Effects of erythropoietin on muscle O2 transport during exercise in patients with chronic renal failure

Hemodynamic and neuromuscular basis of reduced exercise capacity in patients with end-stage renal disease

PURPOSE

The present study aimed to characterize the exercise-induced neuromuscular fatigue and its possible links with cerebral and muscular oxygen supply and utilization to provide mechanistic insights into the reduced exercise capacity characterizing patients with end-stage renal disease (ESRD).

METHODS

Thirteen patients with ESRD and thirteen healthy males (CTR group) performed a constant-force sustained isometric contraction at 50% of their maximal voluntary isometric contraction (MVC) until exhaustion. Quadriceps muscle activation during exercise was estimated from vastus lateralis, vastus medialis, and rectus femoris EMG. Central and peripheral fatigue were quantified via changes in pre- to postexercise quadriceps voluntary activation (ΔVA) and quadriceps twitch force (ΔQtw,pot) evoked by supramaximal electrical stimulation, respectively. To assess cerebral and muscular oxygenation, throughout exercise, near-infrared spectroscopy allowed investigation of changes in oxyhemoglobin (∆O2Hb), deoxyhemoglobin (∆HHb), and total hemoglobin (∆THb) in the prefrontal cortex and in the vastus lateralis muscle.

RESULTS

ESRD patients demonstrated lower exercise time to exhaustion than that of CTR (88.8 ± 15.3 s and 119.9 ± 14.6 s, respectively, P < 0.01). Following the exercise, MVC, Qtw,pot, and VA reduction were similar between the groups (P > 0.05). There was no significant difference in muscle oxygenation (∆O2Hb) between the two groups (P > 0.05). Cerebral and muscular blood volume (∆THb) and oxygen extraction (∆HHb) were significantly blunted in the ESRD group (P < 0.05). A significant positive correlation was observed between time to exhaustion and cerebral blood volume (∆THb) in both groups (r2 = 0.64, P < 0.01).

CONCLUSIONS

These findings support cerebral hypoperfusion as a factor contributing to the reduction in exercise capacity characterizing ESRD patients.

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

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

Exercise for patients with chronic kidney disease: from cells to systems to function

Chronic kidney disease (CKD) is among the leading causes of death and disability, affecting an estimated 800 million adults globally. The underlying pathophysiology of CKD is complex creating challenges to its management. Primary risk factors for the development and progression of CKD include diabetes mellitus, hypertension, age, obesity, diet, inflammation, and physical inactivity. The high prevalence of diabetes and hypertension in patients with CKD increases the risk for secondary consequences such as cardiovascular disease and peripheral neuropathy. Moreover, the increased prevalence of obesity and chronic levels of systemic inflammation in CKD have downstream effects on critical cellular functions regulating homeostasis. The combination of these factors results in the deterioration of health and functional capacity in those living with CKD. Exercise offers protective benefits for the maintenance of health and function with age, even in the presence of CKD. Despite accumulating data supporting the implementation of exercise for the promotion of health and function in patients with CKD, a thorough description of the responses and adaptations to exercise at the cellular, system, and whole body levels is currently lacking. Therefore, the purpose of this review is to provide an up-to-date comprehensive review of the effects of exercise training on vascular endothelial progenitor cells at the cellular level; cardiovascular, musculoskeletal, and neural factors at the system level; and physical function, frailty, and fatigability at the whole body level in patients with CKD.

Muscle oxygen supply impairment during maximal exercise in patients undergoing dialysis therapy

This study aimed to investigate whether Chronic Kidney Disease (CKD) influences O2 supply including O2 delivery and release to the active muscles during maximal physical exercise. Twelve CKD patients undergoing dialysis therapy (HD group) and twelve healthy adults (CTR group) performed an incremental exercise test to determine maximal oxygen uptake (VO2peak). Throughout the exercise, near-infrared spectroscopy allowed the investigation of changes in oxyhemoglobin (∆O2Hb), deoxyhemoglobin (∆HHb), and total hemoglobin (∆THb) in the vastus lateralis muscle. VO2peak was significantly lower in HD group. In addition, HD patients had impaired changes in muscular oxygenation (∆HHb and ∆O2Hb) and blood volume (∆THb) during the exercise (p < 0.05). Moreover, a positive correlation was observed between VO2peak and muscle blood volume (∆THb) in both groups (p < 0.05). This study provides the first evidence that HD patients displayed lower VO2peak and blunted muscular deoxyhemoglobin increase during exercise. This result supports the hypothesis of an increase in oxygen affinity and/or mitochondrial dysfunction in this population.

The relationship between hemoglobin and [Formula: see text]: A systematic review and meta-analysis

OBJECTIVE

There is widespread agreement about the key role of hemoglobin for oxygen transport. Both observational and interventional studies have examined the relationship between hemoglobin levels and maximal oxygen uptake ([Formula: see text]) in humans. However, there exists considerable variability in the scientific literature regarding the potential relationship between hemoglobin and [Formula: see text]. Thus, we aimed to provide a comprehensive analysis of the diverse literature and examine the relationship between hemoglobin levels (hemoglobin concentration and mass) and [Formula: see text] (absolute and relative [Formula: see text]) among both observational and interventional studies.

METHODS

A systematic search was performed on December 6th, 2021. The study procedures and reporting of findings followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Article selection and data abstraction were performed in duplicate by two independent reviewers. Primary outcomes were hemoglobin levels and [Formula: see text] values (absolute and relative). For observational studies, meta-regression models were performed to examine the relationship between hemoglobin levels and [Formula: see text] values. For interventional studies, meta-analysis models were performed to determine the change in [Formula: see text] values (standard paired difference) associated with interventions designed to modify hemoglobin levels or [Formula: see text]. Meta-regression models were then performed to determine the relationship between a change in hemoglobin levels and the change in [Formula: see text] values.

RESULTS

Data from 384 studies (226 observational studies and 158 interventional studies) were examined. For observational data, there was a positive association between absolute [Formula: see text] and hemoglobin levels (hemoglobin concentration, hemoglobin mass, and hematocrit (P<0.001 for all)). Prespecified subgroup analyses demonstrated no apparent sex-related differences among these relationships. For interventional data, there was a positive association between the change of absolute [Formula: see text] (standard paired difference) and the change in hemoglobin levels (hemoglobin concentration (P<0.0001) and hemoglobin mass (P = 0.006)).

CONCLUSION

These findings suggest that [Formula: see text] values are closely associated with hemoglobin levels among both observational and interventional studies. Although our findings suggest a lack of sex differences in these relationships, there were limited studies incorporating females or stratifying results by biological sex.

Cardiopulmonary exercise testing in patients with end-stage kidney disease: principles, methodology and clinical applications of the optimal tool for exercise tolerance evaluation

Chronic kidney disease (CKD), especially end-stage kidney disease (ESKD), is associated with an increased risk for cardiovascular events and all-cause mortality. Exercise intolerance as well as reduced cardiovascular reserve is extremely common in patients with CKD. Cardiopulmonary exercise testing (CPET) is a non-invasive, dynamic technique that provides an integrative evaluation of cardiovascular, pulmonary, neuropsychological and metabolic function during maximal or submaximal exercise, allowing the evaluation of functional reserves of these systems. This assessment is based on the principle that system failure typically occurs when the system is under stress and thus CPET is currently considered to be the gold standard for identifying exercise limitation and differentiating its causes. It has been widely used in several medical fields for risk stratification, clinical evaluation and other applications, but its use in everyday practice for CKD patients is scarce. This article describes the basic principles and methodology of CPET and provides an overview of important studies that utilized CPET in patients with ESKD, in an effort to increase awareness of CPET capabilities among practicing nephrologists.

