The minimum glottal airflow to initiate vocal fold oscillation

The Influence of Voice Training on Vocal Learners' Supraglottal Activities and Aerodynamic Evaluation

OBJECTIVE

Among music majors with only 18 months of training, supraglottal activities and aerodynamic parameters were studied to facilitate understanding of the influence of voice training on characteristics of voice production.

METHODS

Twenty-three students at the Xiamen Music School were examined over the course of 18 months of singing training. Only 17 students completed all data collection sessions. All students had no previous voice training and were confirmed to be without organic voice disorders by a laryngologist but did present with supraglottal compression. Strobolaryngoscopy and aerodynamic assessment were performed every 6 months. Using the laryngoscopic images, anterior-posterior (A-P) compression and medial-lateral compression were analyzed. Aerodynamic assessment was carried out to measure maximum phonation time, phonation threshold flow, glottal resistance, subglottal pressure, phonation threshold pressure, and vocal efficiency. From these measurements, the mean was calculated along with a measurement of reliability. One-way ANOVA with Bonferroni post hoc test was used to evaluate the results between subjects at different time points. Kendall's W test was completed to assure consistency between and within laryngologists.

RESULTS

Referring to the Strobolaryngoscopy Evaluation Rating Form, 4 of the 17 students had decreased A-P compression scores in the second measurement compared to the first (from 2.24 ± 0.20 to 2.12 ± 0.17, P = 0.100). After completion of the program, 6 of the 17 students' anterior-posterior compression scores further improved from the second measurement (from 2.12 ± 0.17 to 1.71 ± 0.17, P = 0.600). The A-P compression scores showed a gradual downward trend and was overall statistically significant (P = 0.004). In addition, there was an improvement of maximum phonation time (P​ ​= 0.016).

CONCLUSION

Professional voice training can improve the supraglottal activities and maximum phonation time. These parameters have potential to be used for voice training evaluation and screening.

The effects of vocal tract constrictions on aerodynamic measures in a synthetic vocal fold model

According to nonlinear source-filter theory, as the strength of the coupling between the source and filter increases, typically by a decrease in the vocal tract cross-sectional area, the resultant increase in the inertance of the vocal tract yields an increase in the interactions between acoustic pressures within the vocal tract and the changing glottal airflow and/or the vibratory pattern of the vocal folds as noted in Titze [(2008). J. Acoust. Soc. Am. 123(4), 1902-1915]. The purpose of the current research was to examine the effects of parametric vocal tract constrictions mimicking epilaryngeal tube and lip narrowing on aerodynamic measures in a dynamic self-oscillating physical model of the vocal folds and vocal tract. Multilayered silicone vocal fold models were created based on Murray and Thomson [(2011). J. Visualized Exp. 58, e3498] and Murray and Thomson [(2012). J. Acoust. Soc. Am. 132(5), 3428-3438] and mounted to a simple synthetic trachea and supraglottal vocal tract model. Four constriction cross-sectional areas were examined at two locations (i.e., at the epilarynx and lip regions). Phonation threshold pressure and flow were measured at phonation onset and offset using four M5-CONV vocal fold models. Results indicated that both constriction magnitude and location are relevant factors in determining glottal aerodynamics. In general, a narrow epilarynx tube or lip constriction resulted in the lowest onset pressures and airflows while the no vocal tract condition resulted in the highest onset pressures and airflows.

Corticosteroid-LABA inhalers increase phonation threshold pressure (PTP) and flow (PTF) in rabbits

OBJECTIVES

This study examined the effects of a combination corticosteroid plus long-acting beta2 -adrenergic agonist inhaler (IC) on rabbit phonation.

METHODS

White New Zealand male rabbits were assigned randomly to experimental and control groups (n = 11 per group). The experimental group received twice-daily doses of Advair HFA™ (fluticasone propionate 45 mcg and salmeterol 21 mcg) via a veterinary facemask with 1-way valve and spacer; the control group received aerosolized saline. After 8 weeks, animals were euthanized, larynges excised, frozen, and subsequently thawed and mounted on a standard bench apparatus. Phonation was elicited during 15 successive trials, and phonation threshold pressure (PTP; cmH2 O) and flow (PTF; L/min) were quantified.

RESULTS

Repeated measures analysis of variance indicated significant differences between the experimental and control groups (p < 0.05). Mean PTP and PTF values were higher (worse) for rabbits that received Advair HFA™.

CONCLUSION

Following 8-week exposure to ICs, rabbit larynges required greater air pressure and flow to initiate phonation. Because even modest phonation onset differences can have a meaningful clinical impact on voice function, these findings suggest that LABA ICs may put patients at risk for voice disorders. Furthermore, these voice disorders may occur within a relatively short timeframe. The results from this study have important clinical implications for voice care in those who use ICs.

LEVEL OF EVIDENCE

NA Laryngoscope, 133:2680-2686, 2023.

Phonation Threshold Pressure/Flow for Reflecting Glottal Closure in Unilateral Vocal Fold Paralysis

OBJECTIVE

Previous theoretical analysis predicted that phonation threshold flow (PTF) could be a more sensitive aerodynamic measure than phonation threshold pressure (PTP) for reflecting glottal incompetence. This study investigated the feasibility of whether PTP and PTF may differentiate subjects with unilateral adductor vocal fold paralysis and paresis (UAVFP) from those without, and whether PTP and PTF could reflect the extent of incomplete glottal closure associated with UAVFP.

METHODS

PTP and PTF were quantified for 13 subjects with UAVFP and 21 control subjects with normal voice, and the normalized glottal gap area (NGGA) based on videostroboscopic image analysis was quantified for subjects with UAVFP.

RESULTS

Significant differences in both PTP and PTF were found between subjects with UAVFP and control subjects. Receiver operating characteristic analysis indicated a higher discriminatory ability of PTP for differentiating subjects with UAVFP from those without (area under the curve of 0.905 for PTP, 0.678 for PTF), yet a significant positive correlation was found between PTF and NGGA (Spearman's ρ = 0.571) but not between PTP and NGGA (ρ = -0.364).

