The effect of blood pressure on compression-induced facial nerve neuropraxia in the cat.

The facial nerves of 21 adult anesthetized cats were exposed from the parotid gland to the orbicularis oculi muscle. The summated action potential (SAP) of the orbicularis oculi muscle was recorded. A calibrated pressure block was applied to the intact facial nerve between the stimulating electrode and the muscle. Pressures of between 150 and 200 mm Hg caused a rapid stable neuropraxia. In ten animals the blood pressure was elevated by a constant levarterenol infusion. In 11 animals the blood pressure was elevated by coarcting the abdominal aorta and volume overloading the rostral vascular system. In both groups, in all animals, when the systolic blood pressure exceeded the pressure applied to the nerve, a substantial increase in SAP amplitude was noted. If the systolic pressure was allowed to fall below the pressure on the nerve, the neuropraxia rapidly returned. This data suggest that within a physiologic pressure range of 150 to 200 mm Hg there is a reversible ischemic phase of compression neuropraxia and it is in complete accord with the earlier work of Devriese.