Clinical Consequences of Metabolic Acidosis-Muscle

Metabolic acidosis is common in people with chronic kidney disease and can contribute to functional decline, morbidity, and mortality. One avenue through which metabolic acidosis can result in these adverse clinical outcomes is by negatively impacting skeletal muscle; this can occur through several pathways. First, metabolic acidosis promotes protein degradation and impairs protein synthesis, which lead to muscle breakdown. Second, metabolic acidosis hinders mitochondrial function, which decreases oxidative phosphorylation and reduces energy production. Third, metabolic acidosis directly limits muscle contraction. The purpose of this review is to examine the specific mechanisms of each pathway through which metabolic acidosis affects muscle, the impact of metabolic acidosis on physical function, and the effect of treating metabolic acidosis on functional outcomes.

Cardiopulmonary reserve examined with cardiopulmonary exercise testing in individuals with chronic kidney disease: A systematic review and meta-analysis

BACKGROUND

Patients with chronic kidney disease (CKD) often present reduced physical activity and exercise tolerance due to factors relevant to co-existing disturbances of the cardiac, nervous and muscular systems. Cardiopulmonary exercise testing (CPET) is used for clinical evaluation of exercise limitation and related symptoms (i.e., dyspnea, fatigue) in several medical fields.

OBJECTIVES

This is a systematic review and meta-analysis of studies using CPET technology to examine cardiopulmonary reserve in individuals with versus without CKD.

METHODS

Literature search involved PubMed, Web of Science and Scopus databases; manual search of article references and of gray literature was also performed. Observational studies and randomized trials that used CPET for patients with CKD stage 1-5 versus controls were eligible. The primary outcome was peak oxygen uptake (VO₂peak). The Newcastle-Ottawa Scale was used to evaluate the quality of retrieved studies.

RESULTS

From an initial 4944 literature records, we identified 29 studies fulfilling the inclusion criteria; of these, 25 studies (2,213 participants) with complete data were included in the final meta-analysis. VO₂peak was significantly lower in CKD patients than controls without CKD [standardized mean difference (SMD) -1.40, 95% confidence interval (CI) -1.68; -1.13)]. Values were lower for CKD than non-CKD individuals for oxygen consumption at anaerobic threshold (SMD -1.06, 95% CI -1.34; -0.79) and maximum workload [weighted mean difference (WMD) -58.26, 95% CI 74.14; -42.38]. In 3 studies, CKD patients had higher VO₂peak than controls with heart failure without CKD (WMD 6.60, 95% CI 3.02; 10.18). Sensitivity analyses confirmed the robustness of these findings.

CONCLUSIONS

VO₂peak and other commonly analyzed CPET variables were lower in patients with CKD than controls, which indicates reduced functional cardiopulmonary reserve in CKD. In contrast, patients with CKD performed better than controls with heart failure without CKD. Overall, rehabilitation programs should be more widely applied to individuals with CKD.

PROSPERO REGISTRATION NUMBER

CRD42021227805.

Acute erythropoietin injection increases muscle mitochondrial respiratory capacity in young men: a double-blinded randomized crossover trial

The aim was to investigate if acute recombinant human erythropoietin (rHuEPO) injection had an effect on mitochondrial function and if exercise would have an additive effect. Furthermore, to investigate if in vitro incubation with rHuEPO had an effect on muscle mitochondrial respiratory capacity. Eight healthy young men were recruited for this double-blinded randomized placebo-controlled crossover study. rHuEPO (400 IU/kg body wt) or saline injection was given intravenously, before an acute bout of exercise. Resting metabolic rate and fat oxidation were measured. Biopsies were obtained at baseline, 120 min after injection, and right after the acute exercise bout. Mitochondrial function (mitochondrial respiration and H₂O₂ emission) was measured in permeabilized skeletal muscle using high-resolution respirometry and fluorometry. Specific gene expression and enzyme activity were measured. Skeletal muscle mitochondrial respiratory capacity was measured with and without incubation with rHuEPO. Fat oxidation at rest increased after rHuEPO injection, but no difference was found in fat oxidation during exercise. Mitochondrial respiratory capacity was increased after rHuEPO injection when pyruvate was in the assay, which was not the case when saline was injected. No changes were seen in H₂O₂ emission after rHuEPO injection or acute exercise. Incubation of skeletal muscle fibers in vitro with rHuEPO increased mitochondrial respiratory capacity. Acute rHuEPO injection increased mitochondrial respiratory capacity when pyruvate was used in the assay. No statistical difference was found in H₂O₂ emission capacity, although a numerical increase was seen after rHuEPO injection. In vitro incubation of the skeletal muscle sample with rHuEPO increases mitochondrial respiratory capacity.NEW & NOTEWORTHY The effect of an acute rHuEPO injection on skeletal muscle mitochondrial function was investigated in young healthy male subjects. rHuEPO has an acute effect on skeletal muscle mitochondrial respiratory capacity in humans, where an increased mitochondrial respiratory capacity was seen. This could be the first step leading to increased mitochondrial biogenesis.

Fatigue in CKD: Epidemiology, Pathophysiology, and Treatment

Fatigue is a commonly reported and debilitating symptom among patients with CKD, yet little is known about its epidemiology, pathogenesis, and treatment. Various measurement tools have been used in published studies to identify and quantify fatigue. These include several single-item measures embedded in longer questionnaires for assessing depression, quality of life, or symptom burden in patients with kidney disease. Approximately 70% of patients with CKD report fatigue, with up to 25% reporting severe symptoms. Patient-reported fatigue is associated with death, dialysis initiation, and hospitalization among individuals with CKD. The pathophysiology is multifactorial and likely includes decreased oxygen delivery and increased reliance on anaerobic metabolism, thus generating lactic acidosis in response to exertion; the effects of chronic metabolic acidosis and hyperphosphatemia on skeletal muscle myocytes; protein-energy wasting and sarcopenia; and depression. Physical activity has been shown to improve fatigue in some small but promising trials, and so should be recommended, given the additional benefits of exercise. Targeting higher hemoglobin levels with erythropoiesis-stimulating agents may improve fatigue, but potential adverse cardiovascular effects preclude their use to solely treat fatigue without the presence of another indication. Current guidelines recommend cautious individualization of hemoglobin targets for those at low cardiovascular risk who still experience fatigue or functional limitation despite a hemoglobin level of 10 g/dl. Sodium bicarbonate supplementation for the treatment of metabolic acidosis may also improve functional status. Selective serotonin reuptake inhibitors have not been consistently shown to improve fatigue in patients with kidney disease, but an ongoing trial will evaluate the effect of alternative antidepressant drug and behavioral activation therapy on fatigue in patients with CKD. Overall, more research is needed to further clarify underlying mechanisms of fatigue and identify effective, targeted treatments for patients with CKD.

Cardiac and Noncardiac Determinants of Exercise Capacity in CKD

BACKGROUND

Impaired exercise capacity is a significant symptom of CKD and is associated with poor survival. Furthermore, there is a growing interest in applying exercise as a diagnostic tool or as therapy in CKD. However, an in-depth understanding of exercise physiology in CKD is still lacking.

METHODS

To evaluate the role of cardiac (central) and noncardiac (peripheral) determinants of exercise capacity in CKD, we conducted a cross-sectional study of 70 male patients with CKD (stages 2-5) without diabetes or cardiac disease, 35 healthy controls, and 25 patients with heart failure. An integrated cardiopulmonary exercise test using a CO₂ rebreathing technique was used to measure peak O₂ consumption (VO_2peak) and peak cardiac output simultaneously, and to calculate peak peripheral O₂ extraction (C[a-v]O₂), the peripheral determinant (the ability of exercising skeletal muscles to extract oxygen). We performed multiple regression analysis and used Bayesian information criteria (BIC) changes to quantitatively assess the individual contribution of central and peripheral factors.

