Cardiorespiratory fitness and cardiovascular burden in chronic kidney disease

Renoprotective mechanisms of exercise training against acute and chronic renal diseases - A perspective based on experimental studies

Regular exercise training can lead to several health benefits, reduce mortality risk, and increase life expectancy. On the other hand, a sedentary lifestyle is a known risk factor for chronic diseases and increased mortality. Acute kidney injury (AKI) and chronic kidney disease (CKD) represent a significant global health problem, affecting millions of people worldwide. The progression from AKI to CKD is well-recognized in the literature, and exercise training has emerged as a potential renoprotective strategy. Thus, this article aims to review the main molecular mechanisms underlying the renoprotective actions of exercise training in the context of AKI and CKD, focusing on its antioxidative, anti-inflammatory, anti-apoptotic, anti-fibrotic, and autophagy regulatory effects. For that, bibliographical research was carried out in Medline/PubMed and Scielo databases. Although the pathophysiological mechanisms involved in renal diseases are not fully understood, experimental studies demonstrate that oxidative stress, inflammation, apoptosis, and dysregulation of fibrotic and autophagic processes play central roles in the development of tissue damage. Increasing evidence has suggested that exercise can beneficially modulate these mechanisms, potentially becoming a safe and effective non-pharmacological strategy for kidney health protection and promotion. Thus, the evidence base discussed in this review suggests that an adequate training program emerges as a valuable tool for preserving renal function in experimental animals, mainly through the production of antioxidant enzymes, nitric oxide (NO), irisin, IL-10, and IL-11. Future research can continue to explore these mechanisms to develop specific guidelines for the prescription of exercise training in different populations of patients with kidney diseases.

Exercise for chronic kidney disease: effects on vascular and cardiopulmonary function

Patients with chronic kidney disease (CKD) have an exacerbated prevalence of cardiovascular disease (CVD). Vascular dysfunction, characterized by impaired endothelial function and arterial stiffness, and markedly low cardiorespiratory fitness levels are hallmark manifestations of the disease that contribute to the CVD burden. Despite advancements in blood pressure and lipid lowering pharmacological therapies, CVD remains markedly prevalent across the spectrum of CKD. This highlights a stagnation in effective clinical strategies to improve cardiovascular health and reinforces the critical need for adjuvant lifestyle strategies such as physical activity and exercise training to be incorporated into routine clinical care. This narrative review provides an overview of the known effects of exercise on vascular and cardiopulmonary function across the spectrum of CKD. The physiological mechanisms of vascular dysfunction that serve as exercise-specific therapeutic targets are highlighted and future perspectives are discussed.

Cardiorespiratory fitness and mortality risk in patients receiving hemodialysis: a prospective cohort

BACKGROUND

Kidney failure reduces life expectancy by one-third compared with the general population, and cardiovascular complications and poor cardiorespiratory fitness (CRF) are the main causes. We aimed to evaluate the association between severely low CRF and all-cause mortality risk in HD patients.

METHODS

This observational prospective cohort study followed-up patients receiving HD from August 2015 until March 2022. Cardiorespiratory fitness was evaluated through the cardiopulmonary exercise test, and the peak oxygen uptake (VO2peak) value was used to determine severely low CRF (< 15 mL∙kg-1∙min-1). Cox regression and univariate Kaplan-Meier analysis were used to evaluate the association of severely low CRF with mortality risk and survival rate.

RESULTS

Forty-eight patients were followed-up for a median of 33.0 [14.3 - 49.3] months. A total of 26 patients had severely low CRF. During the follow-up period, 11 patients (22.92%) died from all causes. From these, eight (30.8%) had severely low CRF. Even so, severely low CRF was not associated with crude death rates for patients stratified by CRF levels (p = 0.189), neither in unadjusted (HR 2.18; CI 95% 0.58-8.23) nor in adjusted (HR 1.32; CI 95% 0.31-5.59) Cox proportional hazard models. As a continuous variable, VO2peak was not associated with mortality risk (HR 1.01; CI 95% 0.84-1.21). Univariate Kaplan-Meier analysis showed that patients with severely low CRF did not have significantly worse survival rates than those with mild-moderate CRF (p = 0.186).

CONCLUSION

Our findings indicated that severely low CRF was not associated with all-cause mortality in patients on HD. Despite severely low CRF being prevalent, larger cohort studies are needed to establish strong conclusions on its association with all-cause mortality.

Resting Heart Rate Independent of Cardiovascular Disease Risk Factors Is Associated With End-Stage Renal Disease: A Cohort Study Based on 476 347 Adults

BACKGROUND

The relationship between resting heart rate (RHR) and the risk of end-stage renal disease (ESRD) among those without cardiovascular disease remains unclear. We aim to establish temporal consistency and elucidate the independent relationship between RHR and the risk of ESRD.

METHODS AND RESULTS

This cohort enrolled participants from 476 347 individuals who had taken part in a screening program from 1996 to 2017. We identified 2504 participants who had ESRD, and the median follow-up was 13 years. RHR was extracted from electrocardiography results, and the study assessed the relationship between RHR and the risk of ESRD using the Cox proportional hazards model. Of the participants, 32.6% had an RHR of 60 to 69 beats per minute (bpm), and 22.2% had an RHR of ≥80 bpm. Participants with an RHR of ≥80 bpm had a higher stage of chronic kidney disease, lower estimated glomerular filtration rate, and more proteinuria than those with an RHR of 60 to 69 bpm. Participants with an RHR of 80 to 89 and ≥90 bpm had a 24% (hazard ratio [HR], 1.24 [95% CI, 1.09-1.42]) and 64% (HR, 1.64 [95% CI, 1.42-1.90]) higher risk of ESRD, respectively. The risk of ESRD remained significantly elevated (HR, 1.32 [95% CI, 1.10-1.58] per 10-beat increase from 60 bpm) after excluding participants who smoked; had hypertension, diabetes, or hyperlipidemia; or were overweight.

