Vocal fold elasticity in the pig, sheep, and cow larynges

Abstract

Elastic characteristics of the pig, sheep, and cow vocal folds were investigated through a series of in vitro experiments. Sample strips of the vocal-fold tissue were dissected from pig, sheep, and cow vocal folds and mounted inside a saline-filled ergometer chamber that was maintained at 37°C ± 1°C. Sinusoidal elongation was applied on the samples to obtain the passive force measurements. Force and elongation data from the samples were recorded electronically with a dual-servo system (ergometer). Stress-Strain data were compared to characterize the interspecies differences in the elastic properties of vocal folds. Pig vocal folds exhibited the most nonlinear stress-strain relationship, indicating the presence of a high level of collagen fibers. Cow vocal folds had the highest Young's modulus, but the tissue displayed a nearly linear stress-strain profile. Previous studies of phonation in these three species have indicated that pig larynges have the highest range of phonation frequencies, making them a good candidate for animal studies. The current study provides quantitative data for the elastic properties of the oscillating laryngeal tissue in these species and indicates that nonlinear behavior of these tissues may lead to wider oscillation ranges.

Figure 1A

Dissected view of Pig hemilarynx with major components marked as superior vocal fold (SVF), inferior vocal fold (IVF), subglottal wall, supraglottal wall, arytenoid, thyroid cartilage (TC), and cricoid cartilage (CC).

Figure 1B

Dissected view of sheep hemilarynx with vocal fold, subglottal wall, supraglottal wall, arytenoid, thyroid cartilage (TC), and cricoid cartilage (CC) marked.

Figure 1C

Dissected view of cow hemilarynx cut with vocal fold, subglottal wall, supraglottal wall, arytenoid, thyroid cartilage (TC), and cricoid cartilage (CC) marked.

Figure 2

Typical force and elongation signals from a pig vocal fold sample. The top panel shows the sample elongation due to the sinusoidal stretch at 1-Hz. The bottom panel shows the force response of the sample measured with ergometer.

Figure 3

Force-elongation hysteresis loops of the same data as Figure 2. Samples are stretched in the upper loop and released in the lower loop.

Figure 4

Stress-strain relations of 6 samples of pig superior vocal fold.

Figure 5

Stress-strain relations of 6 samples of pig inferior vocal fold.

Figure 6

Stress-strain relations of 4 samples of sheep vocal fold.

Figure 7

Stress-strain relations of 3 samples of cow vocal fold.

Figure 8

Average Young's modulus comparison of vocal fold samples from different species. Each bar represents a single sample with its average on its error bar.