Improvement in exercise capacity after correction of anemia in patients with end-stage renal failure

The effect of erythropoiesis-stimulating agents on systolic and diastolic blood pressure in hemodialysis patients: A systematic review and meta-analysis of clinical trials

OBJECTIVE

Anemia is a common condition in end-stage renal disease (ESRD) patients. Erythropoiesis-stimulating agents (ESAs) are commonly used to treat anemia in these patients. However, concerns have been raised regarding their potential effects on blood pressure. This systematic review and meta-analysis aim to investigate the relationship between ESAs and changes in systolic and diastolic blood pressure in hemodialysis patients.

METHOD

This study is a systematic review and meta-analysis based on clinical trial studies published in various databases, including Web of Science, Cochrane Library, Science Direct, PubMed, Embase, Scopus, and Google Scholar, between 1980 and the end of 2022. We evaluated the quality of articles using the Jadad scale checklist and analyzed the data using Stata 15 software.

RESULTS

Our meta-analysis included 34 clinical trial studies. The results showed a significant increase in both systolic blood pressure (SBP) and diastolic blood pressure (DBP) after the consumption of ESAs compared to before consumption. The mean difference in SBP was 4.84mmHg (95% CI: 2.74-6.94; p-value<0.001) and in DBP was 4.69mmHg (95% CI: 2.67-6.71; p-value<0.001). No publication bias was observed. Our meta-regression analysis showed that sample size, quality assessment score, and geographical location of the study were significant factors related to observed heterogenicity in to mean difference of SBP (p-value≤0.20). For DBP, the sample size, quality assessment score and follow-up duration were significant variables (p-value≤0.20).

CONCLUSION

Based on the findings of our study, it appears that receiving ESAs is associated with a significant increase in both SBP and DBP in hemodialysis patients, with an increase of about 5mmHg.

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.

Effects of graded exercise training on functional capacity, muscle strength, and fatigue after renal transplantation: a randomized controlled trial

Successful renal transplantation (RT) recipients suffer residual muscle weakness, fatigue, and low functional capacity. A safe, feasible, structured, early graded exercise training to improve functional capacity, muscle strength, and fatigue is the need of the hour. The aim of the study is to assess the effectiveness of graded exercise training on the functional capacity, muscle strength, and fatigue after RT. It is a randomized controlled trial conducted at a tertiary care hospital from January 2012 to December 2016. This trial included 104 consented, stable renal transplant recipients without cardiopulmonary/neuromuscular impairment. They received either routine care (51) or graded exercise training (53) for 12 weeks after randomization. The functional capacity, isometric quadriceps muscle strength, and fatigue score were measured at baseline, six, and 12 weeks later to induction. The outcomes of the study and control groups were analyzed using the /-test, Wilcoxon signed-rank test, ANOVA, and Pearson's correlation. For all analyses, P <0.05 was fixed acceptable. The functional capacity improved by 147 and 255 m, the muscle strength by 6.35 and 9.27 kg, and fatigue score by 0.784 and 1.781 in the control and the study group (SG), respectively, significantly more in the SG. Functional capacity had a positive and negative correlation with muscle strength and fatigue, respectively (P <0.05). The graded exercise training significantly improved the functional capacity, fatigue levels, and muscle strength after RT.

Effect of anemia on muscle oxygen saturation during submaximal exercise

BACKGROUND

Objective measures to assess the need for transfusion in chronic anemia are lacking. Near-infrared spectroscopy may be used, but there is wide variability. Assessment of muscle oxygen saturation (SmO₂ ) during exercise could be used to measure the impact of anemia on performance of everyday activities.

STUDY DESIGN AND METHODS

Hematology patients and controls were recruited to undertake a 6-minute walk test (6MWT) and a 20-second isometric handgrip exercise. Muscle oxygen saturation in the exercising muscles was measured before and during exercise. Changes in saturation during exercise were described. Correlations between identified variables, hemoglobin concentration, and 6MWT distance were undertaken. The effect of transfusion was assessed on a transfused subset.

RESULTS

There were 95 sets of exercises conducted in 74 participants. Baseline SmO₂ correlated with hemoglobin concentration and negatively with 6MWT distance. Paradoxically, a higher hemoglobin was associated with a greater SmO₂ fall during the 6MWT, likely due to greater consumption from improved walk distances. The fall in SmO₂ was independent of hemoglobin during isometric contraction, although levels were lower during contraction due to the lower starting SmO₂ . There was a longer time to peak SmO₂ during recovery following isometric exercise in anemia. There were 17 paired tests following a change in hemoglobin, with SmO₂ not predicting improvement in those who had improved exercise capacity.

CONCLUSION

While baseline SmO₂ correlated with hemoglobin concentration, the correlation was not strong enough to predict transfusion requirements. Recovery after isometric forearm contraction correlated with hemoglobin and warrants further investigation.

Reduced fitness and abnormal cardiopulmonary responses to maximal exercise testing in children and young adults with sickle cell anemia

Physiologic contributors to reduced exercise capacity in individuals with sickle cell anemia (SCA) are not well understood. The objective of this study was to characterize the cardiopulmonary response to maximal cardiopulmonary exercise testing (CPET) and determine factors associated with reduced exercise capacity among children and young adults with SCA. A cross-sectional cohort of 60 children and young adults (mean 15.1 ± 3.4 years) with hemoglobin SS or S/β⁰ thalassemia and 30 matched controls (mean 14.6 ± 3.5 years) without SCA or sickle cell trait underwent maximal CPET by a graded, symptom-limited cycle ergometry protocol with breath-by-breath, gas exchange analysis. Compared to controls without SCA, subjects with SCA demonstrated significantly lower peak VO₂ (26.9 ± 6.9 vs. 37.0 ± 9.2 mL/kg/min, P < 0.001). Subjects demonstrated slower oxygen uptake (ΔVO₂/ΔWR, 9 ± 2 vs. 12 ± 2 mL/min/watt, P < 0.001) and lower oxygen pulse (ΔVO₂/ΔHR, 12 ± 4 vs. 20 ± 7 mL/beat, P < 0.001) as well as reduced oxygen uptake efficiency (ΔV_E/ΔVO₂, 42 ± 8 vs. 32 ± 5, P < 0.001) and ventilation efficiency (ΔV_E/ΔVCO₂, 30.3 ± 3.7 vs. 27.3 ± 2.5, P < 0.001) during CPET. Peak VO₂ remained significantly lower in subjects with SCA after adjusting for age, sex, body mass index (BMI), and hemoglobin, which were independent predictors of peak VO₂ for subjects with SCA. In the largest study to date using maximal CPET in SCA, we demonstrate that children and young adults with SCA have reduced exercise capacity attributable to factors independent of anemia. Complex derangements in gas exchange and oxygen uptake during maximal exercise are common in this population.

