRS recovery rate constants (P < .02); and (5) correlations between smaller walking distance, slower PCr recovery, and reduced MVC (P < .001). The precision of the key measurements (rate constants and contractile efficiency) was 12% to 18% interstudy and 30% to 40% intersubject.

CONCLUSION

The primary lesion in oxygen supply dominates muscle metabolism. Reduced force-generation in patients who are affected more may protect muscle from metabolic stress.

Gait alterations associated with walking impairment in people with peripheral arterial disease with and without intermittent claudication

OBJECTIVES

To describe gait alterations associated with impaired walking endurance in patients with and without lower-extremity peripheral arterial disease (PAD) and determine whether the Caltrac accelerometer provides a valid measure of physical activity in PAD.

DESIGN

Cross-sectional.

SETTING

Academic medical center.

PARTICIPANTS

PAD (n = 40) and non-PAD patients (n = 22) from two Chicago hospitals.

MEASUREMENTS

Participants underwent measurement of the ankle brachial index (ABI), leg length, and 6-minute walk. Steps per minute and step length were measured during the first and last 100 feet of the 6-minute walk. Participants wore a Caltrac accelerometer, sensitive to vertical acceleration, during the 6-minute walk and for 7 continuous days.

RESULTS

Five PAD participants (13%) and one non-PAD participant (5%) ceased walking before the end of 6 minutes. Among the remaining participants, distance walked in 6 minutes was more highly related to walking velocity during the last 100 feet of the walk than walking velocity during the first 100 feet. ABI was associated significantly with cadence (20.77 steps/minute per unit ABI, P <.001) but not step length (10.12 centimeters/unit ABI, P =.08). ABI was associated significantly with 6-minute walk distance (493 feet/unit ABI, P =.018), but this association disappeared completely after adjustment for step length and cadence. We found no difference in accelerometer scores between PAD and non-PAD participants over a fixed distance of 800 feet (7.34 vs 7.17 activity units, P =.789). However, scores were significantly different after 7 days (730.8 vs 1,485.0 activity units, P =.003).

CONCLUSION

Walking performance in PAD patients who completed 6 minutes of walking was largely determined by a decline in walking velocity rather than slower initial walking velocity. ABI was more closely associated with cadence than step length. Future studies should assess the effect of exercise programs and revascularization on cadence and step length in PAD.

Exercise training and peripheral vascular disease

BACKGROUND

Conservative management is advocated as a treatment of choice for patients with intermittent claudication. This is a review of the mechanisms behind the improvement following an exercise rehabilitation programme.

METHODS

All Medline articles from the National Library of Medicine, USA containing the text words 'claudication' or 'peripheral vascular disease' and 'exercise' were reviewed. Cross-referencing from relevant articles was carried out.

RESULTS AND CONCLUSION

The poor physical status of a patient with intermittent claudication is not solely due to a reduction in blood flow to the lower limbs; associated factors, such as metabolic inefficiency, poor cardiorespiratory reserve and exercise-induced inflammation contribute. An exercise programme frequently improves both the physical aspect and quality of life, and the success of such exercise is multifactorial. An increase in the blood flow to the lower extremity is uncommon. Other factors, such as a redistribution of blood flow, changes in oxidative capacity of the skeletal muscles and greater utilization of oxygen, occur and the associated metabolic dysfunction of the skeletal muscles is rectified. Following exercise training, blood rheology improves and exercise-induced inflammation is ameliorated; cardiorespiratory status also benefits and the oxygen cost of exercise decreases.

Asymptomatic peripheral arterial disease is independently associated with impaired lower extremity functioning: the women's health and aging study

BACKGROUND

We report the implications of asymptomatic lower extremity peripheral arterial disease (PAD) for lower extremity functioning among participants in the Women's Health and Aging Study, an observational study of disabled women > or = 65 years of age living in and around Baltimore.

METHODS AND RESULTS

The ankle brachial index (ABI) and measures of upper and lower extremity functioning were measured among study participants. Of 933 women with ABI < or =1. 50, 328 (31%) [corrected] had an ABI <0.90, consistent with PAD. Sixty-three percent of PAD participants had no exertional leg pain. Among participants without exertional leg pain, lower ABI levels were associated with slower walking velocity, poorer standing balance score, slower time to arise 5 times consecutively from a seated position, and fewer blocks walked per week, adjusting for age, sex, race, cigarette smoking, and comorbidities. ABI was not associated independently with measures of upper extremity functioning.

CONCLUSIONS

Asymptomatic PAD is common and is independently associated with impaired lower extremity functioning. In addition to preventing cardiovascular morbidity and death, further study is warranted to identify effective interventions to improve functioning among the growing number of men and women with asymptomatic PAD.

