Optically mediated nerve stimulation: Identification of injury thresholds
Wells JD, Thomsen S, Whitaker P, Jansen ED, Kao CC, Konrad PE, Mahadevan-Jansen A
Department of Biomedical Engineering, Vanderbilt University
Lasers Surg Med. 2007 Jul;39(6):513-26
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.
Radiant exposures with <1% probability of thermal tissue damage (0.66-0.70 J/cm(2)) are significantly greater than radiant exposures required for reliable stimulation (0.34-0.48 J/cm(2)). The upper limit for safe laser stimulation repetition rate occurs near 5 Hz. Maximum duration for constant low repetition rate stimulation (2 Hz) is approximately 4 minutes with adequate tissue hydration.
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. (c) 2007 Wiley-Liss, Inc.