Subperineurial demyelination associated with reduced nerve blood flow and oxygen tension after epineurial vascular stripping.

Using laser Doppler measurements of nerve blood flow and electron microscopy, we determined that removal of the vasa nervorum from the surface of rat peripheral nerve results in an immediate 58.4% +/- (SD) 12.6% reduction in nerve blood flow (p less than 0.017) and subsequent subperineurial demyelination. To further assess the role of ischemia in demyelination, a second group of Sprague-Dawley rats (250 to 300 gm) was anesthetized and oxygen tensions were recorded with platinum microelectrodes in the tibial epineurial and endoneurial spaces before and 30 minutes after epineurial devascularization. Normal epineurial oxygen tension was 40.4 +/- (SD) 6.5 mm Hg before devascularization and 26.3 +/- 12.3 mm Hg after (p less than 0.012). Normal endoneurial oxygen tension was 22.9 +/- 6.0 mm Hg before devascularization and 14.3 +/- 5.4 mm Hg after (p less than 0.003). The topography of nerve fiber injury in this experimental model is identical with the changes induced in the sciatic nerve by circumferential compression at 30 mm Hg which is also thought to impede epineurial circulation. This subperineurial pattern of demyelination and axonal degeneration is associated with experimental interference with the epineurial circulation and may be contrasted with the central fascicular degeneration caused by microsphere embolization of the vasa nervorum via the common iliac artery. The data suggest that ischemia is the mechanism for subperineurial fiber injury after epineurial devascularization and highlight the importance of the transperineurial vessels which connect the epineurial anastomotic circulation and endoneurial capillary network.