Darbepoetin alfa impact on health status in diabetes patients with kidney disease: a randomized trial

BACKGROUND AND OBJECTIVES

Quality of life (QOL) is markedly impaired in patients with anemia, diabetes mellitus, and chronic kidney disease. Limited data exist regarding the effect of anemia treatment on patient perceptions. The objectives were to determine the longitudinal impact of anemia treatment on quality of life in patients with diabetes and chronic kidney disease and to determine the predictors of baseline and change in QOL.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a large, double blind study, patients with type 2 diabetes mellitus, nondialysis chronic kidney disease (estimated GFR, 20 to 60 ml/min per 1.73 m(2)), and anemia (hemoglobin 10.4 g/dl) were randomized to darbepoetin alfa or placebo. QOL was measured with Functional Assessment of Cancer Therapy-Fatigue, Short Form-36, and EuroQol scores over 97 weeks.

RESULTS

Patients randomized to darbepoetin alfa reported significant improvements compared with placebo patients in Functional Assessment of Cancer Therapy-Fatigue, and EuroQol scores visual analog scores, persisting through 97 weeks. No consistent differences in Short Form-36 were noted. Consistent predictors of worse change scores include lower activity level, older age, pulmonary disease, and duration of diabetes. Interim stroke had a substantial negative impact on fatigue and physical function.

CONCLUSION

Darbepoetin alfa confers a consistent, but small, improvement in fatigue and overall quality of life but not in other domains. These modest QOL benefits must be considered in the context of neutral overall effect and increased risk of stroke in a small proportion of patients. Patient's QOL and potential treatment risk should be considered in any treatment decision.

Physical functioning in elderly persons with kidney disease

Poor physical functioning in dialysis patients has been well documented. Several studies have reported an association of poor kidney function with adverse physical functioning outcomes, even in elderly persons with mild decrements in kidney function. These associations have been observed across multiple domains of physical function. This review summarizes the current research on physical functioning in kidney disease, with a special focus on elderly populations. Elderly persons with kidney disease may especially be at a high risk for disability and other adverse outcomes because of the dual effects of aging and kidney dysfunction on physical functioning. Both the correction of anemia and physical activity are effective for at least moderate improvements in physical function although these studies have been conducted primarily in younger persons with less comorbidity. The evidence that exists on exercise interventions in older adults with kidney disease is promising, although this population has been underrepresented in trials to date. More research on potential interventions to prevent or reduce poor physical functioning is needed in elderly persons with kidney disease.

Hemoglobin levels predict exercise performance, ST-segment depression, and outcome in patients referred for routine exercise treadmill testing

BACKGROUND

While the role of hemoglobin in heart failure and renal disease has been investigated, little is known about its effect on clinical exercise test performance and mortality in patients referred for routine exercise treadmill testing (ETT).

HYPOTHESIS

Patients with low hemoglobin will have poor exercise capacity and would be at increased risk of mortality and cardiovascular (CV) events.

METHODS

Clinical variables, laboratory values, and exercise treadmill data were obtained for 1,799 patients referred for routine ETT from 1997 to 2004. All-cause mortality was obtained from the United States Social Security death index and autopsy reports or clinical notes were used to determine CV events and mortality. P values < 0.05 were considered significant.

RESULTS

Our population had a mean age of 58 +/- 12 years, 16% had diabetes, 53% had hypertension, 35% had hypercholesterolemia, and 67% had a history of smoking. During follow-up, 10.3% of patients died, 3.9% of patients died of CV causes, and 11.6% had cardiovascular events. Anemic patients (hemoglobin [Hgb] < 13 g/dL) achieved lower metabolic equivalents (METs) than nonanemic patients and had more ST-segment depression (15.5% versus 8.6%, p < 0.004). Proportional hazard analysis demonstrated that hemoglobin was significantly associated with all-cause mortality (p < 0.0007), CV mortality (p < 0.009), and CV events (p < 0.01). Kaplan-Meier survival analysis demonstrated that anemic patients had significantly higher mortality and CV events.

CONCLUSION

Hemoglobin is significantly associated with exercise performance, ST-segment depression during ETT, mortality, and cardiovascular events. The incorporation of hemoglobin may add diagnostic and prognostic information to ETT.

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.

Association of anemia correction with health related quality of life in patients not on dialysis

OBJECTIVE

This was an open-label study to asses the association of changes in hemoglobin with changes in health related quality of life (HRQOL) in patients treated with darbepoetin alfa.

METHODS

Originally, 81 chronic kidney disease (CKD) patients not on dialysis and naïve to erythropoiesis stimulating agents (ESA) were randomly assigned into two open-label groups (3 : 1). As a majority of control group patients opted out of control status, this study reports on the single arm study analysis that was performed on the 48 patients who received the drug through week 16. Sixty-two patients received once-weekly darbepoetin alfa in addition to conservative management for CKD. Instruments that measured general (SF-36, FACTanemia, FACT-fatigue, ADL and IADL) and disease specific (KDQOL) HRQOL domains were administered at baseline and after 8, 16, and 24 weeks.

RESULTS

Compared to baseline values, mean HRQOL subscales were significantly improved in the treatment group at 16 weeks (p < 0.05 for SF-36 physical function; p < 0.001 for SF-36 vitality, FACT anemia and FACT fatigue scales). At week 16, the SF-36 mean increase for 48 treatment patients in the Vitality Subscale Score was 14.9 (SD 3.2) and the mean increase in the KDQOL Burden of Kidney Disease Subscale was 5.5 (SD 3.3). Multivariate regression analysis demonstrated a statistically significant association (p < 0.05) between hemoglobin levels and higher HRQOL scores on several physical function, energy and fatigue scales.