CONCLUSION

Results supported the feasibility of using PTP and PTF as potential diagnostic indicators for reflecting glottal closure in UAVFP, with PTP potentially more sensitive for differentiating subjects with and without incomplete glottal closure. These preliminary findings were limited by the small sample size, with further studies needed to verify whether PTF could be more sensitive for reflecting the extent of incomplete glottal closure, as predicted theoretically.

LEVEL OF EVIDENCE

3 Laryngoscope, 131:E1598-E1604, 2021.

Implementation of Telemedicine in a Laryngology Practice During the COVID-19 Pandemic: Lessons Learned, Experiences Shared

Objectives

The novel coronavirus disease 2019 has posed significant limitations and barriers to providing in-person healthcare. We aim to provide a summary of learned experiences and important considerations for implementing and offering telehealth to provide laryngology subspecialty care during the COVID-19 pandemic and thereafter.

Materials and Methods

Four laryngologists and a voice-specialized speech-language pathologist from a tertiary-care academic Voice and Swallowing Center were engaged in a structured group consensus conference. Participants shared input, experiences, and practice patterns employed via telemedicine (via telephone or video-communication) during the early COVID-19 era.

Results

Key identified areas of consideration when offering telemedicine included (1) how to set up and structure a telemedicine visit and maintain patient confidentiality, (2) patient examination and treatment initiation, (3) optimization of the tele-visit, (4) limitations and recognition of when a tele-visit is insufficient for patient care needs, (5) billing/reimbursement considerations. Group consensus for the aforementioned topics is summarized and discussed.

Conclusion

During the COVID-19 pandemic, a telemedicine model can be effectively employed to improve patient access to subspecialty laryngology care, including a multidisciplinary care approach, with initiation of various therapeutic interventions. A major limitation given the preclusion of in-person assessment is the lack of access to laryngoscopy, which can likely be delayed safely in the majority of individuals.

Effects of False Vocal Folds on Intraglottal Velocity Fields

Previous models have theorized that, during phonation, skewing of the glottal waveform (which is correlated with acoustic intensity) occurred because of inertance of the vocal tract. Later, we reported that skewing of the flow rate waveform can occur without the presence of a vocal tract in an excised canine larynx. We hypothesized that in the absence of a vocal tract, the skewing formed when dynamic pressures acted on the glottal wall during the closing phase; such pressures were greatly affected by formation of intraglottal vortices. In this study, we aim to identify how changes in false vocal folds constriction can affect the acoustics and intraglottal flow dynamics. The intraglottal flow measurements were made using particle image velocimetry in an excised canine larynx where a vocal tract model was placed above the larynx and the constriction between the false vocal folds was varied. Our results show that for similar values of subglottal pressures, the skewing of the glottal waveform, strength of the intraglottal vortices, and acoustic energy increased as the constriction between the false vocal folds was increased. These preliminary findings suggest that acoustic intensity during phonation can be increased by the addition of a vocal tract with false fold constriction.

Effects of Angle of Epiglottis on Aerodynamic and Acoustic Parameters in Excised Canine Larynges

OBJECTIVES

The aim of this study is to explore the effects of the angle of epiglottis (Aepi) on phonation and resonance in excised canine larynges.

METHODS

The anatomic Aepi was measured for 14 excised canine larynges as a control. Then, the Aepis were manually adjusted to 60° and 90° in each larynx. Aerodynamic and acoustic parameters, including mean flow rate, sound pressure level, jitter, shimmer, fundamental frequency (F0), and formants (F1'-F4'), were measured with a subglottal pressure of 1.5 kPa. Simple linear regression analysis between acoustic and aerodynamic parameters and the Aepi of the control was performed, and an analysis of variance comparing the acoustic and aerodynamic parameters of the three treatments was carried out.

RESULTS

The results of the study are as follows: (1) the larynges with larger anatomic Aepi had significantly lower jitter, shimmer, formant 1, and formant 2; (2) phonation threshold flow was significantly different for the three treatments; and (3) mean flow rate and sound pressure level were significantly different between the 60° and the 90° treatments of the 14 larynges.

CONCLUSIONS

The Aepi was proposed for the first time in this study. The Aepi plays an important role in phonation and resonance of excised canine larynges.

Effects of a simulated system of straw phonation on the complete phonatory range of excised canine larynges

PURPOSE

This study investigated the effects of straw phonation therapy on the aerodynamic and acoustic parameters of the vocal folds at different levels of elongation and subglottal pressure.

METHODS

20 excised canine larynges were used in both experimental (straw phonation therapy simulation) and control conditions. Aerodynamic parameters, including phonation threshold pressure (PTP), phonation instability pressure (PIP), phonation pressure range (PPR), phonation threshold flow (PTF), phonation instability flow (PIF), phonation flow range (PFR), were obtained at different levels of vocal fold elongation (0%, 10%, 20%). Acoustic parameters, including fundamental frequency (F0), jitter, shimmer, signal noise ratio (SNR) were detected at different levels of vocal fold elongation (0%, 10%, 20%) and subglottal pressure (15 cmH₂O, 20 cmH₂O, 25 cmH₂O).

RESULTS

Significant decreases in PTP and PTF and significant increases in PIP, PIF, PPR, and PFR occurred in experimental condition at all levels of elongation when compared with control condition. However, no significant changes of acoustic parameters were obtained between conditions at all levels.

CONCLUSION

At different levels of vocal fold elongation, straw phonation not only lowered the onset of normal voice, but also elevated the onset of chaotic voice, indicating a better voice economy and voice control. Moreover, the improved phonatory range demonstrated that straw phonation had the potential to prevent voice users who have high voice demand from voice fatigue and vocal damage.

Development of Excised Larynx

The larynx is a complex organ which has a role in a variety of functions such as phonation, breathing, and swallowing. To research these functions, it is widely accepted that in vivo studies provide more anatomically and physiologically relevant findings. However, invasive procedures are generally needed to measure variables such a subglottal pressure, vocal fold tension and stiffness, and cricothyroid muscle stretch. Performing studies using excised larynges is a useful technique which makes it possible to not only measure phonation parameters but control them as well. Early studies using excised larynges mainly focused on controlling specific parameters and mathematical modeling simulations. The use of these studies has helped further research in laryngeal anatomy, imaging techniques, as well as aerodynamic, acoustic, and biomechanical properties. Here, we describe the progress of this research over the past 5 years. The number of accepted animal models has increased and ideas from excised larynx studies are starting to be applied to treatment methods for laryngeal disorders. These experiments are only valid for an excised situation and must continue to be combined with animal experimentation and clinical observations.

