Cardiovascular Functional Reserve Before and After Kidney Transplant

Endothelial dysfunction in the kidney transplant population: Current evidence and management strategies

The endothelium modulates vascular homeostasis owing to a variety of vasoconstrictors and vasodilators. Endothelial dysfunction (ED), characterized by impaired vasodilation, inflammation, and thrombosis, triggers future cardiovascular (CV) diseases. Chronic kidney disease, a state of chronic inflammation caused by oxidative stress, metabolic abnormalities, infection, and uremic toxins damages the endothelium. ED is also associated with a decline in estimated glomerular filtration rate. After kidney transplantation, endothelial functions undergo immediate but partial restoration, promising graft longevity and enhanced CV health. However, the anticipated CV outcomes do not happen due to various transplant-related and unrelated risk factors for ED, culminating in poor CV health and graft survival. ED in kidney transplant recipients is an under-recognized and poorly studied entity. CV diseases are the leading cause of death among kidney transplant candidates with functioning grafts. ED contributes to the pathogenesis of many of the CV diseases. Various biomarkers and vasoreactivity tests are available to study endothelial functions. With an increasing number of transplants happening every year, and improved graft rejection rates due to the availability of effective immunosuppressants, the focus has now shifted to endothelial protection for the prevention, early recognition, and treatment of CV diseases.

Defining the predictors for post renal transplant left ventricular dysfunction in end-stage renal disease patients

Reduced left ventricular (LV) function predicts poor outcomes in end-stage renal disease (ESRD). This study aimed to identify the pre-renal transplantation echocardiographic parameters that can predict post-renal transplantation LV failure. This prospective longitudinal study was conducted on patients with ESRD who underwent renal transplantation during 1 year. All patients underwent echocardiography, including ejection fraction (EF), global longitudinal strain (GLS), left ventricular end-systolic diameter (LVESD), left ventricular end-diastolic volume (LVEDV), left ventricular end-diastolic diameter (LVEDD), interventricular septal (IVS) thickness, peak velocity of early diastolic transmitral flow (E), peak velocity of late transmitral flow (A), early diastolic myocardial relaxation (Em), E/A, E/Em, Left atrial volume (LAV) index, tricuspid regurgitation peak gradient (TRPG), systolic pulmonary artery pressure (SPAP), tricuspid annular plane systolic excursion (TAPSE), 1 week before and 1 month after renal transplantation. Fifty patients participated in the current study. All echocardiographic parameters improved after transplantation. Post-renal transplantation LV dysfunction was observed in 21 (42%) patients. Pre-renal transplantation echocardiographic parameters (LVEDV, LVESD, LVEDD, IVS, E/Em, TRPG, SPAP, and LAV index) could predict post-transplantation LV failure with high accuracy (AUC: 0.978).

Impairment of Cardiovascular Functional Capacity in Mild-to-Moderate Kidney Dysfunction

Key Points

Mild-to-moderate CKD is associated with impairment in cardiovascular functional capacity as assessed by oxygen uptake at peak exercise (VO2Peak). Cardiac output is significantly reduced in patients with mild-to-moderate CKD and is associated with impaired VO2Peak. Assessment of VO2Peak by cardiopulmonary exercise testing can detect decrements in cardiovascular function during early stages of kidney function decline that may not be captured using resting left ventricular geometric indices alone.

Background

Traditional diagnostic tools that assess resting cardiac function and structure fail to accurately reflect cardiovascular alterations in patients with CKD. This study sought to determine whether multidimensional exercise response patterns related to cardiovascular functional capacity can detect abnormalities in mild-to-moderate CKD.

Methods

In a cross-sectional study, we examined 3075 participants from the Framingham Heart Study (FHS) and 451 participants from the Massachusetts General Hospital Exercise Study (MGH-ExS) who underwent cardiopulmonary exercise testing. Participants were stratified by eGFR: eGFR ≥90, eGFR 60–89, and eGFR 30–59. Our primary outcomes of interest were peak oxygen uptake (VO2Peak), VO2 at anaerobic threshold (VO2AT), and ratio of minute ventilation to carbon dioxide production (VE/VCO2). Multiple linear regression models were fitted to evaluate the associations between eGFR group and each outcome variable adjusted for covariates.