CONCLUSION

Improvements in hemoglobin in CKD patients not on dialysis were associated with statistically significant (p < 0.05), clinically meaningful (> 5 points) HRQOL improvements on scales measuring physical activity, vitality and fatigue. Our study did not show an association between increased hemoglobin levels and other aspects of HRQOL, such as those relating to emotional status, sexual activity or cognition. The interpretation of our results is limited by the lack of a control arm to assess whether conservative therapy for CKD, in the absence of ESA administration, would have a comparable effect on patients' HRQOL scores. Further research needs to examine whether other aspects of HRQOL improve with anemia treatment, in the same way as those aspects of HRQOL more closely related to physical activity and fatigue.

Anemia and heart failure: a cause of progression or only a consequence?

Anemia is one of the most frequent co-morbidities in the patients with heart failure. Its prevalence increases from 4-7% in the subjects with asymptomatic left ventricular dysfunction to >30% in the patients with severe heart failure. Renal insufficiency, activation of inflammatory mediators, and treatment with renin-angiotensin antagonists seem to be its main determinants. The results of many studies agree in showing that anemia is a powerful independent determinant of survival in patients with heart failure. However, the mechanisms of this relation are still incompletely understood. Moreover a favourable effect on prognosis of the correction of anemia has not been shown, yet, and also controlled studies assessing its effects on exercise tolerance have yielded controversial results.

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.

Skeletal muscle dysfunction in chronic renal failure: effects of exercise

A number of chronic illnesses such as renal failure (CRF), obstructive pulmonary disease, and congestive heart failure result in a significant decrease in exercise tolerance. There is an increasing awareness that prescribed exercise, designed to restore some level of physical performance and quality of life, can be beneficial in these conditions. In CRF patients, muscle function can be affected by a number of direct and indirect mechanisms caused by renal disease as well as various treatment modalities. The aims of this review are twofold: first, to briefly discuss the mechanisms by which CRF negatively impacts skeletal muscle and, therefore, exercise capacity, and, second, to discuss the available data on the effects of programmed exercise on muscle function, exercise capacity, and various other parameters in CRF.

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.

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.

Physical functioning in end-stage renal disease patients: Update 2005

Physical functioning in patients with end-stage renal disease treated with dialysis is low, whether measured using objective laboratory measures, physical performance testing, or self-reported measures. Peak oxygen uptake (VO2peak), self-reported functioning measures, and physical activity levels are independent predictors of mortality in these patients. Cardiovascular exercise training studies result in improvements in VO2peak, physical performance tests, and self-reported functioning. Resistance exercise training improves muscle strength. Exercise training may have positive benefits on other factors that are important clinical issues in dialysis patients, including cardiovascular risk profile, oxidative stress, and inflammation. Endothelial function, a surrogate marker of atherosclerosis, has been shown to improve with exercise training in dialysis patients. Although there have been numerous recent studies on benefits of exercise, few dialysis clinics or nephrologists provide encouragement or programs as a part of their routine care of their patients. There are many national guidelines that include exercise or increasing physical activity as a part of the treatment of many conditions that are relevant in dialysis patients, including hypertension, hyperlipidemia, and high cardiovascular disease risk. The nephrology community continues to state concern for outcomes; however, a simple, low-tech intervention that has many benefits to their patients (i.e., encouragement, recommendations, and opportunity for increasing physical activity) has not been adopted as part of the standard care. Adoption of routine counseling and encouragement for physical activity has the potential to improve outcomes, improve physical functioning, and optimize quality of life and overall health of dialysis patients.

Altered Ca2+ homeostasis in human uremic skeletal muscle: possible involvement of cADPR in elevation of intracellular resting [Ca2+]

BACKGROUND

Patients with chronic renal failure may develop muscle weakness and fatigability due to disorders of skeletal muscle function, collectively known as the uremic myopathy. Cyclic adenosine diphosphate-ribose (cADPR), an endogenous metabolite of beta-NAD+, activates Ca2+ release from intracellular stores in vertebrate and invertebrate cells. The current study investigated the possible role of cADPR in uremic myopathy.

METHODS

We have examined the effect of cADPR on myoplasmic resting Ca2+ concentration ([Ca2+]i) in skeletal muscle obtained from control subjects and uremic patients (UP). [Ca2+]i was measured using double-barreled Ca2+-selective microelectrodes in muscle fibers, prior to and after microinjections of cADPR.

RESULTS

Resting [Ca2+]i was elevated in UP fibers compared with fibers obtained from control subjects. Removal of extracellular Ca2+, or incubation of cells with nifedipine, did not modify [Ca2+]i in UP or control fibers. Microinjection of cADPR produced an elevation of [Ca2+]i in both groups of cells. This elevation was not mediated by Ca2+ influx, or inhibited by heparin or ryanodine. [cADPR]i was determined to be higher in muscle fibers from UP compared to those from the control subjects. Incubation of cells with 8-bromo-cADPR, a cADPR antagonist, partially reduced [Ca2+]i in UP muscle fibers and blocked the cADPR-elicited elevation in [Ca2+]i in both groups of muscle cells.

CONCLUSION

Skeletal muscles of the UP exhibit chronic elevation of [Ca2+]i that can be partially reduced by application of 8-bromo-cADPR. cADPR was able to mobilize Ca2+ from intracellular stores, by a mechanism that is independent of ryanodine or inositol trisphosphate receptors. It can be postulated that an alteration in the cADPR-signaling pathway may exist in skeletal muscle of the patients suffering from uremic myopathy.

Epoetin alfa's effect on left ventricular hypertrophy and subsequent mortality

BACKGROUND

Improving anemia in patients with chronic renal failure (CRF) and congestive heart failure (CHF) also improves left ventricular hypertrophy (LVH). No previous meta-analyses have been conducted to further examine this association, including the association between LVH and mortality in these patients.

METHODS AND RESULTS

Literature searches on MEDLINE, EMBASE, and OVID were performed using Cochrane Library protocols. Two hundred sixteen abstracts were reviewed preliminarily for inclusion in the meta-analysis of epoetin alfa, anemia and 5 pre-selected parameters of LVH. One hundred seventy-nine abstracts were reviewed for LVH and mortality. The predominant hematologic and left ventricular function changes observed during epoetin alfa treatment in patients with CHF and CRF are (1) increases in hemoglobin (Hb) and hematocrit (Hct); (2) decreases in left ventricular mass (LVM) and LVM index; (3) increase in ejection fraction (EF); and (4) decreases in left ventricular end-diastolic and end-systolic volume. Three independent factors-target Hb, duration of disease, and duration of follow-up-each had a statistically significant association with Hb, Hct, and EF, respectively. A separate meta-analysis using 3 risk models showed LVH is strongly and positively associated with both cardiovascular and all-cause mortality, with two- to three-fold increases in risk.