CONCLUSIONS

An RHR of ≥80 bpm is significantly associated with an increased risk of ESRD. These results suggest that RHR may serve as a risk factor for kidney disease in individuals without established cardiovascular disease risk factors.

Effects of a mitochondrial-targeted ubiquinol on vascular function and exercise capacity in chronic kidney disease: a randomized controlled pilot study

Mitochondria-derived oxidative stress has been implicated in vascular and skeletal muscle abnormalities in chronic kidney disease (CKD). The purpose of this study was to investigate the effects of a mitochondria-targeted ubiquinol (MitoQ) on vascular function and exercise capacity in CKD. In this randomized controlled trial, 18 patients with CKD (means ± SE, age: 62 ± 3 yr and estimated glomerular filtration rate: 45 ± 3 mL/min/1.73 m2) received 4 wk of 20 mg/day MitoQ (MTQ group) or placebo (PLB). Outcomes assessed at baseline and follow-up included macrovascular function measured by flow-mediated dilation, microvascular function assessed by laser-Doppler flowmetry combined with intradermal microdialysis, aortic hemodynamics assessed by oscillometry, and exercise capacity assessed by cardiopulmonary exercise testing. Compared with PLB, MitoQ improved flow-mediated dilation (baseline vs. follow-up: MTQ, 2.4 ± 0.3% vs. 4.0 ± 0.9%, and PLB, 4.2 ± 1.0% vs. 2.5 ± 1.0%, P = 0.04). MitoQ improved microvascular function (change in cutaneous vascular conductance: MTQ 4.50 ± 2.57% vs. PLB -2.22 ± 2.67%, P = 0.053). Central aortic systolic and pulse pressures were unchanged; however, MitoQ prevented increases in augmentation pressures that were observed in the PLB group (P = 0.026). MitoQ did not affect exercise capacity. In conclusion, this study demonstrates the potential for a MitoQ to improve vascular function in CKD. The findings hold promise for future investigations of mitochondria-targeted therapies in CKD.NEW & NOTEWORTHY In this randomized controlled pilot study, we investigated the effects of a mitochondria-targeted ubiquinol (MitoQ) on vascular function and exercise capacity in chronic kidney disease. Our novel findings showed that 4-wk supplementation of MitoQ was well tolerated and improved macrovascular endothelial function, arterial hemodynamics, and microvascular function in patients with stage 3-4 chronic kidney disease. Our mechanistic findings also suggest that MitoQ improved microvascular function in part by reducing the NADPH oxidase contribution to vascular dysfunction.

Cardiopulmonary exercise testing to observe subclinical abnormalities in cardiopulmonary function in patients undergoing peritoneal dialysis

BACKGROUND

Decreased cardiorespiratory fitness (CRF) related to cardiopulmonary function increases the risk of cardiovascular disease in patients with end-stage kidney disease. Thus, early detection of the cause of impaired cardiopulmonary function in patients undergoing peritoneal dialysis (PD) is of important clinical significance.

METHODS

In this cross-sectional study, Symptom-restricted cardiopulmonary exercise testing (CPET) was performed in 30 patients undergoing PD and in 23 age- and sex-matched healthy control subjects.A fixed workload was added every minute until fatigue, and breath-by-breath respiratory gas was analyzed with an automated gas analyzer at 10-second intervals.

RESULTS

The peak oxygen uptake ( 16.39±0.83 vs 25.77±1.33 ml/kg/min p<0.001) and the oxygen uptake at the anerobic threshold of patients undergoing PD (9.61±0.34 vs 14.55± 0.64 ml/kg/min; p<0.001) were lower than in healthy control subjects, and both of these parameters correlated with body mass index and left atrial dimension. A steeper minute ventilation / carbon dioxide production slope (27.20±0.68 vs 24.29±0.69；p<0.01) and a lower end-tidal carbon dioxide partial pressure (37.93±0.54 vs 41.27±0.83mmHg；p<0.05) were observed in patients undergoing PD. The oxygen pulse and oxygen uptake efficiency slope was smaller in patients undergoing PD. The Maximum heart rate (126.07±4.01 vs 149.96±5.29 bpm；p<0.01) and 1-minute heart rate recovery (13.93±1.52 vs 24.39±1.61bpm；p<0.01) were also lower in patients undergoing PD.

CONCLUSION

Subclinical cardiopulmonary dysfunction may exist in patients with PD, and a reduction in CRF in patients undergoing PD is affected by both central and peripheral functions. CPET has potential value in revealing the mechanism of impaired CRF and in discovering subclinical abnormalities in cardiopulmonary function. This article is protected by copyright. All rights reserved.

Klotho: An Emerging Factor With Ergogenic Potential

Sarcopenia and impaired cardiorespiratory fitness are commonly observed in older individuals and patients with chronic kidney disease (CKD). Declines in skeletal muscle function and aerobic capacity can progress into impaired physical function and inability to perform activities of daily living. Physical function is highly associated with important clinical outcomes such as hospitalization, functional independence, quality of life, and mortality. While lifestyle modifications such as exercise and dietary interventions have been shown to prevent and reverse declines in physical function, the utility of these treatment strategies is limited by poor widespread adoption and adherence due to a wide variety of both perceived and actual barriers to exercise. Therefore, identifying novel treatment targets to manage physical function decline is critically important. Klotho, a remarkable protein with powerful anti-aging properties has recently been investigated for its role in musculoskeletal health and physical function. Klotho is involved in several key processes that regulate skeletal muscle function, such as muscle regeneration, mitochondrial biogenesis, endothelial function, oxidative stress, and inflammation. This is particularly important for older adults and patients with CKD, which are known states of Klotho deficiency. Emerging data support the existence of Klotho-related benefits to exercise and for potential Klotho-based therapeutic interventions for the treatment of sarcopenia and its progression to physical disability. However, significant gaps in our understanding of Klotho must first be overcome before we can consider its potential ergogenic benefits. These advances will be critical to establish the optimal approach to future Klotho-based interventional trials and to determine if Klotho can regulate physical dysfunction.