RESULTS

Compared with healthy controls, in patients with CKD, the VO_2peak was impaired proportionate to its severity. Peak cardiac output was the predominant determinant of VO_2peak in healthy controls and patients with heart failure, whereas C(a-v)O₂ played a more significant role in determining VO_2peak in CKD (β=0.68, P<0.001) compared with cardiac output (β=0.63, P<0.001). In addition, the magnitude of BIC reduction was greater for C(a-v)O₂ compared with cardiac output (BIC, 298.72 versus 287.68) in CKD.

CONCLUSIONS

In CKD, both peak cardiac output and peak C(a-v)O₂ are independent predictors of VO_2peak, and the more significant roleplayed by peak C(a-v)O₂ highlights the importance of noncardiac factors in determining exercise capacity in CKD.

A clinical evaluation of VO2 kinetics in kidney transplant recipients

Purpose

Aerobic exercise capacity is reduced in patients with chronic kidney disease, partly due to alterations at the muscular and microvascular level. This study evaluated oxygen uptake (VO₂) kinetics as indicator of muscular oxidative metabolism in a population of Kidney Transplant Recipients (KTRs).

Methods

Two groups of KTRs enrolled 3 (n = 21) and 12 months (n = 14) after transplantation and a control group of healthy young adults (n = 16) underwent cardiopulmonary exercise testing on cycle-ergometer. The protocol consisted in two subsequent constant, moderate-load exercise phases with a final incremental test until exhaustion.

Results

The time constant of VO₂ kinetics was slower in KTRs at 3 and 12 months after transplantation compared to controls (50.4 ± 13.1 s and 43.8 ± 11.6 s vs 28.9 ± 8.4 s, respectively; P < 0.01). Peak VO₂ was lower in KTRs evaluated 3 months after transplantation compared to patients evaluated after 1 year (21.3 ± 4.3 and 26.4 ± 8.0 mL/kg/min; P = 0.04). Blood haemoglobin (Hb) concentration was higher in KTRs evaluated at 12 months (12.8 ± 1.7 vs 14.6 ± 1.7 g/dL; P < 0.01). Among KTRs, τ showed a moderate negative correlation with Peak VO₂ (ρ = − 0.52) and Oxygen uptake efficiency slope (OUES) (r = − 0.57) while no significant correlation with Hb and peak heart rate.

Conclusions

KTRs show slower VO₂ kinetics compared to healthy controls. Hb and peak VO₂ seem to improve during the first year after transplantation. VO₂ kinetics were significantly associated with indices of cardiorespiratory fitness, but less with central determinants of aerobic capacity, thus suggesting a potential usefulness of adding this index of muscular oxidative metabolism to functional evaluation in KTRs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-021-04672-x.

Microvascular disease in chronic kidney disease: the base of the iceberg in cardiovascular comorbidity

Chronic kidney disease (CKD) is a relentlessly progressive disease with a very high mortality mainly due to cardiovascular complications. Endothelial dysfunction is well documented in CKD and permanent loss of endothelial homeostasis leads to progressive organ damage. Most of the vast endothelial surface area is part of the microcirculation, but most research in CKD-related cardiovascular disease (CVD) has been devoted to macrovascular complications. We have reviewed all publications evaluating structure and function of the microcirculation in humans with CKD and animals with experimental CKD. Microvascular rarefaction, defined as a loss of perfused microvessels resulting in a significant decrease in microvascular density, is a quintessential finding in these studies. The median microvascular density was reduced by 29% in skeletal muscle and 24% in the heart in animal models of CKD and by 32% in human biopsy, autopsy and imaging studies. CKD induces rarefaction due to the loss of coherent vessel systems distal to the level of smaller arterioles, generating a typical heterogeneous pattern with avascular patches, resulting in a dysfunctional endothelium with diminished perfusion, shunting and tissue hypoxia. Endothelial cell apoptosis, hypertension, multiple metabolic, endocrine and immune disturbances of the uremic milieu and specifically, a dysregulated angiogenesis, all contribute to the multifactorial pathogenesis. By setting the stage for the development of tissue fibrosis and end organ failure, microvascular rarefaction is a principal pathogenic factor in the development of severe organ dysfunction in CKD patients, especially CVD, cerebrovascular dysfunction, muscular atrophy, cachexia, and progression of kidney disease. Treatment strategies for microvascular disease are urgently needed.

Exercise Capacity in Pediatric Patients with End-Stage Renal Disease

Objective

To evaluate the correlation between exercise capacity and hemoglobin in pediatric patients with end-stage renal disease (ESRD) treated with automated peritoneal dialysis (APD) and hemodialysis.

Design

Prospective case-control study and retrospective review.

Setting

Dialysis summer camp and Children's Mercy Hospital exercise laboratory.

Participants

Prospective evaluation conducted with 14 patients (9 males, mean age 14.5 ± 2.5 years) who received either home APD (5 patients) or in-center hemodialysis (9 patients), and 8 healthy age-matched controls. Retrospective data derived from 10 children (7 males, mean age 12.3 ± 3.3 years), all of whom received APD.

Intervention

Maximal treadmill evaluation conducted with each patient and control. The hemoglobin value of each patient was also assessed.

Main Outcome Measures

Comparison of the following data generated during treadmill protocol: peak heart rate, blood pressure, oxygen saturation, treadmill time, oxygen consumption (VO2), ventilation (Ve), oxygen consumption at anaerobic threshold (VO2 AT), and respiratory exchange ratio.

Results

The hemoglobin value of the current patient group (12.8 ± 1.6 g/dL) was significantly greater than the previously studied patients (10.5 ± 1.1 g/dL) ( p = 0.001). Treadmill time, VO2, and VO2 AT were significantly lower in both groups of dialysis patients compared to the control subjects ( p < 0.05). No differences were noted in any of these variables when comparing these two groups of dialysis patients only.

Conclusion

The exercise capacity of pediatric dialysis patients is significantly poorer than that of healthy children, an outcome apparently related to factors other than normalization of the hemoglobin value.

Aerobic training during hemodialysis improves body composition, muscle function, physical performance, and quality of life in chronic kidney disease patients

[Purpose] We assessed the influences of individualized aerobic training on body composition, knee joint muscle function, physical performance, and quality of life in chronic kidney disease patients. [Subjects] Ten chronic kidney disease patients undergoing dialysis. [Methods] Overall physical function and quality of life before and after 12 weeks of aerobic training were evaluated by body composition, the six-minute walk test, cardiopulmonary exercise tests, and Short Form 36-item questionnaire. [Results] The six-minute walk test distance increased significantly after 12 weeks aerobic training. Resting metabolic rate, lactate threshold, maximum oxygen uptake, and quality of life tended to increase after training. Post-training weight, muscle mass, body fat mass, fat percentage, body mass index, and peak torque of right and left knee extension and flexion did not change significantly. [Conclusion] Intra-dialytic training can a safe approach to maintain or improve physical performance and quality of life of chronic kidney disease patients undergoing hemodialysis without adverse events or negative cardiovascular responses. Aerobic training may prevent a decline in body composition and knee joint muscle function due to inactivity in chronic kidney disease patients. Clinically, aerobic training may initially be adapted to maintain overall physical function or improve quality of life in chronic kidney disease patients undergoing hemodialysis.

Anabolic exercise in haemodialysis patients: a randomised controlled pilot study

BACKGROUND

The anabolic response to progressive resistance exercise training (PRET) in haemodialysis patients is unclear. This pilot efficacy study aimed to determine whether high-intensity intradialytic PRET could reverse atrophy and consequently improve strength and physical function in haemodialysis patients. A second aim was to compare any anabolic response to that of healthy participants completing the same program.

METHODS

In a single blind controlled study, 23 haemodialysis patients and 9 healthy individuals were randomly allocated to PRET or an attention control (SHAM) group. PRET completed high-intensity exercise leg extensions using novel equipment. SHAM completed low-intensity lower body stretching activities using ultra light resistance bands. Exercises were completed thrice weekly for 12 weeks, during dialysis in the haemodialysis patients. Outcomes included knee extensor muscle volume by magnetic resonance imaging, knee extensor strength by isometric dynamometer and lower body tests of physical function. Data were analysed by a per protocol method using between-group comparisons.