Survival in Vivo Canine Phonation Model Without Stimulation

OBJECTIVES

We describe a survival nonstimulated in vivo canine phonation model using distending laryngoscope, cramp frame, and constant humidified glottal airflow to elicit phonation.

METHODS

Five beagle dogs were involved in this study. One cuffed endotracheal tube was placed below the glottis through the tracheotomy and delivered humidified airflow to the glottis. Arytenoids approximation was maintained using a clamp under the distending laryngoscope. Acoustic and aerodynamic parameters were measured using synchronous signal collection system and analysis software. Vocal oscillation also was examined using stroboscope laryngeal imaging.

RESULTS

For the nonstimulated in vivo phonation animal, the sound intensity and fundamental frequency were 78.3 ± 6.8 dB and 127.6 ± 29.2 Hz in the first experiment and 82.9 ± 6.6 dB and 175.2 ± 4.4 Hz 4 weeks later. The aerodynamic analysis revealed the mean subglottal phonation threshold pressure (PTP) and phonation threshold flow (PTF) were 8.5 ± 4.0 cmH₂0 and 683.0 ± 356.4 mL/s in the first experiment and 16.1 ± 8.6 cmH₂0 and 384.8.0 ± 230.6 mL/s in the second experiment 4 weeks later. Stroboscope image revealed sustained vocal vibration during great airflow delivery to glottis in the phonation animal model.

CONCLUSIONS

We developed a survival nonstimulated in vivo phonation canine model that allows the study of long-term animal phonation study as its own control.

The Effect of Vocal Fold Inferior Surface Hypertrophy on Voice Function in Excised Canine Larynges

OBJECTIVE

This study aimed to explore the changes in vocal fold inferior surface hypertrophy (VFISH) on vocal fold vibration by aerodynamic and acoustic analysis. The present study allows us to gain new insights into the subglottal convergence angle (SCA), which will change with VFISH.

STUDY DESIGN

The study is prospective, and designed for repeated measures with each excised canine larynx serving as own control.

SUBJECTS AND METHODS

Three degrees of VFISH, initial, mild, and severe, were simulated by injecting different doses of fructose injections into the inferior surface of the vocal folds of 10 excised canine larynges. Computed tomographic images of the larynx were gathered, and three-dimensional models of the airway and vocal folds were reconstructed using the Mimics software. The SCA was measured from the reconstructed models. Phonation threshold flow (PTF), phonation threshold pressure (PTP), and mean flow rate (MFR) were recorded directly in the excised canine larynx phonation setup. Glottal resistance (GR), sound pressure level (SPL), fundamental frequency (F0), and formants 1-4 (F1-4) were measured when subglottal pressure (P_sub) was at 1.5 kPa or 2.5 kPa, separately. Using ordinary one-way analysis of variance, we compared the aerodynamic outcomes and voice quality among the three groups of hypertrophy.

RESULTS

The SCA, PTP, and PTF increased with the degree of VFISH. When the P_sub was controlled at 1.5 kPa or 2.5 kPa, F0 also increased significantly with the degree of VFISH of the excised canine larynges. The MFR, GR, SPL, and F1-4 had little change between the three groups and were not significantly different.

CONCLUSION

The VFISH makes onset phonation more difficult, increases the SCA, and increases the F0 in sustained phonation.

Oscillatory Onset and Offset in Young Vocally Healthy Adults Across Various Measurement Methods

OBJECTIVE

This study aimed to investigate the relationship between (1) oscillatory onset-offset time across various approaches that use different measurement criteria and (2) oscillatory onset and offset times in vocally healthy young adults.

METHOD

Oscillatory onset-offset times were obtained from 71 vocally normal adults, using high-speed videoendoscopy. Comparisons between the different onset methods involved measurement of the oscillatory onset time (OOT), voice initiation period (VIP), and the phonation onset time (POT), and for offset methods involved computation of the oscillatory offset time (OOT_off) and the phonation offset time.

RESULTS

Correlation of the OOT with the VIP was 0.240 (P = 0.04) and with the POT form glottal area waveform was 0.248 (P = 0.04); however, correlation between the VIP and the POT glottal area waveform was 0.661 (P < 0.001). For offset, there was a moderate correlation (r_S = 0.503, P < 0.001) across OOT_off and vocal offset period. The onset time was longest for the OOT followed by the VIP and the POT. There was no correlation between onset and offset for all methods.

CONCLUSIONS

A framework for quantification of oscillatory onset-offset time was developed for /hi/ tasks, which can be used for future measurements of disordered voice. A positive relationship was observed between VIP and POT and between OOT_off and vocal offset period. There was a nonlinear relationship between the OOT, VIP, and POT measures. Onset-offset times are strongly influenced by the calculation method used, the pros and cons of which are discussed in this paper. Vibratory onset and offset represent physiologically different phenomena.

Effects of Volume, Pitch, and Phonation Type on Oscillation Initiation and Termination Phases Investigated With High-speed Videoendoscopy

OBJECTIVES

This study aimed to investigate the effects of varying volume, pitch, and phonation types on the initiation and termination phases of vocal fold oscillation using high-speed digital videoendoscopy. Specifically, it addressed the effects of the variation of volume, pitch, and phonation type (normal, pressed, and breathy) on the transient duration of the vibrating glottal length (length transient duration, T_len), the transient duration of the glottal area waveform (area transient duration, T_area), the time offset between the beginning (or the end) of the full-length vibration and the full-amplitude vibration, T_Δ, and the variation of the fundamental frequency during the vocal fold oscillation initiation and termination segments (pitch instability, %PI).

METHODS

A female subject with no voice problem produced voices with varying pitch and loudness, including comfortable pitch and comfortable loudness, normal pitch loud, high pitch and comfortable loudness, and high pitch and loud. Breathy and pressed phonations were also recorded. Each of the six phonation types was recorded six times, which resulted in 72 transient segments (each recording included both initiation and termination phases). Mixed model statistical analyses were employed to the five objective high-speed digital videoendoscopy parameters.

