LASER-DOPPLER MEASUREMENTS OF INTRATEMPORAL FACIAL-NERVE BLOOD-FLOW

Whereas the anatomy of the vasculature supplying the intratemporal fac ial nerve is well known, little is known of the dynamics of blood flow within the nerve. The present study was performed to ascertain whethe r laser Doppler flowmetry (LDF) could detect changes in blood flow wit hin the tympanic segment of the rabbit facial nerve. Compression of th e 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. Bl ood flow in the tympanic segment of the nerve fell 40-60 percent durin g ipsilateral common carotid artery occlusion, but no change occurred with contralateral carotid occlusion. Signal-averaging techniques dete cted a sinusoidal amplitude modulation of the LDF flow signal that was synchronous with the cardiac cycle. The peak-to-peak amplitude of thi s modulation was reduced by proximal nerve compression, and the reduct ion in amplitude was in proportion to the overall reduction in the LDE 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 h elp elucidate the pathophysiology of various facial neuropathies.