RESULTS

PRET elicited a statistically and clinically significant anabolic response in haemodialysis patients (PRET-SHAM, mean difference [95 % CI]: 193[63 to 324] cm(3)) that was very similar to the response in healthy participants (PRET-SHAM, 169[-41 to 379] cm(3)). PRET increased strength in both haemodialysis patients and healthy participants. In contrast, PRET only enhanced lower body functional capacity in the healthy participants.

CONCLUSIONS

Intradialytic PRET elicited a normal anabolic and strength response in haemodialysis patients. The lack of a change in functional capacity was surprising and warrants further investigation.

Exercise limitation following transplantation

Organ transplantation is one of the medical miracles or the 20th century. It has the capacity to substantially improve exercise performance and quality of life in patients who are severely limited with chronic organ failure. We focus on the most commonly performed solid-organ transplants and describe peak exercise performance following recovery from transplantation. Across all of the common transplants, evaluated significant reduction in VO2peak is seen (typically renal and liver 65%-80% with heart and/or lung 50%-60% of predicted). Those with the lowest VO2peak pretransplant have the lowest VO2peak posttransplant. Overall very few patients have a VO2peak in the normal range. Investigation of the cause of the reduction of VO2peak has identified many factors pre- and posttransplant that may contribute. These include organ-specific factors in the otherwise well-functioning allograft (e.g., chronotropic incompetence in heart transplantation) as well as allograft dysfunction itself (e.g., chronic lung allograft dysfunction). However, looking across all transplants, a pattern emerges. A low muscle mass with qualitative change in large exercising skeletal muscle groups is seen pretransplant. Many factor posttransplant aggravate these changes or prevent them recovering, especially calcineurin antagonist drugs which are key immunosuppressing agents. This results in the reduction of VO2peak despite restoration of near normal function of the initially failing organ system. As such organ transplantation has provided an experiment of nature that has focused our attention on an important confounder of chronic organ failure-skeletal muscle dysfunction.

Association of frailty with body composition among patients on hemodialysis

Although sarcopenia is thought to underlie the manifestations of frailty, association of frailty with measures of body composition is underinvestigated.

METHODS

Eighty hemodialysis patients were included in the study. Performance-based frailty (PbF) used gait speed over 20 feet and 5 sit-to-stand (1 point each for lowest quintile) for the physical components of the frailty phenotype plus exhaustion (Short Form-36 [SF-36] vitality score <55) and physical activity (lowest quintile of weekly kcal energy expenditure on leisure activity on the Physical Activity Scale for the Elderly questionnaire; 1 point). Function-based frailty (FbF) defined by questionnaire measures of physical functioning (SF-36 Physical Function score <75; 1 point), exhaustion, and physical activity as for PbF. A score of 2 or greater was defined as frail. Outcomes related to muscle size included muscle area of the contractile tissue of the anterior tibialis and quadriceps muscles using magnetic resonance imaging, phase angle using bioimpedance analysis, lean body mass using dual energy X-ray absorptiometry, and body mass index (BMI). Linear regression was used to analyze associations between frailty and muscle size, with and without sex and age covariates.

RESULTS

Fifty-nine percent of individuals met PbF criteria, 63% met FbF criteria, and 55% met both. In univariate analysis, PbF and FbF were associated with smaller muscle area of the quadriceps, smaller phase angle, and higher BMI. Associations remained significant for the quadriceps after adjustment for age and sex. The magnitude of association of PbF with quadriceps muscle area was greater than 10 years of age (-30.3 cm(2)P = .02 vs. -6.6 cm(2)P < .0001) in multivariate analysis. There was no significant association between either measure of frailty and other measures of body composition after adjustment for age and sex.

CONCLUSION

Frailty was associated with measurements related to muscle size in a population of individuals with chronic kidney disease, a known contributor to muscle wasting.

Exertional fatigue in patients with CKD

BACKGROUND

Fatigue is one of the most prevalent symptoms in chronic kidney disease (CKD). However, fatigue mechanisms are poorly understood due in part to nonspecific definitions. This study investigates exertional fatigue during simulated activities of daily living, focusing on oxygen delivery and utilization.

STUDY DESIGN

"Explanatory" matched-cohort study.

PARTICIPANTS & SETTING

13 patients with CKD (stages 3b-4; mean age, 62 ± 13 [SD] years) and 13 healthy controls, mean matched for age, height, body mass and composition, and physical activity level. Participants completed an incremental cycle ergometer test to simulate energy expenditure of typical activities of daily living.

FACTOR

4 exercise intensities: 1, 1.8, 2.4, and 3.1 metabolic equivalent tasks (METs).

OUTCOMES

The primary outcome was exertional fatigue by rating of perceived exertion (RPE) on a 6-20 scale.

MEASUREMENTS

Other multidimensional measures of fatigue: UK Short Form Health Survey 36 (UK SF-36) Vitality and Functional Assessment of Chronic Illness Therapy-Fatigue (FACIT-Fatigue) subscales. Physiologic measures of the oxygen transport and utilization chain (expired gas analysis, cardiac output, and arterial oxygen content) and blood lactate.

RESULTS

RPE was increased in patients compared with controls at 2.4 (10.5 [ie, light] ± 2.7 vs 8.7 [very light] ± 1.7 units) and 3.1 (12.5 [somewhat hard] ± 2.6 vs 10.2 [light] ± 1.7 units) METs (interaction P = 0.03), which was consistent with higher chronic fatigue in patients by both the UK SF-36 Vitality (P = 0.01) and FACIT-Fatigue (P = 0.004) subscales. Arterial oxygen content was decreased in patients (P = 0.001), but cardiac output and oxygen extraction ratio were unchanged, decreasing oxygen delivery (P = 0.04). Respiratory exchange ratio (P = 0.004) and blood lactate production (P = 0.002) were increased.

LIMITATIONS

Those inherent to a matched-cohort study.

CONCLUSIONS

Using a novel application of the outcome measure RPE, patients with non-dialysis-dependent CKD reported considerable exertional fatigue during simulated activities of daily living. Poor compensation for mild anemia contributed to this symptom. In addition to anemia, the entire oxygen transport chain needs to be targeted to treat fatigue in patients with CKD.

Investigation of skeletal muscle quantity and quality in end-stage renal disease

AIM

A more precise understanding of the aetiology and sequelae of muscle wasting in end-stage renal disease (ESRD) is required for the development of effective interventions to target this pathology.

METHODS

We investigated 49 patients with ESRD (62.6 +/- 14.2 years, 0.3-16.7 years on haemodialysis). Thigh muscle cross-sectional area (CSA), intramuscular lipid and intermuscular adipose tissue (IMAT) were measured via computed tomography as indices of muscle quantity (i.e. CSA) and quality (i.e. intramuscular lipid and IMAT). Additional health and clinical measures were investigated to determine associations with these variables.

RESULTS

Age, energy intake, disease burden, pro-inflammatory cytokines, nutritional status, strength and functioning were related to muscle quantity and quality. Potential aetiological factors entered into forward stepwise regression models indicated that hypoalbuminaemia and lower body mass index accounted significantly and independently for 32% of the variance in muscle CSA (r = 0.56, P < 0.001), while older age and interleukin-8 accounted for 41% of the variance in intramuscular lipid (r = 0.64, P < 0.001) and body mass index accounted for 45% of the variance in IMAT (r = 0.67, P < 0.001). Stepwise regression models revealed that intramuscular lipid was independently predictive of habitual gait velocity and 6 min walk distance, while CSA was independently predictive of maximal isometric strength (P < 0.05).

