Differences in skeletal muscle between men and women with chronic heart failure

Histological changes in skeletal muscle induced by heart failure in human patients and animal models: A scoping review

OBJECTIVE

This scoping review aimed to characterize the histological changes in skeletal muscle after heart failure (HF) and to identify gaps in knowledge.

METHODS

On April 03, 2024, systematic searches were performed for papers in which histological analyses were conducted on skeletal muscle sampled from patients with HF or animal models of HF. Screening and data extraction were conducted by two independent authors.

RESULTS AND CONCLUSION

A total of 118 papers were selected, including 33 human and 85 animal studies. Despite some disagreements among studies, some trends were observed. These trends included a slow-to-fast transition, a decrease in muscle fiber size, capillary to muscle fiber ratio, and mitochondrial activity and content, and an increase in apoptosis. These changes may contribute to the fatigability and decrease in muscle strength observed after HF. Although there were some disagreements between the results of human and animal studies, the results were generally similar. Animal models of HF will therefore be useful in elucidating the histological changes in skeletal muscle that occur in human patients with HF. Because the muscles subjected to histological analysis were mostly thigh muscles in humans and mostly lower leg muscles in animals, it remains uncertain whether changes similar to those seen in lower limb (hindlimb) muscles after HF also occur in upper limb (forelimb) muscles. The results of this review will consolidate the current knowledge on HF-induced histological changes in skeletal muscle and consequently aid in the rehabilitation of patients with HF and future studies.

Sex Differences in Skeletal Muscle Pathology in Patients With Heart Failure and Reduced Ejection Fraction

BACKGROUND

Women with heart failure and reduced ejection fraction (HFrEF) have greater symptoms and a lower quality of life compared with men; however, the role of noncardiac mechanisms remains poorly resolved. We hypothesized that differences in skeletal muscle pathology between men and women with HFrEF may explain clinical heterogeneity.

METHODS

Muscle biopsies from both men (n=22) and women (n=16) with moderate HFrEF (New York Heart Association classes I-III) and age- and sex-matched controls (n=18 and n=16, respectively) underwent transcriptomics (RNA-sequencing), myofiber structural imaging (histology), and molecular signaling analysis (gene/protein expression), with serum inflammatory profiles analyzed (enzyme-linked immunosorbent assay). Two-way ANOVA was conducted (interaction sex and condition).

RESULTS

RNA-sequencing identified 5629 differentially expressed genes between men and women with HFrEF, with upregulated terms for catabolism and downregulated terms for mitochondria in men. mRNA expression confirmed an effect of sex (P<0.05) on proatrophic genes related to ubiquitin proteasome, autophagy, and myostatin systems (higher in all men versus all women), whereas proanabolic IGF1 expression was higher (P<0.05) in women with HFrEF only. Structurally, women compared with men with HFrEF showed a pro-oxidative phenotype, with smaller but higher numbers of type I fibers, alongside higher muscle capillarity (Pinteraction<0.05) and higher type I fiber areal density (Pinteraction<0.05). Differences in gene/protein expression of regulators of muscle phenotype were detected between sexes, including HIF1α, ESR1, VEGF (vascular endothelial growth factor), and PGC1α expression (P<0.05), and for upstream circulating factors, including VEGF, IL (interleukin)-6, and IL-8 (P<0.05).

CONCLUSIONS

Sex differences in muscle pathology in HFrEF exist, with men showing greater abnormalities compared with women related to the transcriptome, fiber phenotype, capillarity, and circulating factors. These preliminary data question whether muscle pathology is a primary mechanism contributing to greater symptoms in women with HFrEF and highlight the need for further investigation.

Comparative analysis of health-related fitness in patients with acute versus chronic Chagas disease

INTRODUCTION

Although Chagas disease causes high levels of morbidity, the muscle function and tolerance to physical activity in Chagas disease patients are still not completely understood.

OBJECTIVE

To compare health-related fitness of patient groups with acute Chagas disease versus chronic Chagas disease.

MATERIALS AND METHODS

We conducted a cross-sectional study involving 18 patients. The data were obtained from patient´s records, and functional capacity was measured with the sixminute walk test, the peripheral muscle strength with handgrip strength, and respiratory muscle strength using the maximum inspiratory pressure and the maximum expiratory pressure.

RESULTS

The 18 patients were divided in two groups: acute Chagas disease (n=9) and chronic Chagas disease (n=9). The distance walked in the six-minute walk test was lower than the predicted distance walked in both groups (p < 0.0001). The maximum expiratory pressure was lower than the predicted one (p = 0.005), and statistically significant for chronic Chagas disease patients (p = 0.02). Heart rate increased faster in the chronic Chagas disease group within the first two minutes of the six-minute walk test (p = 0.04). The sixminute walk test in the acute Chagas disease group presented a strong correlation with peripheral muscle strength (p = 0.012) and maximum inspiratory pressure (p = 0.0142), while in the chronic Chagas disease group, only peripheral muscle strength and maximum inspiratory pressure were correlated (p = 0.0259).