CONCLUSIONS

LVH is common in patients with CRF and CHF. Current findings indicate epoetin alfa therapy results in anemia amelioration, as evidenced by higher Hb and Hct levels, and reduction of key LVH parameters. LVM regression is associated with lower incidence of cardiovascular-related morbidity and mortality, therefore epoetin alfa therapy may provide a survival benefit.

Association of chronic kidney disease and anemia with physical capacity: the heart and soul study

Chronic kidney disease (CKD) and anemia are common conditions in the outpatient setting, but their independent and additive effects on physical capacity have not been well characterized. The association of CKD and anemia with self-reported physical function was evaluated and exercise capacity was measured in patients with coronary disease. A cross-sectional study of 954 outpatients enrolled in the Heart and Soul study was performed. CKD was defined as a measured creatinine clearance <60 ml/min, and anemia was defined as a hemoglobin level of <12g/dl. Physical function was self-assessed using the physical limitation subscale of the Seattle Angina Questionnaire (0 to 100), and exercise capacity was defined as metabolic equivalent tasks achieved at peak exercise. In unadjusted analyses, CKD was associated with lower self-reported physical function (67.6 versus 74.9; P < 0.001) and lower exercise capacity (5.5 versus 7.9; P < 0.001). Similarly, anemia was associated with lower self-reported physical function (62.6 versus 74.3; P < 0.001) and exercise capacity (5.7 versus 7.5; P < 0.001). After multivariate adjustment, CKD (69.4 versus 74.2; P = 0.003) and anemia (67.5 versus 73.6; P = 0.009) each remained associated with lower mean self-reported physical function. In addition, patients with CKD (6.3 versus 7.7; P < 0.001) or anemia (6.5 versus 7.4; P = 0.004) had lower adjusted mean exercise capacities. Participants with both CKD and anemia had lower self-reported physical function and exercise capacity than those with either alone. CKD and anemia are independently associated with physical limitation and reduced exercise capacity in outpatients with coronary disease, and these effects are additive. The broad impact of these disease conditions merits further study.

Physical and sexual function in women with chronic kidney disease

BACKGROUND

Cross-sectional studies suggest an association between functional status and chronic kidney disease (CKD). Whether physical function deteriorates with progression of CKD is unknown.

METHODS

To determine associations among CKD, physical function, and sexual function in women, we conducted cross-sectional and longitudinal analyses of 2,761 women enrolled in the Heart and Estrogen/Progestin Replacement Study. Physical and sexual function were evaluated using the Duke Activity Status Index (DASI) and the Sexual Problems Scale of the Medical Outcomes Study, respectively. Glomerular filtration rate (GFR) was estimated using the Modification of Diet in Renal Disease regression equation. In addition to analyses across the spectrum of GFR, CKD was categorized as mild (estimated GFR, 45 to 60 mL/min/1.73 m2), moderate (estimated GFR, 30 to 44 mL/min/1.73 m2), and severe (estimated GFR, <30 mL/min/1.73 m2) according to a modification of recently established classification guidelines.

RESULTS

Mean age of study participants was 67 +/- 7 years, and mean estimated GFR was 61 +/- 14 mL/min/1.73 m2. In unadjusted analyses, mean baseline DASI score was 10 points lower in women with an estimated GFR less than 30 mL/min/1.73 m2 than in women with an estimated GFR of 60 mL/min/1.73 m2 or greater (P < 0.0001). Estimated GFR remained significantly associated with DASI score after multivariable adjustment. In longitudinal analyses, a decline in estimated GFR was associated with a significant decline in DASI score independent of baseline estimated GFR and other factors. There were no significant associations between estimated GFR and psychosocial aspects of sexual function.

CONCLUSION

CKD is associated with impaired physical function, and a decline in estimated GFR is associated with a decline in physical function.

Hemodynamic cardiovascular risk factors in chronic kidney disease: what are the effects of intervention?

Left ventricular (LV) volume and pressure overload occur frequently in chronic kidney disease (CKD). Anemia is a risk factor for left ventricular hypertrophy (LVH) and dilatation, heart failure, and death. Normalization of hemoglobin with erythropoietin may prevent LVH and dilatation in CKD, but in patients in later phases of their cardiac disease, this intervention is not of benefit. Increased vascular volume causes hypertension, which in turn causes LVH, cardiac failure, and ischemic heart disease (IHD). Manifestations of arteriosclerosis are associated with adverse cardiac outcomes, and angiotensin converting enzyme (ACE) inhibitors may improve LVH and markers of arteriosclerosis. Aortic stenosis in dialysis patients occurs infrequently, but may deteriorate rapidly. The hemodialysis milieu is the quintessential model of LV overload cardiomyopathy.

Detection of DNA-recombinant human epoetin-alfa as a pharmacological ergogenic aid

The use of DNA-recombinant human epoetin-alfa (rhEPO) as a pharmacological ergogenic aid for the enhancement of aerobic performance is estimated to be practised by at least 3 to 7% of elite endurance sport athletes. rhEPO is synthesised from Chinese hamster ovary cells, and is nearly identical biochemically and immunologically to endogenous epoetin-alfa (EPO). In a clinical setting, rhEPO is used to stimulate erythrocyte production in patients with end-stage renal disease and anaemia. A limited number of human studies have suggested that rhEPO provides a significant erythropoietic and ergogenic benefit in trained individuals as evidenced by increments in haemoglobin, haematocrit, maximal oxygen uptake (VO2max) and exercise endurance time. The purpose of this review is to summarise the various technologies and methodologies currently available for the detection of illicit use of rhEPO in athletes. The International Olympic Committee (IOC) banned the use of rhEPO as an ergogenic aid in 1990. Since then a number of methods have been proposed as potential techniques for detecting the illegal use of rhEPO. Most of these techniques use indirect markers to detect rhEPO in blood samples. These indirect markers include macrocytic hypochromatic erythrocytes and serum soluble transferrin receptor (sTfr) concentration. Another indirect technique uses a combination of 5 markers of enhanced erythropoiesis (haematocrit, reticulocyte haematocrit, percentage of macrocytic red blood cells, serum EPO, sTfr) to detect rhEPO. The electrophoretic mobility technique provides a direct measurement of urine and serum levels of rhEPO, and is based on the principle that the rhEPO molecule is less negatively charged versus the endogenous EPO molecule. Isoelectric patterning/focusing has emerged recently as a potential method for the direct analysis of rhEPO in urine. Among these various methodologies, the indirect technique that utilises multiple markers of enhanced erythropoiesis appears to be the most valid, reliable and feasible protocol currently available for the detection of rhEPO in athletes. In August 2000, the IOC Medical Commission approved this protocol known as the 'ON model', and it was subsequently used in combination with a second, confirmatory test (isoelectric patterning) to detect rhEPO abusers competing in the 2000 Sydney Summer Olympics. This combined blood and urine test was approved with modifications by the IOC in November 2001 for use in the 2002 Salt Lake City Winter Olympics.

