• Thomas J Wilkinson, Alice E M White, Daniel G D Nixon, Douglas W Gould, Emma L Watson, and Alice C Smith.
• Leicester Kidney Lifestyle Team, Department of Infection, Immunity, and Inflammation, University of Leicester, Leicester, LE5 4PW, UK. t.j.wilkinson@leicester.ac.uk.
• Clin. Exp. Nephrol. 2019 Jan 1; 23 (1): 32-42.

BackgroundChronic kidney disease (CKD) patients have reduced exercise capacity. Possible contributing factors may include impaired muscle O2 utilisation through reduced mitochondria number and/or function slowing the restoration of muscle ATP concentrations via oxidative phosphorylation. Using near-infrared spectroscopy (NIRS), we explored changes in skeletal muscle haemoglobin/myoglobin O2 saturation (SMO2%) during exercise.Methods24 CKD patients [58.3 (± 16.5) years, eGFR 56.4 (± 22.3) ml/min/1.73 m2] completed the incremental shuttle walk test (ISWT) as a marker of exercise capacity. Using NIRS, SMO2% was measured continuously before, during, and after (recovery) exercise. Exploratory differences were investigated between exercise capacity tertiles in CKD, and compared with six healthy controls.ResultsWe identified two discrete phases; a decline in SMO2% during incremental exercise, followed by rapid increase upon cessation (recovery). Compared to patients with low exercise capacity [distance walked during ISWT, 269.0 (± 35.9) m], patients with a higher exercise capacity [727.1 (± 38.1) m] took 45% longer to reach their minimum SMO2% (P = .038) and recovered (half-time recovery) 79% faster (P = .046). Compared to controls, CKD patients took significantly 56% longer to recover (i.e., restore SMO2% to baseline, full recovery) (P = .014).ConclusionsUsing NIRS, we have determined for the first time in CKD, that favourable SMO2% kinetics (slower deoxygenation rate, quicker recovery) are associated with greater exercise capacity. These dysfunctional kinetics may indicate reduced mitochondria capacity to perform oxidative phosphorylation-a process essential for carrying out even simple activities of daily living. Accordingly, NIRS may provide a simple, low cost, and non-invasive means to evaluate muscle O2 kinetics in CKD.

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