Cerebral oxygenation during exercise deteriorates with advancing chronic kidney disease

Objective: Cognitive impairment and exercise intolerance are common in CKD. Cerebral perfusion and oxygenation play a major role in both cognitive function and exercise execution. This study aimed to examine cerebral oxygenation during a mild physical stress in patients at different CKD stages and controls without CKD. Design and method: Ninety-participants (18 per CKD-stage 2,3a,3b,4 and 18 controls) underwent a 3-min intermittent-handgrip-exercise at 35% of their maximal-voluntary-contraction(MVC). During exercise, cerebral oxygenation (oxyhemoglobin-O2Hb, deoxyhemoglobin-HHb, total-hemoglobin-tHb) was assessed by near-infrared-spectroscopy. Indices of microvascular (muscle-hyperemic-response) and macrovascular function (cIMT and PWV), cognitive and physical activity status were also evaluated. Results: No differences in age, sex and BMI were detected among-groups. The MMSE score was significantly reduced with advancing CKD stages (Controls: 29.2±1.2 Stage 2: 28.7±1.0 Stage 3a: 27.8±1.9 Stage 3b: 28.0±1.8 Stage 4: 27.6±1.5; p = 0.019). Similar trends were observed for physical activity levels and handgrip strength. The average response in cerebral oxygenation during exercise was lower with advancing CKD stages (O2Hb: Controls: 2.50±1.54, Stage-2: 1.30±1.05, Stage-3a: 1.24±0.93, Stage-3b: 1.11±0.89, Stage-4: 0.97±0.80micromol/l; p<0.001)). The average tHb response(index of regional-blood-volume) showed a similar decreasing trend (p = 0.003); no differences in HHb among groups were detected. In univariate linear analysis older age, lower eGFR, Hb, microvascular hyperemic response, and increased PWV were associated with poor O2Hb response during exercise; in the multiple model, eGFR was the only parameter independently associated with the O2Hb response. Conclusions: Brain activation during a mild physical task appears to decrease with advancing CKD as suggested by the smaller rise in cerebral oxygenation. This may contribute both to impaired cognitive function and reduced exercise tolerance with advancing CKD.