Phonation threshold pressure measurements during phonation by airflow interruption

The Effects of Hard Voice Onset on Objective Voice Function in Patients With Laryngopharyngeal Reflux

OBJECTIVE

Laryngopharyngeal reflux (LPR) causes laryngopharyngeal hypersensitivity and laryngeal muscle hyperfunction, which may result in hard voice onset in patients with LPR. The purpose of this study is to examine the incidence of hard voice onset in patients with LPR and the effects of hard voice onset on objective voice function in patients with LPR.

METHODS

Forty patients with confirmed LPR were enrolled in the LPR group, and 40 healthy subjects were enrolled in the non-LPR group. Subjects underwent laryngeal high-speed videoendoscopy, and the presence or absence of hard voice onset in each subject was determined by two experienced laryngologists based on whether glottal closure was complete or incomplete before vocal fold vibration. Based on the results, the subjects with LPR were divided into a hard voice onset group and a non-hard voice onset group. The voice onset time (VOT) was measured and compared between the hard and non-hard voice onset groups within the LPR group. Laryngeal aerodynamic assessment was also carried out on the LPR group, and subglottal pressure, phonation threshold pressure (PTP), glottal resistance, and mean flow rate were measured. The voice acoustic signals of subjects were additionally analyzed in the LPR group, and the fundamental frequency, jitter, shimmer, and noise-harmony ratio were determined. The kappa statistic, chi-square test and independent-samples t test in SPSS were used for statistical analysis.

RESULTS

The two laryngologists had substantial inter-rater consistency on the evaluation of hard voice onset and non-hard voice onset, with a kappa statistic of 0.71. In the LPR group, 42.5% of patients had hard voice onset (17/40), significantly more than in the non-LPR group (8/40, 20%) (P < 0.05). The VOT in the LPR group was significantly longer than in the non-LPR group (P < 0.05). Within the LPR group, the VOT, PTP and shimmer were significantly greater in the hard voice onset group than in the non-hard voice onset group (all P < 0.05). The other laryngeal aerodynamic parameters and acoustic parameters were not significantly different between the hard voice onset group and the non-hard voice onset group (P > 0.05).

CONCLUSION

Changes in vocal production may occur in LPR patients, causing them to be more susceptible to hard voice onset. The patients with hard voice onset require longer VOT and greater PTP to initiate phonation.

Varying Supraglottic Pressure Using Controlled Supraglottic Pressure Phonation with a Straw-Shaped Mouthpiece in Healthy Subjects

OBJECTIVE

The objective of this study is to expand on a novel method for semioccluded vocal tract therapy (SOVT) called controlled supraglottic pressure phonation, and investigate the mechanism that introduced supraglottic pressure mediates a decrease in impedance during SOVT therapy. Instead of the previously used CPAP mask, this study analyzes controlled supraglottic pressure phonation by use of a straw mouthpiece to deliver supraglottic pressure.

METHODS

Twenty-six human subjects were randomly assigned to one of four supraglottic pressure levels: 0, 2, 4, and 6 cm H2O, which were controlled through a continuous positive airway pressure device. Subjects were asked to phonate during a SOVT task for one round (referred to as the "short-duration" task) and eight rounds (referred to as the "long-duration" task), in which acoustic and aerodynamic properties were measured before and after. Subjects were surveyed for the levels of discomfort experienced during controlled supraglottic pressure phonation therapy and subjective levels of improvement of vocal economy.

RESULTS

Significant differences were observed between pre- and post-task measurement for phonation threshold pressure for the long-duration task for the 2 cmH2O group. Frequency measurement was not found to have statistically significant differences. The perceived phonatory effort was not significantly different at any pressure levels.

CONCLUSIONS

Lower supraglottic pressure levels will improve ease of phonation for longer durations, however, shorter-duration tasks will not be effective. Controlled supraglottic pressure phonation coupled with straw phonation may produce an improved vocal economy for those who have access to an oppositional airflow setup.

Identification and analysis of Nonlinear behaviors of vocal fold biomechanics during phonation to assess efficacy of surgery for benign laryngeal Diseases

BACKGROUND

Current voice assessments focus on perceptive evaluation and acoustic analysis. The interaction of vocal tract pressure (PVT) and vocal fold (VF) vibrations are important for volume and pitch control. However, there are currently little non-invasive ways to measure PVT. Limited information has been provided by previous human trials, and interactions between PVT and VF vibrations and the potential clinical application remain unclear. Here, we propose a non-invasive method for monitoring the nonlinear characteristics of PVT and VF vibrations, analyze voices from pathological and healthy individuals, and evaluate treatment efficacy.

