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Objective: Studies showed that photodynamic therapy (PDT) might be able to prevent vocal fold scar formation when treating laryngeal lesions. We aim to investigate if PDT improves vocal wound healing and reduces scar formation in both prophylactic and remodeling procedures performed in vivo. Study Design: In vivo. Methods: Vocal fold stripping was performed in Sprague–Dawley rats. PDT was performed with intraperitoneal injection of 100 mg/kg 5‐Aminolevulinic Acid (5‐ALA) and 635 nm laser irradiation of 20, 40, and 60 J/cm2. PDT was performed immediately after surgery to study the prophylactic effect and 4 weeks after surgery to study the remodeling effect. Gene expression was evaluated with real‐time PCR at 1 week after PDT. Histologic evaluations were performed 12 weeks after PDT, including hematoxylin–eosin, Masson, Alcian blue staining, and immunohistochemical staining of collagen I and III. Results: PDT induced similar effects on the vocal fold wound healing outcomes in both prophylactic and remodeling procedures. Expression of MMP8, MMP13, HAS2, and TGFβ1 was significantly elevated. Histologic evaluation revealed significantly increased thickness, decreased density of collagen, and increased deposition of hyaluronic acid in the lamina propria. Immunohistochemistry also revealed better distribution and reduced density of collagen I and III. The most obvious changes were seen in the 60 J/cm2 PDT group. Conclusion: PDT could significantly improve vocal wound healing by providing both prophylactic effects and remodeling effects. It may be a minimally invasive treatment for vocal fold lesions with slight vocal scarring, and may be used to treat acute or chronic vocal injury to reduce vocal scarring. Level of Evidence: N/A Laryngoscope, 133:1943–1951, 2023 [ABSTRACT FROM AUTHOR]

Purpose: The present study was a methodological study designed to reveal the dynamic mechanisms of phonation instability pressure (PIP) using bifurcation analysis. Phonation pressure range (PPR) was also proposed for assessing the pressure range of normal vocal fold vibrations. Method: The authors first introduced the concept of bifurcation on the basis of a symmetric vocal fold model and then applied the bifurcation analysis to data from excised larynges. By recording acoustic signals from 10 excised larynges, the authors measured phonation threshold pressure (PTP), PIP, and PPR at the bifurcation pressure points from the spectrograms as subglottal pressure was progressively increased. Furthermore, to investigate the effects of vocal fold elongation on PTP, PIP, and PPR, the authors manipulated the elongation of the vocal folds at 0%, 5%, 10%, and 15% of the resting vocal fold length. Results: The authors found that PTP, PIP, and PPR were effectively determined using the bifurcation analysis. When vocal fold elongation was increased from 0% to 15%, PTP was significantly increased (p less than 0.001), PIP was not significantly changed (p = 0.54), and PPR was significantly decreased (p = 0.003). Conclusion: PIP and PPR represent important parameters to assess phonation instability. Bifurcation analysis represents a valuable procedure for revealing the mechanisms behind PTP, PIP, and PPR and for investigating the effects of vocal fold biomechanical parameters on these 3 pressure parameters.