Direct measurement and modeling of intraglottal, subglottal, and vocal fold collision pressures during phonation in an individual with a hemilaryngectomy

Vocal Demands of Musical Theatre Rehearsals: A Dosimetry Study

OBJECTIVE

To investigate singers' vocal load by documenting three types of vocal doses (time, cycle, and distance doses) and sound pressure levels during the four phases of rehearsal and how the vocal doses vary between singers across rehearsals in the musical Nine, written by Maury Yeston.

METHODS/DESIGN

Five student-singers participating in the musical Nine gave informed consent to participate in the study. All five participants were assigned female at birth and female-identifying individuals. They attached a KayPENTAX APM 3300 dosimeter sensor to their lower neck and wore the accelerometer during four three-hour rehearsals throughout the rehearsal process (the music learning phase, the choreography learning phase, the blocking learning phase, and the dress rehearsal) of the musical. The dosimeter records neck vibrations at a rate of 20 samples per second. but it does not record linguistic content.

RESULTS

A dosimetric analysis of five student singers identified variability in voice production throughout the rehearsal process. According to the dosimetry findings, singers employed extensive low-frequency voicing below the first passaggio, with belting and mixed vocal strategies as the predominant stylistic choices when performing in Nine. Additionally, the singers used an occasional head voice effect at specific moments. The roles of Carla, Saraghina, La Fleur, and Ensemble One and Two required specific vocal ranges due to the musical score.

CONCLUSIONS

Researchers have yet to establish a safe baseline vocal dose for singers. The vocal dose is affected by many factors, such as duration of phonation, frequency range, SPL, and styles of vocalism required by the score. Louder and heavier vocalization produces larger distance doses, representing the cumulative load placed on vibrating tissue. The cycle dose, distance dose, and SPL reported in this study varied within and between singers. The phonation density graphs show this variability and the low tessitura required by the score. Time doses ranged from 4% to 7% of rehearsal time; this short dose suggests that the rehearsals provided healthy conditions for the successful rehearsal process with efficient attention to the vocalization of a score that requires heavy vocal styles, including belting. While the rehearsal pace was not alarming, the demands of the score alone may prove to be much greater than the vocal dose reported through the rehearsal. Further studies are needed to establish the overall dose of each Broadway role to serve as parameters for vocal pacing and voice care.

Effect of nodule size and stiffness on phonation threshold and collision pressures in a synthetic hemilaryngeal vocal fold model

Synthetic vocal fold (VF) replicas were used to explore the role of nodule size and stiffness on kinematic, aerodynamic, and acoustic measures of voiced speech production. Emphasis was placed on determining how changes in collision pressure may contribute to the development of phonotrauma. This was performed by adding spherical beads with different sizes and moduli of elasticity at the middle of the medial surface of synthetic silicone VF models, representing nodules of varying size and stiffness. The VF models were incorporated into a hemilaryngeal flow facility. For each case, self-sustained oscillations were investigated at the phonation threshold pressure. It was found that increasing the nodule diameter increased the open quotient, phonation threshold pressure, and phonation threshold flow rate. However, these values did not change considerably as a function of the modulus of elasticity of the nodule. Nevertheless, the ratio of collision pressure to subglottal pressure increased significantly for both increasing nodule size and stiffness. This suggests that over time, both growth in size and fibrosis of nodules will lead to an increasing cycle of compensatory vocal hyperfunction that accelerates phonotrauma.