METHOD

Healthy volunteers and patients with benign laryngeal lesions were recruited for this study. PVT was estimated using an airflow interruption method, VF vibrational frequency was calculated from accelerometer signals, and nonlinear relationships between PVT and VF vibrations were analyzed. Results from healthy volunteers and patients, as well as pre- and post-operation for the patients, were compared.

RESULTS

For healthy volunteers, nonlinearity was exhibited as an initial increase and then prompt decrease in vibrational frequency at the end of phonation, coinciding with PVT equilibrating with the subglottal pressure upon airflow interruption. For patients, nonlinearity was present throughout the phonation period pre-operatively, but showed a similar trend to healthy volunteers post-operatively.

CONCLUSION

This novel method simultaneously monitors PVT and VF vibration and helps clarify the role of PVT. The results demonstrate differences in nonlinear characteristics between healthy volunteers and patients, and pre-/post-operation in patients. The method may serve as an analysis tool for clinicians to assess pathological phonation and treatment efficacy.

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.

Optimizing Aerodynamic Vocal Parameters by Varying Supraglottic Pressure Using "Controlled Supraglottic Pressure Phonation" in Healthy Subjects

OBJECTIVE

The objective of this study is to introduce a novel method for semi-occluded vocal tract (SOVT) therapy called "controlled supraglottic pressure phonation," determine the mechanism by which supraglottic pressure contributes to lowering impedance during SOVT therapy, and provide the optimal supraglottic pressure range for SOVT exercises.

METHODS

Twenty-five human subjects were assigned to one of five supraglottic pressure levels, 0, 2, 4, 6, and 8 cmH2O, which were controlled through a continuous positive airway pressure device. Subjects were asked to phonate during both a short- and long-duration task, in which vocal properties were measured before and after. At the end of each task, the subjects reported the levels of discomfort and phonation difficulty on a 0-10 scale to assess the subjective improvement of vocal economy.

RESULTS

Significant differences were observed between pre- and post-task measurements for phonation threshold pressure for both the short-duration and long-duration tasks. Phonation threshold flow and frequency measurements were found to have no statistically significant differences. The subjective measures showed elevated discomfort in the higher pressure inputs for both tasks relative to no air.

CONCLUSION

Higher supraglottic pressure levels will improve ease of phonation, but the treatment discomfort needs to be considered as well, yielding an optimal supraglottic pressure range of 4-6 cmH2O. "Controlled supraglottic pressure phonation" serves as an alternative to straw phonation that may produce additional benefits.

Scoping review of the relationship between xerostomia and voice quality

PURPOSE

This scoping review aims to synthesize all of the currently available information on how xerostomia correlates with vocal function and the mechanisms that underpin it.

METHODS

Our scoping review used PubMed, Scopus, Embase, and Web of Science databases to review articles published between January 1999 and July 2022 in accordance with the PRISMA-ScR guidelines. In addition to the academic databases, we also conducted a manual search of Google Scholar. Further investigation was conducted on studies that examined the relationship between xerostomia and vocal function.

RESULTS

Of the 682 initially identified articles, 21 met our inclusion criteria. Among the included studies, two articles (n = 2) revealed the mechanistic relationship between xerostomia and vocal function. Most studies (n = 12) focused on xerostomia secondary to other underlying conditions or treatments, among which radiotherapy and Sjögren's syndrome were commonly investigated. Seven studies (n = 7) provided details about common vocal parameters measured in studies of xerostomia and the voice.

CONCLUSION

The literature currently lacks publications regarding the relationship between xerostomia and vocal function. Most of the studies included in this review were about xerostomia secondary to other conditions or medical treatments. Therefore, the impacts on the voice that were observed were very multifaceted and the role of xerostomia alone in phonation could not be ascertained. Nevertheless, it is clear that dryness in the mouth plays some role in vocal function and further research should focus on clarifying and finding the underlying mechanism behind this relationship by incorporating high-speed imaging and cepstral peak prominence analyses.