Association of Daily Physical Activity with Disability in Community-Dwelling Older Adults With/Without Chronic Kidney Disease

OBJECTIVES

Physical activity is recommended for disability prevention in the older adult population; however, the level of physical activity required for older adults with chronic kidney disease (CKD) remains unknown. This study aimed to examine the associations between daily physical activity and disability incidence in older adults with and without CKD to determine relevant daily physical activity levels.

DESIGN

Prospective observational study.

SETTING AND PARTICIPANTS

3,786 community-dwelling older adults aged ≥65 years.

MEASUREMENTS

Mean daily times spent in light- (LPA) and moderate-to-vigorous physical activity (MVPA) were measured using triaxial accelerometers. CKD was defined by a creatinine estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m2. Disability incidence was identified as long-term care insurance certification during a 60-month follow-up period. Associations between physical activity and disability incidence were examined using Cox proportional hazard models stratified by the CKD status. Non-linear and linear associations were tested using the restricted cubic spline.

RESULTS

A total of 1,054 individuals were identified to have CKD. Disability incidence was higher in the CKD group than in the non-CKD group. The adjusted cox proportional hazard models indicated that a 10-minute increase in MVPA time was associated with lower disability incidence in the non-CKD group (hazard ratio [HR], 0.838; 95% confidence interval [CI]: 0.764-0.918) and the CKD group (HR, 0.859; 95% CI: 0.766-0.960). Linear associations were observed in MVPA for the non-CKD and CKD groups.

CONCLUSION

Increasing MVPA was associated with lower disability incidence in older adults with and without CKD. These findings can help devise disability prevention strategies for older CKD patients.

Prognostic Value of Cardiorespiratory Fitness in Patients with Chronic Kidney Disease: The FIT (Henry Ford Exercise Testing) Project

PURPOSE

We conducted this study to investigate the association of cardiorespiratory fitness and all-cause mortality among patients with chronic kidney disease.

METHODS

We studied a retrospective cohort of patients from the Henry Ford Health System who underwent clinically indicated exercise stress testing with baseline cardiorespiratory fitness and estimated glomerular filtration rate measurement. Cardiorespiratory fitness was expressed as metabolic equivalents of task, and kidney function was categorized into stages according to estimated glomerular filtration rate. Multivariable-adjusted Cox proportional hazard models were used to examine the association between metabolic equivalents of task and all-cause mortality among patients with chronic kidney disease stages 3-5. Discrimination of mortality was assessed using receiver operating characteristic curves, while reclassification was evaluated using net reclassification index (NRI).

RESULTS

Among 50,121 participants, the mean age was 55 ± 12.6 years; 47.5% were women, 64.5% were white, and 6877 (13.7%) participants had chronic kidney disease stage 3-5. Over a median follow-up of 6.7 years, 6308 participants died (12.6%). Each 1-unit higher metabolic equivalents of task was associated with a significant 15% reduction in all-cause mortality (hazard ratio 0.85; 95% confidence interval [CI], 0.84-0.87). Metabolic equivalents of task improved discriminatory ability of mortality prediction when added to traditional risk factors and estimated glomerular filtration rate (area under the curve 0.7996; 95% CI, 0.789-0.810 vs 0.759; 95% CI, 0.748-0.770, respectively; P < .001). The addition of metabolic equivalents of task to traditional risk factors resulted in significant reclassification (6% for events, 5% for non-events: NRI = 0.13, P < .001).

CONCLUSIONS

Cardiorespiratory fitness improves mortality risk prediction among patients with chronic kidney disease. Cardiorespiratory fitness provides incremental prognostic information when added to traditional risk factors and may help guide treatment options among patients with renal dysfunction.

VO2peak prior to transplant differentiates survival post kidney transplant

The OPTN/UNOS utilizes the calculated estimated posttransplant survival (EPTS) score as the measure of post-kidney transplant survival to guide allocation of deceased donor kidney transplantation. This score does not include any metric of functional capacity. Peak oxygen uptake (VO_2peak ), is an established predictor of survival among both the general and diseased populations. We assessed the association and discriminative capacity of VO_2peak and that of EPTS score and all-cause mortality post-kidney transplant. Additionally, we assessed the "mortality risk" lower VO_2peak conferred on those patients with low EPTS score. Among a cohort of 293 transplant recipients with at least 3-years post-transplant follow-up, the median VO_2peak was 15.0 ml/Kg/min. Lower pre-transplant VO_2peak and higher EPTS score conferred higher risk of post-transplant mortality. Among the cohort of "low-risk" patients (patients with EPTS score < 50) those with lower VO_2peak had significantly higher risk of mortality (log rank p = 0.045). In fact, the mortality risk among those with low-EPTS (< 50) and low VO_2peak  < 12 ml/Kg/min was equivalent to those with high EPTS (> 80) score. We concluded functional capacity as defined by VO_2peak is an important reflection of post-transplant survival. VO_2peak is able to identify those with low EPTS who have similar survival to that of high EPTS phenotype.

Association of physical function and performance with peak VO2 in elderly patients with end stage kidney disease

BACKGROUND

Physical function is impaired in end stage renal disease (ESRD). Various instruments have been used to assess the functional capabilities and health status of patients with ESRD, but it is not known which has the best association with peak VO₂.

AIMS

To assess the association between functional measures in ESRD.

METHODS

Thirty nine elderly ESRD patients were evaluated with commonly used functional, health status, and quality of life measures, including maximal cardiopulmonary exercise testing (CPET), 6-min walk (6MWT), sit-to-stand test (STS), Veterans Specific Activity Questionnaire (VSAQ), upper and lower body strength, pulmonary function tests, and body composition determined by dual X-ray absorptiometry. The association between performance on these functional tools, clinical variables, and exercise test responses was assessed, and a non-exercise test multivariate model was developed to predict peak VO₂.

