Mediating effect of cardiorespiratory fitness on the relationship between inspiratory muscle strength and quality of life in people on hemodialysis.

Abstract

Introduction: Patients undergoing hemodialysis often exhibit inspiratory muscle weakness, which has been associated with a reduced health-related quality of life (HRQoL). However, the extent to which this relationship is mediated by cardiorespiratory fitness remains unclear.

Objective: To evaluate the mediating effect of cardiorespiratory fitness on the association between inspiratory muscle strength and HRQoL in hemodialysis patients.

Methods: Cross-sectional study in which hemodialysis patients underwent assessment of inspiratory muscle strength by measuring Maximum Inspiratory Pressure (MIP), cardiorespiratory fitness by the Incremental Shuttle Walk Test (ISWT), and HRQoL by measuring the physical, mental, and general health component summary scores of the Kidney Disease Quality of Life questionnaire (KDQOL-SF). Simple mediation analyses were performed using the PROCESS macro (version 3.5) for SPSS, with HRQoL as the dependent variable, MIP as the independent variable, and cardiorespiratory fitness as the mediating variable.

Results: 64 individuals, 67.2% male, with a mean age of 48.1 years (95%CI 44.3-51.9), were evaluated. Cardiorespiratory fitness exerted a partial mediating effect on the association between MIP and PCS (β = 0.14; 95%CI: 0.02-0.27), resulting in a 6% reduction in PCS variance explained by MIP (6% of R2). The mediating proportion was 32.5%. There was no association between MIP and the mental component, and cardiorespiratory fitness did not mediate the relationship between MIP and the general component of HRQoL (β = 0.13; p = 0.350).

Conclusion: In the sample studied, the association between inspiratory muscle strength and the physical aspects of HRQoL is partially mediated by cardiorespiratory fitness. However, this mediating effect was not observed for the mental or general aspects of HRQoL.