CONCLUSION

The results suggest lowered functional capacity and reduced respiratory and peripheral muscle strength in patients with Chagas disease, although no differences were observed between groups. The early increase in heart rate during exercise in the chronic Chagas disease group implies a greater myocardial overload.

Divergent skeletal muscle mitochondrial phenotype between male and female patients with chronic heart failure

BACKGROUND

Previous studies in heart failure with reduced ejection fraction (HFrEF) suggest that skeletal muscle mitochondrial impairments are associated with exercise intolerance in men. However, the nature of this relationship in female patients remains to be elucidated. This study aimed to determine the relationship between skeletal muscle mitochondrial impairments and exercise intolerance in male and female patients with HFrEF.

METHODS

Mitochondrial respiration, enzyme activity, and gene expression were examined in pectoralis major biopsies from age-matched male (n = 45) and female (n = 11) patients with HFrEF and healthy-matched male (n = 24) and female (n = 11) controls. Mitochondrial variables were compared between sex and related to peak exercise capacity.

RESULTS

Compared with sex-matched controls, complex I mitochondrial oxygen flux was 17% (P = 0.030) and 29% (P = 0.013) lower in male and female patients with HFrEF, respectively, which correlated to exercise capacity (r = 0.71; P > 0.0001). Female HFrEF patients had a 32% (P = 0.023) lower mitochondrial content compared with controls. However, after adjusting for mitochondrial content, male patients demonstrated lower complex I function by 15% (P = 0.030). Expression of key mitochondrial genes regulating organelle dynamics and maintenance (i.e. optic atrophy 1, peroxisome proliferator-activated receptor γ coactivator-1α, NADH:ubiquinone oxidoreductase core subunit S1/S3, and superoxide dismutase 2) were selectively lower in female HFrEF patients.

CONCLUSIONS

These data provide novel evidence that HFrEF induces divergent sex-specific mitochondrial phenotypes in skeletal muscle that predispose towards exercise intolerance, impacting mitochondrial 'quantity' in female patients and mitochondrial 'quality' in male patients. Therapeutic strategies to improve exercise tolerance in HFrEF should consider targeting sex-specific mitochondrial abnormalities in skeletal muscle.

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

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

Skeletal muscle fiber characteristics in patients with chronic heart failure: impact of disease severity and relation with muscle oxygenation during exercise

INTRODUCTION

Skeletal muscle function in patients with heart failure and reduced ejection fraction (HFrEF) greatly determines exercise capacity. However, reports on skeletal muscle fiber dimensions, fiber capillarization, and their physiological importance are inconsistent.

METHODS

Twenty-five moderately-impaired patients with HFrEF and 25 healthy control (HC) subjects underwent muscle biopsy sampling. Type I and type II muscle fiber characteristics were determined by immunohistochemistry. In patients with HFrEF, enzymatic oxidative capacity was assessed, and pulmonary oxygen uptake (VO₂) and skeletal muscle oxygenation during maximal and moderate-intensity exercise were measured using near-infrared spectroscopy.

RESULTS

While muscle fiber cross-sectional area (CSA) was not different between patients with HFrEF and HC, percentage of type I fibers was higher in HC (46±15% versus 37±12%, respectively, P=0.041). Fiber type distribution and CSA were not different between patients in New York Heart Association (NYHA) class II and III. Type I muscle fiber capillarization was higher in HFrEF compared with controls (capillary-to-fiber perimeter exchange (CFPE) index: 5.70±0.92 versus 5.05±0.82, respectively, P=0.027). Patients in NYHA class III had slower VO₂ and muscle deoxygenation kinetics during onset of exercise, and lower muscle oxidative capacity than those in class II (P<0.05). Also, fiber capillarization was lower, but not compared with HC. Higher CFPE index was related to faster deoxygenation (r_spearman=-0.682, P=0.001), however, not to muscle oxidative capacity (r=-0.282, P=0.216).

CONCLUSIONS

Type I muscle fiber capillarization is higher in HFrEF compared with HC, but not in patients with greater exercise impairment. Greater capillarization may positively affect VO₂ kinetics by enhancing muscle oxygen diffusion.

Skeletal muscle abnormalities and exercise intolerance in older patients with heart failure and preserved ejection fraction