RESULTS

Peak VO₂ was modestly related to VSAQ score (r = 0.59, p < 0.01), indices of upper and lower body strength (r = 0.45, p < 0.01 for both), and FEV₁ (r = 0.51, p < 0.01). Functional and quality of life questionnaires were generally poorly related to one another and to peak VO₂. In a multivariate model, 6MWT performance, forced expiratory volume in 1 s (FEV₁), and VSAQ score were the best predictors of peak VO₂, yielding a multiple R = 0.82, accounting for 67% of the variance in peak VO₂.

CONCLUSION

Exercise capacity can be reasonably estimated using non-exercise test variables in patients with ESRD, including a symptom questionnaire (VSAQ), 6MWT and FEV₁.

CLINICAL TRIAL INFORMATION

ClinicalTrials.gov identifier: NCT01990495. Registered Nov 21, 2013.

Cardiorespiratory fitness assessed by cardiopulmonary exercise testing between different stages of pre-dialysis chronic kidney disease: A systematic review and meta-analysis

AIM

The burden of several cardiovascular risk factors increases in parallel to renal function decline. Exercise intolerance is common in patients with chronic kidney disease (CKD) and has been associated with increased risk of adverse outcomes. Whether indices of cardiorespiratory capacity deteriorate with advancing CKD stages is unknown.

METHODS

We conducted a systematic review and meta-analysis of studies assessing cardiorespiratory capacity in adult patients with pre-dialysis CKD using cardiopulmonary exercise testing (CPET) and reporting data for different stages. Our primary outcome was differences in peak oxygen uptake (VO₂ peak) between patients with CKD Stages 2-3a and those with Stages 3b-5(pre-dialysis). Literature search was undertaken in PubMed, Web of Science and Scopus databases, and abstract books of relevant meetings. Quality assessment was undertaken with Newcastle-Ottawa-Scale.

RESULTS

From 4944 records initially retrieved, six studies with 512 participants fulfilling our inclusion criteria were included in the primary meta-analysis. Peak oxygen uptake (VO₂ peak) was significantly higher in patients with CKD Stages 2-3a versus those with Stages 3b-5(pre-dialysis) [weighted-mean-difference, WMD: 2.46, 95% CI (1.15, 3.78)]. Oxygen consumption at ventilatory threshold (VO₂ VT) was higher in Stages 2-3a compared with those in Stages 3b-5(pre-dialysis) [standardized-mean-difference, SMD: 0.59, 95% CI (0.06, 1.1)], while no differences were observed for maximum workload and respiratory-exchange-ratio. A secondary analysis comparing patients with CKD Stages 2-3b and Stages 4-5(pre-dialysis), yielded similar results [WMD: 1.78, 95% CI (1.34, 2.22)]. Sensitivity analysis confirmed the robustness of these findings.

CONCLUSION

VO₂ peak and VO₂ VT assessed with CPET are significantly lower in patients in CKD Stages 3b-5 compared with Stages 2-3a. Reduced cardiorespiratory fitness may be another factor contributing to cardiovascular risk increase with advancing CKD.

The effect of dietary nitrate on exercise capacity in chronic kidney disease: a randomized controlled pilot study

BACKGROUND

Chronic Kidney Disease (CKD) patients exhibit a reduced exercise capacity that impacts quality of life. Dietary nitrate supplementation has been shown to have favorable effects on exercise capacity in disease populations by reducing the oxygen cost of exercise. This study investigated whether dietary nitrates would acutely improve exercise capacity in CKD patients.

METHODS AND RESULTS

In this randomized, double-blinded crossover study, 12 Stage 3-4 CKD patients (Mean ± SEM: Age, 60 ± 5yrs; eGFR, 50.3 ± 4.6 ml/min/1.73 m²) received an acute dose of 12.6 mmol of dietary nitrate in the form of concentrated beetroot juice (BRJ) and a nitrate depleted placebo (PLA). Skeletal muscle mitochondrial oxidative function was assessed using near-infrared spectroscopy. Cardiopulmonary exercise testing was performed on a cycle ergometer, with intensity increased by 25 W every 3 min until volitional fatigue. Plasma nitric oxide (NO) metabolites (NOm; nitrate, nitrite, low molecular weight S-nitrosothiols, and metal bound NO) were determined by gas-phase chemiluminescence. Plasma NOm values were significantly increased following BRJ (BRJ vs. PLA: 1074.4 ± 120.4 μM vs. 28.4 ± 6.6 μM, p < 0.001). Total work performed (44.4 ± 10.6 vs 39.6 ± 9.9 kJ, p = 0.03) and total exercise time (674 ± 85 vs 627 ± 86s, p = 0.04) were significantly greater following BRJ. Oxygen consumption at the ventilatory threshold was also improved by BRJ (0.90 ± 0.08 vs. 0.74 ± 0.06 L/min, p = 0.04). These changes occurred in the absence of improved skeletal muscle mitochondrial oxidative capacity (p = 0.52) and VO_2peak (p = 0.35).

CONCLUSIONS

Our findings demonstrate that inorganic nitrate can acutely improve exercise capacity in CKD patients. The effects of chronic nitrate supplementation on CKD related exercise intolerance should be investigated in future studies.

A randomized trial of aerobic exercise in chronic kidney disease: evidence for blunted cardiopulmonary adaptations

BACKGROUND

Patients with chronic kidney disease have reduced cardiorespiratory fitness levels that contribute to mortality.

OBJECTIVES

The purpose of this study was to investigate the effects of aerobic exercise on cardiopulmonary function in patients with chronic kidney disease.

METHODS

A total of 36 patients (mean [SD] estimated glomerular filtration rate 44 [12] ml/min/1.73m2) were randomly allocated to an exercise training or a control arm over 12 weeks. The exercise training group performed aerobic exercise for 45 min 3 times/week at 65% to 80% heart rate reserve. The control group received routine care. Outcome measures were assessed at baseline and 12 weeks. Cardiopulmonary exercise testing was performed on a cycle ergometer with workload increased by 15 W/min. A battery of physical function tests were administered. Habitual physical activity levels were recorded via accelerometry. Data are mean (SD).