CONCLUSION

Ageing, poor nutritional status and elevated interleukin-8 are factors potentially contributing to the loss of muscle quality and quantity in ESRD. These deficits can predict functional impairments, with intramuscular lipid accumulation most closely related to decline of submaximal musculoskeletal performance (walking), and low muscle CSA most closely related to decline of maximal performance (peak isometric strength).

Effects of modality change and transplant on peak oxygen uptake in patients with kidney failure

BACKGROUND

Exercise capacity as measured by peak oxygen uptake (Vo₂(peak)) is low in hemodialysis patients. The present study assesses determinants of VO₂(peak) in patients with chronic kidney failure who either changed kidney replacement modality to frequent hemodialysis therapy or received a kidney transplant.

STUDY DESIGN

Cohort study with assessment at baseline and 6 months after modality change.

SETTING & PARTICIPANTS

Participants included nondiabetic individuals receiving conventional hemodialysis who: (1) remained on conventional hemodialysis therapy (n = 13), (2) changed to short daily hemodialysis therapy (n = 10), or (3) received a transplant (n = 5) and (4) individuals who underwent a pre-emptive transplant (n = 15). Additionally, 34 healthy controls were assessed at baseline only.

PREDICTOR

Modality change.

MEASUREMENT & OUTCOMES

Exercise capacity, assessed using the physiologic components of the Fick equation (Vo₂ = cardiac output × a-vo₂(dif), where a-vo₂(dif) is arterial to venous oxygen difference) was determined using measurement of Vo₂(peak) and cardiac output during symptom-limited exercise testing. Analysis of covariance was used to compare differences in changes in Vo₂(peak), cardiac output, heart rate, stroke volume, and a-vo₂(dif) at peak exercise between participants who remained on hemodialysis therapy and those who underwent transplant.

RESULTS

Transplant was the only modality change associated with a significant change in Vo₂(peak), occurring as a result of increased peak cardiac output and reflecting increased heart rate without a change in peak a-vo₂(dif) despite increased hemoglobin levels. There were no differences in participants who changed to daily hemodialysis therapy compared with those who remained on conventional hemodialysis therapy.

LIMITATIONS

Small nonrandomized study.

CONCLUSIONS

Vo₂(peak) increases significantly after kidney transplant, but not with daily hemodialysis; this improvement reflects increased peak cardiac output through increased peak heart rate. Despite statistical significance, the increase in Vo₂(peak) was not clinically significant, suggesting the need for interventions such as exercise training to increase Vo₂(peak) in all patients regardless of treatment modality.

Erythropoietin activates mitochondrial biogenesis and couples red cell mass to mitochondrial mass in the heart

RATIONALE

Erythropoietin (EPO) is often administered to cardiac patients with anemia, particularly from chronic kidney disease, and stimulation of erythropoiesis may stabilize left ventricular and renal function by recruiting protective effects beyond the correction of anemia.

OBJECTIVE

We examined the hypothesis that EPO receptor (EpoR) ligand-binding, which activates endothelial NO synthase (eNOS), regulates the prosurvival program of mitochondrial biogenesis in the heart.

METHODS AND RESULTS

We investigated the effects of EPO on mitochondrial biogenesis over 14 days in healthy mice. Mice expressing a mitochondrial green fluorescent protein reporter construct demonstrated sharp increases in myocardial mitochondrial density after 3 days of EPO administration that peaked at 7 days and surpassed hepatic or renal effects and anteceded significant increases in blood hemoglobin content. Quantitatively, in wild-type mice, complex II activity, state 3 respiration, and mtDNA copy number increased significantly; also, resting energy expenditure and natural running speed improved, with no evidence of an increase in left ventricular mass index. Mechanistically, EPO activated cardiac mitochondrial biogenesis by enhancement of nuclear respiratory factor-1, PGC-1alpha (peroxisome proliferator-activated receptor gamma coactivator 1alpha), and mitochondrial transcription factor-A gene expression in wild-type but not in eNOS(-/-) or protein kinase B (Akt1)(-/-) mice. EpoR was required, because EpoR silencing in cardiomyocytes blocked EPO-mediated nuclear translocation of nuclear respiratory factor-1.

CONCLUSIONS

These findings support a new physiological and protective role for EPO, acting through its cell surface receptor and eNOS-Akt1 signal transduction, in matching cardiac mitochondrial mass to the convective O(2) transport capacity as erythrocyte mass expands.

The Clinical Application of Ozonetherapy

The reader may be eager to examine in which diseases ozonetherapy can be proficiently used and she/he will be amazed by the versatility of this complementary approach (Table 9 1). The fact that the medical applications are numerous exposes the ozonetherapist to medical derision because superficial observers or sarcastic sceptics consider ozonetherapy as the modern panacea. This seems so because ozone, like oxygen, is a molecule able to act simultaneously on several blood components with different functions but, as we shall discuss, ozonetherapy is not a panacea. The ozone messengers ROS and LOPs can act either locally or systemically in practically all cells of an organism. In contrast to the dogma that “ozone is always toxic”, three decades of clinical experience, although mostly acquired in private clinics in millions of patients, have shown that ozone can act as a disinfectant, an oxygen donor, an immunomodulator, a paradoxical inducer of antioxidant enzymes, a metabolic enhancer, an inducer of endothelial nitric oxide synthase and possibly an activator of stem cells with consequent neovascularization and tissue reconstruction.

Microcirculatory changes and skeletal muscle oxygenation measured at rest by non-infrared spectroscopy in patients with and without diabetes undergoing haemodialysis

Introduction

Haemodialysis has direct and indirect effects on skin and muscle microcirculatory regulation that are severe enough to worsen tolerance to physical exercise and muscle asthenia in patients undergoing dialysis, thus compromising patients' quality of life and increasing the risk of mortality. In diabetes these circumstances are further complicated, leading to an approximately sixfold increase in the incidence of critical limb ischaemia and amputation. Our aim in this study was to investigate in vivo whether haemodialysis induces major changes in skeletal muscle oxygenation and blood flow, microvascular compliance and tissue metabolic rate in patients with and without diabetes.

Methods

The study included 20 consecutive patients with and without diabetes undergoing haemodialysis at Sant Andrea University Hospital, Rome from March to April 2007. Near-infrared spectroscopy (NIRS) quantitative measurements of tissue haemoglobin concentrations in oxygenated [HbO₂] and deoxygenated forms [HHb] were obtained in the calf once hourly for 4 hours during dialysis. Consecutive venous occlusions allowed one to obtain muscular blood flow (mBF), microvascular compliance and muscle oxygen consumption (mVO₂). The tissue oxygen saturation (StO₂) and content (CtO₂) as well as the microvascular bed volume were derived from the haemoglobin concentration. Nonparametric tests were used to compare data within each group and among the groups and with a group of 22 matched healthy controls.

Results

The total haemoglobin concentration and [HHb] increased significantly during dialysis in patients without and with diabetes. Only in patients with diabetes, dialysis involved a [HbO₂], CtO₂ and increase but left mVO₂ unchanged. Multiple regression StO₂ analysis disclosed a significant direct correlation of StO₂ with HbO₂ and an inverse correlation with mVO₂. Dialysis increased mBF only in diabetic patients. Microvascular compliance decreased rapidly and significantly during the first hour of dialysis in both groups.

Conclusions

Our NIRS findings suggest that haemodialysis in subjects at rest brings about major changes in skeletal muscle oxygenation, blood flow, microvascular compliance and tissue metabolic rate. These changes differ in patients with and without diabetes. In all patients haemodialysis induces changes in tissue haemoglobin concentrations and microvascular compliance, whereas in patients with diabetes it alters tissue blood flow, tissue oxygenation (CtO₂, [HbO₂]) and the metabolic rate (mVO₂). In these patients the mVO₂ is correlated to the blood supply. The effects of haemodialysis on cell damage remain to be clarified. The absence of StO₂ changes is probably linked to an opposite [HbO₂] and mVO₂ pattern.

