Reduced nerve blood flow in edematous neuropathies: a biomechanical mechanism.

Reduced nerve blood flow has been reported in two experimental neuropathies in which edema is an early and significant finding. While the mechanisms of fluid accumulation differed, both resulted in increases of endoneurial fluid pressure up to five times the normal value. As increased endoneurial fluid distends the nerve, the perineurial sheath resists expansion and endoneurial fluid pressure increases. The semirigid perineurium is also a conduit for regional nutritive vessels which provide the greater part of peripheral nerve blood flow. Engineering structural analysis of blood vessels entering the endoneurium suggests that moderate elevations in endoneurial fluid pressure can deform cylindrical vessels in the perineurium into elliptical shapes by creating circumferential elongation and longitudinal compression of the vessels which reduce the cross-sectional area of the lumen. We propose that the pathogenesis of reduced nerve blood flow in edematous neuropathies is linked to the unique structure of the peripheral nerve perineurium and the nerve vasculature, in particular to deformation of anastomotic vessels traversing it.