Neurophysiologic studies in peripheral arterial disease

The purpose of the study was to compare the electrophysiological parameters (nerve conduction studies and quantitative electromyography [EMG]) between patients with chronic peripheral arterial disease (PAD) and normal control subjects. Forty patients with PAD and 30 control subjects (40 legs) were evaluated clinically and electrophysiologically using previously described methods. The amplitude of compound muscle action potentials (CMAPs) and the motor conduction velocities (MCVs) of peroneal and tibial nerve for most patients with PAD were within normal limits but compared with those of the controls, it was found that the peroneal and tibial MCVs as well as the amplitude of sural nerve were significantly decreased. The EMG testing of patients with PAD and controls of the anterior tibialis and the gastrocnemius muscle did not show evidence of denervation or myopathic abnormalities. However, the mean amplitude and duration of both muscles were significantly larger compared with the controls. Routine electrophysiological studies are not the appropriate (sensitive enough) tests for detecting peripheral nerve or muscle dysfunction associated with PAD.

Morphological changes during early trans-tibial prosthetic fitting

Morphological changes in the amputation stump may have serious implications regarding the suspension and fit of the prosthetic socket. In an earlier study (Lilja and Oberg, 1997) the authors have shown that the volume of the trans-tibial amputation stump decreases according to a negative power function after amputation, and that the stump volume does not stabilise until four months after the operation. In the present study, Magnetic Resonance Imaging (MRI) technique was used to examine morphological changes in the amputation stump after trans-tibial amputation in a small number of cases. The authors expected to find a decrease in the cross-sectional area of the stump and of the separate muscles similar to the findings in earlier studies. However, two different patterns were found. The cross-sectional area of the entire stump as well as that of the medial muscle group changed according to the authors' hypothesis, i.e. an initial fast decrease, followed by a more moderate decrease of the area. In the lateral muscle group another pattern was found. After an initial rapid decrease the area increased, sometimes to a magnitude larger than the initial value. After the amputation the lateral muscle group may acquire a new function, contributing to the suspension of the socket. Despite the limited number of patients, this study presents findings which may be important in the clinical fitting of trans-tibial prostheses.

Altered surface myoelectric signals in peripheral vascular disease: correlations with muscle fiber composition

Conduction velocity (CV) and median frequency (MDF) during tetanic electrical stimulation of the tibialis anterior muscle were evaluated in patients with uncomplicated peripheral arterial occlusive disease. Results were analyzed with respect to biopsy determination of diameter and proportion of types 1 and 2 muscles fibers. Initial MDF and CV correlated positively with type 2, but not type 1 fiber diameter. Initial MDF was reduced bilaterally in patients with unilateral peripheral arterial occlusive disease as compared to normal subjects, indicating that chronic ischemia alone cannot explain the altered myoelectric signal. Physical training increased pain-free walking distance and raised initial MDF, though CV remained unchanged. Fatigue indices were highly interrelated, but showed no correlation with any of the other evaluation variables. Thus, initial MDF, a correlate of type 2 muscle fiber distribution in chronically ischemic tibialis anterior muscles, is altered in peripheral vascular disease. However, muscle ischemia alone cannot explain all aspects of this abnormality.

Sensory axonopathy in mild to moderate peripheral arterial disease

The effect of mild to moderate arterial occlusive disease on peripheral nervous system conduction was prospectively investigated in 18 subjects and 18 control subjects, aged 40 to 85 years. Experimental and control subjects underwent a thorough history and physical followed by vascular and electrophysiologic studies. The primary outcome measure was the sensory nerve action potential. Although 33% of the subjects with peripheral arterial disease had experienced paresthesias, the clinical evaluation of sensation was relatively unaffected. Sensory conduction studies revealed 30% absent sural responses and 56% absent superficial peroneal nerve responses in subjects with peripheral arterial disease compared with 3 and 14% absent responses in control subjects, respectively (P = 0.044; 0.025). There were no differences in distal latency or sensory amplitude, although the superficial peroneal amplitude did approach significance (P = 0.06). No significant differences were found in motor distal latency, amplitude, or conduction velocity. Age, leg length, temperature, disease severity, presence of paresthesias, cholesterol levels, and past alcohol or tobacco ingestion did not account for the difference in sensory responses. These results support the presence of a mild sensory axonopathy in subjects with peripheral arterial disease. Electromyographers should be cognizant of absent distal responses from peripheral arterial disease so as not to ascribe the findings to an alternative pathology and should not attribute abnormal motor conduction results to the presence of this degree of peripheral arterial disease.

Exercise intolerance in patients with chronic heart failure

Patients with chronic heart failure (CHF) experience significant morbidity because of dyspnea and fatigue with activities of daily living. Although central hemodynamic abnormalities are the hallmark of this disorder, investigators have not shown a relationship between left ventricular ejection fraction or exercise pulmonary capillary wedge pressure and exercise intolerance in this disorder. Recent studies have focused on the contributions of pulmonary abnormalities and alterations in peripheral vasomotor control and skeletal muscle in exercise intolerance in this disorder. Early anaerobic metabolism occurs in patients with CHF and appears to be caused by a combination of reduced skeletal muscle blood flow and decreased aerobic enzyme content in skeletal muscle. Atrophy in skeletal muscle and alterations in skeletal muscle fiber typing are accompanied by alterations in contractile function in skeletal muscle. These results suggest that exercise intolerance in patients with CHF is multifactorial, and that research efforts must consider central hemodynamic abnormalities, pulmonary abnormalities, and alterations in peripheral blood flow and skeletal muscle biochemistry and histology. The present review will explore current research in this area and develop a model for understanding exercise intolerance in CHF.

