Six-minute walk test distance does not reflect oxygen uptake in patients undergoing maintenance hemodialysis

Abstract

Aims: By evaluating the exercise capacity of patients on maintenance hemodialysis (MHD), this study aimed to determine the representability of a 6-minute walk test (6MWT) distance for the cardiopulmonary endurance capacity of patients on MHD.

Materials and methods: The volume of oxygen uptake (VO₂) at a respiratory exchange ratio equal to 1 (VO_2(RER=1)) was measured during a graded cycling test, and the 6MWT distance was tested in 27 Chinese patients on MHD and 44 age-matched non-MHD subjects (CON).

Results: VO_2(RER=1) in MHD was lower than the levels of CON (834.44 ± 232.73 and 1,255.08 ± 340.49 mL/min, respectively (t = 5.65, p < 0.001)). The 6MWT distance of MHD was ~ 92 m shorter than that of CON (t = 7.58, p < 0.001). Additionally, a positive linear correlation between 6MWT distance and VO_2(RER=1) during the graded cycling test was found in CON (r = 0.57, p < 0.001) but was absent in MHD (r = 0.12, p = 0.582).

Conclusion: Results indicate a significantly reduced cardiopulmonary endurance capacity and functional walk ability among Chinese patients on MHD. Moreover, 6MWT may not be a proper method to evaluate the cardiopulmonary endurance capacity of patients on MHD due to the absence of a correlation between 6MWT distance and oxygen uptake during exercise.