Age-related changes of collagenous fibers in the human vocal fold mucosa.

The viscoelastic properties of the vocal fold mucosa depend on the extracellular matrices. Collagenous fibers provide tensile strength and resilience and serve as a stabilizing scaffold in the extracellular matrices. Light and electron microscopic investigations of age-related changes of collagenous fibers in vocal fold mucosa were carried out on excised normal human adult larynges. Twelve human vocal fold mucosae were examined (10 from older adults with ages ranging from 70 to 97 years, and 2 from younger adults for comparison). The results for the aged mucosae can be summarized as follows. 1) Especially in men, collagenous fibers had increased and reticular fibers had decreased. 2) Collagenous fibers had formed bundles, and their density was high. 3) The spaces between collagenous fibers and the interstitial spaces for other extracellular matrices had decreased. 4) The collagenous fibril diameters differed, and their outline was irregular. 5) Twisted collagenous fibrils were present. 6) Occasionally, masses of dense collagenous fibers and fibrous tissue could be seen in the mucosa. 7) Occasionally, the collagenous fibers were increased all the way from the deep layer to the superficial layer of the mucosa, and consequently, there was no layered structure. Not only changes in the 3-dimensional structure of the collagenous fibers, but also their qualitative and quantitative changes, have an effect on the 3-dimensional structure of the extracellular matrices. Thus, the viscoelasticity must change to ensure normal phonation, and this change in viscoelasticity would explain one component of aging of the voice.