RESULTS

Preliminary findings demonstrated significant findings for voice type effects for the length and area transient durations for the oscillation initiation segment but not for the oscillation termination segment.

CONCLUSIONS

This study demonstrates that voice types appear to influence vibration initiation patterns more than the vibration termination patterns.

Transient dynamic mechanical properties of resilin-based elastomeric hydrogels

The outstanding high-frequency properties of emerging resilin-like polypeptides (RLPs) have motivated their development for vocal fold tissue regeneration and other applications. Recombinant RLP hydrogels show efficient gelation, tunable mechanical properties, and display excellent extensibility, but little has been reported about their transient mechanical properties. In this manuscript, we describe the transient mechanical behavior of new RLP hydrogels investigated via both sinusoidal oscillatory shear deformation and uniaxial tensile testing. Oscillatory stress relaxation and creep experiments confirm that RLP-based hydrogels display significantly reduced stress relaxation and improved strain recovery compared to PEG-based control hydrogels. Uniaxial tensile testing confirms the negligible hysteresis, reversible elasticity and superior resilience (up to 98%) of hydrated RLP hydrogels, with Young's modulus values that compare favorably with those previously reported for resilin and that mimic the tensile properties of the vocal fold ligament at low strain (<15%). These studies expand our understanding of the properties of these RLP materials under a variety of conditions, and confirm the unique applicability, for mechanically demanding tissue engineering applications, of a range of RLP hydrogels.

Measurement of phonation threshold power in normal and disordered voice production

OBJECTIVES

Phonation threshold pressure (PTP) and phonation threshold flow (PTF) are useful aerodynamic parameters, but each is sensitive to different disorders. A single comprehensive aerodynamic parameter sensitive to a variety of disorders might be beneficial in quantitative voice assessment. We performed the first study of phonation threshold power (PTW) in human subjects.

METHODS

PTP and PTF were measured in 100 normal subjects, 19 subjects with vocal fold immobility, and 94 subjects with a benign mass lesion. PTW was calculated from these two parameters. In 41 subjects with a polyp, measurements were obtained before and after excision. Receiver operating characteristic (ROC) analysis was used to determine the ability of the three parameters to distinguish between controls and disordered groups.

RESULTS

The PTW (p < 0.001), PTP (p < 0.001), and PTF (p < 0.001) were different among the three groups. All parameters decreased after polyp excision. PTW had the highest area under the ROC curve for all analyses.

CONCLUSIONS

PTW is sensitive to the presence of mass lesions and vocal fold mobility disorders. Additionally, changes in PTW can be observed after excision of mass lesions. PTW could be a useful parameter to describe the aerodynamic inputs to voice production.

Effect of variations to a simulated system of straw phonation therapy on aerodynamic parameters using excised canine larynges

OBJECTIVES/HYPOTHESIS

Resonance tubes are commonly used in voice therapy. These devices modify supraglottal impedance, potentially decreasing the aerodynamic power necessary for phonation. We modeled phonation with resonance tubes in excised larynges and evaluated the effects of varying tube width, tube length, and flow input on phonation threshold pressure (PTP) and phonation threshold flow (PTF). We hypothesized that the increased vocal economy observed in human subjects and several other models would be observed in excised larynges.

STUDY DESIGN

Repeated measures excised canine larynx bench experiment with each larynx serving as own control.

METHODS

Nine conditions were evaluated, namely control, two tube diameters (17.5 and 6.5mm), three tube lengths (7.8, 15.0, and 30.0cm), and three levels of flow input (80, 114, and 200mL/s). Aerodynamic data were collected for 11 excised canine larynges attached to an artificial vocal tract, and results from each experimental configuration were compared with control.

RESULTS

A significant decrease in average PTP occurred compared with control for the 114- and 200-mL/s flow inputs, 30-cm extension, and 17.5- and 6.5-mm constrictions. Average PTF decreased compared with control for every configuration, although statistically significant changes were only observed for 200-mL/s flow and 6.5-mm constriction.

CONCLUSIONS

Knowledge regarding the effect of vocal tract alterations could be clinically useful in determining the optimal "straw" configuration for voice therapy. Further exploration of the relationships among width, length, and flow input could provide theoretical support for the development of new therapies and resonance tube devices.

Aerodynamic and nonlinear dynamic acoustic analysis of tension asymmetry in excised canine larynges

PURPOSE

To model tension asymmetry caused by superior laryngeal nerve paralysis (SLNP) in excised larynges and apply perturbation, nonlinear dynamic, and aerodynamic analyses.

METHOD

SLNP was modeled in 8 excised larynges using sutures and weights to mimic cricothyroid (CT) muscle function. Weights were removed from one side to create tension asymmetry, mimicking unilateral SLNP. Two sets of weights were used, 1 light and 1 heavy. Five conditions were evaluated: (a) no tension, (b) symmetrical light tension, (c) asymmetrical light tension, (d) symmetrical heavy tension, and (e) asymmetrical heavy tension.

RESULTS

Perturbation parameters were not significantly different across conditions: percent jitter, χ(2)(4) = 3.70, p = .451; percent shimmer, F(4) = 0.95, p = .321. In addition, many measurements were invalid (error values >10). Second-order entropy was significantly different across conditions, F(4) = 5.432, p = .002, whereas correlation dimension was not, F(4) = 0.99, p = .428. Validity of these nonlinear dynamic parameters was demonstrated by low standard deviations. Phonation threshold pressure, χ (2)(4) = 22.50, p < .001, and power, χ (2)(4) = 9.50, p = .05, differed significantly across conditions, whereas phonation threshold flow did not, χ (2)(4) = 4.08, p = .396.

CONCLUSIONS

Nonlinear dynamic analysis differentiated between symmetrical and asymmetrical tension conditions, whereas traditional perturbation analysis was less useful in characterizing type 2 or 3 vocal signals. Supplementing acoustic with aerodynamic parameters may help distinguish among laryngeal disorders of neuromuscular origin.

Modulating phonation through alteration of vocal fold medial surface contour

OBJECTIVES/HYPOTHESIS

1) To test whether alteration of the vocal fold medial surface contour can improve phonation and 2) to demonstrate that implant material properties affect vibration even when implantation is deep to the vocal fold lamina propria.

STUDY DESIGN

Induced phonation of excised human larynges.

