Laser Doppler measurements of intratemporal facial nerve blood flow.

Whereas the anatomy of the vasculature supplying the intratemporal facial nerve is well known, little is known of the dynamics of blood flow within the nerve. The present study was performed to ascertain whether laser Doppler flowmetry (LDF) could detect changes in blood flow within the tympanic segment of the rabbit facial nerve. Compression of the facial nerve immediately distal to the geniculate ganglion resulted in an 80-95 percent reduction in blood flow in the tympanic segment of the nerve, whereas distal neurovascular compression had no effect. Blood flow in the tympanic segment of the nerve fell 40-60 percent during ipsilateral common carotid artery occlusion, but no change occurred with contralateral carotid occlusion. Signal-averaging techniques detected a sinusoidal amplitude modulation of the LDF flow signal that was synchronous with the cardiac cycle. The peak-to-peak amplitude of this modulation was reduced by proximal nerve compression, and the reduction in amplitude was in proportion to the overall reduction in the LDF flow signal. The authors conclude that the direction of blood flow in the tympanic segment of the rabbit facial nerve is primarily proximal to distal. Acute changes in blood flow within the tympanic segment of the nerve could readily be detected using LDF. This technique offers the possibility of monitoring human facial nerve blood flow, and may help elucidate the pathophysiology of various facial neuropathies.