RESULTS

Exercise training improved VO2peak as compared with the control group (exercise: 17.89 [4.18] vs 19.98 [5.49]; control: 18.29 [6.49] vs 17.36 [5.99] ml/kg/min; p<0.01). Relative O2 pulse improved following exercise, suggestive of improved left ventricular function (exercise: 0.12 [0.02] vs 0.14 [0.04]; control: 0.14 [0.05] vs 0.14 [0.04] ml/beat/kg; p=0.03). Ventilation perfusion mismatching (VE/VCO2) remained evident after exercise (exercise: 32 [5] vs 33 [5]; control: 32 [7] vs 34 [5] AU; p=0.1). Exercise did not affect the ventilatory cost of oxygen uptake (VE/VO2; exercise: 40 [7] vs 42 [8]; control: 3 [7] vs 41 [8] AU; p=0.5) and had no effect on autonomic function assessed by maximal and recovery heart rates. We found no changes in physical function or habitual physical activity levels.

CONCLUSIONS

Cardiopulmonary adaptations appeared to be attenuated in patients with chronic kidney disease and were not fully restored to levels observed in healthy individuals. Improvements in exercise capacity did not confer benefits to physical function. Interventions coupled with exercise may be required to enhance adaptations in chronic kidney disease. Performed according to CONSORT guidelines; ClinicalTrials.gov: NCT02050035.

Exercise intolerance in kidney diseases: physiological contributors and therapeutic strategies

Exertional fatigue, defined as the overwhelming and debilitating sense of sustained exhaustion that impacts the ability to perform activities of daily living, is highly prevalent in chronic kidney disease (CKD) and end-stage renal disease (ESRD). Subjective reports of exertional fatigue are paralleled by objective measurements of exercise intolerance throughout the spectrum of the disease. The prevalence of exercise intolerance is clinically noteworthy, as it leads to increased frailty, worsened quality of life, and an increased risk of mortality. The physiological underpinnings of exercise intolerance are multifaceted and still not fully understood. This review aims to provide a comprehensive outline of the potential physiological contributors, both central and peripheral, to kidney disease-related exercise intolerance and highlight current and prospective interventions to target this symptom. In this review, the CKD-related metabolic derangements, cardiac and pulmonary dysfunction, altered physiological responses to oxygen consumption, vascular derangements, and sarcopenia are discussed in the context of exercise intolerance. Lifestyle interventions to improve exertional fatigue, such as aerobic and resistance exercise training, are discussed, and the lack of dietary interventions to improve exercise tolerance is highlighted. Current and prospective pharmaceutical and nutraceutical strategies to improve exertional fatigue are also broached. An extensive understanding of the pathophysiological mechanisms of exercise intolerance will allow for the development of more targeted therapeutic approached to improve exertional fatigue and health-related quality of life in CKD and ESRD.

Response of the oxygen uptake efficiency slope to exercise training in patients with chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) patients have poor cardiorespiratory fitness. Although cardiopulmonary exercise testing (CPET) is a universal assessment of cardiorespiratory fitness, values taken at 'peak' effort are strongly influenced by motivation and the choice of test endpoint. The oxygen uptake efficiency slope (OUES) integrates cardiovascular, musculoskeletal, and respiratory function into a single index to provide a more pragmatic and safer alternative to maximal testing. No research has explored whether exercise can improve the OUES in CKD patients.

METHODS

Thirty-two patients with non-dialysis CKD were recruited into a 12-week exercise program consisting of mixed aerobic and resistance training three times a week. CPET was conducted at baseline, and then, following a 6-week control period, at pre- and post-exercise intervention. Direct measurements of oxygen consumption (V̇O2) and ventilatory parameters were collected. The OUES was calculated as the relationship between V̇O2 and the log10 of minute ventilation (V̇E).

RESULTS

No changes were observed in any variable during the control period, although modest increases in V̇O2peak were observed. No meaningful changes were observed as a result of exercise in any cardiorespiratory value obtained. The OUES calculated at 100%, 90%, 75%, and 50% of exercise duration did not change significantly after 12 weeks of exercise training.

CONCLUSION

Our results show that 12 weeks of exercise training had no beneficial effects on the OUES, which supports the modest change observed in V̇O2peak. The lack of change in the OUES and other parameters could indicate a dysfunctional cardiorespiratory response to exercise in patients with CKD, likely mediated by dysfunctional peripheral metabolic mechanisms.

Effects of intradialytic exercise on cardiopulmonary capacity in chronic kidney disease: systematic review and meta-analysis of randomized clinical trials

Patients with chronic kidney disease show poorer functional and cardiorespiratory capacity than healthy individuals, and these impairments result in sedentarism. The aim of this study was to conduct a systematic review and meta-analysis of randomized clinical trials on the effects of different intradialytic exercise protocols on cardiopulmonary capacity in chronic kidney disease patients. The primary outcome was peak oxygen consumption (VO_2peak) and the secondary outcomes were exercise duration and ventilation in the cardiopulmonary test. The quality of the evidence was evaluated using the GRADE guidelines. Seven studies with a total of 124 participants met the inclusion criteria. Compared to the non-exercise group, the exercise group improved in mean VO_2peak (MD 4.06 [IC 0.81; 7.31]). In a separate analysis according to exercise modality, aerobic exercise plus strength training performed better than aerobic exercise alone (MD 5.28 [IC 3.90; 6.66]). In the exercise group, both exercise tolerance values (MD 3.10 [IC 1.70; 4.51]) and ventilation values in the cardiopulmonary test were better than those of the control group (MD 13.10 [IC 7.12; 19.09]). Thus, intradialytic exercise protocols can improve cardiopulmonary function, exercise tolerance and ventilatory efficiency in chronic kidney disease patients.

