加齢に伴う音声変化：声の老化

Age-related change of voice: Geriatric voice

　「老化(senescence)」と「加齢(aging)」は混同されやすい．通常，「加齢」とは，生まれてから死までの物理的な時間経過を意味している．一方，「老化」は，「加齢」の間に進行すると考えられる．つまり，「老化」とは，「加齢」に伴って生体機能や病気に対する抵抗力などが低下することを意味している．

　発声発語器官も老化によって解剖生理学的な変化が生じる．例えば，発声のActivatorとしての胸郭・呼吸器系は，呼吸筋の筋力低下や胸郭の硬化などが生じるので，胸郭の動きそのものが制限され，声量や発声持続時間に影響を与える．Generatorとしての喉頭は，喉頭軟骨の骨化や声帯粘膜の変化(声帯萎縮)により声門の閉鎖不全が起きて，結果として嗄声が生じる．また，外喉頭筋の変化により喉頭位置も低下する．Resonatorとしての声道は，咽頭筋群や舌の萎縮，鼻腔拡大などにより，共鳴腔としての形態と働きに変化が生じる．その結果，第1フォルマント周波数の低下や構音操作の遅延などが起こる．本稿では，このような発声発語器官の生理的老化と高齢者に多い老人性音声障害のような病的老化と呼ばれる喉頭の病態像について解説する．そのうえで，こうした老人性音声障害へ言語聴覚士としてどのような対処ができるか，理論的モデルを提案する．

　“Senescence” and “aging” are frequently confused. “Aging” usually means the physical time course from birth to death. On the other hand, “senescence” progresses during “aging”. In other words, “senescence” refers to the decrease in biological functions and resistance to diseases with “aging”. The speech organs also undergo physiological changes due to aging. For example, in the respiratory system which serves as a voice activator, weakness in the respiratory muscles and stiffening of the thorax reduce the movement of the rib cage, vocal intensity, and duration of phonation. In the larynx, the voice generator, insufficiency of the glottal closure occurs due to changes in the laryngeal cartilage and the vocal cord mucosa (vocal fold atrophy), resulting in hoarseness. Changes in the external laryngeal muscles lower the laryngeal position. The vocal tract changes the form and function as a resonance cavity due to atrophy of the pharyngeal muscles and tongue as well as enlargement of the nasal cavity, resulting in a lowering of formant frequency and a delay in articulation. In this paper, the author explains in detail the physiological aging of the speech organs and the pathological features of the larynx called presbyphonia including vocal cord atrophy, which is common in the elderly. In addition, a theoretical model of how speech-language hearing therapists can deal with presbyphonia is proposed.