Low-volume exercise rehabilitation improves functional capacity and self-reported functional status of dialysis patients

OBJECTIVE

The purpose of this study was to examine the effects of a program of low-volume exercise rehabilitation on the functional capacity and self-reported functional status of nonanemic dialysis patients.

DESIGN

This was a controlled study in a clinical setting with a repeated measures design. Functional capacity and functional status were assessed before and after 12 wk of exercise rehabilitation or 12 wk of normal activity for two groups of dialysis patients.

RESULTS

Mixed-model repeated measures analysis of variance revealed significant group by time interactions characterized by improvements for the exercise rehabilitation group alone in total walk, stair-climb, and stair-descent times of 15+/-5.8%, 22+/-11%, and 18+/-12% respectively. Self-reported walking speed, walking impairment-leg weakness, and walking impairment-shortness of breath were also observed to improve significantly for the exercise rehabilitation group alone by 15+/-13%, 25+/-11%, and 28+/-16%, respectively.

CONCLUSION

Low-volume exercise rehabilitation can improve activity of daily living-related functional capacity and self-reported functional status of nonanemic dialysis patients.

Effects of exercise training plus normalization of hematocrit on exercise capacity and health-related quality of life

The limitation to exercise capacity in hemodialysis patients has been attributed to anemia. We report the effects of normalization of hematocrit levels by using r-hu-recombinant erythropoietin and exercise training on exercise capacity and self-reported physical functioning in hemodialysis patients. Sixty-five patients were randomized into 1 of 4 groups: usual hematocrit (30%-33%) with no exercise training (UH); usual hematocrit (30%-33%) plus exercise training (UHX); normalized hematocrit (40%-42%) with no exercise training (NH); and normalized hematocrit (40%-42%) plus exercise training (NHX). Treadmill exercise testing was conducted at baseline and at 5 months after the initiation of the interventions. Analysis was performed on the data collapsed for 48 patients who met the criteria for hematocrit and exercise adherence and completed both baseline and post intervention (5.6 +/- 1.6 months) testing. Significant effects of exercise were found in peak oxygen uptake measurements (P = 0.03) and in self-reported physical functioning as measured by the Short Form-36 questionnaire (P = 0.01). There was a significant effect of hematocrit on the General Health scale on the SF-36 (P = 0.03). The changes in peak oxygen uptake with exercise training were small and levels remained lower than age-predicted values at the end of the study. These results indicate that there are other physiologic limitations to exercise capacity that are not overcome by exercise training or normalization of hematocrit. The effects of exercise training on self-reported physical functioning may be of clinical importance because these scores have been shown to be highly predictive of outcomes such as hospitalizations and mortality in hemodialysis patients.

Clinical and demographic predictors of exercise capacity in end-stage renal disease

Patients on maintenance hemodialysis therapy for end-stage renal disease have reduced exercise tolerance. Multiple processes related to uremia and hemodialysis have been implicated in the pathophysiology of this impairment. However, limited data are available to identify the separate and combined effects of clinical factors on the degree of impairment for individuals within this population. For this purpose, data from 193 patients who had undergone exercise testing for two clinical trials were retrospectively analyzed. Univariate and multiple linear regression analyses were used to identify demographic and clinical correlates of peak exercise oxygen uptake (VO2). Peak VO2 averaged 18.5 +/- 6.4 mL/min/kg. On univariate analysis, peak VO2 correlated positively with male sex and hemoglobin, serum albumin, and serum creatinine concentrations and correlated negatively with dialytic age and diagnosis of diabetes or chronic heart failure. In a multiple linear regression model, sex, hemoglobin concentration, age, and diagnosis of diabetes each remained statistically significant. Together, factors included in the model accounted for 41% of the variability in peak VO2 (P = 0.0001). Among factors not correlating significantly with peak VO2 were resting blood pressure, serum carnitine level, and urea clearance assessed by Kt/V. Findings show the range of exercise impairment among clinically stable ambulatory hemodialysis patients, which may be sufficient to interfere with normal daily activities for many of these patients. Although this impairment may be broadly attributable to physiological consequences of uremia, the degree of impairment for individual patients is predicted by demographic factors, coexistent disease, and factors potentially modified by medical therapeutics.

Determinants of physical performance in ambulatory patients on hemodialysis

BACKGROUND

Physical performance measures, particularly gait speed, have been useful as predictors of loss of independence, institutionalization, and mortality in older nonuremic individuals. Gait speed has not been evaluated as a predictor of these important outcomes in patients on hemodialysis, nor have the determinants of gait speed in the dialysis population been studied.

METHODS

We performed a cross-sectional analysis to determine whether demographic, clinical, or nutritional status variables were related to physical performance in a group of 46 hemodialysis patients treated at three University of California San Francisco-affiliated dialysis units. Three physical performance measures were examined, including gait speed, time to climb stairs, and time to rise from a chair five times in succession. Forward stepwise linear-regression analysis was performed with each physical performance measure as the dependent variable and the following candidate predictor variables: age, gender, body mass index, dialysis vintage, Kt/V, albumin, blood urea nitrogen, creatinine, hematocrit, lean body mass, phase angle, ferritin, and the following comorbidities: hypertension, diabetes mellitus, coronary artery disease, peripheral vascular disease, and cerebrovascular disease.