METHODS

Thirteen larynges were harvested within 24 hours postmortem. Phonation threshold pressure (PTP) and flow (PTF) were measured before and after vocal fold injections using either calcium hydroxylapatite (CaHA) or hyaluronic acid (HA). Small-volume injections (median, 0.0625 mL) were targeted to the inferomedial aspect of the thyroarytenoid muscle. Implant locations were assessed histologically.

RESULTS

The effect of implantation on PTP was material dependent. CaHA tended to increase PTP, whereas HA tended to decrease PTP (Wilcoxon test, P = .00013 for onset). In contrast, the effect of implantation on PTF was similar, with both materials tending to decrease PTF (P = .16 for onset). Histology confirmed implant presence in the inferior half of the vocal fold vertical thickness.

CONCLUSIONS

Taken together, these data suggested the implants may have altered the vocal fold medial surface contour, potentially resulting in a less convergent or more rectangular glottal geometry as a means to improve phonation. An implant with a closer viscoelastic match to vocal fold cover is desirable for this purpose, as material properties can affect vibration even when the implant is not placed within the lamina propria. This result is consistent with theoretical predictions and implies greater need for surgical precision in implant placement and care in material selection.

Effect of source-tract acoustical coupling on the oscillation onset of the vocal folds

This paper analyzes the interaction between the vocal folds and vocal tract at phonation onset due to the acoustical coupling between both systems. Data collected from a mechanical replica of the vocal folds show that changes in vocal tract length induce fluctuations in the oscillation threshold values of both subglottal pressure and frequency. Frequency jumps and maxima of the threshold pressure occur when the oscillation frequency is slightly above a vocal tract resonance. Both the downstream and upstream vocal tracts may produce those same effects. A simple mathematical model is next proposed, based on a lumped description of tissue mechanics, quasi-steady flow and one-dimensional acoustics. The model shows that the frequency jumps are produced by saddle-node bifurcations between limit cycles forming a classical pattern of a cusp catastrophe. The transition from a low frequency oscillation to a high frequency one may be achieved through two different paths: in case of a large acoustical coupling (narrow vocal tract) or high subglottal pressure, the bifurcations are crossed, which causes a frequency jump with a hysteresis loop. By reducing the acoustical coupling (wide vocal tract) or the subglottal pressure, a path around the bifurcations may be followed with a smooth frequency variation.

Phonation instability flow in excised canine larynges

OBJECTIVE

Disordered voices are often associated with abnormal changes in aerodynamic parameters of subglottal pressure (P(s)) and airflow. Phonation instability pressure (PIP) has been previously proposed to evaluate P(s) at the onset of chaotic phonation. We propose the concept of and measure phonation instability flow (PIF), the airflow at which phonation becomes chaotic. Phonation flow range (PFR), PIF minus phonation threshold flow (PTF), is proposed to assess the range over which normal vocal fold vibration occurs.

STUDY DESIGN

Repeated measures with each ex vivo larynx serving as its own control.

METHODS

Pressure and airflow were measured at phonation onset and chaos onset in seven excised canine larynges under three experimental conditions: 0% elongation with no glottal gap; 20% elongation with no glottal gap; 20% elongation with a 3-mm posterior glottal gap. Paired t tests were performed to determine if experimental measurements differed between elongations (0% and 20%) or degrees of abduction (20% elongation with and without a 3-mm glottal gap).

RESULTS

Both PIF and PFR were dependent on abduction but not elongation. PIP was not significantly dependent on either condition. PIF and PFR showed greater differences for abduction than either phonation threshold pressure (PTP) or PTF.

CONCLUSIONS

PIF and PFR may be useful parameters in the experimental or clinical settings, particularly when evaluating disorders characterized by a glottal gap, such as vocal fold paralysis and presbylaryngis.

Phonation threshold pressure and flow in excised human larynges

OBJECTIVES/HYPOTHESIS

To determine the phonation threshold pressure (PTP) and phonation threshold flow (PTF) in excised human larynges; determine the effects of posterior glottal width, glottal area, and gender on PTP and PTF; test the hypothesis that hysteresis is present in excised human laryngeal phonation; and compare these results to those from canine experiments and human subject measurements.

STUDY DESIGN

Induced phonation of excised human larynges in the laboratory.

METHODS

Nine human larynges were harvested within 24 hours postmortem. PTP and PTF at phonation onset and offset were measured on a bench apparatus. The effects of posterior glottal width, glottal area, and gender were examined.

RESULTS

Large intersubject variability was observed in PTP and PTF. PTP was comparable to those measured in vivo, whereas PTF was substantially higher. One-way ANOVA showed no significant dependence of PTP and PTF on posterior glottal width. Hysteresis was observed, with offset PTP and PTF lower than onset values. Offset measurements had significantly less variability than onset measurements (P = .012 for PTP, P = .0001 for PTF).

CONCLUSIONS

This study is one of the first to report onset and offset PTP and PTF in fresh excised human larynges. The high PTF observed likely reflects a large direct current flow component due to vocal fold bowing. Offset PTP and PTF values may be intrinsically more reliably measured than onset values. The large intersubject variability in PTP and PTF may have implication for the clinical application of these aerodynamic parameters of phonation.

Mechanism of and threshold biomechanical conditions for falsetto voice onset

The sound source of a voice is produced by the self-excited oscillation of the vocal folds. In modal voice production, a drastic increase in transglottal pressure after vocal fold closure works as a driving force that develops self-excitation. Another type of vocal fold oscillation with less pronounced glottal closure observed in falsetto voice production has been accounted for by the mucosal wave theory. The classical theory assumes a quasi-steady flow, and the expected driving force onto the vocal folds under wavelike motion is derived from the Bernoulli effect. However, wavelike motion is not always observed during falsetto voice production. More importantly, the application of the quasi-steady assumption to a falsetto voice with a fundamental frequency of several hundred hertz is unsupported by experiments. These considerations suggested that the mechanism of falsetto voice onset may be essentially different from that explained by the mucosal wave theory. In this paper, an alternative mechanism is submitted that explains how self-excitation reminiscent of the falsetto voice could be produced independent of the glottal closure and wavelike motion. This new explanation is derived through analytical procedures by employing only general unsteady equations of motion for flow and solids. The analysis demonstrated that a convective acceleration of a flow induced by rapid wall movement functions as a negative damping force, leading to the self-excitation of the vocal folds. The critical subglottal pressure and volume flow are expressed as functions of vocal fold biomechanical properties, geometry, and voice fundamental frequency. The analytically derived conditions are qualitatively and quantitatively reasonable in view of reported measurement data of the thresholds required for falsetto voice onset. Understanding of the voice onset mechanism and the explicit mathematical descriptions of thresholds would be beneficial for the diagnosis and treatment of voice diseases and the development of artificial vocal folds.