Heart failure (HF) with preserved ejection fraction (HFPEF) is the most common form of HF in older persons. The primary chronic symptom in HFPEF is severe exercise intolerance, and its pathophysiology is poorly understood. To determine whether skeletal muscle abnormalities contribute to their severely reduced peak exercise O2 consumption (Vo2), we examined 22 older HFPEF patients (70 ± 7 yr) compared with 43 age-matched healthy control (HC) subjects using needle biopsy of the vastus lateralis muscle and cardiopulmonary exercise testing to assess muscle fiber type distribution and capillarity and peak Vo2. In HFPEF versus HC patients, peak Vo2 (14.7 ± 2.1 vs. 22.9 ± 6.6 ml·kg(-1)·min(-1), P < 0.001) and 6-min walk distance (454 ± 72 vs. 573 ± 71 m, P < 0.001) were reduced. In HFPEF versus HC patients, the percentage of type I fibers (39.0 ± 11.4% vs. 53.7 ± 12.4%, P < 0.001), type I-to-type II fiber ratio (0.72 ± 0.39 vs. 1.36 ± 0.85, P = 0.001), and capillary-to-fiber ratio (1.35 ± 0.32 vs. 2.53 ± 1.37, P = 0.006) were reduced, whereas the percentage of type II fibers was greater (61 ± 11.4% vs. 46.3 ± 12.4%, P < 0.001). In univariate analyses, the percentage of type I fibers (r = 0.39, P = 0.003), type I-to-type II fiber ratio (r = 0.33, P = 0.02), and capillary-to-fiber ratio (r = 0.59, P < 0.0001) were positively related to peak Vo2. In multivariate analyses, type I fibers and the capillary-to-fiber ratio remained significantly related to peak Vo2. We conclude that older HFPEF patients have significant abnormalities in skeletal muscle, characterized by a shift in muscle fiber type distribution with reduced type I oxidative muscle fibers and a reduced capillary-to-fiber ratio, and these may contribute to their severe exercise intolerance. This suggests potential new therapeutic targets in this difficult to treat disorder.

Skeletal muscle abnormalities in chronic heart failure

Skeletal muscle abnormalities are well-established in patients with heart failure from an early stage in the progression of the disease and contribute to their symptoms and the limitation of physical activity. Heart failure-induced skeletal muscle pathology includes morphologic, histologic, and enzymatic changes along with derangements in skeletal muscle metabolism and autonomic function. These alterations influence both peripheral and ventilatory muscles, are present at rest, and deteriorate during exercise and their occurrence depends upon the severity and the duration of CHF syndrome. Future studies will be needed to elucidate the origin of skeletal "myopathy" and its reversibility, which is associated with improvement in exercise capacity, observed after physical training programs.

Chronic heart failure and exercise intolerance: the hemodynamic paradox

Heart failure represents a major source of morbidity and mortality in industrialized nations. As the leading hospital discharge diagnosis in the United States in patients over the age of 65, it is also associated with substantial economic costs. While the acute symptoms of volume overload frequently precipitate inpatient admission, it is the symptoms of chronic heart failure, including fatigue, exercise intolerance and exertional dyspnea, that impact quality of life. Over the last two decades, research into the enzymatic, histologic and neurohumoral alterations seen with heart failure have revealed that hemodynamic derangements do not necessarily correlate with symptoms. This “hemodynamic paradox” is explained by alterations in the skeletal musculature that occur in response to hemodynamic derangements. Importantly, gender specific effects appear to modify both disease pathophysiology and response to therapy. The following review will discuss our current understanding of the systemic effects of heart failure before examining how exercise training and cardiac resynchronization therapy may impact disease course.

Cardiovascular sex differences influencing microvascular exchange

The vital role of the cardiovascular (CV) system is maintenance of body functions via the matching of exchange to tissue metabolic demand. Sex-specific differences in the regulatory mechanisms of CV function and the metabolic requirements of men and women, respectively, have been identified and appreciated. This review focuses on sex differences of parameters influencing exchange at the point of union between blood and tissue, the microvasculature. Microvascular architecture, blood pressure (hydrostatic and oncotic), and vascular permeability, therefore, are discussed in the specific context of sex in health and disorders. It is notable that when sex differences exist, they are generally subtle but significant. In the aggregate, though, they can give rise to profoundly different phenotypes. The postulated mechanisms responsible for sex differences are attributed to genomics, epigenetics, and sex hormones. Depending on specific circumstances, the effect of the combined factors can range from insignificant to lethal. Identifying and understanding key signalling mechanisms bridging genomics/sex hormones and microvascular exchange properties within the scope of this review holds significant promise for sex-specific prevention and treatment of vascular barrier dysfunction.

Sex differences in global mRNA content of human skeletal muscle

Women oxidize more fat as compared to men during endurance exercise and several groups have shown that the mRNA content of selected genes related to fat oxidation are higher in women (e.g. hormone sensitive lipase, β-hydroxyacyl-CoA dehydrogenase, CD36). One of the possible mechanisms is that women tend to have a higher area percentage of type I skeletal muscle fibers as compared with men. Consequently, we hypothesized that sex would influence the basal mRNA and protein content for genes involved in metabolism and the determination of muscle fiber type. Muscle biopsies from the vastus lateralis were collected from healthy men and women. We examined mRNA content globally using Affymetrix GeneChips, and selected genes were examined and/or confirmed by RT-PCR. Furthermore, we examined protein content by Western blot analysis. Stringent gene array analysis revealed 66 differentially expressed genes representing metabolism, mitochondrial function, transport, protein biosynthesis, cell proliferation, signal transduction pathways, transcription and translation. Stringent gene array analysis and RT-PCR confirmed that mRNA for; acyl-coenzyme A acyltransferase 2 (ACAA2), trifunctional protein β (HADHB), catalase, lipoprotein lipase (LPL), and uncoupling protein-2 (UCP-2) were higher in women. Targeted gene analysis revealed that myosin heavy chain I (MHCI), peroxisome proliferator-activated receptor (PPAR)δ were higher in women compared with men. Surprisingly, there were no significant sex based differences in protein content for HADHB, ACAA2, catalase, PPARδ, and MHC1. In conclusion, the differences in the basal mRNA content in resting skeletal muscle suggest that men and women are transcriptionally “primed” for known physiological differences in metabolism however the mechanism behind sex differences in fiber type remains to be determined.

