Six-Minute Walk Test in Renal Failure Patients: Representative Results, Performance Analysis and Perceived Dyspnea Predictors

Abstract

Objectives: Six-minute walk test in dialysis population hasn't been consistently evaluated for the isolated impact of renal failure and other predictive factors. We measured six-minute walk distance in patients representative for low level of comorbidity and searched for potentially modifiable predictive factors of performance and dyspnea.

Methods: This was a cross-sectional study with hemodialysis patients (N = 90) and control subjects (N = 140).

Main outcome measures: six-minute walk test distance and dyspnea severity using the 10-item Borg scale.

Results: Median distance decreased from 600m below the 6th decade to 420m in the 8th decade of age. Dialysis dependence predicted 101.5m shorter distance in the adjusted model that explained 70% of variability in results. Adjusted for significant covariates of age, height and spontaneous gait speed, fat mass (but not lean body mass) and serum total iron binding capacity were significantly associated with distance (95% CI for B coefficients -4.6 to -1.4 m/kg and 0.1 to 5 m/μmol/l, respectively). Serum total iron binding capacity as an explanatory variable was superior to C-reactive protein and albumin. Dialysis dependence, odds ratio (OR) 2.97 (1.11-7.94), spontaneous gait speed, OR 0.08 (0.02-0.41), rate-pressure product, OR 1.15 (1.08-1.23) and hemoglobin, OR 0.95 (0.92-0.98) predicted dyspnea in the adjusted model.

Conclusions: Renal failure without the confounding effect of comorbidity is a significant negative predictor of performance at six-minute walk test and perceived level of dyspnea. Body fat mass and serum total iron binding capacity are the main potentially modifiable predictors of performance, total iron binding capacity being superior to C-reactive protein and albumin. Although hemoglobin is not associated with test performance, it negatively predicts perceived shortness of breath.

Fig 1. Flow of patients with end-stage renal disease through recruitment process.

We also invited 180 community dwelling subjects to participation and 140 of them responded and performed the full study protocol. All participants were of European (white) descent.

Fig 2. The results of 6-minute walk test by age group.

Median values for dialysis patients–solid line and controls–dashed line. Interquartile range for dialysis patients is marked by error bars. 25^th, 75^th percentile and median values for dialysis patients are presented below the chart together with median values for control subjects.