Ambulatory Monitoring of Subglottal Pressure Estimated from Neck-Surface Vibration in Individuals with and without Voice Disorders

The aerodynamic voice assessment of subglottal air pressure can discriminate between speakers with typical voices from patients with voice disorders, with further evidence validating subglottal pressure as a clinical outcome measure. Although estimating subglottal pressure during phonation is an important component of a standard voice assessment, current methods for estimating subglottal pressure rely on non-natural speech tasks in a clinical or laboratory setting. This study reports on the validation of a method for subglottal pressure estimation in individuals with and without voice disorders that can be translated to connected speech to enable the monitoring of vocal function and behavior in real-world settings. During a laboratory calibration session, a participant-specific multiple regression model was derived to estimate subglottal pressure from a neck-surface vibration signal that can be recorded during natural speech production. The model was derived for vocally typical individuals and patients diagnosed with phonotraumatic vocal fold lesions, primary muscle tension dysphonia, and unilateral vocal fold paralysis. Estimates of subglottal pressure using the developed method exhibited significantly lower error than alternative methods in the literature, with average errors ranging from 1.13 to 2.08 cm H₂O for the participant groups. The model was then applied during activities of daily living, thus yielding ambulatory estimates of subglottal pressure for the first time in these populations. Results point to the feasibility and potential of real-time monitoring of subglottal pressure during an individual's daily life for the prevention, assessment, and treatment of voice disorders.

Collision Pressure and Dissipated Power Dose in a Self-Oscillating Silicone Vocal Fold Model With a Posterior Glottal Opening

PURPOSE

The goal of this study was to experimentally evaluate how compensating for the adverse acoustic effects of a posterior glottal opening (PGO) by increasing subglottal pressure and changing supraglottal compression, as have been associated with vocal hyperfunction, influences the risk of vocal fold (VF) trauma.

METHOD

A self-oscillating synthetic silicone model of the VFs with an airflow bypass that modeled a PGO was investigated in a hemilaryngeal flow facility. The influence of compensatory mechanisms on collision pressure and dissipated collision power was investigated for different PGO areas and supraglottal compression. Compensatory behaviors were mimicked by increasing the subglottal pressure to achieve a target sound pressure level (SPL).

RESULTS

Increasing the subglottal pressure to compensate for decreased SPL due to a PGO produced higher values for both collision pressure and dissipated collision power. Whereas a 10-mm² PGO area produced a 12% increase in the peak collision pressure, the dissipated collision power increased by 122%, mainly due to an increase in the magnitude of the collision velocity. This suggests that the value of peak collision pressure may not fully capture the mechanisms by which phonotrauma occurs. It was also found that an optimal value of supraglottal compression exists that maximizes the radiated SPL, indicating the potential utility of supraglottal compression as a compensatory mechanism.

CONCLUSIONS

Larger PGO areas are expected to increase the risk of phonotrauma due to the concomitant increase in dissipated collision power associated with maintaining SPL. Furthermore, the risk of VF damage may not be fully characterized by only the peak collision pressure.

LaDIVA: A neurocomputational model providing laryngeal motor control for speech acquisition and production

Many voice disorders are the result of intricate neural and/or biomechanical impairments that are poorly understood. The limited knowledge of their etiological and pathophysiological mechanisms hampers effective clinical management. Behavioral studies have been used concurrently with computational models to better understand typical and pathological laryngeal motor control. Thus far, however, a unified computational framework that quantitatively integrates physiologically relevant models of phonation with the neural control of speech has not been developed. Here, we introduce LaDIVA, a novel neurocomputational model with physiologically based laryngeal motor control. We combined the DIVA model (an established neural network model of speech motor control) with the extended body-cover model (a physics-based vocal fold model). The resulting integrated model, LaDIVA, was validated by comparing its model simulations with behavioral responses to perturbations of auditory vocal fundamental frequency (fo) feedback in adults with typical speech. LaDIVA demonstrated capability to simulate different modes of laryngeal motor control, ranging from short-term (i.e., reflexive) and long-term (i.e., adaptive) auditory feedback paradigms, to generating prosodic contours in speech. Simulations showed that LaDIVA’s laryngeal motor control displays properties of motor equivalence, i.e., LaDIVA could robustly generate compensatory responses to reflexive vocal fo perturbations with varying initial laryngeal muscle activation levels leading to the same output. The model can also generate prosodic contours for studying laryngeal motor control in running speech. LaDIVA can expand the understanding of the physiology of human phonation to enable, for the first time, the investigation of causal effects of neural motor control in the fine structure of the vocal signal.