Effect of exercise intensity and volume on persistence of insulin sensitivity during training cessation

The purpose of this study was to determine whether exercise prescriptions differing in volume or intensity also differ in their ability to retain insulin sensitivity during an ensuing period of training cessation. Sedentary, overweight/obese subjects were assigned to one of three 8-mo exercise programs: 1) low volume/moderate intensity [equivalent of approximately 12 miles/wk, 1,200 kcal/wk at 40-55% peak O(2) consumption (Vo(2peak)), 200 min exercise/wk], 2) low volume/vigorous intensity ( approximately 12 miles/wk, 1,200 kcal/wk at 65-80% Vo(2peak), 125 min/wk), and 3) high volume/vigorous intensity ( approximately 20 miles/wk, 2,000 kcal/wk at 65-80% Vo(2peak), 200 min/wk). Insulin sensitivity (intravenous glucose tolerance test, S(I)) was measured when subjects were sedentary and at 16-24 h and 15 days after the final training bout. S(I) increased with training compared with the sedentary condition (P < or = 0.05) at 16-24 h with all of the exercise prescriptions. S(I) decreased to sedentary, pretraining values after 15 days of training cessation in the low-volume/vigorous-intensity group. In contrast, at 15 days S(I) was significantly elevated compared with sedentary (P < or = 0.05) in the prescriptions utilizing 200 min/wk (low volume/moderate intensity, high volume/vigorous intensity). In the high-volume/vigorous-intensity group, indexes of muscle mitochondrial density followed a pattern paralleling insulin action by being elevated at 15 days compared with pretraining; this trend was not evident in the low-volume/moderate-intensity group. These findings suggest that in overweight/obese subjects a relatively chronic persistence of enhanced insulin action may be obtained with endurance-oriented exercise training; this persistence, however, is dependent on the characteristics of the exercise training performed.

Relationship of physical function to vastus lateralis capillary density and metabolic enzyme activity in elderly men and women

BACKGROUND AND AIMS

There are no data showing whether or not age-related declines in physical function are related to in vitro properties of human skeletal muscle. The purpose of this study was to determine whether physical function is independently associated with histologic and metabolic properties of skeletal muscle in elderly adults.

METHODS

The study was a cross-sectional observational study of 39 sedentary, older (60-85 yrs) men and women. A needle biopsy of the vastus lateralis for assessment of muscle fiber type, fiber area, capillary density and citrate synthase and aldolase activities was performed. Physical function tests included the Short Physical Performance Battery (balance, walking speed, and chair rise time), as well as self-reported disability.

RESULTS

Total fiber area (R=-0.41, p=0.02), number of Type II fibers (R=-0.33, p=0.05), and aldolase activity (R=-0.54, p=0.01) were inversely related to age. Persons who reported greater difficulty with daily activities had lower capillary density (R=-0.51, p=0.03) and lower citrate synthase activity (R=-0.66, p=0.03). Walking speed was directly related to fiber area (R=0.40, p=0.02), capillary density (R=0.39, p=0.03), citrate synthase (R=0.45, p=0.03) and aldolase (R=0.55, p<0.01) activities, even after adjustment for age, BMI and disease status.

CONCLUSIONS

In older adults, skeletal muscle capillary density and metabolic enzymatic activity are independent predictors of lower extremity physical function.

Increased levels of apoptosis in gastrocnemius skeletal muscle in patients with peripheral arterial disease

Intermittent claudication (IC) is the major clinical manifestation of peripheral arterial disease (PAD). Apoptosis has been linked to skeletal muscle pathophysiology in other chronic diseases such as congestive heart failure. This study tested the hypothesis that there would be increased levels of apoptosis in the skeletal muscle of patients with PAD compared with control individuals. In total, 26 individuals with PAD and 28 age-appropriate controls underwent studies of peak oxygen consumption (peak VO2) and a gastrocnemius muscle biopsy in the most symptomatic leg. Muscle biopsies were analyzed for apoptosis and caspase-3 activity. Patients with PAD had a reduced peak VO2 compared with controls. Apoptosis was increased in those with PAD compared with age-appropriate controls (3.83% +/- 2.6 vs 1.53% +/- 0.96; p < 0.001). In conclusion, PAD is associated with increased levels of apoptosis in the peripheral skeletal muscle. Further study is required to ascertain whether apoptosis plays a role in decreased functional capacity.

Implications of chronic heart failure on peripheral vasculature and skeletal muscle before and after exercise training

The pathophysiology of chronic heart failure (CHF) is typically conceptualized in terms of cardiac dysfunction. However, alterations in peripheral blood flow and intrinsic skeletal muscle properties are also now recognized as mechanisms for exercise intolerance that can be modified by therapeutic exercise. This overview focuses on blood delivery, oxygen extraction and utilization that result from heart failure. Related features of inflammation, changes in skeletal muscle signaling pathways, and vulnerability to skeletal muscle atrophy are discussed. Specific focus is given to the ways in which perfusion and skeletal muscle properties affect exercise intolerance and how peripheral improvements following exercise training increase aerobic capacity. We also identify gaps in the literature that may constitute priorities for further investigation.