Peak aerobic capacity from incremental shuttle walk test in chronic kidney disease

BACKGROUND

Assessment of cardiorespiratory fitness is an important outcome in chronic kidney disease (CKD). We aimed to develop a predictive equation to estimate peak oxygen uptake (VO_2peak ) and power output (W_Peak ), as measured during a cardiopulmonary exercise test (CPET), from the distance walked (DW) during the incremental shuttle walk test (ISWT).

METHODS

Thirty-six non-dialysing patients with CKD [17 male, age: 61 ± 12 years, eGFR: 25±7 ml/min/1.73 m² , body mass index (BMI): 31 ± 6 kg/m² ] carried out laboratory-based CPET on a cycle ergometer and ISWT on two separate occasions.

RESULTS

Linear regression revealed that DW/BMI was a significant predictor of VO_2Peak (r = 0.78) (VO_2Peak (ml/min/kg) = [0.5688 × (DW/BMI) (m)] + 11.50). No difference (p = 0.66) between CPET VO_2Peak (19.9 ± 5.5 ml/min/kg) and predicted VO_2Peak (19.9 ± 4.3 ml/min/kg) was observed. DW multiplied by body mass (BM) was a significant predictor of W_Peak (r = 0.80) [W_Peak (W) = (0.0018 × (DW × BM)) + 50.47]. No difference (p = 0.97) between CPET W_Peak (116.2 ± 38.9 W) and estimated W_Peak (113.9 ± 30.1 W) was seen.

CONCLUSION

The present study demonstrates that VO_2Peak and W_Peak can be accurately estimated using the DW during an ISWT in CKD populations.

Association of renal function with ambulation in mild acute stroke patients

Background: Renal dysfunction has affected the functional outcome after stroke. However, the association of renal function with walking endurance after stroke is poorly understood. Objectives: This study aimed to investigate the relationship between renal function and walking endurance and speed in mild acute stroke patients. Methods: Eighty-nine patients with mild acute stroke were enrolled. Walking endurance and speed were assessed by the 6-minute walk test (6MWT) and comfortable and maximal 10-meter walk tests (10MWT) within 7 days of hospital admission. Stroke severity was assessed using the National Institutes of Health stroke scale (NIHSS) on admission. The estimated glomerular filtration rate (eGFR) was calculated based on creatinine levels as a renal function. Pearson's correlation coefficients were calculated between eGFR and walking ability. Multivariate regression analysis was used to investigate the relationship between eGFR and walking ability in mild acute stroke patients. Results: The 6MWT distance was significantly correlated with eGFR (r = 0.212, p = .046). On multivariate regression analysis, the 6MWT was significantly associated with age (p = .029), body mass index (p = .020), NIHSS score (p = .016), and eGFR (p = .028), whereas the comfortable 10MWT was significantly associated with the NIHSS score alone (p = .009) and the maximal 10MWT was significantly associated with age (p = .032) and NIHSS score (p = .007). Conclusion: The eGFR based on creatinine levels of acute stroke patients may be important factor to predict the walking endurance in mild acute stroke patients.

Effects of aerobic exercise on vascular function in nondialysis chronic kidney disease: a randomized controlled trial

Endothelial dysfunction and arterial stiffness are nontraditional risk factors of chronic kidney disease (CKD)-related cardiovascular disease (CVD) that could be targeted with exercise. This study investigated the effect of moderate to vigorous aerobic exercise on vascular function in nondialysis CKD. In this randomized, controlled trial, 36 nondialysis patients with CKD (means ± SE, age: 58 ± 2 yr, estimated glomerular filtration rate: 44 ± 2 ml·min-1·1.73 m-2) were allocated to an exercise training (EXT) or control (CON) arm. The EXT group performed 3 × 45 min of supervised exercise per week at 60-85% heart rate reserve for 12 wk, whereas the CON group received routine care. Outcomes were assessed at 0 and 12 wk. The primary outcome, microvascular function, was assessed via cutaneous vasodilation during local heating measured by laser-Doppler flowmetry coupled with microdialysis. Participants were instrumented with two microdialysis fibers for the delivery of 1) Ringer solution and 2) the superoxide scavenger tempol. Conduit artery function was assessed via brachial artery flow-mediated dilation. Aortic pressure waveforms and pulse wave velocity were acquired with tonometry and oscillometry. Microvascular function improved after EXT (week 0 vs.week 12, EXT: 87 ± 2% vs. 91 ± 2% and CON: 86 ± 2% vs. 84 ± 3%, P = 0.03). At baseline, pharmacological delivery of tempol improved microvascular function (Ringer solution vs. tempol: 86 ± 1% vs. 90 ± 1%, P = 0.02) but was no longer effective after EXT (91 ± 2% vs. 87 ± 1%, P = 0.2), suggesting that an improved redox balance plays a role in EXT-related improvements. Brachial artery flow-mediated dilation was maintained after EXT (EXT: 2.6 ± 0.4% vs. 3.8 ± 0.8% and CON: 3.5 ± 0.6% vs. 2.3 ± 0.4%, P = 0.02). Central arterial hemodynamics and arterial stiffness were unchanged after EXT. Aerobic exercise improved microvascular function and maintained conduit artery function and should be considered as an adjunct therapy to reduce CVD risk in CKD.

High-intensity interval training in chronic kidney disease: A randomized pilot study

INTRODUCTION

High-intensity interval training (HIIT) increases mitochondrial biogenesis and cardiorespiratory fitness in chronic disease populations, however has not been studied in people with chronic kidney disease (CKD). The aim of this study was to compare the feasibility, safety, and efficacy of HIIT with moderate-intensity continuous training (MICT) in people with CKD.

METHODS

Fourteen individuals with stage 3-4 CKD were randomized to 3 supervised sessions/wk for 12 weeks, of HIIT (n = 9, 4 × 4 minute intervals, 80%-95% peak heart rate [PHR]) or MICT (n = 5, 40 minutes, 65% PHR). Feasibility was assessed via session attendance and adherence to the exercise intensity. Safety was examined by adverse event reporting. Efficacy was determined from changes in cardiorespiratory fitness (VO₂ peak), exercise capacity (METs), and markers of mitochondrial biogenesis (PGC1α protein levels), muscle protein catabolism (MuRF1), and muscle protein synthesis (p-P70S6k ^Thr389 ).