A lumped mucosal wave model of the vocal folds revisited: recent extensions and oscillation hysteresis

This paper examines an updated version of a lumped mucosal wave model of the vocal fold oscillation during phonation. Threshold values of the subglottal pressure and the mean (DC) glottal airflow for the oscillation onset are determined. Depending on the nonlinear characteristics of the model, an oscillation hysteresis phenomenon may occur, with different values for the oscillation onset and offset threshold. The threshold values depend on the oscillation frequency, but the occurrence of the hysteresis is independent of it. The results are tested against pressure data collected from a mechanical replica of the vocal folds, and oral airflow data collected from speakers producing intervocalic /h/. In the human speech data, observed differences between voice onset and offset may be attributed to variations in voice pitch, with a very small or inexistent hysteresis phenomenon.

Optimal arytenoid adduction based on quantitative real-time voice analysis

HYPOTHESIS

The optimal degree of arytenoid rotation for arytenoid adduction (AA) can be determined using quantitative real-time voice analysis.

STUDY DESIGN

Repeated measures with each larynx serving as its own control.

METHODS

Unilateral vocal fold paralysis (VFP) was modeled in five excised canine larynges. Medialization laryngoplasty (ML) was performed, followed by AA. The optimal degree of arytenoid rotation was determined using real-time measurements of vocal efficiency (V(E) ), percent jitter, and percent shimmer. After the optimal degree of rotation was determined, the arytenoid was hypo- and hyperrotated 10% ± 2% of the optimal angle to mimic hypoadducted and hyperadducted states. Aerodynamic, acoustic, and mucosal wave measurements were recorded.

RESULTS

Mean optimal angle of arytenoid adduction was 151.4 ± 2.5°. V(E) differed significantly across experimental conditions (P = .003). Optimal AA produced the highest V(E) of any treatment, but this value did not reach that produced in the normal condition. Percent jitter (P < .001) and percent shimmer (P < .001) differed across groups and were lowest for optimal AA. Mucosal wave amplitude of the normal (P = .001) and paralyzed fold (P = .043) differed across treatments. Amplitude of both folds was highest for optimal AA.

CONCLUSIONS

V(E) and perturbation parameters were sensitive to the degree of arytenoid rotation. Using real-time voice analysis may aid surgeons in determining the optimal degree of arytenoid rotation when performing AA. Testing this method in patients and determining if optimal vocal outcomes are associated with optimal respiratory and swallowing outcomes will be essential to establishing clinical viability.

Phonation threshold power in ex vivo laryngeal models

This study hypothesized that phonation threshold power is measureable and sensitive to changes in the biomechanical properties of the vocal folds. Phonation threshold power was measured in three sample populations of 10 excised canine larynges treated with variable posterior glottal gap, variable bilateral vocal fold elongation, and variable vocal fold lesioning. Posterior glottal gap varied from 0 to 4mm in 0.5 mm intervals. Bilateral vocal fold elongation varied from 0% to 20% in 5% intervals. Vocal fold lesion treatments included unilateral and bilateral vocal fold lesion groups. Each treatment was investigated independently in a sample population of 10 excised canine larynges. Linear regression analysis indicated that phonation threshold power was sensitive to posterior glottal gap (R2=0.298, P<0.001) and weakly to vocal fold elongation (R2=0.052, P=0.003). A one-way repeated measures analysis of variance indicated that phonation threshold power was sensitive to the presence of lesions (P<0.001). Theoretical and experimental evidence presented here suggests that phonation threshold power could be used as a broad screening parameter sensitive to certain changes in the biomechanical properties of the larynx. It has not yet been measured in humans, but because it has the potential to represent the airflow-tissue energy transfer more completely than the phonation threshold pressure or flow alone, it may be a more useful parameter than these and could be used to indicate that laryngeal health is likely abnormal.

Multiparameter comparison of injection laryngoplasty, medialization laryngoplasty, and arytenoid adduction in an excised larynx model

OBJECTIVES/HYPOTHESIS

Evaluate the effect of injection laryngoplasty (IL), medialization laryngoplasty (ML), and ML combined with arytenoid adduction (ML-AA) on acoustic, aerodynamic, and mucosal wave measurements in an excised larynx setup.

STUDY DESIGN

Comparative case study using ex vivo canine larynges.

METHODS

Measurements were recorded for eight excised canine larynges with simulated unilateral vocal fold paralysis before and after vocal fold injection with Cymetra. A second set of eight larynges was used to evaluate medialization laryngoplasty using a Silastic implant without and with arytenoid adduction.

RESULTS

IL and ML led to comparable decreases in phonation threshold flow (PTF), phonation threshold pressure (PTP), and phonation threshold power (PTW). ML-AA led to significant decreases in PTF (P = .008), PTP (P = .008), and PTW (P = .008). IL and ML led to approximately equal decreases in percent jitter and percent shimmer. ML-AA caused the greatest increase in signal-to-noise ratio. ML-AA discernibly decreased frequency (P = 0.059); a clear trend was not observed for IL or ML. IL significantly reduced mucosal wave amplitude (P = 0.002), whereas both ML and ML-AA increased it. All procedures significantly decreased glottal gap, with the most dramatic effects observed after ML-AA (P = 0.004).

CONCLUSIONS

ML-AA led to the greatest improvements in phonatory parameters. IL was comparable to ML aerodynamically and acoustically, but caused detrimental changes to the mucosal wave. Incremental improvements in parameters recorded from the same larynx were observed after ML and ML-AA. To ensure optimal acoustic outcome, the arytenoid must be correctly rotated. This study provides objective support for the combined ML-AA procedure in tolerant patients.