Long-term prognostic value of peak oxygen consumption in women versus men with heart failure and severely impaired left ventricular systolic function

Although peak oxygen consumption (VO(2)) during exercise is frequently used to help predict optimal timing for heart transplantation, its long-term prognostic value in women is not known. We followed 2,105 adult patients with heart failure (HF) and with impaired left ventricular (LV) systolic function for 5 years, including 525 women (25%) who underwent metabolic stress testing between January 1995 and December 2002. Multivariable proportional hazards modeling related VO(2) to survival with adjustments for >30 confounders and with transplantation considered as a time-dependent covariate. During follow-up, 129 women (26%) died, as did 572 men (36%). There were 175 transplants, including 34 women. Women and men were similar in age (54 vs 55 years), but women were less likely to have coronary artery disease (28% vs 58%). Peak VO(2) was strongly predictive of time to death in women (adjusted hazard ratio [HR] for peak VO(2) decreasing from 15 to 14 ml/kg/min, 1.11, 95% confidence interval [CI] 1.05 to 1.18, p <0.0001) and in men (adjusted HR 1.12, 95% CI 1.08 to 1.16, p <0.0001). There was no gender interaction with peak VO(2) (p = 0.80), but for any given peak VO(2) women were at lower risk (adjusted HR for men compared with women 2.22, 95% CI 1.58 to 3.10, p <0.0001). A significant interaction was found between gender and presence of coronary artery disease (p for interaction 0.02); in women, those with ischemic cardiomyopathy had a worse survival for any given peak VO(2). In conclusion, in this large cohort, peak VO(2) predicted survival in women and men whether or not coronary artery disease was present, but an interaction was noted between coronary artery, gender, and survival.

Oxidative phenotype protects myofibers from pathological insults induced by chronic heart failure in mice

The fiber specificity of skeletal muscle abnormalities in chronic heart failure (CHF) has not been defined. We show here that transgenic mice (8 weeks old) with cardiac-specific overexpression of calsequestrin developed CHF (50.9% decrease in fractional shortening and 56.4% increase in lung weight, P<0.001), cachexia (37.8% decrease in body weight, P<0.001), and exercise intolerance (69.3% decrease in running distance to exhaustion, P<0.001) without a significant change in muscle fiber-type composition. Slow oxidative soleus muscle maintained muscle mass, whereas fast glycolytic tibialis anterior and plantaris muscles underwent atrophy (11.6 and 13.3%, respectively; P<0.05). In plantaris muscle, glycolytic type IId/x and IIb, but not oxidative type I and IIa, fibers displayed significant decreases in cross-sectional area (20.3%, P<0.05). Fast glycolytic white vastus lateralis muscle showed sarcomere degeneration and decreased cytochrome c oxidase IV (39.5%, P<0.01) and peroxisome proliferator-activated receptor gamma co-activator 1alpha protein expression (30.3%, P<0.01) along with a dramatic induction of the MAFbx/Atrogin-1 mRNA. These findings suggest that exercise intolerance can occur in CHF without fiber type switching in skeletal muscle and that oxidative phenotype renders myofibers resistant to pathological insults induced by CHF.

Oxidative stress of myosin contributes to skeletal muscle dysfunction in rats with chronic heart failure

Intrinsic muscle abnormalities affecting skeletal muscle are often reported during chronic heart failure (CHF). Because myosin is the molecular motor of force generation, we sought to determine whether its dysfunction contributes to skeletal muscle weakness in CHF and, if so, to identify the underlying causative factors. Severe CHF was induced in rats by aortic stenosis. In diaphragm and soleus muscles, we investigated in vitro mechanical performance, myosin-based actin filament motility, myosin heavy (MHC) and light (MLC) chain isoform compositions, MLC integrity, caspase-3 activation, and oxidative damage. Diaphragm and soleus muscles from CHF exhibited depressed mechanical performance. Myosin sliding velocities were 16 and 20% slower in CHF than in sham in diaphragm (1.9 ± 0.1 vs. 1.6 ± 0.1 μm/s) and soleus (0.6 ± 0.1 vs. 0.5 ± 0.1 μm/s), respectively (each P < 0.05). The ratio of slow-to-fast myosin isoform did not differ between sham and CHF. Immunoblots with anti-MLC antibodies did not detect the presence of protein fragments, and no activation of caspase-3 was evidenced. Immunolabeling revealed oxidative damage in CHF muscles, and MHC was the main oxidized protein. Lipid peroxidation and expression of oxidized MHC were significantly higher in CHF than in shams. In vitro myosin exposure to increasing ONOO−concentrations was associated with an increasing amount of oxidized MHC and a reduced myosin velocity. These data provide experimental evidence that intrinsic myosin dysfunction occurs in CHF and may be related to oxidative damage to myosin.