Results

In the FHS cohort, 1712 participants (56%) had an eGFR ≥90 ml/min per 1.73 m2, 1271 (41%) had an eGFR of 60–89 ml/min per 1.73 m2, and 92 (3%) had an eGFR of 30–59 ml/min per 1.73 m2. In the MGH-ExS cohort, 247 participants (55%) had an eGFR ≥90 ml/min per 1.73 m2, 154 (34%) had an eGFR of 60–89 ml/min per 1.73 m2, and 50 (11%) had an eGFR of 30–59 ml/min per 1.73 m2. In FHS, VO2Peak and VO2AT were incrementally impaired with declining kidney function (P < 0.001); however, this pattern was attenuated after adjustment for age. Percent-predicted VO2Peak at AT was higher in the lower eGFR groups (P < 0.001). In MGH-ExS, VO2Peak and VO2AT were incrementally impaired with declining kidney function in unadjusted and adjusted models (P < 0.05). VO2Peak was associated with eGFR (P < 0.05) in all models even after adjusting for age. On further mechanistic analysis, we directly measured cardiac output (CO) at peak exercise by right heart catheterization and found impaired CO in the lower eGFR groups (P ≤ 0.007).

Conclusions

Cardiopulmonary exercise testing–derived indices may detect impairment in cardiovascular functional capacity and track CO declines in mild-to-moderate CKD.

Left Ventricular Hypertrophy After Renal Transplantation: Systematic Review and Meta-analysis

Background

Left ventricular hypertrophy (LVH) in patients with end stage renal disease undergoing renal replacement is linked to an increased risk for cardiovascular diseases. Dialysis does not completely prevent or correct this abnormality, and the evidence for kidney transplantation (KT) varies. This analysis aims to explore the relationship between KT and LVH.

Methods

MEDLINE and Scopus were systematically searched in October 2023. All cross-sectional and longitudinal studies that fulfilled our inclusion criteria were included. Outcome was left ventricular mass index (LVMI) changes. We conducted a meta-analysis using a random effects model. Meta-regression was applied to examine the LVMI changes dependent on various covariates. Sensitivity analysis was used to handle outlying or influential studies and address publication bias.

Results

From 7416 records, 46 studies met the inclusion criteria with 4122 included participants in total. Longitudinal studies demonstrated an improvement of LVMI after KT -0.44 g/m2 (-0.60 to -0.28). Blood pressure was identified as a predictor of LVMI change. A younger age at the time of KT and well-controlled anemia were also associated with regression of LVH. In studies longitudinally comparing patients on dialysis and renal transplant recipients, no difference was detected -0.09 g/m2 (-0.33 to 0.16). Meta-regression using changes of systolic blood pressure as a covariate showed an association between higher blood pressure and an increase in LVMI, regardless of the modality of renal replacement treatment.

Conclusions

In conclusion, our results indicated a potential cardiovascular benefit, defined as the regression of LVH, after KT. This benefit was primarily attributed to improved blood pressure control rather than the transplantation itself.

Epimeric vitamin D and cardiovascular structure and function in advanced CKD and after kidney transplantation

BACKGROUND

25-hydroxyvitamin D can undergo C-3 epimerization to produce 3-epi-25(OH)D3. 3-epi-25(OH)D3 levels decline in chronic kidney disease (CKD), but its role in regulating the cardiovascular system is unknown. Herein, we examined the relationship between 3-epi-25(OH)D3, and cardiovascular functional and structural endpoints in patients with CKD.

METHODS

We examined n = 165 patients with advanced CKD from the Cardiopulmonary Exercise Testing in Renal Failure and After Kidney Transplantation (CAPER) study cohort, including those who underwent kidney transplant (KTR, n = 76) and waitlisted patients who did not (NTWC, n = 89). All patients underwent cardiopulmonary exercise testing and echocardiography at baseline, 2 months and 12 months. Serum 3-epi-25(OH)D3 was analyzed by liquid chromatography-tandem mass spectrometry.