Effects of surgery on the relationship between subglottic pressure and fundamental frequency in vocal fold dynamics in patients with benign laryngeal diseases

PURPOSE

Subglottic pressure (P_s) and fundamental frequency (F₀) play important roles in governing vocal fold (VF) dynamics. Theoretical description, model simulation, excised larynx and animal models have been used in previous studies, yet clinically applicable measurements are still lacking. This study aimed to evaluate the effects of surgery for benign laryngeal lesions by investigating the relationship between F₀ and P_s.

METHODS

Patients with benign laryngeal lesions who underwent phonosurgery were prospectively recruited. Participants were instructed to sustain voicing the vowel /o/ at three incremental frequencies four semitones apart in the modal register (F01, F02, F03). F₀ was estimated by VF vibration on the accelerometer. P_s change was achieved and measured using the airflow interruption method.

RESULTS

Thirteen patients with a mean age (SD) of 43.5 (12.4) years were included. The change in F₀ per unit change of P_s, which is the slope (Hz/kPa) of the regression line of the frequency-pressure data pairs, decreased as the tension of the VF increased. The slopes significantly increased after the operation for F01 and F02 (36.43 ± 14.68 preoperatively, 53.91 ± 30.71 postoperatively, p = 0.011 and 26.02 ± 10.71; 34.85 ± 17.92, p = 0.046, respectively). In addition, there was a significant decrease in phonation threshold pressure and improvements in the grade, roughness, breathiness, asthenia, strain scale, and the voice handicap inventory-10.

CONCLUSIONS

The relationship between F₀ and P_s may serve as an objective assessment of the outcomes in the treatment of benign laryngeal diseases with clinical relevance.

Variability in Voice Characteristics of Female Speakers With Phonotraumatic Vocal Fold Lesions

OBJECTIVE

To examine the variability of lesion characteristics and vocal function in female speakers with phonotraumatic vocal fold lesions (PVFLs).

STUDY DESIGN

Prospective Cohort Study METHODS: Thirty adult female speakers with PVFL who were participating in voice therapy were recruited to complete a multidimensional voice analysis at four time points across 1 month. Analysis comprised self-ratings of effort and vocal function, expert ratings of videostroboscopy and audio recordings, and instrumental evaluation by selected aerodynamic and acoustic parameters. The degree of variability across time for each individual was assessed against a minimal clinically important difference threshold.

RESULTS

A high degree of variability across time was observed for participant self-ratings of perceived effort and vocal function, and for instrumental parameters. The greatest degree of variability was observed in aerodynamic measures of airflow and pressure, and the acoustic parameter semitone range. Comparatively less variability was observed in perceptual evaluation of speech, and lesion characteristics via stroboscopy still images. Findings suggest that individuals with all PVFL types and sizes present with variability in function across time, with the greatest degree of variability in function observed in participants with large lesions and vocal fold polyps.

CONCLUSION

Variability is observed in voice characteristics of female speakers with PVFLs across 1 month despite general stability in lesion presentation, suggesting vocal function can change despite the presence of laryngeal pathology. This study highlights the need to explore individual functional and lesion responses across time to determine potential for change and improvement in both aspects when selecting treatment options.

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.

Age and Sex Comparison of Aerodynamic Phonation Measurements Using Noninvasive Assessment

Purpose The goal of this study was to present vocal aerodynamic measurements from pediatric and adult participant pools. There are a number of anatomical changes involving the larynx and vocal folds that occur as children age and become adults. Data were collected using two methods of noninvasive aerodynamic assessment: mechanical interruption and labial interruption. Method A total of 154 participants aged 4-24 years old took part in this study. Ten trials were performed for both methods of airway interruption. To perform mechanical interruption, participants phonated /α/ for 10 s trials while a balloon valve interrupted phonation 5 times. For labial interruption, participants said /pα/ 5 times at comfortable and quiet volumes. Aerodynamic measures included subglottal pressure, phonation threshold pressure, mean airflow, laryngeal resistance, and others. Results One hundred one participants (51 females) successfully completed testing with both methods. Eight out of 20 measurements were found to have a statistically significant effect of participant age on measurements. Sex alone had a significant effect on vocal efficiency for the labial quiet method. Conclusions The data discussed here can be used to view age and sex trends in vocal aerodynamic measurements. When using either method of mechanical or labial interruption, participant age needs to be taken into account to properly interpret several aerodynamic parameters. A participant's sex is not as important when using these methods.