Role of Gender in Heart Failure with Normal Left Ventricular Ejection Fraction

Heart failure with normal ejection fraction (HF-NEF) is frequently believed to be more common in women than in men. However, the interaction of gender and age has rarely been analyzed in detail, and knowledge of the distinction between pre- and postmenopausal women is lacking. Some of the studies that have described a higher prevalence of HF-NEF in women relied on clinical diagnoses of HF together with normal systolic function and did not measure diastolic function. This applies to the analysis of patients hospitalized for HF and some epidemiological investigations that agree on the greater prevalence of HF-NEF in women. Population-based studies with echocardiographic determination of diastolic function have suggested equal or greater prevalence of diastolic dysfunction in men. Major risk factors for HF-NEF include hypertension, aging, obesity, diabetes, and ischemia. Hypertension is more frequent in women and can contribute to left ventricular and arterial stiffening in a gender-specific way. Aging, obesity, and diabetes affect myocardial and vascular stiffness differently and lead to different forms of myocardial hypertrophy in women and men. In contrast, ischemia may play a greater role in men. Gender differences in ventricular diastolic distensibility, in vascular stiffness and ventricular/vascular coupling, in skeletal muscle adaptation to HF, and in the perception of symptoms may contribute to a greater rate of HF-NEF in women. The underlying molecular mechanisms include gender differences in calcium handling, in the NO system, and in natriuretic peptides. Estrogen affects collagen synthesis and degradation and inhibits the renin-angiotensin system. Effects of estrogen may provide benefit to premenopausal women, and the loss of its protective mechanisms may render the heart of postmenopausal women more vulnerable. Thus, a number of molecular mechanisms can contribute to the gender differences in HF-NEF.

The influence of sex on right ventricular dysfunction in patients with severely depressed left ventricular ejection fraction

AIM

To assess the influence of sex on right ventricular dysfunction (RVD) in patients with severe left ventricular systolic dysfunction.

METHODS AND RESULTS

We studied 385 consecutive patients with left ventricular ejection fraction (LVEF) <0.35. All patients underwent invasive measurement of right ventricular and pulmonary artery pressures and evaluation of RVD by standard transthoracic echocardiography. Female patients (n=84, 21.8%) were significantly older than male patients (62.0+/-11.4 vs. 58.2+/-10.7 years), p=0.005. The prevalence of RVD was lower in women (26.5%) than in men (38.9%), p=0.03; both in patients with and without coronary artery disease (19.4% vs. 34.5% and 31.9% vs. 44.4%, respectively). Haemodynamic parameters and LVEF were similar in men and women. Low LVEF, pulmonary systolic pressure, degree of mitral regurgitation, male sex, and absence of significant coronary artery disease were independently correlated with RVD.

CONCLUSION

Women with severe left ventricular systolic dysfunction have less RVD than men, despite similar haemodynamic parameters and LVEF.

Sex differences in respiratory exercise physiology

Respiratory exercise physiology research has historically focused on male subjects. In the last 20 years, important physiological and functional differences have been noted between the male and female response to dynamic exercise where sex differences have been reported for most of the major determinants of exercise capacity. Female participation in competitive and recreational sport is growing worldwide and it is universally accepted that participation in regular physical activity is of health benefit for both sexes. Understanding sex differences is of potential importance to both the clinician-scientist and the exercise physiologist since differences could impact upon exercise rehabilitation programmes for patient populations, exercise prescription for disease prevention in healthy individuals and training strategies for competitive athletes. Sex differences have been shown in resting pulmonary function, which may impact on the respiratory response to exercise. Women typically have smaller lung volumes and maximal expiratory flow rates even when corrected for height relative to men. Differences in resting and exercising ventilation across the menstrual cycle and relative to men have also been reported, although the functional significance remains unclear. Expiratory flow limitation and a high work of breathing are seen in women. Pulmonary system limitations, in particular exercise-induced arterial hypoxia, have been reported in both men and women; however, the prevalence in women is not yet known. From the available literature, it appears that there are sex differences in some areas of respiratory exercise physiology. However, detailed sex comparisons are difficult because the number of subjects studied to date has been woefully small.

Reduced exercise tolerance in CHF may be related to factors other than impaired skeletal muscle oxidative capacity

BACKGROUND

We sought to determine whether skeletal muscle oxidative capacity, fiber type proportions, and fiber size, capillary density or muscle mass might explain the impaired exercise tolerance in chronic heart failure (CHF). Previous studies are equivocal regarding the maladaptations that occur in the skeletal muscle of patients with CHF and their role in the observed exercise intolerance. Methods and results Total body O(2) uptake (VO(2peak)) was determined in 14 CHF patients and 8 healthy sedentary similar-age controls. Muscle samples were analyzed for mitochondrial adenosine triphosphate (ATP) production rate (MAPR), oxidative and glycolytic enzyme activity, fiber size and type, and capillary density. CHF patients demonstrated a lower VO(2peak) (15.1+/-1.1 versus 28.1+/-2.3 mL.kg(-1).min(-1), P<.001) and capillary to fiber ratio (1.09+/-0.05 versus 1.40+/-0.04; P<.001) when compared with controls. However, there was no difference in capillary density (capillaries per square millimeter) across any of the fiber types. Measurements of MAPR and oxidative enzyme activity suggested no difference in muscle oxidative capacity between the groups.