RESULTS

Patients were stratified into quartiles of baseline 3-epi-25(OH)D3 (Q1: <0.4 ng/mL, n = 51; Q2: 0.4 ng/mL, n = 26; Q3: 0.5-0.7 ng/mL, n = 47; Q4: ≥0.8 ng/mL, n = 41). Patients in Q1 exhibited lower peak oxygen uptake [VO2Peak = 18.4 (16.2-20.8) mL/min/kg] compared with Q4 [20.8 (18.6-23.2) mL/min/kg; P = .009]. Linear mixed regression model showed that 3-epi-25(OH)D3 levels increased in KTR [from 0.47 (0.30) ng/mL to 0.90 (0.45) ng/mL] and declined in NTWC [from 0.61 (0.32) ng/mL to 0.45 (0.29) ng/mL; P < .001]. Serum 3-epi-25(OH)D3 was associated with VO2Peak longitudinally in both groups [KTR: β (standard error) = 2.53 (0.56), P < .001; NTWC: 2.73 (0.70), P < .001], but was not with left ventricular mass or arterial stiffness. Non-epimeric 25(OH)D3, 24,25(OH)2D3 and the 25(OH)D3:24,25(OH)2D3 ratio were not associated with any cardiovascular outcome (all P > .05).

CONCLUSIONS

Changes in 3-epi-25(OH)D3 levels may regulate cardiovascular functional capacity in patients with advanced CKD.

Exercise Rehabilitation for People With End-Stage Kidney Disease: Who Will Fill the Gaps?

Exercise rehabilitation is a well established therapy for reducing morbidity and mortality and improving quality of life and function across chronic conditions. People with dialysis-dependent kidney failure have a high burden of comorbidity and symptoms, commonly characterised as fatigue, dyspnoea, and the inability to complete daily activities. Despite more than 30 years of exercise research in people with kidney disease and its established benefit in other chronic diseases, exercise programs are rare in kidney care and are not incorporated into routine management at any stage. In this review, we describe the mechanisms contributing to exercise intolerance in those with end-stage kidney disease and outline the role of exercise rehabilitation in addressing the major challenges to kidney care: cardiovascular disease, symptom burden, and physical frailty. We also draw on existing models of exercise rehabilitation from other chronic conditions to inform the way forward and challenge the status quo of exercise rehabilitation in both practice and research.

Effect of kidney transplantation on indices of cardiorespiratory fitness assessed with cardiopulmonary exercise testing: a systematic review and meta-analysis

BACKGROUND

Patients with kidney failure often present with reduced cardiovascular reserve. Kidney transplantation (KT) is the optimal treatment for patients with end-stage kidney disease as it is associated with longer survival and improved quality of life compared to dialysis.

METHODS

This is a systematic review and meta-analysis of studies using cardiopulmonary-exercise-testing to examine the cardiorespiratory fitness of patients with kidney failure before and after KT. The primary outcome was difference in pre- and post-transplantation values of peak oxygen uptake (VO2peak). Literature search involved three databases (PubMed-Web of Science-Scopus), manual search, and grey literature.

RESULTS

From 379 records initially retrieved, six studies were included in final meta-analysis. A marginal, but not significant, improvement was observed in VO2peak after KT compared to pre-transplantation values (SMD: 0.32, 95%CI -0.02; 0.67). Oxygen consumption at anaerobic threshold was significantly improved after KT (WMD: 2.30 ml/kg/min, 95%CI 0.50; 4.09). Consistent results were shown between preemptive and after-dialysis-initiation transplantation and a trend for improvement in VO2peak was observed at least 3 months post-transplantation, but not earlier.

CONCLUSION

Several major indices of cardiorespiratory fitness tend to improve after KT. This finding may represent another modifiable factor contributing to better survival rates of kidney transplant recipients compared to patients undergoing dialysis.

Cardiopulmonary Exercise Test Parameters among Dialysis Patients with End-Stage Renal Disease

Background

The current study aimed to assess some parameters of the cardiopulmonary exercise test (CPET) among end-stage renal disease patients who underwent dialysis. The ultimate goal is to improve disease management to achieve optimal quality of life and exercise capacity in this group of patients.

