Heart Twin for Space Cardiology: Multiphysics Simulation of Hemodynamics and Remodeling in Long-Duration Missions

Spaceflight imposes profound cardiovascular challenges owing to fluid shifts, reduced preload, and altered autonomic control; however, predictive tools for long-duration missions remain limited. We developed a finite element–based cardiac digital twin using COMSOL Multiphysics® to simulate cardiovascular adaptation under Earth (1 g), Martian (0.38 g), and microgravity (0 g) conditions. The model integrates anatomical fidelity, fiber-aligned electromechanics, fluid–structure interaction, and baroreflex regulation, and is calibrated against echocardiography, cardiac MRI, and analog datasets. Simulations revealed progressive impairment of diastolic vortex formation, decreased left ventricular strain, disrupted systolic ejection jets, and reduced wall shear stress with gravity unloading. Long-term adaptation predicted wall thinning, preload decline, and compliance increase, consistent with astronaut and bed rest data. Validation demonstrated that the stroke volume, ejection fraction, and cardiac output were within ±3% of the experimental measurements (R² ≥ 0.91). By capturing graded gravity transitions and regulatory resetting, a digital twin provides a physiologically credible framework for astronaut monitoring and countermeasure planning during extended missions.