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Keywords:

  • laser;
  • laser irradiation;
  • histological analysis;
  • optical nerve stimulation;
  • peripheral nerve;
  • thermal damage

Abstract

Background and Objective

Transient optical nerve stimulation is a promising new non-contact, spatially precise, artifact-free neural excitation technique useful in research and clinical settings. This study evaluates safety of this pulsed infrared laser technique by histopathologic examination of stimulated peripheral nerves.

Study Design/Materials and Methods

Exposed rat sciatic nerves were functionally stimulated with the pulsed Holmium:YAG laser, previously validated as an effective tool for optical stimulation. Nerves were removed immediately and up to 2 weeks after stimulation and assessed histologically for thermal damage. Laser parameters studied include upper limits for radiant exposure, repetition rate, and duration of stimulation.

Results

Radiant exposures with <1% probability of thermal tissue damage (0.66–0.70 J/cm2) are significantly greater than radiant exposures required for reliable stimulation (0.34–0.48 J/cm2). The upper limit for safe laser stimulation repetition rate occurs near 5 Hz. Maximum duration for constant low repetition rate stimulation (2 Hz) is ∼4 minutes with adequate tissue hydration.

Conclusion

Results confirm that optical stimulation has the potential to become a powerful non-contact clinical and research tool for brief nerve stimulation with low risk of nerve thermal damage. Lasers Surg. Med. 39:513–526, 2007. © 2007 Wiley-Liss, Inc.