Materials and Methods

Through a cross-sectional design, the current study enrolled 46 dialysis patients by simple sampling between Jan 2019 and Jan 2020. Some CPET parameters such as AT, VO2, VO2/kg, SPO2, minute ventilation CO2 production/O2 consumption ratios (VE/VCO2 and VE/VO2, respectively), O2 pulse, heart rate reserve (HRR), breathing reserve (BR) and end-tidal carbon dioxide pressure (PETCO2) were focused.

Results

Although a limited sample size, the current study showed that VO2/Kg, VE/VCO2, PETCO2, and SPO2 are the main parameters affected by dialysis as expected.

Conclusion

The current study suggests using cardiopulmonary rehabilitation for all chronic medical conditions such as chronic kidney disease and end-stage renal disease that increase the rate of metabolic acidosis.

Changes in myocardial work associated with pediatric kidney transplantation: A pilot study of short-term postoperative effect

The study was mainly to evaluate the changes of left ventricular (LV) myocardial work (MW) in children with CKD stage 5 within 3 months after kidney transplantation (KTx). Forty-three successful KTx recipients (mean age 10.6 years, 58% male) in childhood and 28 healthy children were enrolled. General clinical characteristics and laboratory parameters were collected. Cardiac structure, function, and LV MW were assessed by echocardiography before and after KTx. The results showed that significantly improvement was observed in LV global MW index (GWI), constructive MW (GCW), and wasted MW (GWW) (p < .01), but not in MW efficiency (GWE) and global longitudinal strain (GLS) (p > .05). Besides, blood pressure (BP), renal graft function, LV ejection fraction (LVEF), and LV mass index (LVMi) had obviously improved after KTx (p < .05). Nevertheless, compared with healthy children, higher BP, LVMi, GWW, more deteriorated LV diastolic function and lower GWE were still observed in patients after KTx. The ratio of dialysis duration to CKD course were negatively correlated with the improvements of GWE (p = .004), GWI (p = .01), and GCW (p = .01). In conclusion, a portion of LV MW parameters were obviously improved in children received KTx. Thus, LV MW was superior to GLS in evaluating LV systolic function recovery in these patients. Those patients with insignificant MW improvement should be closely monitored, and adjusted the treatment strategies timely to avoid serious and irreversible myocardial injury after KTx.

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.

Significant Improvement of Cardiac Dysfunction After Kidney Transplant: A Case Report

Kidney transplant is known to reverse cardiac dysfunction in patients with end-stage renal disease, and low ejection fraction in kidney transplant candidates is considered to be a contraindication for transplant. We present a significant improvement in cardiac dysfunction after successful kidney transplant in a 21-year-old male recipient. Kidney transplant may be beneficial for cardiac function in transplant recipients who have impaired cardiac function prior to the procedure and caused by uremic toxins.

FGF23 and Cardiovascular Structure and Function in Advanced Chronic Kidney Disease

Background

Fibroblast growth factor 23 (FGF23) is a bone-derived phosphatonin that is elevated in chronic kidney disease (CKD) and has been implicated in the development of cardiovascular disease. It is unknown whether elevated FGF23 in CKD is associated with impaired cardiovascular functional capacity, as assessed by maximum exercise oxygen consumption (VO2Max). We sought to determine whether FGF23 is associated with cardiovascular functional capacity in patients with advanced CKD and after improvement of VO2Max by kidney transplantation.

Methods

We performed secondary analysis of 235 patients from the Cardiopulmonary Exercise Testing in Renal Failure and After Kidney Transplantation (CAPER) cohort, which recruited patients with stage 5 CKD who underwent kidney transplantation or were waitlisted and hypertensive controls. All patients underwent cardiopulmonary exercise testing (CPET) and echocardiography and were followed longitudinally for 1 year after study enrollment.

