Page 64 - Fall2021

PHYSICS OF VOCAL HEALTH
Figure 3. Adduction of the supraglottal structures may lead to medial-lateral (A: left to right) or anterior-posterior (B: front to back) constriction of the airway immediately above the vocal folds, as often observed in muscle tension dysphonia.
fold swelling. This swelling may also occur following an upper respiratory infection (such as the cold or flu), chemical exposure of the vocal folds due to laryngopha- ryngeal reflux (stomach acid reflux into the throat), or smoking. Vocal fold swelling makes it difficult to com- pletely close the glottis along the length of the vocal folds, allowing air to escape through gaps around the swollen portion of the vocal folds. When vocal fold inflamma- tion leads to an irregular medial edge of the vocal folds, irregular glottal closure may ensue, resulting in hoarse voice quality.
Vocal fold swelling is often transient and will resolve over time with vocal rest or when the underlying medical con- ditions have cleared. However, if one were to talk through these voice changes, one often has to increase lung pres- sure, tighten adduction of the vocal folds, and possibly adduct the false folds and epiglottis. This adaptation may lead to increased contact pressure between the vocal folds, further exacerbating the underlying vocal fold inflammation. If this adaptive behavior persists after the triggering conditions are resolved, the vocal fold inflam- mation may further develop into vocal fold lesions such as vocal fold nodules, polyps, and contact ulcers, with a more permanent change in voice quality (Hillman et al., 1989). For voice professionals, particularly singers, it is often recommended that they reduce voice use in the presence of vocal fold inflammation and avoid adaptive changes in vocal behavior.
Muscular Tension Around the Larynx
Voice disorders may also occur from increased tension in the perilaryngeal muscles that support the larynx
(muscles connecting the larynx to other structures around the neck). This is often due to adaptive behav- iors to compensate for glottal insufficiency but may also result from psychological stress (Dietrich and Verdolini
Abbott, 2012).
Tension in the perilaryngeal muscles often raises the vertical position of the larynx. This results in increased adduction of the vocal folds and the squeezing of supraglottal structures such as the false vocal folds and epiglottis (Figure 3) (Vilkman et al., 1996), allowing a speaker to compensate for glottal insufficiency. However, in the absence of glottal insufficiency, such increased vocal fold adduction often leads to excessively high con- tact forces between the vocal folds and poses a high risk of vocal fold injury. Due to the high tension in the peri- laryngeal muscles, the speaker often experiences vocal fatigue after an extended period of talking and may even feel pain around the neck.
Although voice production is primarily controlled by activities of the intrinsic laryngeal muscles (muscles with origin and insertion within the larynx), these muscles act on the laryngeal framework that is supported and stabilized by the perilaryngeal muscles. Excessive ten- sion in the perilaryngeal muscles acting on the laryngeal cartilages makes it more difficult to adjust the relative position among the thyroid, cricoid, and arytenoid car- tilages to which the vocal folds are attached. This may interfere with the delicate control of vocal fold geom- etry and mechanical properties by the intrinsic muscles and limit the range of vocal fold posturing. Tension in the perilaryngeal muscles may also lead to undesired
64 Acoustics Today • Fall 2021