The Feasibility of Gastroesophageal Manometry for Continuously Evaluating the Degree of Expiratory Effort During Successful Crescendo Phonation

OBJECTIVES

This study aimed to assess the feasibility of gastroesophageal manometry for continuously evaluating the degree of expiratory effort by measuring the pressures in the digestive tract during crescendo phonation.

METHODS

Each of 18 healthy nondysphonic speakers had a probe with a four-channel gastroesophageal manometer inserted through the nasal cavity to place four pressure sensors in the hypopharynx, cervical-/thoracic esophagus, and stomach, and was asked to gradually increase the vocal loudness during sustained phonation of the vowel /e:/ (vowel-crescendo task), while the sound pressure level and the pressures were simultaneously recorded.

RESULTS

50% of the successful vowel-crescendo task samples with a gradual and adequate sound pressure level increase showed a concomitant gradual increase in both the intra-thoracic-esophageal/intra-gastric pressure values from approximately -5 mmHg /6 mmHg to -10 mmHg/20 mmHg, respectively. The maximum pressure value was the highest in the intra-gastric pressure followed by the intra-thoracic-esophageal and intra-cervical-esophageal pressures in order. However, most of the samples showed less than one of atypical pressure changes, such as fluctuations in the intra-thoracic-esophageal and intra-gastric pressure changes and dispersion in the intra-cervical-esophageal and intra-hypopharyngeal pressure values (perhaps due to the peristaltic motions, and the contact of the sensors to the membranous wall).

CONCLUSION

These results show that, during successful crescendo phonation, gastroesophageal manometry reveals a gradual increase in the intra-thoracic and intra-abdominal pressures with increasing the vocal intensity, even though showing some systematic errors, suggesting the usefulness of gastroesophageal manometry for continuously evaluating the degree of expiratory effort without influence by the laryngeal condition.

Estimating vocal fold stiffness: Using the relationship between subglottic pressure and fundamental frequency of phonation as an analog

OBJECTIVE

The stiffness of the vocal folds is an important factor in voice production, yet clinically applicable measurements are still lacking. It has been demonstrated in an in vivo canine model that fundamental frequency (F₀ ) increased linearly as subglottic pressure (P_s ) increased, but with a lesser slope for higher levels of vocal fold tension. In this study, the relationship between F₀ and P_s was investigated using the airflow interruption method in awake patients non-invasively.

DESIGN

Healthy volunteers enrolled for evaluation.

SETTING

Single-centre.

PARTICIPANTS

Thirty-three healthy volunteers aged 20 and older were recruited, with one excluded for a recent asthma attack.

MAIN OUTCOME MEASURES

The relationships between F₀ and P_s , described as the slope (Hz/kPa), were investigated when the participants sustained voicing the vowel/o/at 3 incremental frequencies 4 semitones apart in the modal register (F1, F2 and F3).

RESULTS

Thirty-two healthy volunteers (20 females, 12 males) aged 20-47 years were enrolled for final analyses. There was a statistically significant difference in the slopes of the linear regression lines of F₀ -P_s , depending on the frequency with which the vowel/o/ was produced (P < .001). The slope differed significantly between F2 and F1 (P < .001; P = .015), F3 and F1 (P < .001; P = .002) and F3 and F2 (P < .001; P = .005) for both women and men, respectively.

CONCLUSIONS

It was demonstrated that the higher the vocal fold tension, the smaller the slope between F₀ and P_s . Using the relationship between F₀ and P_s as an analog of vocal fold stiffness is potentially practical for clinical application.