Determinants of exercise capacity in CKD patients treated with hemodialysis

There are many ways to measure physical functioning. Oxygen uptake at peak exercise is considered to be the most objective or 'gold-standard' measure and is determined by the integrated functioning of multiple physiological systems. Renal failure can affect the functioning of several of these systems which results in low levels of peak oxygen uptake. This review examines the determinants of oxygen uptake as defined by the Fick Equation, and presents data from studies that have reported these physiological measures. It becomes clear that there are many factors that may limit peak oxygen uptake in these patients and any one mechanism may be difficult to identify.

Optimal health and function among the elderly: lessening severity of ADL disability

Despite mounting evidence implicating sedentary behavior as a significant risk factor among the elderly, there is a limited amount of information on the type and amount of activity needed to promote optimal health and function in older people. Overall muscle strength and mass decline 30–50% between the ages of 30 and 80. The loss of muscle mass accounts for most of the observed loss of strength. The loss of muscle tissue is due to a decrease in the number of muscle fibers and to atrophy of the type II muscle fibers. The declining strength reduces the capacity to carry out basic activities of daily life and puts people at risk for falls and dependence on others. The objective of the present review is to examine the role of exercise training as a primary tool for increasing cardiopulmonary and muscular fitness in order to lessen the severity of disability in activities of daily living and to attain optimal health and functioning among the elderly.

Review article: Tackling the survival issue in end-stage renal disease: time to get physical on haemodialysis

Life expectancy in haemodialysis patients is reduced fourfold on average versus healthy age-matched individuals. The purpose of this review is to present empirical evidence that intradialytic exercise can mitigate primary independent risk factors for early mortality in end-stage renal disease. These risk factors include measures of skeletal muscle wasting, systemic inflammation, cardiovascular functioning and dialysis adequacy. Overall, the available literature provides support for the integration of exercise within the conventional outpatient haemodialysis unit. The amelioration of various physiological risk factors through an appropriate exercise prescription may enhance survival in this vulnerable cohort. Investigations are required to determine the effects of various doses of intradialytic exercise on a broad range of clinical outcomes, and more thoroughly elucidate the relationship between exercise-induced adaptations and survival advantage in end-stage renal disease.

Exercise pressor reflex in humans with end-stage renal disease

Previous work has suggested that end-stage renal disease (ESRD) patients may have an exaggerated sympathetic nervous system (SNS) response during exercise. We hypothesized that ESRD patients have an exaggerated blood pressure (BP) response during moderate static handgrip exercise (SHG 30%) and that the exaggerated BP response is mediated by SNS overactivation, characterized by augmented mechanoreceptor activation and blunted metaboreceptor control, as has been described in other chronic diseases. We measured hemodynamics and muscle sympathetic nerve activity (MSNA) in 13 ESRD and 16 controls during: 1) passive hand movement (PHM; mechanoreceptor isolation); 2) low-level rhythmic handgrip exercise (RHG 20%; central command and mechanoreceptor activation); 3) SHG 30%, followed by posthandgrip circulatory arrest (PHGCA; metaboreceptor activation); and 4) cold pressor test (CPT; nonexercise stimulus). ESRD patients had exaggerated increases in systolic BP during SHG 30%; however, the absolute and relative increase in MSNA was not augmented, excluding SNS overactivation as the cause of the exaggerated BP response. Increase in MSNA was not exaggerated during RHG 20% and PHM, demonstrating that mechanoreceptor activation is not heightened in ESRD. During PHGCA, MSNA remained elevated in controls but decreased rapidly to baseline levels in ESRD, indicative of markedly blunted metaboreceptor control of MSNA. MSNA response to CPT was virtually identical in ESRD and controls, excluding a generalized sympathetic hyporeactivity in ESRD. In conclusion, ESRD patients have an exaggerated increase in SBP during SHG 30% that is not mediated by overactivation of the SNS directed to muscle. SBP responses were also exaggerated during mechanoreceptor activation and metaboreceptor activation, but without concomitant augmentation in MSNA responses. Metaboreceptor control of MSNA was blunted in ESRD, but the overall ability to mount a SNS response was not impaired. Other mechanisms besides SNS overactivation, such as impaired vasodilatation, should be explored to explain the exaggerated exercise pressor reflex in ESRD.

Anemia of Chronic Kidney Disease

Chronic kidney disease may result in complete kidney failure and contribute to many other health issues. Anemia is a logical consequence of the disease because the kidneys are the primary source of erythropoietin, the hormone that acts to stimulate red blood cell production in the bone marrow. All patients with chronic kidney disease are at risk for anemia, and treating anemia is extremely important to their health and well-being. Preventing or reversing the effects of anemia on the heart may decrease morbidity and mortality and improve quality of life. Many patients fail to receive treatment for anemia before requiring renal replacement therapy for end-stage renal disease. Pharmacists can play a vital role in screening, evaluating, designing proper treatment regimens, and monitoring patients with anemia of chronic kidney disease. Current recommendations regarding anemia are reviewed, including evaluation, pharmacotherapeutic agents, monitoring parameters, and goals of therapy.

Myosin heavy-chain isoform distribution, fibre-type composition and fibre size in skeletal muscle of patients on haemodialysis

OBJECTIVE

Chronic uraemia is associated with abnormalities in skeletal muscles, which can affect their working capacity. It is also well known that the fibre-type composition of skeletal muscles influences endurance, muscle strength and power. In this study we therefore determined the size and distribution of muscle fibres and the myosin heavy-chain (MHC) isoform composition in patients on haemodialysis (HD) in order to establish any differences with values for untrained control subjects.

MATERIAL AND METHODS

Muscle biopsies were obtained from the vastus lateralis muscle of 14 non-diabetic patients on HD. The size and distribution of muscle fibres were evaluated using adenosine triphosphate synthase (ATPase) histochemistry, whilst MHC isoform composition was determined in muscle homogenates using sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Values were compared to those for a group of age-, gender- and BMI-matched untrained control subjects. The aerobic work capacity of the patients was also determined.

RESULTS

The MHC composition for I, IIA and IIX isoforms was found to be 35.3% +/- 18.2%, 35.9% +/- 7.1% and 28.9% +/- 15.6%, respectively, findings supported by the ATPase histochemically determined fibre-type composition of the vastus lateralis muscle. The mean fibre area of type 1 and 2 fibres was 3283 +/- 873 and 3594 +/- 1483 MICROm2, respectively. The MHC composition and the size of the type 1 fibres of the patients on HD were significantly different from those of the control subjects.

CONCLUSIONS

The data demonstrate relatively fewer type 1 and consequently more type 2x fibres, with a corresponding change in MHC isoforms (MHC I and MHC IIX) in the skeletal muscle of patients on HD. Several patients on HD were found to have <15% type 1 (or relative percentage of MHC I) fibres. Such a low percentage of type 1 fibres is very rarely observed in normal untrained subjects. Chronic uraemia more severely affects the composition than the size of fibres.

Exercise limb blood flow response to acute and chronic hypoxia in Danish lowlanders and Aymara natives

AIM

The femoral artery blood flow response to submaximal, one-legged, dynamic, knee-extensor exercise was determined in acute and chronic hypoxia to investigate the hypotheses that with adaptation to chronic hypoxia blood haemoglobin increases, allowing preservation of blood flow as in normoxia.

METHODS

Sixteen Danish lowlanders participated, in groups of six to eight, in the experiments at sea level normoxia (FiO2 congruent with 0.21) and acute hypoxia (FiO2 congruent with 0.11), and chronic hypoxia after approximately 7 and 9-10 weeks at approximately 5260 m altitude breathing ambient air (FiO2 congruent with 0.21) or a hyperoxic gas (FiO2 congruent with 0.55). The response was compared with that in six Aymara natives.