Results

Patients across FGF23 quartiles differed in BMI (P=0.004) and mean arterial pressure (P<0.001) but did not significantly differ in sex (P=0.5) or age (P=0.08) compared with patients with lower levels of FGF23. Patients with higher FGF23 levels had impaired VO2Max (Q1: 24.2±4.8 ml/min per kilogram; Q4: 18.6±5.2 ml/min per kilogram; P<0.001), greater left ventricular mass index (LVMI; P<0.001), reduced HR at peak exercise (P<0.001), and maximal workload (P<0.001). Kidney transplantation conferred a significant decline in FGF23 at 2 months (P<0.001) before improvement in VO2Max at 1 year (P=0.008). Multivariable regression modeling revealed that changes in FGF23 was significantly associated with VO2Max in advanced CKD (P<0.001) and after improvement after kidney transplantation (P=0.006). FGF23 was associated with LVMI before kidney transplantation (P=0.003), however this association was lost after adjustment for dialysis status (P=0.4). FGF23 was not associated with LVMI after kidney transplantation in all models.

Conclusions

FGF23 levels are associated with alterations in cardiovascular functional capacity in advanced CKD and after kidney transplantation. FGF23 is only associated with structural cardiac adaptations in advanced CKD but this was modified by dialysis status, and was not associated after kidney transplantation.

Initiation of Dialysis Is Associated With Impaired Cardiovascular Functional Capacity

Background The transition to dialysis period carries a substantial increased cardiovascular risk in patients with chronic kidney disease. Despite this, alterations in cardiovascular functional capacity during this transition are largely unknown. The present study therefore sought to assess ventilatory exercise response measures in patients within 1 year of initiating dialysis. Methods and Results We conducted a cross-sectional study of 241 patients with chronic kidney disease stage 5 from the CAPER (Cardiopulmonary Exercise Testing in Renal Failure) study and from the intradialytic low-frequency electrical muscle stimulation pilot randomized controlled trial cohorts. Patients underwent cardiopulmonary exercise testing and echocardiography. Of the 241 patients (age, 48.9 [15.0] years; 154 [63.9%] men), 42 were predialytic (mean estimated glomerular filtration rate, 14 mL·min-1·1.73 m-2), 54 had a dialysis vintage ≤12 months, and 145 had a dialysis vintage >12 months. Dialysis vintage ≤12 months exhibited a significantly impaired cardiovascular functional capacity, as assessed by oxygen uptake at peak exercise (18.7 [5.8] mL·min-1·kg-1) compared with predialysis (22.7 [5.2] mL·min-1·kg-1; P<0.001). Dialysis vintage ≤12 months also exhibited reduced peak workload, impaired peak heart rate, reduced circulatory power, and increased left ventricular mass index (P<0.05 for all) compared with predialysis. After excluding those with prior kidney transplant, dialysis vintage >12 months exhibited a lower oxygen uptake at peak exercise (17.0 [4.9] mL·min-1·kg-1) compared with dialysis vintage ≤12 months (18.9 [5.9] mL·min-1·kg-1; P=0.033). Conclusions Initiating dialysis is associated with a significant impairment in oxygen uptake at peak exercise and overall decrements in ventilatory and hemodynamic exercise responses that predispose patients to functional dependence. The magnitude of these changes is comparable to the differences between low-risk New York Heart Association class I and higher-risk New York Heart Association class II to IV heart failure.

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.

Maximal Exercise Capacity in Chronic Kidney Disease Stage 4-5 Patients Transitioning to Renal Replacement Therapy or Continuing Conservative Care: A Longitudinal Follow-Up Study

INTRODUCTION

Chronic kidney disease (CKD) is associated with impaired maximal exercise capacity (MEC). However, data are scarce on the development of MEC in CKD stage 4-5 patients transitioning to renal replacement therapy (RRT).

METHODS

We explored the change in MEC measured in watts (Wlast4) with 2 consecutive maximal bicycle stress ergometry tests in 122 CKD stage 4-5 patients transitioning to dialysis and transplantation in an observational follow-up study.

RESULTS

Mean age was 58.9 ± 13.9 years and 43 (35.2%) were female. Mean time between the baseline and follow-up ergometry tests was 1,012 ± 327 days and 29 (23.8%) patients had not initiated RRT, 50 (41.0%) were undergoing dialysis, and 43 (35.2%) had received a kidney transplant at the time of the follow-up ergometry test. The mean Wlast4 was 91 ± 37 W and 84 ± 37 W for the baseline and follow-up ergometry tests, respectively (p < 0.001). The mean Wlast4 declined between the baseline and follow-up ergometry tests in patients not requiring RRT (p = 0.001) and transplant recipients (p = 0.005), but not in dialysis patients (p = 0.478). There were no differences in the ratio of Wlast4 of the follow-up to the baseline ergometry tests (∆Wlast4) between patients on different treatment modalities at the time of the follow-up test (p = 0.097). Mean capillary blood bicarbonate was significantly associated with ∆Wlast4 after adjusting for age and treatment modality in the multivariate linear regression analysis (β = 0.226, p = 0.012).