RESULTS

Subjects included 31 men and 15 women aged 22 to 87 years (mean +/- SD, 52 +/- 17). The mean gait speed for the group was 113.1 +/- 34.5 cm/s (low compared with norms established for persons of similar age). Results of multivariable regression showed that age, albumin, and Kt/V were important determinants of gait speed in this population. Overall, the model explained 52% of the variability in gait speed (r = 0.72, P < 0.0001). Qualitatively similar results were obtained using stair-climbing time or chair-rising time as the dependent variables, except that comorbidity was more important than age for stair climbing. The addition of physical activity level to the models did not eliminate the associations of albumin or Kt/V with physical performance.

CONCLUSIONS

Physical performance is significantly impaired in ambulatory hemodialysis patients and is related to age, serum albumin, and dialysis dose. Prospective studies are needed to determine whether modification of dialysis dose or nutritional interventions can improve physical performance in patients on hemodialysis.

Muscle angiogenic growth factor gene responses to exercise in chronic renal failure

Patients with chronic renal failure (CRF) have impaired exercise capacity even after erythropoietin treatment. We recently showed that although this is explained in part by reduced convective O(2) delivery to muscles, there is also an impairment of O(2) transport from muscle capillaries to the mitochondria. Given the importance of the capillary surface area for capillary mitochondrial O(2) transport and reports of reduced capillarity in CRF, we hypothesized that the angiogenic gene response to exercise is impaired in such patients. Six patients with CRF and six control subjects matched for age, size, and sedentary lifestyle exercised on a single occasion for 1 h at similar work intensities averaging 50% of maximal capacity. Exercise was confined to the knee extensors of a single leg by means of a specially designed leg-kick ergometer. A percutaneous biopsy of the quadriceps was taken within 30 min of cessation of exercise and compared with a similar biopsy done at different times without any prior exercise for 24 h. Conventional Northern blots were prepared and probed for vascular endothelial growth factor (VEGF; the major putative angiogenic growth factor for muscle), basic fibroblast growth factor (bFGF), and transforming growth factor (TGF)-beta(1). Data during both rest and exercise were successfully obtained in four subjects of each group. We also assessed muscle capillarity and mitochondrial oxidative capacity to relate to these changes. Mitochondrial oxidative capacity was normal, whereas capillary number per fiber was 12% lower than in normal subjects. VEGF mRNA abundance was increased after exercise by about one order of magnitude, with no reduction in response in CRF. For bFGF and TGF-beta(1), exercise elicited no response in either group. Reduced muscle capillarity in CRF does not, therefore, stem from reduced transcription of VEGF. To the extent that VEGF is important to exercise-induced angiogenesis in muscle, we suspect a posttranscriptional aberration in this response occurs in CRF to explain reduced capillarity.

Impaired muscle oxygen transfer in patients with chronic renal failure

We hypothesized that impaired O2 transport plays a role in limiting exercise in patients with chronic renal failure (CRF). Six CRF patients (25 +/- 6 yr) and six controls (24 +/- 6 yr) were examined twice during incremental single-leg isolated quadriceps exercise. Leg O2 delivery (QO2(leg)) and leg O2 uptake (VO2(leg)) were obtained when subjects breathed gas of three inspired O2 fractions (FI(O2)) (0.13, 0.21, and 1.0). On a different day, myoglobin O2 saturation and muscle bioenergetics were measured by proton and phosphorus magnetic resonance spectroscopy. CRF patients, but not controls, showed O2 supply dependency of peak VO2 (VO2(peak)) by a proportional relationship between peak VO2(leg) at each inspired O2 fraction (0.59 +/- 0.20, 0.47 +/- 0.10, 0.43 +/- 0.10 l/min, respectively) and 1) work rate (933 +/- 372, 733 +/- 163, 667 +/- 207 g), 2) QO(2leg) (0.80 +/- 0.20, 0.64 +/- 0.10, 0.59 +/- 0.10 l/min), and 3) cell PO2 (6.3 +/- 5.4, 1.7 +/- 1.3, 1.2 +/- 0.7 mmHg). CRF patients breathing 100% O2 and controls breathing 21% O2 had similar peak QO2(leg) (0.80 +/- 0.20 vs. 0.79 +/- 0.10 l/min) and similar peak VO2(leg) (0.59 +/- 0.20 vs. 0.57 +/- 0.10 l/min). However, mean capillary PO2 (47.9 +/- 4.0 vs. 38.2 +/- 4.6 mmHg) and the capillary-to-myocite gradient (40.7 +/- 6.2 vs. 34.4 +/- 4.0 mmHg) were both higher in CRF patients than in controls (P < 0.03 each). We conclude that low muscle O2 conductance, but not limited mitochondrial oxidative capacity, plays a role in limiting exercise tolerance in these patients.

Worsening of left ventricular diastolic function during long-term correction of anemia with erythropoietin in chronic hemodialysis patients--an assessment by radionuclide ventriculography at rest and exercise

We studied the effect of correction of anemia with erythropoietin on left ventricular systolic and diastolic function at rest and exercise in 17 chronic hemodialysis patients by means of maximum exercise testing and equilibrium gated radionuclide angiocardiography on three occasions: 1) initial--before erythropoietin administration, 2) intermediate--at the time when the target hemoglobin level reached 100 g/l, and 3) long-term--after 12 months of therapy. After correction of anemia, the patients showed a significant improvement in their response to exercise regarding maximal work load achieved, exercise duration and recovery time. Ejection fraction and peak ejection rate remained unchanged during therapy. At rest, peak filling rate was reduced from 2.62 +/- 1.0 (baseline) to 2.28 +/- 0.9 (intermediate) end-diastolic volume per second, p < 0.01, while no significant difference was observed during exercise. The time to peak filling rate was prolonged significantly during EPO therapy from 157 +/- 30 to 177 +/- 28 ms at rest, p < 0.05, and from 101 +/- 24 to 130 +/- 27 ms during exercise, p < 0.01. By the time of the late study, there were no significant differences between the late and intermediate study. In conclusion, amelioration of anemia with erythropoietin in hemodialysis patients produced improvement in exercise capacity, but diastolic function worsened with therapy and this effect was maintained during the long-term treatment, while systolic function at rest and exercise remained unchanged.