Intraglottal Aerodynamics at Vocal Fold Vibration Onset

The most frequently observed type of voice onset in spontaneous speech in normal subjects is the soft onset, and it may be considered as the "physiological" onset. It starts from an immobile narrow glottal slit crossed by a continuous airflow, and then a few oscillations (even a single one in some cases) precede the first glottal closure. It is a transient event, during which the acting forces, lung pressure, intraglottal pressure, myoelastic tension of the vocal fold (VF) oscillator and inertance of the supraglottal vocal tract, interact to progressively reach the steady state of a sustained oscillation. Combined measurements of flow, area, and pressure provide a detailed qualitative and quantitative analysis of the intraglottal mechanical events at the precise moment of starting oscillation in a physiological (soft or soft/breathy) onset. Our in vivo measurements of airflow and glottal area show that the very first oscillation occurs exactly at the time when turbulence appears at the level of the glottal narrowing, ie, when the Reynolds number reaches its critical value. The turbulence may be assumed to trigger an oscillator consisting in the ensemble of the VFs and the air of the vocal tract, which is known to be weakly damped. Turbulence can act here as an aspecific flick, triggering the oscillator, the frequency of oscillation being determined by its mechanical properties. Furthermore, the first noticeable glottal oscillations are sinusoidal: the VFs are neither steeply sucked together by a negative Bernoulli pressure, nor burst apart by the lung pressure. Our measurements show that, at the critical time, the rising positive lung pressure is balanced by the rising negative Bernoulli pressure generated by the transglottal flow.

Measurement reliability of phonation threshold pressure in pediatric subjects

OBJECTIVES/HYPOTHESIS

Phonation threshold pressure (PTP), the minimum subglottal pressure (P_s ) required for phonation, is sensitive to changes in laryngeal biomechanics and is often elevated with pathology. Little is reported on PTP in children; challenges with task performance and measurement reliability represent barriers to routine clinical assessment.

STUDY DESIGN

Pilot study evaluating PTP and P_s measurement reliability in children using labial and mechanical interruption.

METHODS

Twenty-two subjects aged 4 to 17 years (10.7 ± 3.9 years) participated. Ten trials were performed for each method; task order was randomized. For labial interruption, subjects produced /pα/ five times at softest (onset PTP) and comfortable amplitude. For mechanical interruption, subjects produced a sustained /α/ while a balloon valve interrupted phonation five times for 250 ms each; mechanical interruption was performed with a mouthpiece and mask. PTP was recorded as the difference between P_s and supraglottal pressure at phonation cessation (offset PTP). Mean PTP and P_s and intrasubject coefficients of variation were compared. Correlations with age were evaluated.

RESULTS

Mean PTP (P < .001) and P_s (P = .005) were higher for labial interruption. Intrasubject coefficients of variation for PTP (P = .554) and P_s (P = .305) were similar across methods. Coefficient of variation was related to age for mechanical-mask trials only (r = -0.628, P = .00175).

CONCLUSIONS

Differences in means are likely related to differences in task and PTP hysteresis effect. Reliability is comparable with all methods; using a mouthpiece may be preferable to a mask for mechanical interruption. Measurement of PTP is noninvasive, reliable, and may be a useful adjunct in pediatric voice assessment.

LEVEL OF EVIDENCE

3b Laryngoscope, 129:1520-1526, 2019.

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.

Evaluation of an asymmetric anterior glottic web in an excised canine larynx model

The main objective of the study is to model asymmetry within anterior glottic webs in excised larynges using sutures and apply aerodynamic and acoustic analyses. Anterior glottic webs (AGW) were modeled in eight excised larynges using sutures secured at the level of the glottis to mimic the scar tissue of the web. Each of the eight larynges were tested under three different pressure increments for each of the three models of AGW: symmetric, vertically asymmetric, and laterally asymmetric. Phonation threshold pressure (PTP) and flow (PTF) differed significantly across AGW conditions (p = 0.006 and p = 0.005, respectively). Additionally, vocal efficiency was significantly different among conditions (p = 0.005) as well as significantly lower in the asymmetric groups (p = 0.015 and p = 0.007). Perturbation measures were not significantly different across conditions. Correlation dimension (D2) was significantly different at PTP, 1.25 × PTP, and 1.5 × PTP (p = 0.003, p = 0.010, and p < 0.001, respectively) as well as significantly higher in the asymmetric groups at each pressure increment. The increased PTP, PTF, and D2 values as well as decreased vocal efficiency among the asymmetric conditions indicates a significant decrease in vocal function, and thus represents that asymmetries could be a contributing factor to the pathological symptoms associated with glottic webs.