CONCLUSION

MEC declined or remained poor in advanced CKD patients transitioning to RRT or continuing conservative care in this observational study. Mean capillary blood bicarbonate was independently associated with the development of MEC.

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

BACKGROUND

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

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

PROSPERO REGISTRATION NUMBER

CRD42021227805.

Skeletal Muscle Phenotype in Patients Undergoing Long-Term Hemodialysis Awaiting Kidney Transplantation

BACKGROUND AND OBJECTIVES

Age and comorbidity-related sarcopenia represent a main cause of muscle dysfunction in patients on long-term hemodialysis. However, recent findings suggest muscle abnormalities that are not associated with sarcopenia. The aim of this study was to isolate functional and cellular muscle abnormalities independently of other major confounding factors, including malnutrition, age, comorbidity, or sedentary lifestyle, which are common in patients on maintenance hemodialysis. To overcome these confounding factors, alterations in skeletal muscle were analyzed in highly selected patients on long-term hemodialysis undergoing kidney transplantation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In total, 22 patients on long-term hemodialysis scheduled for kidney transplantation with few comorbidities, but with a long-term uremic milieu exposure, and 22 age, sex, and physical activity level frequency-matched control participants were recruited. We compared biochemical, functional, and molecular characteristics of the skeletal muscle using maximal voluntary force and endurance of the quadriceps, 6-minute walking test, and muscle biopsy of vastus lateralis. For statistical analysis, mean comparison and multiple regression tests were used.

RESULTS

In patients on long-term hemodialysis, muscle endurance was lower, whereas maximal voluntary force was not significantly different. We observed a transition from type I (oxidative) to type II (glycolytic) muscle fibers, and an alteration of mitochondrial structure (swelling) without changes in DNA content, genome replication (peroxisome proliferator activator receptor γ coactivator-1α and mitochondrial transcription factor A), regulation of fusion (mitofusin and optic atrophy 1), or fission (dynamin-related protein 1). Notably, there were autophagosome structures containing glycogen along with mitochondrial debris, with a higher expression of light chain 3 (LC3) protein, indicating phagophore formation. This was associated with a greater conversion of LC3-I to LC3-II and the expression of Gabaralp1 and Bnip3l genes involved in mitophagy.

CONCLUSIONS

In this highly selected long-term hemodialysis population, a low oxidative phenotype could be defined by a poor endurance, a fiber-type switch, and an alteration of mitochondria structure, without evidence of sarcopenia. This phenotype could be related to uremia through the activation of autophagy/mitophagy.

CLINICAL TRIAL REGISTRATION NUMBERS

NCT02794142 and NCT02040363.

Cardiorespiratory fitness in kidney transplant recipients compared to patients with kidney failure: a systematic review and meta-analysis

Patients with kidney failure often present with reduced cardiovascular functional reserve and exercise tolerance. Previous studies on cardiorespiratory fitness examined with cardiopulmonary exercise testing (CPET) in kidney transplant recipients (KTR) had variable results. This is a systematic review and meta-analysis of studies examining cardiovascular functional reserve with CPET in KTR in comparison with patients with kidney failure (CKD-Stage-5 before dialysis, hemodialysis or peritoneal dialysis), as well as before and after kidney transplantation. Literature search involved PubMed, Web-of-Science and Scopus databases, manual search of article references and grey literature. From a total of 4,944 identified records, eight studies (with 461 participants) were included in quantitative analysis for the primary question. Across these studies, KTR had significantly higher oxygen consumption at peak/max exercise (VO₂ peak/VO₂ max) compared to patients with kidney failure (SMD = 0.70, 95% CI [0.31, 1.10], I²  = 70%, P = 0.002). In subgroup analyses, similar differences were evident among seven studies comparing KTR and hemodialysis patients (SMD = 0.64, 95% CI [0.16, 1.12], I²  = 65%, P = 0.009) and two studies comparing KTR with peritoneal dialysis subjects (SMD = 1.14, 95% CI [0.19, 2.09], I²  = 50%, P = 0.16). Across four studies with relevant data, oxygen consumption during peak/max exercise showed significant improvement after kidney transplantation compared to pretransplantation values (WMD = 2.43, 95% CI [0.01, 4.85], I²  = 68%, P = 0.02). In conclusion, KTR exhibit significantly higher cardiovascular functional reserve during CPET compared to patients with kidney failure. Cardiovascular reserve is significantly improved after kidney transplantation in relation to presurgery levels.