CONCLUSIONS

Neither reductions in muscle oxidative capacity nor capillary density appear to be the cause of exercise limitation in this cohort of patients. Therefore, we hypothesize that the low VO(2peak) observed in CHF patients may be the result of fiber atrophy and possibly impaired activation of oxidative phosphorylation.

Physiology of the abnormal response of heart failure patients to exercise

Chronic heart failure is associated with reduced exercise capacity. Altered diastolic function and reduced chronotropic response play an important role. However, there is no clear correlation between any hemodynamic parameter and exercise capacity. Peripheral factors, long overlooked, seem to play a major role. Altered peripheral vasodilatation, involving endothelial abnormalities, alters the optimal distribution of blood flow. Muscular abnormalities are constant: aside from muscle atrophy, altered muscle metabolism results in an altered utilization of oxygen. A comprehensive understanding of all these determinants of exercise response is important to optimize the care of the patient. Sole improvement of cardiac function may be insufficient to correct their exercise intolerance; regular training may well have beneficial effects on exercise capacity, functional impairment, and quality of life.

Exercise Performance and Skeletal Muscles in Patients With Advanced Chagas Disease

STUDY OBJECTIVE

This study was designed to evaluate the peripheral muscle metabolic and structural characteristics in patients with advanced Chagas disease (ChD), and whether they were related with exercise performance.

DESIGN

Cross-sectional study.

SETTING

Outpatient cardiomyopathy clinic of a university hospital.

PATIENTS AND METHODS

We studied 11 stage II patients, 8 stage III patients, and 11 healthy volunteers. All patients underwent exercise testing and peripheral muscle biopsies. The muscles were also studied in control subjects. Muscle biopsy specimens were analyzed for histochemical characteristics. In six patients, the muscle was studied ultrastructurally.

RESULTS

The data demonstrate more glycolytic and less oxidative capacity of the peripheral muscle in patients with advanced ChD (increased proportion of type IIb fibers, increased proportion of fibers with low nicotinamide adenine dinucleotide diaphorase activity, high proportion of darkly stained fibers for alpha-glycerophosphate dehydrogenase activity, and lower levels of citrate synthase). Many capillaries in patients with ChD had an abnormal aspect: they were either closed or showed a thicker wall. The ultrastructural study also showed fiber atrophy and abnormal capillaries even in patients with normal functional capacity. Some muscle characteristics (enzyme activity, mean cross-sectional area of the fiber, and capillarity) related with exercise parameters (anaerobic threshold, and peak oxygen pulse).

CONCLUSIONS

These findings indicate that patients with advanced ChD have decreased oxidative capacity and a shift to anaerobic metabolism in the skeletal muscle. They also suggest that muscular abnormalities are related to oxygen delivery, which is probably reduced in part by the abnormal muscle microvasculature. Those changes could affect oxygen extraction, and therefore exercise tolerance in these patients.

Therapeutic exercise for individuals with heart failure: special attention to older women with heart failure

BACKGROUND

A cardinal feature of heart failure (HF) is the reduced peak aerobic power (VO(2peak)) secondary to alterations in cardiovascular and musculoskeletal function. Methods and results During the last decade, a number of randomized trials have examined the role that exercise training plays in attenuating the HF-mediated decline in VO(2peak) and muscle strength. The major finding of these investigations was that aerobic or strength training was an effective intervention to increase VO(2peak), muscular strength, distance walked in 6 minutes, and quality of life without negatively altering left ventricular systolic function. Despite these benefits, a limitation of these investigations was the primary focus on males <60 years with impaired left ventricular systolic function. Thus the role that exercise training may play in attenuating the HF-mediated decline in VO(2peak) in women > or =65 years of age remains unknown.

CONCLUSION

Older women with HF have a VO(2peak) that is below the minimal threshold level required for independent living. Moreover, older women with HF have greater disability then men and are less likely to be referred to an exercise rehabilitation program. Accordingly, future exercise intervention trials are required to examine the role that exercise training may play in attenuating the HF-mediated decline in cardiorespiratory and musculoskeletal fitness and disability in older women with HF.

Mechanisms of exercise training in patients with heart failure

BACKGROUND

The reduction of exercise capacity because of fatigue and dyspnea in patients with heart failure can be improved with exercise training. We sought to examine the mechanisms of exercise training as an adjunctive treatment strategy for patients with heart failure.

METHODS

We reviewed the published data on the possible mechanisms of effect of exercise training in heart failure.

RESULTS

Symptoms of heart failure may be explained on the basis of abnormal skeletal muscle perfusion and structure and endothelial function. Exercise training has been shown to engender changes in muscle structure and biochemistry and vascular function, although effects on cardiac function have not been detected uniformly and may require longer training periods.

CONCLUSIONS

A suitable, long-term program of exercise training may reverse unfavorable interactions among the heart, vessels, and skeletal muscles. These improvements may be preserved with an ongoing maintenance program.

