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OBJECTIVES The primary objective was to investigate the left-right vocal fold symmetry in rheological and histological properties using a rabbit model. The other objective was to develop statistical models for the comparison of rheological properties between paired vocal folds. METHODS Viscoelastic shear properties of six pairs of vocal fold lamina propria specimens were measured over a frequency range of 1 to 250 Hz by a linear, controlled-strain, simple-shear rheometer. The rheological data of the left and right vocal folds was statistically compared using the mixed-effects model approach. Six additional rabbit larynges were histologically analyzed for left-right symmetry in distribution patterns and relative densities of major extracellular matrix constituents. RESULTS There were no significant differences in elastic shear modulus (P = 0.1069) and dynamic viscosity (P = 0.944) of the lamina propria between the two vocal folds of the same larynx. Left-right vocal fold symmetry in densities and distribution patterns of the key molecular constituents was also demonstrated in histological results. CONCLUSION By showing that the left and right vocal folds were rheologically and histologically symmetrical in rabbit, this study validated an underlying assumption made in many previous reports. Statistical models for the analysis of hierarchically correlated left-right vocal fold rheological data were also presented. LEVEL OF EVIDENCE NA. Laryngoscope, 128:E359-E364, 2018.

Objectives/Hypothesis To develop a vocal fold scarring model using an ablative laser in the rabbit as a platform for testing bioengineered therapies for missing or damaged lamina propria. Study Design Prospective controlled animal study. Methods An optimal laser energy level was first determined by assessing the depths of vocal fold injury created by a Holmium:YAG laser at various energy levels on fresh cadaveric rabbit larynges. The selected energy level was then used to create controlled unilateral injuries in vocal folds of New Zealand white rabbits, with the contralateral folds serving as uninjured controls. After 4 weeks, the larynges were harvested and subjected to excised-larynx phonation with high-speed imaging and immunohistochemical staining for collagen types I and III, elastin, and hyaluronic acid (HA) with quantitative histological analysis. Results A total of 1.8 joules produced full-thickness injury of the lamina propria without extensive muscle injury. After 4 weeks, the injured vocal folds vibrated with reduced amplitude (P = 0.036) in excised-larynx phonation compared to normal vocal folds. The injured vocal folds contained a higher relative density of collagen type I (P = 0.004), higher elastin (P = 0.022), and lower HA (P = 0.030) compared to normal controls. Collagen type III was unchanged. Conclusions With its potential for higher precision of injury, this laser vocal fold scarring model may serve as an alternative to scarring produced by cold instruments for studying the effects of vocal fold lamina propria bioengineered therapies. Level of Evidence N/A. Laryngoscope 124:2321–2326, 2014