Facial nerve: electrophysiological reactions during in-vitro treatment with the ER:YAG laser

Our studies on the facial nerve of the rabbit are concerned with the development of a laser system by means of which tissue can be removed in the immediate vicinity of nerves without causing functional damage to the nerves. The risk of mechanical damage to nerve tissue, which inevitably occurs through pulling and through pressure in conventional surgery, is minimized by touch-free use of the laser. The basic necessary examinations involved bathing the freshly removed facial nerve from rabbit specimens in a nutrient medium inside a specially developed 'organ chamber' which enabled the nerve to be kept alive for many hours. Using successive laser treatment with pulse intensities of up to 100 mJ the laser spot was gradually approached from a lateral angle or radially through a small agarose plate and the electrical activity registered at the respective pulse intensity. The nerve and the conducting electrode were located in the organ chamber on a carriage which could be perceptibly shifted. In this way it proved possible to accurately record the position of the laser treatment for the histological examination. Our studies showed that an individual pulse of only 15 mJ striking the peripheral area of the facial nerve was sufficient to generate a clearly perceptible total action potential. A necessary precondition is, however, that a conducting electrode is placed directly over the nerve fiber bundle which is being irradiated. During conduction of the total action potential there is no observable transfer to the neighboring fiber bundle.