FUSE: Filter-Free Unified Spatiotemporal Estimation of SpO2 via Wave-Transport Modeling

Blood oxygen saturation (SpO2 ) is a vital indicator of respi-ratory and cardiovascular health, increasingly targeted by camera-based,contactless monitoring systems. Existing video-based approaches typi-cally rely on predefined frequency filtering to separate pulsatile (AC)and baseline (DC) components. Such spectral decomposition propagatesband-limited noise and assumes signal stationarity, limiting robustnessunder motion, illumination variation, and subject diversity.We propose FUSE, a filter-free, physics-guided framework that learnsAC and DC representations via structured differential constraints ratherthan static spectral filtering. The pulsatile component is regularized as aband-limited harmonic field through a second-order ordinary differentialequation, while spatial coherence is enforced by modeling it as a trans-ported density field under an advection-based partial differential con-straint. This coupled wave-transport formulation enforces physiologicallyconsistent spatiotemporal dynamics without explicit frequency-domain