Physical functioning and exercise capacity in patients on dialysis

Patients on dialysis have extremely limited exercise capacity, and poor physical functioning has been linked to low quality of life and high mortality in this population. The reason for the debility of patients on dialysis is far from clear despite years of study. The anemia of chronic renal disease is clearly a contributing factor, but uremic myopathy and resulting decreased muscle oxygen utilization have a significant impact on the physical functioning of patients on dialysis as well. Although it is likely that factors related to uremia adversely affect muscle function, some of the abnormalities demonstrated in uremic muscle are consistent with disuse atrophy. The clear contribution of anemia and the possible role of limited physical activity have led to studies of the effects of erythropoietin and aerobic exercise training on exercise capacity in end-stage renal disease patients. Both of these interventions result in increased exercise capacity. Thus vigorous treatment of anemia and uremia and encouragement of physical activity are important interventions to maximize the physical functioning of patients on dialysis. In addition, more studies are needed to clarify the causes of debility in this population and the impact of interventions on physical functioning, quality of life, and mortality.

Health promotion for end-stage renal disease patients

Health promotion is the desired objective of dialysis treatment. Achieving the highest level of functioning not only improves the life of the patient but rewards the staff through the positive feedback that improvement produces. The facility is rewarded by a stable population producing a more secure stream of income. The therapeutic environment is improved through better communication, positive attitudes, and more active participation of patients in their care. When maximum health is the focus of care, activities to achieve health are part of routine clinical contact, not additional effort requiring more staff. Fundamental to achieving health is adequate dialysis, control of anemia, good nutrition, and attention to comorbid conditions. The "Five Es" Life Options model of rehabilitation is a pattern for pursuing health and life enhancement. Encouragement is the positive attitude and expectations for each patient. Evaluation is individualized planning and periodic assessment of progress. Education prepares the patient for participation and responsibility. Exercise (on dialysis and off) improves physical capacity and well being. Employment is sought for those of working age and capability. A number of facilities have shown the effectiveness and benefits of these practices. In addition, using health status/quality of life measures to obtain patient-reported assessment of condition allows objective scoring. Comparisons and compilations can be made to evaluate the effect of interventions or illness on status. This can be accomplished for groups or individuals to document the effect of health promotion.

Maximal and submaximal exercise testing in heart failure

Although reduced exercise capacity is the main complaint of patients with congestive heart failure (CHF), the best method to measure it remains controversial. Peak VO2, obtained using maximal exercise testing, is the most accurate measure of maximal functional capacity. It is related to peak exercise cardiac output and is one of the most important independent variables for the prognostic assessment of patients with CHF. It has, however, a low sensitivity for measurement of changes induced by therapy and is poorly related to everyday physical activity, patient symptoms, and quality of life. The anerobic threshold may also be regarded as a parameter of maximal functional capacity. Its value is mainly indirect, because it shows that the patient is performing a maximal effort limited by the cardiovascular system. The VO2 kinetics at the start and at the end of exercise are probably more related to patient symptoms, but it is unresolved which protocols and parameters might best be used to study this aspect of exercise performance. Duration of a submaximal exercise at a constant work rate and the distance walked during a 6-min walking test are gaining wide popularity as parameters of submaximal performance. However, when these exams are carried out up to exhaustion in patients with severe functional limitation, they may involve attainment of the anerobic threshold and therefore their clinical meaning may be similar to the one of a maximal exercise test. Moreover, tests based on the assessment of submaximal exercise capacity have been useful for assessment of therapy in single-center trials but have been often inadequate in multicenter trials.

Physiological implications of altitude training for endurance performance at sea level: a review

Acclimatisation to environmental hypoxia initiates a series of metabolic and musculocardio-respiratory adaptations that influence oxygen transport and utilisation, or better still, being born and raised at altitude, is necessary to achieve optimal physical performance at altitude, scientific evidence to support the potentiating effects after return to sea level is at present equivocal. Despite this, elite athletes continue to spend considerable time and resources training at altitude, misled by subjective coaching opinion and the inconclusive findings of a large number of uncontrolled studies. Scientific investigation has focused on the optimisation of the theoretically beneficial aspects of altitude acclimatisation, which include increases in blood haemoglobin concentration, elevated buffering capacity, and improvements in the structural and biochemical properties of skeletal muscle. However, not all aspects of altitude acclimatisation are beneficial; cardiac output and blood flow to skeletal muscles decrease, and preliminary evidence has shown that hypoxia in itself is responsible for a depression of immune function and increased tissue damage mediated by oxidative stress. Future research needs to focus on these less beneficial aspects of altitude training, the implications of which pose a threat to both the fitness and the health of the elite competitor. Paul Bert was the first investigator to show that acclimatisation to a chronically reduced inspiratory partial pressure of oxygen (P1O2) invoked a series of central and peripheral adaptations that served to maintain adequate tissue oxygenation in healthy skeletal muscle, physiological adaptations that have been subsequently implicated in the improvement in exercise performance during altitude acclimatisation. However, it was not until half a century later that scientists suggested that the additive stimulus of environmental hypoxia could potentially compound the normal physiological adaptations to endurance training and accelerate performance improvements after return to sea level. This has stimulated an exponential increase in scientific research, and, since 1984, 22 major reviews have summarised the physiological implications of altitude training for both aerobic and anaerobic performance at altitude and after return to sea level. Of these reviews, only eight have specifically focused on physical performance changes after return to sea level, the most comprehensive of which was recently written by Wolski et al. Few reviews have considered the potentially less favourable physiological responses to moderate altitude exposure, which include decreases in absolute training intensity, decreased plasma volume, depression of haemopoiesis and increased haemolysis, increases in sympathetically mediated glycogen depletion at altitude, and increased respiratory muscle work after return to sea level. In addition, there is a risk of developing more serious medical complications at altitude, which include acute mountain sickness, pulmonary oedema, cardiac arrhythmias, and cerebral hypoxia. The possible implications of changes in immune function at altitude have also been largely ignored, despite accumulating evidence of hypoxia mediated immunosuppression. In general, altitude training has been shown to improve performance at altitude, whereas no unequivocal evidence exists to support the claim that performance at sea level is improved. Table 1 summarises the theoretical advantages and disadvantages of altitude training for sea level performance. This review summarises the physiological rationale for altitude training as a means of enhancing endurance performance after return to sea level. Factors that have been shown to affect the acclimatisation process and the subsequent implications for exercise performance at sea level will also be discussed. Studies were located using five major database searches, which included Medline, Embase, Science Citation Index, Sports Discus, and Sport, in