Receiver Operating Characteristic Analysis of Aerodynamic Parameters Obtained by Airflow Interruption: A Preliminary Report

Aerodynamic parameters provide objective and quantitative measures of laryngeal functional status. Jiang et al previously introduced an airflow interruption technique that can determine mean phonatory airflow, subglottic pressure, and phonation threshold pressure simultaneously and noninvasively. In this study, we performed receiver operating characteristic (ROC) analysis to evaluate this airflow interruption apparatus for voice profile analysis in subjects with laryngeal polyps or nodules or with Parkinson's disease. Patients with polyps (n = 14), nodules (n = 9), and Parkinson's disease (n = 12) were evaluated with the airflow interruption apparatus. Normal subjects served as controls. Mean airflow, subglottic pressure, and phonation threshold pressure were determined. Discriminant analysis was used to create linear equations combining all three parameters in order to obtain a new combined parameter. Solutions to the linear equations yielded values for the combined parameter that took into account mean airflow, subglottic pressure, and phonation threshold pressure. Combined parameter values were used as data to generate ROC curves. Laryngeal polyps were distinguished from the normal larynx with a sensitivity of 0.929 and a specificity of 0.933 at the point of maximal efficiency. The area under the ROC curve was 0.977 (Az). Patients with Parkinson's disease were distinguished from normal subjects with a sensitivity of 0.667 and a specificity of 0.909 at the point of maximal efficiency. The area under the ROC curve was 0.7958 (Az). Nodules were able to be distinguished from normal with a sensitivity of 0.889 and a specificity of 1.00. The area under the ROC curve was 0.9565 (Az). Our conclusions are twofold. First, aerodynamic parameters may be combined for simultaneous consideration by the construction of linear equations by means of discriminant analysis. Second, the airflow interruption apparatus, when used for voice function evaluation, has high sensitivity and specificity.

Vocal Efficiency Measurements in Subjects with Vocal Polyps and Nodules: A Preliminary Report

Vocal efficiency is a quantitative measure of the ability of the larynx to convert subglottal power to acoustic power. On the basis of the scant previous literature and clinical intuition, we tested the hypothesis that vocal efficiency, as an indicator of the functional status of the larynx, is abnormally reduced in persons with vocal nodules and polyps. Because the most difficult aspect of obtaining measures of vocal efficiency has been the determination of subglottal pressure, we applied a noninvasive airflow interruption technique for this purpose. Subjects with normal voices (n = 22), vocal polyps (n = 14), and vocal nodules (n = 16) phonated at different intensities into a mask connected by way of piping to a flow meter, a pressure transducer, and an acoustic microphone. Inflation of a balloon-type valve located within the piping provided interruption of phonation. The intraoral pressure plateau occurring during flow interruption was used to estimate subglottal pressure. Subglottal power and acoustic power were determined, and their quotient provided a measure of vocal efficiency. The vocal efficiency in the normal subjects averaged 1.15 × 10−5 at 70 dB, 3.17 × 10−5 at 75 dB, 7.52 × 10−5 at 80 dB, and 1.41 × 10−4 at 85 dB. The vocal efficiency in the patients with vocal polyps averaged 3.62 × 10−6 at 70 dB, 8.34 × 10−6 at 75 dB, 2.10 × 10−5 at 80 dB, and 4.26 × 10−5 at 85 dB. The vocal efficiency in the patients with vocal nodules averaged 4.32 × 10−6 at 70 dB, 1.57 × 10−5 at 75 dB, 4.26 × 10−5 at 80 dB, and 8.34 × 10−5 at 85 dB. As compared to the normal subjects, the patients with laryngeal polyps or vocal nodules had significantly reduced vocal efficiency. These results provide quantitative verification of the clinical impression of inefficient phonation in patients with mass lesions of the vocal folds.

Evaluation of type II thyroplasty on phonatory physiology in an excised canine larynx model

OBJECTIVES/HYPOTHESIS

Type II thyroplasty is an alternative treatment for spasmodic dysphonia, addressing hyperadduction by incising and lateralizing the thyroid cartilage. We quantified the effect of lateralization width on phonatory physiology using excised canine larynges.

METHODS

Normal closure, hyperadduction, and type II thyroplasty (lateralized up to 5 mm at 1-mm increments with hyperadducted arytenoids) were simulated in excised larynges (N = 7). Aerodynamic, acoustic, and videokymographic data were recorded at three subglottal pressures relative to phonation threshold pressure (PTP). One-way repeated measures analysis of variance assessed effect of condition on aerodynamic parameters. Random intercepts linear mixed effects models assessed effects of condition and subglottal pressure on acoustic and videokymographic parameters.

