Page 60 - Fall2021

FEATURED ARTICLE
The Physical Aspects of Vocal Health
Zhaoyan Zhang
For most people, not much conscious thought or effort is needed to produce a voice with the desired pitch, loud- ness, and voice quality. However, voice disorders are quite common. When disorders occur, the voice may require more effort to produce, be too weak to be heard, or have undesired quality changes that draw unwanted attention. Such changes can affect a speaker’s personal identity and the ability to effectively communicate, thus limiting the ability to participate in educational, occupational, or social activities.
Most people have experienced difficulty with their voice after screaming at a sports event or after an upper respira- tory infection such as the cold or flu. For teachers, singers, and other professional voice users, voice problems occur more often and the symptoms are often severe. For these people, the voice may get tired toward the end of the day. Sometimes the voice is no longer able to meet the higher expectations and greater demands of one’s profession and those individuals have to make career changes.
This article focuses on voice disorders that are related to the production of sound by vocal fold vibration. Voice disorders are often grouped into three major catego- ries based on their etiology. The first category includes organic voice disorders arising from structural changes to the larynx (e.g., inflammation due to an infection or voice overuse) that interfere with the vocal mechanisms.
The second category, neurogenic voice disorders, is related to neurological dysfunctions due to either paralysis, pare- sis, or neurological disease (e.g., Parkinson’s disease) that impact neurological control of the vocal system.
The third category has been characterized in many ways, including as “functional” voice disorders. This category includes voice disorders with no known underlying organic or neurological origins that are presumably related to the improper use of vocal mechanisms and are thus “functional” in some aspect. A widely held
assumption is that these disorders may have psycho- logical origins, but more often they are adaptations to transient tissue changes (e.g., laryngitis) or compromised vocal mechanisms (e.g., paresis or paralysis).
The purpose of this article is not to discuss every voice disorder or category of disorders (but for more informa- tion, see Boone et al., 2010; Colton et al., 2011). Instead, it providesanupdatedreviewofthephysicalaspectsofvocal health. The focus is on the physical components involved in healthy voice production, the major pathophysiology of voice disorders, and clinical care of common voice prob- lems. The article ends by briefly discussing the existing knowledge gaps between current scientific understanding and the practice of clinical voice care.
Physiology of Voice Production
The human voice is produced in the larynx (Figure 1A), which houses the two opposing vocal folds. Each vocal fold consists of a soft membranous cover layer folded around an inner muscular layer. The vocal folds are connected together anteriorly but slightly separated posteriorly, forming a triangular-shaped airway (the glot- tis) (Figure 1B). At rest, the glottis remains open and allows airflow in and out of the lungs during breathing. During voice production (also known as phonation), the two vocal folds are brought together to close the glot- tis (Figure 1C). When the lung pressure is high enough (about 200 Pa), the vocal folds will be excited into a self- sustained vibration, which periodically opens and closes the glottis. This modulates airflow through the glottis and produces sound, which then propagates through the vocal tract and radiates from the mouth and nasal open- ing into the voice we hear.
An important feature of normal voice production is that the glottis remains closed for an extended duration withineachcycleofvocalfoldvibration(seeMultimedia 1 at acousticstoday.org/zzhangmedia), which interrupts the glottal flow. The rapid decline of the glottal flow
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60 Acoustics Today • Fall 2021 | Volume 17, issue 3
https://doi.org/10.1121/AT.2021.17.3.60