Cellular bioenergetics after erythropoietin therapy in chronic renal failure

After erythropoietin (rHuEPO) therapy, patients with chronic renal failure (CRF) do not improve peak O2 uptake (VO2 peak) as much as expected from the rise in hemoglobin concentration ([Hb]). In a companion study, we explain this phenomenon by the concurrent effects of fall in muscle blood flow after rHuEPO and abnormal capillary O2 conductance observed in CRF patients. The latter is likely associated with a poor muscle microcirculatory network and capillary-myofiber dissociation due to uremic myopathy. Herein, cellular bioenergetics and its relationships with muscle O2 transport, before and after rHuEPO therapy, were examined in eight CRF patients (27 +/- 7.3 [SD] yr) studied pre- and post-rHuEPO ([Hb] = 7.8 +/- 0.7 vs. 11.7 +/- 0.7 g x dl-1) during an incremental cycling exercise protocol. Eight healthy sedentary subjects (26 +/- 3.1 yr) served as controls. We hypothesize that uremic myopathy provokes a cytosolic dysfunction but mitochondrial oxidative capacity is not abnormal. 31P-nuclear magnetic resonance spectra (31P-MRS) from the vastus medialis were obtained throughout the exercise protocol consisting of periods of 2 min exercise (at 1.67 Hz) at increasing work-loads interspersed by resting periods of 2.5 min. On a different day, after an identical exercise protocol, arterial and femoral venous blood gas data were obtained together with simultaneous measurements of femoral venous blood flow (Qleg) to calculate O2 delivery (QO2leg) and O2 uptake (VO2leg). Baseline resting [phosphocreatine] to [inorganic phosphate] ratio ([PCr]/[Pi]) did not change after rHuEPO (8.9 +/- 1.2 vs. 8.8 +/- 1.2, respectively), but it was significantly lower than in controls (10.9 +/- 1.5) (P = 0.01 each). At a given submaximal or peak VO2leg, no effects of rHuEPO were seen on cellular bioenergetics ([PCr]/[Pi] ratio, %[PCr] consumption halftime of [PCr] recovery after exercise), nor in intracellular pH (pHi). The post-rHuEPO bioenergetic status and pHi, at a given VO2leg, were below those observed in the control group. However, at a given pHi, no differences in 31P-MRS data were detected between post-rHuEPO and controls. After rHuEPO, at peak VO2, Qleg fell 20% (P < 0.04), limiting the change in QO2leg to 17%, a value that did not reach statistical significance. The corresponding O2 extraction ratio decreased from 73 +/- 4% to 68 +/- 8.2% (P < 0.03). These changes indicate that maximal O2 flow from microcirculation to mitochondria did not increase despite the 50% increase in [Hb] and explain how peak VO2leg and cellular bioenergetics (31P-MRS) did not change after rHuEPO. Differences in pHi, possibly due to lactate differences, between post-rHeEPO and controls appear to be a key factor in the abnormal muscle cell bioenergetics during exercise observed in CRF patients.

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

Erythropoietin (rHuEPO) has proven to be effective in the treatment of anemia of chronic renal failure (CRF). Despite improving the quality of life, peak oxygen uptake after rHuEPO therapy is not improved as much as the increase in hemoglobin concentration ([Hb)] would predict. We hypothesized that this discrepancy is due to failure of O2 transport rates to rise in a manner proportional to [Hb]. To test this, eight patients with CRF undergoing regular hemodialysis were studied pre- and post-rHuEPO ([Hb] = 7.5 +/- 1.0 vs. 12.5 +/- 1.0 g x dl-1) using a standard incremental cycle exercise protocol. A group of 12 healthy sedentary subjects of similar age and anthropometric characteristics served as controls. Arterial and femoral venous blood gas data were obtained and coupled with simultaneous measurements of femoral venous blood flow (Qleg) by thermodilution to obtain O2 delivery and oxygen uptake (VO2). Despite a 68% increase in [Hb], peak VO2 increased by only 33%. This could be explained largely by reduced peak leg blood flow, limiting the gain in O2 delivery to 37%. At peak VO2, after rHuEPO, O2 supply limitation of maximal VO2 was found to occur, permitting the calculation of a value for muscle O2 conductance from capillary to mitochondria (DO2). While DO2 was slightly improved after rHuEPO, it was only 67% of that of sedentary control subjects. This kept maximal oxygen extraction at only 70%. Two important conclusions can be reached from this study. First, the increase in [Hb] produced by rHuEPO is accompanied by a significant reduction in peak blood flow to exercising muscle, which limits the gain in oxygen transport. Second, even after restoration of [Hb], O2 conductance from the muscle capillary to the mitochondria remains considerably below normal.

Role of exercise ventilation in the limitation of functional capacity in patients with congestive heart failure

Patients with heart failure have, compared with normal subjects, an increased minute ventilation (VE) at matched workloads. This heightened ventilatory drive may contribute to their limitation of functional capacity through an increase in the work of breathing and further worsening in the lung ventilation-perfusion mismatch. To measure the ventilatory response to exercise, VE should not be assessed in absolute units but be related to one of its main determinants, e.g., carbon dioxide production (VCO2). Particularly, as VE is closely related to VCO2 during exercise, the ventilatory response to exercise has been assessed using the slope of the relation of VE versus VCO2. This slope is significantly increased in heart failure patients compared with normal subjects and is inversely related to other parameters of maximal exercise capacity, namely peak VO2. The mechanisms of exercise hyperpnea in heart failure patients are still unsettled. A first possibility is that it is a compensatory response to the abnormal exercise hemodynamics with secondary increase of the pulmonary dead space to tidal volume ratio. This mechanism should be aimed to maintain constancy of the arterial gas composition and acid-base balance. However, exercise-induced hypoxemia and/or hypercapnia do not generally develop in heart failure patients. This might imply that other mechanisms, such as an increased sensitivity of the arterial chemoreceptors and/or the activation of reflexes by the abnormal skeletal muscles, stimulate the ventilatory response in heart failure patients. Regardless of its mechanisms, exercise hyperpnea may be clinically relevant in the assessment of patients with chronic heart failure. In fact, it is inversely related with peak exercise capacity, and interventions known to improve peak functional capacity such as therapy with ACE inhibitors, physical training and heart transplantation, also tend to normalize exercise hyperpnea.