Modeling source-filter interaction in belting and high-pitched operatic male singing

Nonlinear source-filter theory is applied to explain some acoustic differences between two contrasting male singing productions at high pitches: operatic style versus jazz belt or theater belt. Several stylized vocal tract shapes (caricatures) are discussed that form the bases of these styles. It is hypothesized that operatic singing uses vowels that are modified toward an inverted megaphone mouth shape for transitioning into the high-pitch range. This allows all the harmonics except the fundamental to be "lifted" over the first formant. Belting, on the other hand, uses vowels that are consistently modified toward the megaphone (trumpet-like) mouth shape. Both the fundamental and the second harmonic are then kept below the first formant. The vocal tract shapes provide collective reinforcement to multiple harmonics in the form of inertive supraglottal reactance and compliant subglottal reactance. Examples of lip openings from four well-known artists are used to infer vocal tract area functions and the corresponding reactances.

Phonation threshold flow measurements in normal and pathological phonation

OBJECTIVES/HYPOTHESIS

Phonation threshold flow (PTF) may provide a tool to assess laryngeal function and could differentiate between normal and pathological voices. Both polyps and nodules contribute to an increased PTF by creating an incomplete glottal closure and increased vocal fold mass and thickness.

STUDY DESIGN

Prospective study.

METHODS

The Kay Elemetrics Phonatory Aerodynamic System (PAS) (Kay Elemetrics Corp., Lincoln Park, NJ) was used to collect mean flow rate (MFR) and PTF measurements from 40 normal subjects, 21 patients with vocal fold nodules, and 23 patients with vocal fold polyps. Gender-based differences were assessed using a t test. The effect of vocal pathology on PTF and MFR was determined with an ANOVA. Diagnostic potential was evaluated using a receiver operation characteristics (ROC) analysis.

RESULTS

Both PTF (P = .047) and MFR (P = .008) were significantly affected by gender. Using a two-way ANOVA and correcting for gender differences, the influence of pathology on PTF was determined to be significant (P < .001). Post hoc tests found a significant difference between normal and polyp subjects (P < .001) but not normal and nodule subjects (P = .177) or nodule and polyp subjects (P = .246). ROC analysis found that PTF (area under the curve [AUC] = 0.691) and MFR (AUC = 0.684) had a similar diagnostic utility.

CONCLUSIONS

PTF can be used to differentiate between normal and pathological voices. As a parameter that is experimentally sensitive to the biomechanical parameters providing its theoretical basis, it could be used clinically to analyze laryngeal functionality. Future research could focus on measuring PTF in other pathologies, such as paralysis or scarring, which would also affect the effort required to produce voice.

Effect of dehydration on phonation threshold flow in excised canine larynges

OBJECTIVES

The minimum airflow necessary to initiate stable vocal fold vibration--phonation threshold flow (PTF)--may increase as exposure to dry air increases. A critical period of dehydration may exist after which phonation can no longer be initiated.

METHODS

We collected PTF data for 11 excised canine larynges mounted on a bench apparatus. Trials consisted of cycles of 10 seconds of phonation followed by 3 seconds of rest. During the experimental trials, subglottal flow of comparatively dry air was increased until phonation was initiated, and phonation was sustained for the remainder of the 10-second period. The subglottal flow was then decreased until phonation ceased. No saline solution was applied during the dehydration trials. During the control trials, subglottal airflow was humidified and saline solution was applied frequently to the vocal folds.

RESULTS

The PTF increased as exposure to dry air increased during the experimental trials (p = 0.010); this relationship was not statistically significant in control trials. A point existed after which phonation could not be initiated.

CONCLUSIONS

Knowledge of the effect of exposure to dry air on PTF could be useful in the clinical assessment and prevention of dehydration. Further exploration of this relationship in vivo could be used to evaluate the effectiveness of current hydration therapies and provide theoretical support for the development of new ones.

A computational study of the effect of false vocal folds on glottal flow and vocal fold vibration during phonation

The false vocal folds are believed to be components of the acoustic filter that is responsible for shaping the voice. However, the effects of false vocal folds on the vocal fold vibration and the glottal aerodynamic during phonation remain unclear. This effect has implications for computational modeling of phonation as well as for understanding laryngeal pathologies such as glottal incompetence resulting from unilateral vocal fold paralysis. In this study, a high fidelity, two-dimensional computational model, which combines an immersed boundary method for the airflow and a continuum, finite-element method for the vocal folds, is used to examine the effect of the false vocal folds on flow-induced vibration (FIV) of the true vocal folds and the dynamics of the glottal jet. The model is notionally based on a laryngeal CT scan and employs realistic flow conditions and tissue properties. Results show that the false vocal folds potentially have a significant impact on phonation. The false vocal folds reduce the glottal flow impedance and increase the amplitude as well as the mean glottal jet velocity. The false vocal folds also enhance the intensity of the monopole acoustic sources in the glottis. A mechanism for reduction in flow impedance due to the false vocal folds is proposed.

Phonation threshold flow in elongated excised larynges

OBJECTIVES

This study proposes the use of a new parameter of vocal aerodynamics, phonation threshold flow (PTF). The sensitivities of the PTF and the phonation threshold pressure (PTP) were quantitatively compared to the percent of vocal fold elongation from physiologic length.

METHODS

Ten excised canine larynges were mounted on a bench apparatus capable of controlling vocal fold elongation. Subglottal airflow was gradually increased until the onset of phonation. Elongation of the vocal folds was varied from +0% (physiologic length) to +15%, and the PTF and PTP were measured.

RESULTS

The mean PTFs at physiologic vocal fold length ranged from 101 to 217 mL/s. No statistically significant relationship was found to exist between the size of the larynx and the measured PTF values (p = .404). The average percent change of PTF compared to the magnitude of elongation was found to be statistically significant (p < .001). The data indicated that the PTF was proportional to the percent of vocal fold elongation.

CONCLUSIONS

The PTF was positively correlated with vocal fold elongation and the PTP for small magnitudes of elongation. The results suggest that the PTF may be indicative of the biomechanical properties of the vocal folds, thus providing a possibly valuable tool in the clinical evaluation of laryngeal function.

