A Theoretical and Computational Design Framework for a Geometrically Optimized Retroperitoneal Vascular Access Port for Hemodialysis (the "ISPS" Concept)

End-stage renal disease (ESRD) vascular access remains constrained by a persistent trade-off between the durability of arteriovenous fistulae (AVF) and the infection burden of central venous catheters (CVC). This paper presents a purely theoretical and computational engineering-design study of a proposed device concept, the Intelligent Secret Port System (ISPS): a geometrically optimized, hermetically valved vascular access port intended for retroperitoneal implantation at the L4–L5 level, designed to exploit the native arterio-venous trans-mural pressure gradient for on-demand, pump-free hemofiltration. We derive the governing fluid-mechanical and mass-transport equations from first principles (incompressible Navier–Stokes reduction to Hagen–Poiseuille flow, Reynolds-number laminarity criteria, wall-shear-stress estimation, and Kedem–Katchalsky convective–diffusive transport), and we present a fully reproducible computational analysis of the resulting lumped-parameter flow model, comprising Monte Carlo uncertainty propagation, variance-based (Sobol') global sensitivity analysis, Bayesian (Metropolis–Hastings) parameter inference, a non-Newtonian (Carreau–Yasuda) consistency check evaluated at the true operating point, and a multi-parameter robustness analysis. Every numerical result is generated by the single consolidated source script provided in the appendix and is reported to the precision that this computation supports. This work is explicitly not accompanied by physical experimentation: no computational fluid dynamics (CFD) solver, finite-element analysis (FEA) package, magnetic-resonance-imaging (MRI) safety bench test, or in-vitro/ex-vivo flow-loop study has been executed for this device. Sections describing CFD/FEA, MRI safety testing, in-vitro/ex-vivo validation, and health-economic modeling are therefore presented as proposed protocols and illustrative, assumption-transparent projections rather than as completed experimental results, consistent with the device's pre-clinical, concept stage. Dedicated sections on scientific and technical risk and on falsifiability specify the critical assumptions whose failure would most undermine the concept and the concrete measurements that would refute it. Under the design-basis parameters, the analysis indicates that the native aortocaval gradient can, in principle, drive a laminar (Re ≈ 643), moderate-wall-shear-stress (τw ≈ 3.75 Pa) flow of Q ≈ 404 ml/min (95% CI 325–483), with the system flow rate governed almost entirely by filter resistance and driving pressure rather than by port geometry. The framework is intended as a rigorous, falsifiable starting point for a translational research program, not as evidence of clinical readiness.