Abstract
Urinary oxygen tension (PuO2) is a promising continuous biomarker of renal medullary oxygenation, but distal catheter measurements are distorted by transit delay and wall diffusion, especially during oliguria. We developed and validated a physics-based algorithm that reconstructs bladder PuO2 from the distal signal. We formulated complementary steady-state and transient diffusion-transport models that couple wall diffusion to a lumen mass balance and solve an inverse problem to estimate bladder PuO2. Performance was assessed on a bench-top catheter system with controlled flows and in eight swine undergoing hemorrhagic shock and resuscitation (68,788 paired samples). On the bench top, adjustment reduced mean bias relative to bladder PuO2 from - 10.9 to -0.64 mmHg, narrowed 95% limits of agreement from 39.1 to 15.8 mmHg, and improved correlation with ground truth (R2 0.53→0.94). In vivo, pooled bias decreased from + 20.9 ± 11.5 to -4.1 ± 13.5 mmHg and mean absolute error from 21.1 to 9.5 mmHg, with the largest gains at low urinary flow. Modeling transport delay and wall diffusion enables reconstruction of bladder PuO2 from distal catheter measurements, supporting reliable, real-time urinary hypoxia monitoring and broader application to other conduit-based analyte measurements.