Onset and offset phonation threshold flow in excised canine larynges

OBJECTIVES/HYPOTHESIS

In this study, we examined the hypothesis that the minimum flow required for phonation onset, the onset phonation threshold flow (PTF), is greater than the minimum flow to sustain phonation, the offset PTF. We also explored the hypothesis that the ratio of these two (PTF offset divided by PTF onset) falls within [0.707, 1.0].

STUDY DESIGN

This was a methodology study to measure onset and offset PTFs in 10 excised canine larynges; their ratio (PTF offset divided by PTF onset) was predicted to fall in a specific domain.

METHODS

The onset and offset PTF and phonation threshold pressure (PTP) values were observed using 10 excised canine larynges mounted on a bench apparatus. The subglottal flow was increased until phonation was observed, and then decreased until phonation ceased; airflow and pressure measurements at critical conditions of phonation were observed as the PTF and PTP. Larynges with elongated vocal folds were then tested to observe PTF and determine if the hypothesis was observed in pathologic-like larynges.

RESULTS

The offset PTF was always less than the onset PTF (P << .0001) and 80.0% of the observed onset-offset PTF ratios were bound by [0.707, 1.0].

CONCLUSIONS

PTF onset or offset could be a useful diagnostic parameter of the voice, particularly when used in conjunction with PTP to describe laryngeal resistance and aerodynamic power. Further exploration of the relationship between onset and offset PTF values could augment clinical diagnostic ability and advance current theories on the physics of phonation.

Voice assessment: updates on perceptual, acoustic, aerodynamic, and endoscopic imaging methods

PURPOSE OF REVIEW

This paper describes recent advances in perceptual, acoustic, aerodynamic, and endoscopic imaging methods for assessing voice function.

RECENT FINDINGS

We review advances from four major areas. PERCEPTUAL ASSESSMENT: Speech-language pathologists are being encouraged to use the new consensus auditory-perceptual evaluation of voice inventory for auditory-perceptual assessment of voice quality, and recent studies have provided new insights into listener reliability issues that have plagued subjective perceptual judgments of voice quality. ACOUSTIC ASSESSMENT: Progress is being made on the development of algorithms that are more robust for analyzing disordered voices, including the capability to extract voice quality-related measures from running speech segments. AERODYNAMIC ASSESSMENT: New devices for measuring phonation threshold air pressures and air flows have the potential to serve as sensitive indices of glottal phonatory conditions, and recent developments in aeroacoustic theory may provide new insights into laryngeal sound production mechanisms. ENDOSCOPIC IMAGING: The increased light sensitivity of new ultra high-speed color digital video processors is enabling high-quality endoscopic imaging of vocal fold tissue motion at unprecedented image capture rates, which promises to provide new insights into the mechanisms of normal and disordered voice production.

SUMMARY

Some of the recent research advances in voice function assessment could be more readily adopted into clinical practice, whereas others will require further development.

Nonlinear source-filter coupling in phonation: theory

A theory of interaction between the source of sound in phonation and the vocal tract filter is developed. The degree of interaction is controlled by the cross-sectional area of the laryngeal vestibule (epilarynx tube), which raises the inertive reactance of the supraglottal vocal tract. Both subglottal and supraglottal reactances can enhance the driving pressures of the vocal folds and the glottal flow, thereby increasing the energy level at the source. The theory predicts that instabilities in vibration modes may occur when harmonics pass through formants during pitch or vowel changes. Unlike in most musical instruments (e.g., woodwinds and brasses), a stable harmonic source spectrum is not obtained by tuning harmonics to vocal tract resonances, but rather by placing harmonics into favorable reactance regions. This allows for positive reinforcement of the harmonics by supraglottal inertive reactance (and to a lesser degree by subglottal compliant reactance) without the risk of instability. The traditional linear source-filter theory is encumbered with possible inconsistencies in the glottal flow spectrum, which is shown to be influenced by interaction. In addition, the linear theory does not predict bifurcations in the dynamical behavior of vocal fold vibration due to acoustic loading by the vocal tract.

The phonation critical condition in rectangular glottis with wide prephonatory gaps

The effect of the pressure recovery at glottal exit is introduced to modify the one-mass model. Using the modified one-mass model, the phonation critical condition, including phonation threshold pressure and phonation threshold flow, is analyzed by using the small-amplitude oscillation theory. It is found that the phonation threshold pressure is not sensitive to the change of the prephonatory glottal width at a wide glottal gap. This result agrees with previous experimental observations and suggests that the low slope of dependence of phonation threshold pressure on prephonatory gap found by Chan and Titze [J. Acoust. Soc. Am. 119, 2351-2362 (2006)] could be a consequence of the pressure recovery effect at the glottal exit. In addition, it is predicted that the phonation threshold flow is always significantly increased with the prephonatory gap even at a wide prephonatory glottal gap. Therefore, the phonation threshold flow has an advantage in assessing the phonatory system at a wide prephonatory gap in comparison with the phonation threshold pressure. The phonation threshold flow can be a useful aerodynamic parameter for pathological conditions in which the incomplete glottal gap is often seen.

Comparing phonation threshold flow and pressure by abducting excised larynges

OBJECTIVES/HYPOTHESIS

This experiment studied a new aerodynamic parameter, phonation threshold flow, along with phonation threshold pressure, by varying prephonatory glottal width in canine larynges ex vivo. Goals were to examine phonation threshold flow as a measurable parameter sensitive to physiologic changes in the vocal folds and compare the relative sensitivities of phonation threshold flow and phonation threshold pressure.

METHODS

Ten excised canine larynges were tested on a bench apparatus for subglottal pressure and airflow at phonation onset. Metal shims simulated abduction levels ranging from 0.0 to 4.0 mm. For each glottal configuration, airflow through the larynx was increased until the vocal folds began vibrating, and onset airflow and pressures were recorded.

RESULTS

One-way analysis of variance (ANOVA) found significant differences in the aggregate phonation threshold flow means over the latter portion of the width domain (1.0-4.0 mm). Phonation threshold flow increased as posterior glottal width increased and was modeled linearly. One-way ANOVA of phonation threshold pressure means was insignificant, with a P value of .941.

CONCLUSION

Results showed phonation threshold flow to be more sensitive to posterior glottal width changes than phonation threshold pressure. Therefore, phonation threshold flow could be a more effective indicator than phonation threshold pressure for those vocal diseases related to abduction.