title: Focal delivery during direct infusion to brain: role of flow rate, catheter diameter, and tissue mechanics.
abstract: Direct interstitial infusion is a technique capable of delivering agents over both small and large dimensions of brain tissue. However, at a sufficiently high volumetric inflow rate, backflow along the catheter shaft may occur and compromise delivery. A scaling relationship for the finite backflow distance along this catheter in pure gray matter (x(m)) has been determined from a mathematical model based on Stokes flow, Darcy flow in porous media, and elastic deformation of the brain tissue: x(m) = constant Q(o)(3)R(4)r(c)(4)G(-3)mu(-1) 1/5 [corrected] = volumetric inflow rate, R = tissue hydraulic resistance, r(c) = catheter radius, G = shear modulus, and mu = viscosity). This implies that backflow is minimized by the use of small diameter catheters and that a fixed (minimal) backflow distance may be maintained by offsetting an increase in flow rate with a similar decrease in catheter radius. Generally, backflow is avoided in rat gray matter with a 32-gauge catheter operating below 0.5 microliter/min. An extension of the scaling relationship to include brain size in the resistance term leads to the finding that absolute backflow distance obtained with a given catheter and inflow rate is weakly affected by the depth of catheter tip placement and, thus, brain size. Finally, an extension of the model to describe catheter passage through a white matter layer before terminating in the gray has been shown to account for observed percentages of albumin in the corpus callosum after a 4-microliter infusion of the compound to rat striatum over a range of volumetric inflow rates.
authors.affiliation: Bioengineering and Physical Science Program, Office of Research Services, National Institutes of Health, Bethesda, Maryland 20892, USA. pmorris@box-p.nih.gov
authors.forename: P F
authors.initials: PF
authors.lastname: Morrison
authors.forename: M Y
authors.initials: MY
authors.lastname: Chen
authors.forename: R S
authors.initials: RS
authors.lastname: Chadwick
authors.forename: R R
authors.initials: RR
authors.lastname: Lonser
authors.forename: E H
authors.initials: EH
authors.lastname: Oldfield
mesh_terms: D000818:Animals; D001345:Autoradiography; D001921:Brain / Q000502:physiology; D002404:Catheterization; D002421:Caudate Nucleus / Q000378:metabolism; D016503:Drug Delivery Systems / Q000295:instrumentation; D008959:Models, Neurological; D051381:Rats; D012709:Serum Albumin / Q000008:administration & dosage / Q000493:pharmacokinetics
chemical_list: D012709:Serum Albumin