Renal Metabolic Rate of Oxygen in Response to Hypoxia Challenges by Means of Quantitative MRI in Humans

In early kidney disease, tissue hypoxia occurs due to an imbalance between ATP supply and demand. Whole-organ renal metabolic rate of oxygen (rMRO₂) is therefore a potential biomarker for assessing renal function. This study evaluated the sensitivity of a quantitative MRI method to detect within-subject changes in metabolic parameters during hypoxic gas challenges. Ten healthy adults were imaged at 3 T (5 female, ages 23-53 years) while undergoing mild and moderate hypoxia (P_ETO₂ 62 and 52 mmHg, respectively). The utilized MRI sequence simultaneously quantified blood flow rate (BFR) and venous oxygen saturation (SvO₂) at the left renal vein, yielding, together with arterial oxygen saturation (SaO₂) obtained by pulse oximetry, whole-organ rMRO₂ by invoking Fick's Principle. Repeated-measures ANOVA was used to test differences in metabolic parameters between baseline and hypoxic conditions. SaO₂ at baseline was 99% ± 1%, while renal SvO₂ was 92% ± 3%. During progressive hypoxemia, the drop in SvO₂ (mild 83% ± 4%, moderate 76% ± 5%, p < 0.01) paralleled the drop in SaO₂ (mild 90% ± 1%, moderate 84% ± 2%), such that the arteriovenous difference in oxygenation (AVDO₂) was constant when compared to baseline (p = 1). Renal BFR did not vary significantly between baseline (410 ± 65 mL/min) and hypoxemic conditions (mild, moderate of 430 ± 56 and 440 ± 48 mL/min, p > 0.34). Thus, rMRO₂ did not significantly change during hypoxemia (baseline, mild, and moderate of 140 ± 50, 180 ± 80, and 170 ± 90 (μmol O₂/min)/100 g, respectively, p = 1). In conclusion, the results demonstrate the method's sensitivity in detecting within-subject changes in metabolic parameters in response to graded hypoxia. Quantitative MRI oximetry may be a feasible tool to assess and longitudinally monitor early metabolic changes in kidney disease.