EXPRESS: Ventricular CSF-to-blood water transport kinetics in adult hydrocephalus

Water exchange between cerebrospinal fluid (CSF) and blood is fundamental to brain fluid homeostasis, yet ventricular CSF-to-blood water transport has never been quantified as a physiological parameter in adult humans. We investigated ventricular water absorption kinetics in 40 adults undergoing diagnostic evaluation for hydrocephalus. During ventricular infusion testing, 15O-labelled water was administered intraventricularly via an external ventricular drain, with continuous jugular bulb blood sampling and simultaneous intracranial pressure (ICP) monitoring. Ventricular water absorption was estimated using non-parametric population pharmacokinetic modelling of venous radioactivity–time curves.

Model performance demonstrated robust individual parameter estimation. Ventricular water absorption showed substantial inter-individual variability (mean half-time 65.2 ± 34.3 s; range 31.5–196.8 s). Absorption kinetics were not associated with static or pulsatile ICP metrics (overnight or during infusion), ventricular volume or surface area, or CSF–blood osmotic gradients. No associations were observed with demographic variables. A modest positive association was detected with the CSF–blood protein concentration difference.

These findings establish ventricular CSF-to-blood water transport as a quantifiable physiological metric in adult hydrocephalus and suggest that ventricular water exchange is regulated independently of global intracranial pressure and ventricular morphology, consistent with intrinsic barrier and microvascular exchange mechanisms.