Age-Related Changes of Collagenous Fibers in the Human Vocal Fold Mucosa

To examine the interstitial proteins of the vocal fold and their influence on the biomechanical properties of that tissue. Anatomic study of the lamina propria of human cadaveric vocal folds combined with some viscosity testing. Identification of proteoglycans is performed with histochemical staining. Quantitative analysis is performed using an image analysis system. A rheometer is used for viscosity testing. Three-dimensional rendering program is used for the computer images. Proteoglycans play an important role in tissue biomechanics. Hyaluronic acid is a key molecule that affects viscosity. The proteoglycans of the lamina propria have important biological and biomechanical effects. The role of hyaluronic acid in determining tissue viscosity is emphasized. Viscosity, its effect on phonatory threshold pressure and energy expended due to phonation is discussed. Proteoglycans, particularly hyaluronic acid, play important roles in determining biomechanical properties of tissue oscillation. Future research will likely make these proteins of important therapeutic interest.

This study was carried out to determine the fine structure of the membranous portion of the human newborn and infant vocal fold mucosae and to clarify how the human vocal fold mucosa begins to grow after birth. Light and electron microscopic observations were made on the vocal fold mucosae excised from human newborn and infant larynges. Our findings are summarized as follows. 1) Reinke's space of the newborn vocal fold is a loose structure composed of ground substance and sparse fibers. 2) Ground substance is abundant and glycoproteins (fibronectin) are present in the lamina propria. 3) In the maculae flavae of newborn vocal folds, fibroblasts begin to form collagenous, reticular, and elastic fibers. 4) In the infant maculae flavae, fibroblasts are activated to become stellate in shape and synthesize extracellular matrices such as collagenous and reticular fibers. 5) After birth, the collagenous and reticular fibers synthesized in the maculae flavae extend toward the middle of the membranous portion of the vocal fold mucosa. 6) Glycoprotein (fibronectin) determines the orientation of collagenous and reticular fiber deposition. 7) Glycoprotein (fibronectin) decreases with the increase of the fibrous components in Reinke's space. 8) Elastic fibers increase after collagenous and reticular fibers appear in Reinke's space. 9) Much hyaluronic acid (glycosaminoglycan) is actively produced in the infant maculae flavae. 10) The collagenous and reticular fibers serve as stabilizing scaffolds for the other extracellular matrices, such as elastic fibers and glycosaminoglycan. During infancy, the extracellular matrices synthesized in the maculae flavae appear in the membranous portion of the vocal fold, each at a different time, so as to initiate the 3-dimensional formation of the vocal fold mucosa.