Vocal loading

Abstract: A well-functioning voice is an essential tool for one third of the labour force Vocal demands vary to a great extent between the different voice and speech professions In professions with heavy vocal loading (eg school and kindergarten teachers), occupational voice disorders threatening working ability are common Vocal loading is a combination of prolonged voice use and additional loading factors (eg background noise, acoustics, air quality) affecting the fundamental frequency, type and loudness of phonation or the vibratory characteristics of the vocal folds as well as the external frame of the larynx The prevention and treatment of occupational voice disorders calls for improved occupational safety and health (OSH) arrangements for voice and speech professionals On the basis of epidemiological and acoustic-physiological research, the presence of risk to vocal health can be substantiated From the point of view of the physical load on the vocal apparatus, loading-related physiological changes (adaptation) may play a role in the occupational risk Environmental factors affect vocal loading changes In teaching professions, the working environment is shared with children, who benefit from amendments of OSH legislation concerning their teachers

Abstract: To measure the exposure to self-induced tissue vibration in speech, three vocal doses were defined and described: distance dose, which accumulates the distance that tissue particles of the vocal folds travel in an oscillatory trajectory; energy dissipation dose, which accumulates the total amount of heat dissipated over a unit volume of vocal fold tissues; and time dose, which accumulates the total phonation time. These doses were compared to a previously used vocal dose measure, the vocal loading index, which accumulates the number of vibration cycles of the vocal folds. Empirical rules for viscosity and vocal fold deformation were used to calculate all the doses from the fundamental frequency (F0) and sound pressure level (SPL) values of speech. Six participants were asked to read in normal, monotone, and exaggerated speech and the doses associated with these vocalizations were calculated. The results showed that large F0 and SPL variations in speech affected the dose measures, suggesting that accumulation of phonation time alone is insufficient. The vibration exposure of the vocal folds in normal speech was related to the industrial limits for hand-transmitted vibration, in which the safe distance dose was derived to be about 500 m. This limit was found rather low for vocalization; it was related to a comparable time dose of about 17 min of continuous vocalization, or about 35 min of continuous reading with normal breathing and unvoiced segments. The voicing pauses in normal speech and dialogue effectively prolong the safe time dose. The derived safety limits for vocalization will likely require refinement based on a more detailed knowledge of the differences in hand and vocal fold tissue morphology and their response to vibrational stress, and on the effect of recovery of the vocal fold tissue during voicing pauses.