Viscoelastic shear properties of human vocal fold mucosa: Measurement methodology and empirical results

A standard method for the empirical rheological characterization of viscoelastic materials was adopted to measure the viscoelastic shear properties of human vocal-fold mucosal tissues (the superficial layer of lamina propria). A parallel-plate rotational rheometer was employed to measure shear deformation of viscoelastic tissue samples, which were deformed between two rigid circular plates rotating in small-amplitude sinusoidal oscillations. Elastic and viscous shear moduli of the samples were then quantified as a function of oscillation frequency (0.01 to 15 Hz) based on shear stresses and strains recorded by the rheometer. Data were obtained from 15 excised human larynges (10 male and 5 female). Results showed that the elastic shear modulus μ and the damping ratio ζ of human vocal-fold mucosa were relatively constant across the range of frequencies observed, while the dynamic viscosity η decreased monotonically with frequency (i.e., shear thinning). Intersubject differences in μ and η as large as an order of magnitude were observed, part of which may reflect age-related and gender- related differences. Some molecular interpretations of the findings are discussed.