Dose-related tissue effects of the CO2 and noncontact Nd:YAG lasers in the canine glottis

Objectives: The CO2 laser is the standard for control of recurrent respiratory papillomatosis because of its predictable action on laryngeal tissue. The noncontact neodymium:yttrium aluminum garnet (Nd:YAG) 1064‐nm laser is generally not used in the larynx owing to the lack of data on its tissue effects, and its potential lack of safety in the larynx. Combined Nd:YAG and CO2 laser treatments have been used safely in the tracheobronchial tree to eradicate recurrent respiratory papillomas. The objectives of this study were to describe and evaluate a method for applying the noncontact Nd:YAG laser to the larynx, to compare the tissue effects of the Nd:YAG, CO2, and combined Nd:YAG and CO2 lasers in the canine larynx, and to extrapolate canine tissue data to the human. Methods: The CO2, Nd:YAG, and combined Nd:YAG/CO2 lasers were applied to the glottis in four mongrel dogs. Laryngectomy was performed and the tissue was examined histologically. The nature and degree of tissue injury were analyzed relative to laser type and energy data. Results: In the canine larynx, the CO2 laser vaporized the surface epithelium and caused varying degrees of edema and necrosis of the lamina propria. The Nd:YAG laser did not cause ulceration but did show a greater degree of thermal damage to the lamina propria. Combined Nd:YAG/CO2 applications resulted in separation of the perimysial fibers from the muscle fibers of the vocalis muscle. Conclusion: These findings suggest that the noncontact Nd:YAG laser can be applied in a controlled fashion to the canine larynx at appropriate power densities. Anatomical differences between human and canine larynges are considered. Extrapolation to humans is proposed. Key Words: Laser, larynx, tissue effects, papillomatosis.