Diffusion Rates Across the Blood-Brain Barrier

compound

glycerol

spirohydantoin

pyrimethamine

H

2

O

animate graphic

blood-brain surface area (

2

m

)

15

brain volume (L)

1.45

barrier thickness (nm)

300

concentration of drug in blood (mM)

15

time (min)

0.

blood

barrier

brain

The blood-brain barrier is a semipermeable membrane that separates the brain from the capillaries that pass through it. A relevant question in medical technology is the rate at which drugs are able to pass through this barrier, which subsequently informs studies in pharmacology and physiology. The Demonstration illustrates a series of structural variables applied to the cells in a simulated human brain. The comparative rates of diffusion in a variety of biologically active compounds were found by applying an integrated form of Fick's Law, given by

C

brain

=

C

capillary

(1-

-DAt/T

V

brain

e

)

,

where

C

brain

is the concentration of the compound in the brain,

C

capillary

is the concentration of the compound in the capillaries,

D

is the diffusion coefficient,

A

is the blood-brain barrier surface area,

T

is the thickness and

V

brain

is the volume of the brain.