Cardiovascular Functional Changes in Chronic Kidney Disease: Integrative Physiology, Pathophysiology and Applications of Cardiopulmonary Exercise Testing

The development of cardiovascular disease during renal impairment involves striking multi-tiered, multi-dimensional complex alterations encompassing the entire oxygen transport system. Complex interactions between target organ systems involving alterations of the heart, vascular, musculoskeletal and respiratory systems occur in Chronic Kidney Disease (CKD) and collectively contribute to impairment of cardiovascular function. These systemic changes have challenged our diagnostic and therapeutic efforts, particularly given that imaging cardiac structure at rest, rather than ascertainment under the stress of exercise, may not accurately reflect the risk of premature death in CKD. The multi-systemic nature of cardiovascular disease in CKD patients provides strong rationale for an integrated approach to the assessment of cardiovascular alterations in this population. State-of-the-art cardiopulmonary exercise testing (CPET) is a powerful, dynamic technology that enables the global assessment of cardiovascular functional alterations and reflects the integrative exercise response and complex machinery that form the oxygen transport system. CPET provides a wealth of data from a single assessment with mechanistic, physiological and prognostic utility. It is an underutilized technology in the care of patients with kidney disease with the potential to help advance the field of cardio-nephrology. This article reviews the integrative physiology and pathophysiology of cardio-renal impairment, critical new insights derived from CPET technology, and contemporary evidence for potential applications of CPET technology in patients with kidney disease.

Ventilatory and chronotropic incompetence during incremental and constant load exercise in end-stage renal disease: a comparative physiology study

Maximal O₂ uptake is impaired in end-stage renal disease (ESRD), reducing quality of life and longevity. While determinants of maximal exercise intolerance are well defined, little is known of limitation during submaximal constant load exercise. By comparing individuals with ESRD and healthy controls, the aim of this exploratory study was to characterize mechanisms of exercise intolerance in participants with ESRD by assessing cardiopulmonary physiology at rest and during exercise. Resting spirometry and echocardiography were performed in 20 dialysis-dependent participants with ESRD (age: 59 ± 12 yr, 14 men and 6 women) and 20 healthy age- and sex-matched controls. Exercise tolerance was assessed with ventilatory gas exchange and central hemodynamics during a maximal cardiopulmonary exercise test and 30 min of submaximal constant load exercise. Left ventricular mass (292 ± 102 vs. 185 ± 83 g, P = 0.01) and filling pressure (E/e': 6.48 ± 3.57 vs. 12.09 ± 6.50 m/s, P = 0.02) were higher in participants with ESRD; forced vital capacity (3.44 ± 1 vs. 4.29 ± 0.95 L/min, P = 0.03) and peak O₂ uptake (13.3 ± 2.7 vs. 24.6 ± 7.3 mL·kg^-1·min^-1, P < 0.001) were lower. During constant load exercise, the relative increase in the arterial-venous O₂ difference (13 ± 18% vs. 74 ± 18%) and heart rate (32 ± 18 vs. 75 ± 29%) were less in participants with ESRD despite exercise being performed at a higher percentage of maximum minute ventilation (48 ± 3% vs. 39 ± 3%) and heart rate (82 ± 2 vs. 64 ± 2%). Ventilatory and chronotropic incompetence contribute to exercise intolerance in individuals with ESRD. Both are potential targets for medical and lifestyle interventions.