The Mechanisms of Physical Fatigue in Kidney Transplant Recipients.

Abstract

PURPOSE The mechanisms of physical fatigue in kidney transplant recipients (KTRs) remained unexplored. The primary objectives were to determine the prevalence of physical fatigue in KTRs; assess its impact on quality of life (QoL); and identify the mechanisms of physical fatigue through examinations of cardiorespiratory function (VO2max), perceived exertion, as well as muscle mass, function and conditioning. The secondary objective was to investigate the predictors of raised perceived exertion, a determinant of physical fatigue in KTRs. METHODS This single-centre cross-sectional study enrolled 55 KTRs ≥1 year post-transplantation. Mean age=46±14 years; 58% male. Physical fatigue was measured by multi-dimensional fatigue inventory-20. QoL was assessed with SF-36. VO2max was estimated by sub-maximal exercise test. Rating of perceived exertion (RPE) was determined by age-adjusted Borg-ratings during exercise, with RPE index calculated. Lean body mass (LBM) was quantified with dual energy x-ray absorptiometry. Muscle function was assessed by jumping mechanography (single 2-legged jump [S2LJ] and chair rise test [CRT]). Muscle conditioning was determined by changes in myokine (serum IL-6) levels, taken at rest (Trest), immediately (Timmediate) and 1-hour (T1-hour) after exercise. Demographic, clinical, psychosocial and behavioural predictors of perceived exertion were assessed. RESULTS Physical fatigue was found in 22% of KTRs, and exerted a negative impact on QoL (p<0.001). Median RPE index=1.2 (0.8-2.0). Mean values of VO2max=26.7±9.0 ml/kg/min; LBM=50.7±11.5 kg; muscle function measured by S2LJ=4045±1136 W, and CRT=1118±268 W. No significant changes of serum IL-6 levels were detected between Trest, Timmediate, and T1-hour. Independent predictors of physical fatigue were reduced VO2max in male (p=0.04) and increased perceived exertion in female (p=0.003). Independent predictors of raised perception were mental fatigue (p=0.03), anxiety (p=0.01), new-onset diabetes after transplantation (p=0.04), absence of cyclosporine (p=0.03), and low alcohol intake (p=0.03). CONCLUSION Physical fatigue in KTRs is driven by reduced VO2max in male, and increased perception in female. Predictors of raised perception were identified, paving the way for future interventional studies. Further research is needed to identify causes of reduced VO2max in KTRs.