Respiration is a driver for parenchyma hydrodynamics: insights from dynamic DWI

Motivation: The drivers of cerebrospinal and interstitial fluid dynamics in brain parenchyma remain debated, with respiration increasingly considered alongside cardiac pulsation. Goal(s): To compare the roles of respiration and cardiac pulsation in driving the parenchyma hydrodynamics. Approach: Dynamic diffusion-weighted imaging was employed to capture the incoherent fluid motion within the brain while suppressing the fast blood flow. Cross-correlation analysis evaluated its coupling with respiration and cardiac pulsation. Results: Respiration was a stronger driver than cardiac pulsation in gray and white matter, whereas cardiac pulsation dominated in the paravascular subarachnoid space and ventricles. Impact: This study highlights robust, respiration-driven hydrodynamics in the parenchyma, with inhalation slowing and exhalation accelerating fluid motion.