RESULTS

Participants completed a similar number of sessions in each group (HIIT = 33.0[7.0] vs MICT = 33.5[3.3] sessions), and participants adhered to the target heart rates. There were no adverse events attributable to exercise training. There was a significant time effect for exercise capacity (HIIT = +0.8 ± 1.2; MICT = +1.3 ± 1.6 METs; P = 0.01) and muscle protein synthesis (HIIT = +0.6 ± 1.1; MICT = +1.4 ± 1.7 au; P = 0.04). However, there were no significant (P > 0.05) group × time effects for any outcomes.

CONCLUSION

This pilot study demonstrated that HIIT is a feasible and safe option for people with CKD, and there were similar benefits of HIIT and MICT on exercise capacity and skeletal muscle protein synthesis. These data support a larger trial to further evaluate the effectiveness of HIIT.

Altered vascular function in chronic kidney disease: evidence from passive leg movement

Chronic kidney disease (CKD) is an independent risk factor for the development of cardiovascular disease and is characterized by reduced nitric oxide (NO) bioavailability and vascular dysfunction, typically assessed using brachial artery flow-mediated dilation (FMD). It has been previously reported that passive leg movement (PLM)-induced hyperemia, an assessment of lower extremity vascular function, is highly dependent on NO, but has not yet been utilized to assess vascular function in patients with CKD. The purpose of this study was to comprehensively assess vascular function in patients with CKD using PLM, in addition to the traditional FMD technique. Assessment of vascular function via PLM and FMD was performed on 12 patients (CKD, 66 ± 3 years) and 16 age-matched healthy controls (CON, 60 ± 2 years). Blood velocity and artery diameters during PLM and FMD were measured using duplex ultrasound of the femoral and brachial arteries, respectively. Habitual physical activity, assessed by accelerometry, was performed in a subset of each group. CKD patients had reduced peak leg blood flow (LBF) (384 ± 39 vs. 569 ± 77 mL/min, P < 0.05) and change in LBF from baseline to peak (∆peakLBF) (143 ± 22 vs. 249 ± 34 mL/min, P < 0.05) during PLM compared to CON. Additionally, PLM responses were significantly associated with kidney function and physical activity levels. As anticipated, FMD was significantly attenuated in CKD patients (5.2 ± 1.1 vs. 8.8 ± 1.2%, P < 0.05). In conclusion, both upper and lower extremity measures of vascular function indicate impairment in CKD patients when compared to controls. PLM appears to be a novel and feasible approach to assessing lower extremity vascular function in CKD.

Gradual reduction in exercise capacity in chronic kidney disease is associated with systemic oxygen delivery factors

Background

The cause of reduced exercise capacity (ExCap) in chronic kidney disease (CKD) is multifactorial. The aim of this study was to investigate determinants of aerobic ExCap in patients with mild to severe CKD not undergoing dialysis.

Methods

We included 52 individuals with CKD stage 2–3, 47 with stage 4–5, and 54 healthy controls. Peak workload and peak heart rate (HR) were assessed by a maximal cycle exercise test. Cardiac function including stroke volume (SV) and vascular stiffness were evaluated by ultrasound at rest. Handgrip strength, body composition, haemoglobin level and self-reported physical activity were assessed.

Results

Peak workload (221±60, 185±59, 150±54 W for controls, CKD 2–3 and CKD 4–5 respectively), peak HR (177±11, 161±24, 144±31 beats/min) and haemoglobin level (14.2±1.2, 13.5±1.4, 12.2±1.3 g/dL) were all three significantly lower in CKD 2–3 than in controls, (p = 0.001, 0.001 and 0.03 respectively) and were even lower in stages 4–5 CKD than in CKD 2–3 (p = 0.01, 0.001 and <0.001 respectively). Resting SV and lean body mass did not differ between groups and handgrip strength was significantly lower only in CKD 4–5 compared to controls (p = 0.02). Peak workload was strongly associated with the systemic oxygen delivery factors: SV, peak HR and haemoglobin level. These three factors along with age, sex and height² explained 82% of variation in peak workload. Peak HR contributed most to the variation; the peripheral variables handgrip strength and vascular stiffness did not improve the explanatory value in regression analysis.

Conclusions

In this cross-sectional study of CKD patients not on dialysis, aerobic ExCap decreased gradually with disease severity. ExCap was associated mainly with systemic oxygen delivery factors, in particular peak HR. Neither muscle function and mass, nor vascular stiffness were independent determinants of aerobic ExCap in this group of CKD patients.

Exercise capacity and clinical outcomes in adults followed in the Cooperative Study of Sickle Cell Disease (CSSCD)

OBJECTIVES

To determine the factors associated with exercise capacity in adults with sickle cell disease (SCD) and its relationship to hospitalizations and mortality.

METHODS

A total of 223 participants in the Cooperative Study of Sickle Cell Disease (CSSCD) (64% female, 70% hemoglobin SS/Sβ⁰ thalassemia, mean age 43.3 ± 7.5 years) underwent maximal exercise testing using a treadmill protocol with a mean duration of 11.6 ± 5.2 minutes.

RESULTS

Female sex (β = -3.34, 95% CI [-1.80, -4.88], P < 0.001), older age (β = -0.14, 95% CI [-0.24, -0.04], P = 0.005), higher body mass index (β = -0.23, 95% CI [-0.37, -0.10]; P = 0.001), and lower hemoglobin (β = 0.56, 95% CI [0.08, 1.04], P = 0.02) were independently associated with lower fitness, while there was a trend with abnormal pulmonary function testing (β = -1.42, 95% CI [-2.92, 0.07]; P = 0.06). Lower percent-predicted forced expiratory volume in 1 second (FEV₁ ) was independently associated with lower fitness (β = 0.08, 95% CI [0.03, 0.13], P = 0.001). Genotype and hospitalization rates for pain and acute chest syndrome (ACS) prior to testing were not associated with exercise capacity. Baseline exercise capacity predicted neither future pain or ACS nor survival in our cohort. Adults with SCD tolerated maximal exercise testing.

