Correcting diffusion artifacts in urinary oxygen tension monitoring

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.