Differential effects of exercise training in men and women with chronic heart failure

BACKGROUND

Abnormalities of myosin heavy chain (MHC) isoforms, enzyme activity, and capillarity contribute to the exercise intolerance that is characteristic of patients with heart failure. To what extent these changes can be reversed with exercise training and whether differences exist in the responses of men and women remains uncertain. We described and compared the effects of exercise training on exercise capacity and skeletal muscle histochemistry in men and women with chronic heart failure.

METHODS

Fifteen patients (10 male) undergoing standard medical therapy completed a 14- to 24-week exercise training program. Peak oxygen consumption, MHC isoforms, capillary density, and selected metabolic enzymes were assessed before and after training.

RESULTS

Peak oxygen consumption was improved 14% (P <.05); however, this increase was mostly because of the improvement observed in men versus women (+20% versus +2%, respectively, P <.01). At baseline, MHC I content was lower in men than in women (33% +/- 3% vs 49.6% +/- 5.5%, P <.05). MHC I improved with training in men, to 45.6% +/- 4.5% (+38%, P <.05), versus women (-3%, P =.82), and the increase in men tended (P =.12) to be significant when compared with that in women. There were no significant changes in capillary density or muscle enzyme activity with training in the group as a whole or in men and women separately.

CONCLUSION

Among patients with chronic heart failure, improvements in peak exercise capacity may be more pronounced in men than in women. This difference in response of functional capacity to training paralleled differences observed between men and women for changes in MHC I isoforms.

Sex-based differences in the effect of digoxin for the treatment of heart failure

BACKGROUND

The Digitalis Investigation Group trial reported that treatment with digoxin did not decrease overall mortality among patients with heart failure and depressed left ventricular systolic function, although it did reduce hospitalizations slightly. Even though the epidemiologic features, causes, and prognosis of heart failure vary between men and women, sex-based differences in the effect of digoxin were not evaluated.

METHODS

We conducted a post hoc subgroup analysis to assess whether there were sex-based differences in the effect of digoxin therapy among the 6800 patients in the Digitalis Investigation Group study. The presence of an interaction between sex and digoxin therapy with respect to the primary end point of death from any cause was evaluated with the use of Mantel-Haenszel tests of heterogeneity and a multivariable Cox proportional-hazards model, adjusted for demographic and clinical variables.

RESULTS

There was an absolute difference of 5.8 percent (95 percent confidence interval, 0.5 to 11.1) between men and women in the effect of digoxin on the rate of death from any cause (P=0.034 for the interaction). Specifically, women who were randomly assigned to digoxin had a higher rate of death than women who were randomly assigned to placebo (33.1 percent vs. 28.9 percent; absolute difference, 4.2 percent, 95 percent confidence interval, -0.5 to 8.8). In contrast, the rate of death was similar among men randomly assigned to digoxin and men randomly assigned to placebo (35.2 percent vs. 36.9 percent; absolute difference, -1.6 percent; 95 percent confidence interval, -4.2 to 1.0). In the multivariable analysis, digoxin was associated with a significantly higher risk of death among women (adjusted hazard ratio for the comparison with placebo, 1.23; 95 percent confidence interval, 1.02 to 1.47), but it had no significant effect among men (adjusted hazard ratio, 0.93; 95 percent confidence interval, 0.85 to 1.02; P=0.014 for the interaction).

CONCLUSIONS

The effect of digoxin therapy differs between men and women. Digoxin therapy is associated with an increased risk of death from any cause among women, but not men, with heart failure and depressed left ventricular systolic function.

Deconditioning fails to explain peripheral skeletal muscle alterations in men with chronic heart failure

It remains controversial whether the skeletal muscle alterations in chronic heart failure (CHF) are due to disease pathophysiology or result from chronic deconditioning. The purpose of this study was to compare the skeletal muscle of CHF patients to peak oxygen consumption (peak VO(2)) matched sedentary controls. It has been established that skeletal muscle abnormalities are related to the exercise intolerance observed in patients with CHF. We studied the skeletal muscle of sedentary controls and patients with CHF matched for age, gender and peak VO(2). Hypothesis testing for the effects of group (CHF vs. normal), gender, and the interaction group x gender were performed. For capillary density only gender (p = 0.002) and the interaction of group x gender (p = 0.007) were significantly different. For 3-hydroxyl coenzyme A (CoA) dehydrogenase only group effect (p = 0.004) was significantly different. Mean values for capillary density were 1.46 +/- 0.28 for CHF men versus 1.87 +/- 0.32 for sedentary control men, 1.40 +/- 0.32 for CHF women versus 1.15 +/- 0.35 for sedentary control women. The activities for 3-hydroxyl CoA dehydrogenase were 3.09 +/- 0.88 for CHF men versus 4.05 +/- 0.42 for sedentary control men, 2.93 +/- 0.72 for CHF women versus 3.51 +/- 0.78 for sedentary control women. This study suggests that women and men adapt to CHF differently: men develop peripheral skeletal muscle abnormalities that are not attributable to deconditioning; women do not develop the same pathologic responses in skeletal muscle when compared with normal women matched for aerobic capacity.