CONCLUSIONS

Prospective studies are needed to further evaluate the impact of regular exercise and improved fitness on clinical outcomes and mortality in SCD.

Cardiopulmonary exercise testing reveals subclinical abnormalities in chronic kidney disease

Background

Reductions in exercise capacity associated with exercise intolerance augment cardiovascular disease risk and predict mortality in chronic kidney disease. This study utilized cardiopulmonary exercise testing to (a) investigate mechanisms of exercise intolerance; (b) unmask subclinical abnormalities that may precede cardiovascular disease in chronic kidney disease.

Design

The design of this study was cross-sectional.

Methods

Cardiopulmonary exercise testing was carried out in 31 Stage 3–4 chronic kidney disease patients (60 ± 11 years; estimated glomerular filtration rate 43 ± 13 ml/min/1.73 m2) and 21 matched healthy individuals (healthy controls; 56 ± 5 years; estimated glomerular filtration rate>90 ml/min/1.73 m2) on a cycle ergometer with workload increased by 15 W every minute until volitional fatigue. Breath-by-breath respiratory gas analysis was performed with an automated gas analyzer and averaged over 10 s intervals.

Results

Peak oxygen uptake was reduced in chronic kidney disease compared to healthy controls (17.43 ± 1.03 vs 28 ± 2.05 ml/kg/min; p < 0.01), as was oxygen uptake at the ventilatory threshold (9.44 ± 0.53 vs15.55 ± 1.34 ml/kg/min; p < 0.01). A steeper minute ventilation rate/carbon dioxide production slope (32 ± 0.8 vs 28 ± 1; p < 0.01) and a lower expired carbon dioxide pressure in chronic kidney disease (27 ± 0.6 vs 31 ± 0.9 vs 0.9; p < 0.01) indicated ventilation perfusion mismatching in these patients. The ventilatory cost of oxygen uptake was higher in chronic kidney disease (37 ± 0.8 vs 33 ± 1; p < 0.01). Maximum heart rate (134 ± 5 vs 159 ± 3 bpm) and one-minute heart rate recovery (15 ± 1 vs 20 ± 2 bpm) were reduced in chronic kidney disease ( p < 0.01).

Conclusion

This study suggests that both central and peripheral limitations likely contribute to reduced exercise capacity in non-dialysis chronic kidney disease. Additionally, cardiopulmonary exercise testing revealed subclinical cardiopulmonary abnormalities in these patients in the absence of overt cardiovascular disease. Cardiopulmonary exercise testing could potentially be a tool for unmasking cardiopulmonary abnormalities preceding cardiovascular disease in chronic kidney disease.

Effects of acute exercise on endothelial function in patients with abdominal aortic aneurysm

Endothelial dysfunction is observed in patients with abdominal aortic aneurysm (AAA), who have increased risk of cardiovascular events and mortality. This study aimed to assess the acute effects of moderate- and higher-intensity exercise on endothelial function, as assessed by flow-mediated dilation (FMD), in AAA patients (74 ± 6 yr old, n = 22) and healthy adults (72 ± 5 yr old, n = 22). Participants undertook three randomized visits, including moderate-intensity continuous exercise [40% peak power output (PPO)], higher-intensity interval exercise (70% PPO), and a no-exercise control. Brachial artery FMD was assessed at baseline and at 10 and 60 min after each condition. Baseline FMD was lower [by 1.10% (95% confidence interval: 0.72-.81), P = 0.044] in AAA patients than in healthy adults. There were no group differences in FMD responses after each condition ( P = 0.397). FMD did not change after no-exercise control but increased by 1.21% (95% confidence interval: 0.69-1.73, P < 0.001) 10 min after moderate-intensity continuous exercise in both groups and returned to baseline after 60 min. Conversely, FMD decreased by 0.93% (95% confidence interval: 0.41-1.44, P < 0.001) 10 min after higher-intensity interval exercise in both groups and remained decreased after 60 min. We found that the acute response of endothelial function to exercise is intensity-dependent and similar between AAA patients and healthy adults. Our findings provide evidence that regular exercise may improve vascular function in AAA patients, as it does in healthy adults. Improved FMD after moderate-intensity exercise may provide short-term benefit. Whether the decrease in FMD after higher-intensity exercise represents an additional risk and/or a greater stimulus for vascular adaptation remains to be elucidated. NEW & NOTEWORTHY Abdominal aortic aneurysm patients have vascular dysfunction. We observed a short-term increase in vascular function after moderate-intensity exercise. Conversely, higher-intensity exercise induced a prolonged reduction in vascular function, which may be associated with both short-term increases in cardiovascular risk and signaling for longer-term vascular adaptation in abdominal aortic aneurysm patients.

The Vascular Endothelium in Chronic Kidney Disease: A Novel Target for Aerobic Exercise

Endothelial dysfunction occurs in chronic kidney disease (CKD) and increases the risk for cardiovascular disease. The mechanisms of endothelial dysfunction seem to evolve throughout kidney disease progression, culminating in reduced L-arginine transport and impaired nitric oxide bioavailability in advanced disease. This review examines the hypothesis that aerobic exercise may reverse endothelial dysfunction by improving endothelial cell L-arginine uptake in CKD.

Myocardial Ischemia Assessment in Chronic Kidney Disease: Challenges and Pitfalls

Coronary artery disease is the leading cause of mortality and morbidity in the chronic kidney disease (CKD) population and often presents with atypical symptoms. Current diagnostic investigations of myocardial ischemia in CKD lack sensitivity and specificity or may have adverse effects. We present a case vignette and explore the challenges of diagnostic myocardial stress investigation in patients with CKD.