Effects Of Hypobaric Hypoxia During Intermittent Cycling Bouts On Markers Of Acute Kidney Injury

Many individuals travel to high altitudes for recreational or occupational purposes. Hypobaric hypoxia (HH) at altitude decreases arterial oxygen saturation (SaO2), reduces oxygen delivery to tissues, and can adversely affect organ function. Exercise, independent of HH, significantly decreases renal blood flow (RBF). Therefore, performing exercise in HH may further impair oxygen delivery and place additional strain on the kidneys. While the impact of chronic HH on kidneys has been documented, there is limited research on the risk of acute kidney injury (AKI) under these conditions. PURPOSE: To investigate the effects of acute HH exposure during intermittent exercise on markers of AKI. METHODS: Thirteen (5 females) participants completed a 120-min protocol consisting of two 30-minute cycling bouts at 50% VO2peak in a randomized, counterbalanced design under either 1) normoxic (NORM, control ~1600 m) or 2) hypoxic (HYP, simulated altitude of 4267 m) conditions. Blood and urine samples were collected pre- to post-trials to assess urine specific gravity (USG) and urine flow rate, blood bicarbonate (HCO3), hematocrit, hemoglobin, and change in plasma volume (ΔPV); and AKI biomarkers: insulin-like growth factor-binding protein 7 (IGFBP7), tissue inhibitor of metalloproteinase 2 (TIMP-2), neutrophil gelatinase-associated lipocalin (NGAL), and cystatin C. RESULTS: Findings for USG, urine flow rate, hematocrit, hemoglobin, and ΔPV were not significant (p > 0.05). The only significant finding was that blood HCO3 decreased (time effect: p < 0.001) from pre- to post-trial. Findings for IGFBP7, TIMP-2, NGAL, and cystatin C were not significant (p > 0.05). Observing the non-transformed data, no participants in the normoxia trial exceeded IGFBP7×TIMP-2 concentrations of 0.3 (ng/mL)2/1000 post-exercise, while three individuals exceeded this threshold in the post-trial HYP condition. CONCLUSION: Two hours of HH exposure while performing intermittent moderate intensity cycling exercise in acute hypoxia does not appear to increase AKI risk in recreationally active healthy individuals. This is the first study investigating acute HH and exercise, and while findings were not significant, future research should focus on protocols of longer duration and continuous exercise.