Progression of neuropathy in peripheral arterial disease

Atherosclerotic peripheral arterial disease (PAD) can cause muscle denervation, but whether it is associated with more severe peripheral nerve disease is not clear. Equally unclear is the effect of exercise training on the neuromuscular aspects of this disease. We performed serial electrophysiologic studies (nerve conduction studies and quantitative electromyography) and muscle strength assessment on 16 patients with moderately severe PAD. Seven of the patients were assigned to a natural history (control) group and 9 to an exercise training group. Over study periods ranging from 3 to 23 months, 6 of 7 patients in the control group and 8 of 9 patients in the exercise training group showed progression of multifocal neuropathic disease in their ischemic legs. For equivalent lengths of time, the degree of neuropathic progression was not significantly different between the control and exercise training groups. There was a significant decline in muscle strength for the control group but not for the exercise training group. These results demonstrate that PAD can be associated with the development of a multifocal predominantly motor neuropathy, which is most likely ischemic in etiology. Furthermore, exercise training does not pose an additional risk for the development of neuropathy in patients with moderately severe PAD.

Functional status and mobility among elderly women with lower extremity arterial disease: the Study of Osteoporotic Fractures

OBJECTIVE

To investigate the relationship between lower extremity arterial disease, functional status, and mobility among elderly women.

DESIGN

Cross-sectional study.

SETTING

Community.

PARTICIPANTS

1492 healthy white women, 65 years of age or older, residing in a rural community, able to walk without the assistance of another person, and enrolled in the Pittsburgh clinic of the multicenter Study of Osteoporotic Fractures. Those with bilateral hip replacement were excluded.

MEASUREMENTS

Ankle/arm index (AAI); instrumental activities of daily living (IADLs); measures of recent physical activity, muscle strength, gait and balance; general demographic, lifestyle, and physical variables.

RESULTS

Women with lower extremity arterial disease (defined as an AAI of 0.9 or less) were more likely to report difficulty with one or more IADLs than were women free of this disease. After adjusting for age and other potential confounders, only difficulty with walking 2-3 blocks remained highly correlated with disease (relative risk (RR) 2.8, 95% confidence interval (CI) 1.6, 4.8). Several measures of physical activity were inversely and independently related to a low AAI. Muscle strength in the hip, arm, knee, and hand and measures of static and dynamic balance were correlated with low AAI in the univariate analysis, but most of these trends were not statistically significant after adjustment for age and other confounders. Exclusion of women with symptomatic arterial disease did not substantially affect the results obtained.

CONCLUSION

Women with mild, predominantly subclinical, lower extremity arterial disease living in the community have decreased functional status and mobility.

Chronic changes in skeletal muscle histology and function in peripheral arterial disease

BACKGROUND

Peripheral arterial disease (PAD) is associated with an impairment in exercise performance and muscle function that is not fully explained by the reduced leg blood flow during exercise. This study characterized the effects of PAD on muscle function, histology, and metabolism.

METHODS AND RESULTS

Twenty-six patients with PAD and six age-matched control subjects were studied. Ten of the PAD patients had unilateral disease, which permitted paired comparisons between their diseased and nonsymptomatic legs. All PAD patients had a lower peak treadmill walking time and peak oxygen consumption than controls. Vascular disease (diseased leg in unilateral patients and the most severely diseased leg in bilateral patients) was associated with decreased calf muscle strength compared with control values. In patients with unilateral disease, the diseased legs had a greater percentage of angular fibers (indicating chronic denervation) and a decreased type II fiber cross-sectional area (expressed as percent of total fiber area) compared with the nonsymptomatic, or control, legs. In diseased legs, gastrocnemius muscle strength was correlated with the total calf cross-sectional area (r = 0.78, p < 0.05) and type II fiber cross-sectional area (r = 0.63, p < 0.05). Activities of citrate synthase, phosphofructokinase, and lactate dehydrogenase in all 26 PAD patients (most diseased leg) did not differ from control values. Despite a wide range in citrate synthase activity in PAD patients, activity of this enzyme was not correlated with muscle strength or treadmill exercise performance.

CONCLUSIONS

In patients with PAD, gastrocnemius muscle weakness is associated with muscle fiber denervation and a decreased type II fiber cross-sectional area. In contrast, the PAD patients displayed substantial heterogeneity in muscle enzyme activities that was not associated with exercise performance. Denervation and type II fiber atrophy may contribute to the muscle dysfunction in patients with PAD and further confirm that the pathophysiology of chronic PAD extends beyond arterial obstruction.