Multiscale modeling of posture-dependent cerebrovascular hemodynamics with autoregulatory coupling

Cerebral blood flow is maintained through complex autoregulatory mechanisms that compensate for systemic and postural changes to preserve stable perfusion. We investigate the coupled effects of aortic pressure, body posture, and vessel wall stiffness on cerebrovascular hemodynamics using a multiscale modeling framework. A comprehensive cerebrovascular model was developed that incorporates both arterial and venous networks down to the precapillary and postcapillary levels, coupled with a three-dimensional perfusion domain. The framework integrates passive vessel mechanics and active autoregulatory control to simulate arteriolar dilation and constriction in response to pressure and metabolic demand. Simulations were performed across a wide range of aortic pressures (30-150 mmHg) and body postures (supine, upright, inverted) while varying wall stiffness to assess the impact of compliance. Arterial deformation and total vascular volume were strongly influenced by both systemic and gravitational loading, whereas venous volume remained relatively stable across pressure variations but changed markedly with posture due to hydrostatic effects. Active autoregulation attenuated these changes by dynamically adjusting arteriolar diameters to maintain near-constant cerebral blood flow. Increased vascular compliance amplified posture-induced volume changes and the resulting autoregulatory response, whereas higher stiffness attenuated both. The proposed framework elucidates how vascular wall mechanics and autoregulatory capacity jointly stabilize cerebral perfusion under varying physiological conditions. These findings advance the biomechanical understanding of posture-dependent cerebrovascular regulation and establish a foundation for future investigations linking cerebral hemodynamics to impaired autoregulation and vessel wall remodeling in disease.