RESULTS

The haemoglobin and haematocrit increased (P < 0.003) in the lowlanders at altitude vs. at sea level by approximately 39 and 27% respectively; i.e. to a similar (P = ns) level as in the natives. At rest, blood flow was the same (P = ns) in the lowlanders at sea level and altitude, as in the natives at altitude. During the onset of and incremental exercise, blood flow was the same (P = ns) in the lowlanders at sea level and altitude, as in the natives at altitude. Acute hypoxia increased (P < 0.05) blood flow by approximately 55% during exercise in the lowlanders at sea level. Acute hyperoxia decreased (P < 0.05) blood flow by approximately 22-29% during exercise in the lowlanders and natives at altitude.

CONCLUSION

In chronic hypoxia, blood haemoglobin increases, allowing normalization of the elevated exercise blood flow response in acute hypoxia, and preservation of the kinetics and steady-state exercise blood flow as in normoxia, being similar as in the natives at altitude.

Randomized Controlled Trial of Intradialytic Resistance Training to Target Muscle Wasting in ESRD: The Progressive Exercise for Anabolism in Kidney Disease (PEAK) Study

BACKGROUND

To determine whether prolonged (24 weeks) intradialytic progressive resistance training (PRT) could counteract muscle wasting more effectively than short-duration training (12 weeks) in patients with end-stage renal disease.

STUDY DESIGN

Randomized controlled trial.

SETTING & PARTICIPANTS

49 patients (age, 62.6 +/- 14.2 years; 0.3 to 16.7 years on hemodialysis therapy) were randomly assigned to PRT plus usual care for 24 weeks (24WK group) or a crossover control group that received usual care for the first 12 weeks, then PRT plus usual care for the latter 12 weeks (12WK group).

INTERVENTION

Two sets of 10 free-weight PRT exercises were performed at a high intensity during routine thrice-weekly hemodialysis treatment under direct supervision.

OUTCOMES & MEASUREMENTS

Primary outcomes include thigh muscle cross-sectional area by means of computed tomography and intramuscular lipid content estimated through attenuation. Secondary outcomes include muscular strength, exercise capacity, and C-reactive protein level.

RESULTS

The 24WK group increased muscle cross-sectional area (+1.82 +/- 3.25 cm(2)) compared with losses in the 12WK group (-1.37 +/- 6.87 cm(2); relative effect size, 0.59; 95% confidence interval [CI], -0.27 to 6.65; P = 0.04). However, this outcome did not achieve the level of statistical significance required (P = 0.025) after Bonferroni correction for multiple primary outcomes. There was no significant change in intramuscular lipid content between groups (+0.19 +/- 1.32 versus +0.16 +/- 1.69 Hounsfield units in the 24WK and 12WK groups, respectively; P = 0.31). Log C-reactive protein level tended to decrease in the 24WK group compared with the 12WK group (relative effect size, -0.63; 95% CI, -0.27 [-0.54 to 0.00]; P = 0.05). The 24WK group improved muscular strength measures and exercise capacity throughout the trial.

LIMITATIONS

Single geographic site used; no control group without exercise exposure; unblinded assessment of some secondary outcome measures.

CONCLUSIONS

Prolonged intradialytic PRT did not significantly improve muscle cross-sectional area or intramuscular lipid content compared with a shorter duration of exercise. Future trials are required to more thoroughly investigate the clinical importance and magnitude of myogenic adaptations to PRT in this cohort.

Pulmonary Rehabilitation: Joint ACCP/AACVPR Evidence-Based Clinical Practice Guidelines

BACKGROUND

Pulmonary rehabilitation has become a standard of care for patients with chronic lung diseases. This document provides a systematic, evidence-based review of the pulmonary rehabilitation literature that updates the 1997 guidelines published by the American College of Chest Physicians (ACCP) and the American Association of Cardiovascular and Pulmonary Rehabilitation.

METHODS

The guideline panel reviewed evidence tables, which were prepared by the ACCP Clinical Research Analyst, that were based on a systematic review of published literature from 1996 to 2004. This guideline updates the previous recommendations and also examines new areas of research relevant to pulmonary rehabilitation. Recommendations were developed by consensus and rated according to the ACCP guideline grading system.

RESULTS

The new evidence strengthens the previous recommendations supporting the benefits of lower and upper extremity exercise training and improvements in dyspnea and health-related quality-of-life outcomes of pulmonary rehabilitation. Additional evidence supports improvements in health-care utilization and psychosocial outcomes. There are few additional data about survival. Some new evidence indicates that longer term rehabilitation, maintenance strategies following rehabilitation, and the incorporation of education and strength training in pulmonary rehabilitation are beneficial. Current evidence does not support the routine use of inspiratory muscle training, anabolic drugs, or nutritional supplementation in pulmonary rehabilitation. Evidence does support the use of supplemental oxygen therapy for patients with severe hypoxemia at rest or with exercise. Noninvasive ventilation may be helpful for selected patients with advanced COPD. Finally, pulmonary rehabilitation appears to benefit patients with chronic lung diseases other than COPD.

CONCLUSIONS

There is substantial new evidence that pulmonary rehabilitation is beneficial for patients with COPD and other chronic lung diseases. Several areas of research provide opportunities for future research that can advance the field and make rehabilitative treatment available to many more eligible patients in need.

Physiological Basis of Fatigue

This work summarizes our knowledge of the physiological basis of fatigue and the effects of exercise and pharmacological interventions on fatigue. Fatigue may be defined as physical and/or mental weariness resulting from exertion, that is, an inability to continue exercise at the same intensity with a resultant deterioration in performance. The concept of deconditioning in patients is discussed as well as the implications for their rehabilitation and exercise. Because fatigue may result from a number of causes, including loss of muscle mass, deconditioning, nutritional deficiencies, oxygen delivery, and anemia, it should be treated comprehensively. Antifatigue therapy should be the standard of care for most chronic conditions associated with fatigue.

Progressive resistance training during hemodialysis: Rationale and method of a randomized-controlled trial

Skeletal muscle wasting in patients receiving maintenance hemodialysis (HD) has been well documented. The rationale for prescribing progressive resistance training (PRT) in this cohort in an attempt to reverse this catabolism and induce a wide spectrum of physiological, functional, and psychological health-related adaptations is extremely strong. Unfortunately, the barriers to exercise adoption in this cohort are many, which may explain the persisting sedentariness of this population and the lack of widespread clinical programs such as are now commonplace in cardiac rehabilitation and pulmonary rehabilitation units. Current health care practices for HD patients do not address the negative health issues of inactivity and muscle wasting. Therefore, we conducted the first randomized-controlled trial to prescribe PRT during maintenance HD treatment. The purpose of this paper is to present the rationale and methodology that we utilized for implementing intradialytic PRT in a conventional outpatient HD clinic. Potential areas for modification of PRT regimens in this setting are also presented.

