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

Six-minute walk test may be a reliable predictor of peak oxygen uptake in patients undergoing hemodialysis

Background

Cardiorespiratory fitness seems to play an important role in the general health of patients undergoing hemodialysis (HD). However, the prediction of peak oxygen uptake (V̇O2peak) in a clinical setting is not widely adopted for these patients.

Objectives

Evaluate the agreement and reliability between directly and indirectly V̇O2peak measurements in patients undergoing HD.

Methods

This is a cross-sectional study with patients undergoing HD that performed a cardiopulmonary exercise test (CPET) with 5/10 watts incremental load in each minute using a cycle ergometry to directly evaluate the V̇O2peak, and the 6-min walk test (6MWT) in a 30-m corridor to indirect measures it. Both tests were performed on a midweek non-dialysis day. Bland–Altman analysis of agreement limits was used with direct and indirect V̇O2peak values. Intraclass correlation coefficient (ICC) and Cronbach’s Alpha was used to evaluate the reproducibility and reliability between direct and indirect V̇O2peak values.

Results

Twenty-six patients (54.4 ± 14.5 years, 53.8% of male) were evaluated. The V̇O2peak direct mean obtained through CPET was 15.91 ± 5.26 (ml/kg/min), while the indirect mean obtained through 6MWT was V̇O2peak of 14.89 ± 4.21 (ml/kg/min). There was a strong positive correlation between both V̇O2peak values (r = 0.734; p < 0.001). The Bland–Altman analysis demonstrated that the methods agreed with each other (p = 0.103). Also, the ICC (0.829) and Cronbach's Alpha (0.846) showed excellent reproducibility and reliability.

Conclusions

6MWT is a reliable tool for estimating V̇O2peak in patients undergoing HD.

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.

Quantitative Muscle Ultrasonography Using 2D Textural Analysis: A Novel Approach to Assess Skeletal Muscle Structure and Quality in Chronic Kidney Disease

Chronic kidney disease (CKD) is characterized by progressive reductions in skeletal muscle function and size. The concept of muscle quality is increasingly being used to assess muscle health, although the best means of assessment remains unidentified. The use of muscle echogenicity is limited by an inability to be compared across devices. Gray level of co-occurrence matrix (GLCM), a form of image texture analysis, may provide a measure of muscle quality, robust to scanner settings. This study aimed to identify GLCM values from skeletal muscle images in CKD and investigate their association with physical performance and strength (a surrogate of muscle function). Transverse images of the rectus femoris muscle were obtained using B-mode 2D ultrasound imaging. Texture analysis (GLCM) was performed using ImageJ. Five different GLCM features were quantified: energy or angular second moment (ASM), entropy, homogeneity, or inverse difference moment (IDM), correlation, and contrast. Physical function and strength were assessed using tests of handgrip strength, sit to stand-60, gait speed, incremental shuttle walk test, and timed up-and-go. Correlation coefficients between GLCM indices were compared to each objective functional measure. A total of 90 CKD patients (age 64.6 (10.9) years, 44% male, eGFR 33.8 (15.7) mL/minutes/1.73 m2) were included. Better muscle function was largely associated with those values suggestive of greater image texture homogeneity (i.e., greater ASM, correlation, and IDM, lower entropy and contrast). Entropy showed the greatest association across all the functional assessments (r = -.177). All GLCM parameters, a form of higher-order texture analysis, were associated with muscle function, although the largest association as seen with image entropy. Image homogeneity likely indicates lower muscle infiltration of fat and fibrosis. Texture analysis may provide a novel indicator of muscle quality that is robust to changes in scanner settings. Further research is needed to substantiate our findings.