Muscle Oxygenation and Microvascular Reactivity Across Different Stages of CKD: A Near-Infrared Spectroscopy Study

Rationale & Objective: Previous studies in chronic kidney disease (CKD) showed that vascular dysfunction in different circulatory beds progressively deteriorates with worsening CKD severity. This study evaluated muscle oxygenation and microvascular reactivity at rest, during an occlusion-reperfusion maneuver, and during exercise in patients with different stages of CKD versus controls.Study Design: Observational controlled study.Setting & Participants: 90 participants (18 per CKD stage 2, 3a, 3b, and 4, as well as 18 controls).Predictor: CKD stage.Outcome: The primary outcome was muscle oxygenation at rest. Secondary outcomes were muscle oxygenation during occlusion-reperfusion and exercise, and muscle microvascular reactivity (hyperemic response).Analytical Approach: Continuous measurement of muscle oxygenation [tissue saturation index (TSI)] using near-infrared spectroscopy at rest, during occlusion-reperfusion, and during a 3 -minute handgrip exercise (at 35% of maximal voluntary contraction). Aortic pulse wave velocity and carotid intima-media thickness were also recorded.Results: Resting muscle oxygenation did not differ across the study groups (controls: 64.3% & PLUSMN; 2.9%; CKD stage 2: 63.8% & PLUSMN; 4.2%; CKD stage 3a: 64.1% & PLUSMN; 4.1%; CKD stage 3b: 62.3% & PLUSMN; 3.3%; CKD stage 4: 62.7% & PLUSMN; 4.3%; P = 0.6). During occlusion, no significant differences among groups were detected in the TSI occlu-sion magnitude and TSI occlusion slope. How-ever, during reperfusion the maximum TSI value was significantly lower in groups of patients with more advanced CKD stages compared with controls, as was the hyperemic response (con-trols: 11.2% & PLUSMN; 3.7%; CKD stage 2: 8.3% & PLUSMN; 4.6%; CKD stage 3: 7.8% & PLUSMN; 5.5%; CKD stage 3b: 7.3% & PLUSMN; 4.4%; CKD stage 4: 7.2% & PLUSMN; 3.3%; P = 0.04). During the handgrip exercise, the average decline in TSI was marginally lower in patients with CKD than controls, but no signifi-cant differences were detected across CKD stages.Limitations: Moderate sample size, cross-sectional evaluation. Conclusions: Although no differences were observed in muscle oxygenation at rest or during occlusion, the microvascular hyperemic response during reperfusion was significantly impaired in CKD and was most prominent in more advanced CKD stages. This impaired ability of microvas-culature to respond to stimuli may be a crucial component of the adverse vascular profile of patients with CKD and may contribute to exercise intolerance.