Factors Affecting Exercise Capacity in Renal Transplantation Candidates on Continuous Ambulatory Peritoneal Dialysis Therapy

It is well known that reduced peak oxygen uptake (peak VO2) is a predictor for mortality in several chronic diseases and during the preoperative period. The aim of this study was to investigate the factors that influence peak VO2 in renal transplant candidates receiving continuous ambulatory peritoneal dialysis (CAPD) therapy. We included 22 chronic renal failure patients (12 men, 10 women; ages 29.64 +/- 8.29 years; CAPD duration, 37.35 +/- 7.15 months) in this study. Pulmonary function tests and symptom-limited cardiopulmonary exercise tests were administered to all patients. Cardiopulmonary exercise tests were performed on a cycle ergometry at the same time of day for all patients. We analyzed the exercise duration, maximum work rate, and peak VO2 level during cycle ergometry. Serum hemoglobin, hematocrit, total cholesterol, triglyceride, blood urea nitrogen, creatinine, albumin, prealbumin, C-reactive protein, sedimentation rate, ferritin, sodium, potassium, parathyroid hormone, calcium, and phosphorus levels were analyzed from samples. Mean values of exercise duration (6.86 +/- 1.56 minutes), peak VO2 (17.20 +/- 4.91 mL/min/kg), and maximum work rate (77.09 +/- 26.09 watts) were lower when we compared them with predicted values for a healthy population. Peak VO2 was well correlated with serum phosphorus levels (4.51 +/- 1.28 mg/dL, r = .592, P = .004). Test duration was correlated with peak VO2 (r = .489, P = .025) and serum phosphorus levels (r = .530, P = .024). There were no significant correlations with other factors. As a component of ATP, phosphorus is at the hub of the energy-related mechanisms operative in muscles of the respiratory and musculoskeletal systems. Therefore, we suggest that low exercise capacity might be related to low serum phosphorus levels, and that optimal control of serum phosphorus therapy would increase exercise capacity, exercise duration, and oxygen consumption resulting in a decrease of postoperative mortality in renal transplantation candidates.

Restoration of normoxia by ozone therapy may control neoplastic growth: a review and a working hypothesis

In contrast to normal tissues, tumors thrive in hypoxic environments. This appears to be because they can metastasize and secrete angiopoietins for enhancing neoangiogenesis and further tumor spread. Thus, during chronic ischemia, normal tissues tend to die, while neoplasms tend to grow. During the past two decades, it has been shown in arteriopathic patients that ozonated autohemotherapy is therapeutically useful because it increases oxygen delivery in hypoxic tissues, leading to normoxia. Although several oxygenation approaches have been tested, none is able to restore normoxia permanently in patients with cancer. We postulate that a prolonged cycle of ozonated autohemotherapy may correct tumor hypoxia, lead to less aggressive tumor behavior, and represent a valid adjuvant during or after chemo- or radiotherapy. Moreover, it may re-equilibrate the chronic oxidative stress and reduce fatigue.

Neural and metabolic mechanisms of excessive muscle fatigue in maintenance hemodialysis patients

Dialysis patients have severe exercise limitations related to metabolic disturbances, but muscle fatigue has not been well studied in this population. We investigated the magnitude and mechanisms of fatigue of the ankle dorsiflexor muscles in patients on maintenance hemodialysis. Thirty-three dialysis patients and twelve healthy control subjects performed incremental isometric dorsiflexion exercise, beginning at 10% of their maximal voluntary contraction (MVC) and increasing by 10% every 2 min. Muscle fatigue (fall of MVC), completeness of voluntary activation, and metabolic responses to exercise were measured. Before exercise, dialysis subjects exhibited reduced strength and impaired peripheral activation (lower compound muscle activation potential amplitude) but no metabolic perturbation. During exercise, dialysis subjects demonstrated threefold greater fatigue than controls with evidence of central activation failure but no change in peripheral activation. All metabolic parameters were significantly more perturbed at end exercise in dialysis subjects than in controls, including lower phosphocreatine (PCr) and pH, and higher Pi, Pi/PCr, and H2PO4−. Oxidative potential was markedly lower in patients than in controls [62.5 (SD 27.2) vs. 134.6 (SD 31.7), P < 0.0001]. Muscle fatigue was negatively correlated with oxidative potential among dialysis subjects ( r = −0.52, P = 0.04) but not controls. Changes in central activation ratio were also correlated with muscle fatigue in the dialysis subjects ( r = 0.59, P = 0.001) but not the controls. This study provides new information regarding the excessive muscular fatigue of dialysis patients and demonstrates that the mechanisms of this fatigue include both intramuscular energy metabolism and central activation failure.

Influence of recombinant human erythropoietin treatment on pulmonary O2 uptake kinetics during exercise in humans

We hypothesized that 4 weeks of recombinant human erythropoietin (RhEPO) treatment would result in a significant increase in haemoglobin concentration ([Hb]) and arterial blood O(2)-carrying capacity and that this would (1) increase peak pulmonary oxygen uptake during ramp incremental exercise, and (2) speed kinetics during 'severe'-, but not 'moderate'- or 'heavy'-intensity, step exercise. Fifteen subjects (mean +/- s.d. age 25 +/- 4 years) were randomly assigned to either an experimental group which received a weekly subcutaneous injection of RhEPO (150 IU kg(-1); n = 8), or a control group (CON) which received a weekly subcutaneous injection of sterile saline (10 ml; n = 7) as a placebo, for four weeks. The subjects and the principal researchers were both blind with respect to the group assignment. Before and after the intervention period, all subjects completed a ramp test for determination of the gas exchange threshold (GET) and , and a number of identical 'step' transitions from 'unloaded' cycling to work rates requiring 80% GET (moderate), 70% of the difference between the GET and (heavy), and 105% (severe) as determined from the initial ramp test. Pulmonary gas exchange was measured breath-by-breath. There were no significant differences between the RhEPO and CON groups for any of the measurements of interest ([Hb], kinetics) before the intervention. Four weeks of RhEPO treatment resulted in a 7% increase both in [Hb] (from 15.8 +/- 1.0 to 16.9 +/- 0.7 g dl(-1); P < 0.01) and (from 47.5 +/- 4.2 to 50.8 +/- 10.7 ml kg(-1).min(-1); P < 0.05), with no significant change in CON. RhEPO had no significant effect on kinetics for moderate (Phase II time constant, from 28 +/- 8 to 28 +/- 7 s), heavy (from 37 +/- 12 to 35 +/- 11 s), or severe (from 33 +/- 15 to 35 +/- 15 s) step exercise. Our results indicate that enhancing blood O(2)-carrying capacity and thus the potential for muscle O(2) delivery with RhEPO treatment enhanced the peak but did not influence kinetics, suggesting that the latter is principally regulated by intracellular (metabolic) factors, even during exercise where the requirement is greater than the , at least in young subjects performing upright cycle exercise.

Similarities in skeletal muscle strength and exercise capacity between renal transplant and hemodialysis patients

Exercise intolerance is common in hemodialysis (HD) and renal transplant (RTx) patients. Aim of the study was to assess to what extent exercise capacity and skeletal muscle strength of RTx patients differ from HD patients and healthy controls and to elucidate potential determinants of exercise capacity in RTx patients. Exercise capacity, muscle strength, lean body mass (LBM) and physical activity level (PAL) were measured by cycle-ergometry, isokinetic dynamometry, DEXA and Baecke Questionnaire, respectively, in 35 RTx, 16 HD and 21 controls. VO2peak and muscle strength of the RTx patients were significantly lower compared to controls (p<0.01), but not different compared to HD patients. In RTx patients, strength (p<0.001), PAL (p=0.001) and age (p=0.045) were significant predictors of VO2peak. Muscle strength was related to LBM (p=0.001) and age (p=0.001), whereas gender (p<0.001) and renal function (p=0.01) turned out to be significant predictors of LBM. No effects of corticosteroids were observed. Exercise capacity and muscle strength seem equally reduced in RTx and HD patients compared to controls. In RTx patients, muscle strength and PAL are highly related to exercise capacity. Renal function appears to be a significant predictor of LBM, and through the LBM, of muscle strength and exercise capacity.

Chronic Kidney Disease: A Risk Factor for Cardiovascular Disease

The goal of risk stratification of CVD inpatients with CKD is to lead to effective and early intervention and to prevent the adverse outcomes associated with this complex multisystem disease that is characteristic of growing number of patients with CKD in the general population and of patients receiving dialysis therapy or kidney transplantation. By 2030, there will be 2.24 million patients with ESRD in the United States, and approximately 1.3 million of these cases of ESRD will be caused by diabetes mellitus. Thus, CVD in this high-risk population presents a challenge for the nephrology and the cardiology community.