RESULTS

PTP differed across conditions (P < .001). Condition affected percent shimmer (P < .005) but not percent jitter. Both pressure (P < .03) and condition (P < .001) affected fundamental frequency. Pressure affected vibratory amplitude (P < .05) and intrafold phase difference (P < .05). Condition affected phase difference between the vocal folds (P < .001).

CONCLUSIONS

Hyperadduction increased PTP and worsened perturbation compared to normal, with near normal physiology restored with 1-mm lateralization. Further lateralization deteriorated voice quality and increased PTP. Acoustic and videokymographic results indicate that normal physiologic relationships between subglottal pressure and vibration are preserved at optimal lateralization width, but then degrade with further lateralization. The 1-mm optimal width observed here is due to the small canine larynx size. Future human trials would likely demonstrate a greater optimal width, with patient-specific value potentially determined based on larynx size and symptom severity.

LEVEL OF EVIDENCE

NA Laryngoscope, 2016 127:396-404, 2017.

Central Nervous System Control of Voice and Swallowing

This review of the central nervous control systems for voice and swallowing has suggested that the traditional concepts of a separation between cortical and limbic and brain stem control should be refined and be more integrative. For voice production, a separation of the nonhuman vocalization system from the human learned voice production system has been posited based primarily on studies of nonhuman primates. However, recent humans studies of emotionally based vocalizations and human volitional voice production have shown more integration between these two systems than previously proposed. Recent human studies have shown that reflexive vocalization as well as learned voice production not involving speech involve a common integrative system. However, recent studies of nonhuman primates have provided evidence that some cortical activity vocalization and cortical changes occur with training during vocal behavior. For swallowing, evidence from the macaque and functional brain imaging in humans indicates that the control for the pharyngeal phase of swallowing is not primarily under brain stem mechanisms as previously proposed. Studies suggest that the initiation and patterning of swallowing for the pharyngeal phase is also under active cortical control for both spontaneous as well as volitional swallowing in awake humans and nonhuman primates.

An Oral Pressure Conversion Ratio as a Predictor of Vocal Efficiency

Voice production is an inefficient process in terms of energy expended versus acoustic energy produced. A traditional efficiency measure, glottal efficiency, relates acoustic power radiated from the mouth to aerodynamic power produced in the trachea. This efficiency ranges between 0.0001% and 1.0%. It involves lung pressure and hence would appear to be a useful effort measure for a given acoustic output. Difficulty in the combined measurement of lung pressure and tracheal airflow, however, has impeded clinical application of glottal efficiency. This article uses the large data base from Schutte (1980) and a few new measurements to validate a pressure conversion ratio (PCR) as a substitute for glottal efficiency. PCR has the potential for wide application because of low cost and ease of use in clinics and vocal studios.

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.

Vocal exercise may attenuate acute vocal fold inflammation

OBJECTIVES/HYPOTHESES

The objective was to assess the utility of selected "resonant voice" (RV) exercises for the reduction of acute vocal fold inflammation. The hypothesis was that relatively large-amplitude, low-impact vocal fold exercises associated with RV would reduce inflammation more than spontaneous speech (SS) and possibly more than voice rest.

STUDY DESIGN

The study design was prospective, randomized, and double blind.

METHODS

Nine vocally healthy adults underwent a 1-hour vocal loading procedure, followed by randomization to a SS condition, vocal rest condition, or RV exercise condition. Treatments were monitored in clinic for 4 hours and continued extraclinically until the next morning. At baseline (BL), immediately after loading, after the 4-hour in-clinic treatment, and 24 hours post-BL, secretions were suctioned from the vocal folds bilaterally and submitted to enzyme-linked immunosorbent assay to estimate concentrations of key markers of tissue injury and inflammation: interleukin (IL)-1β, IL-6, IL-8, tumor necrosis factor α, matrix metalloproteinase (MMP)-8, and IL-10.

RESULTS

Complete data sets were obtained for three markers--IL-1β, IL-6, and MMP-8--for one subject in each treatment condition. For these markers, results were poorest at 24-hour follow-up in the SS condition, sharply improved in the voice rest condition, and was the best in the RV condition. Average results for all markers and responsive subjects with normal BL mediator concentrations revealed an almost identical pattern.

CONCLUSIONS

Some forms of tissue mobilization may be useful to attenuate acute vocal fold inflammation.

Evaluation of auditory and visual feedback for airflow interruption

INTRODUCTION

Clinical application of mechanical interruption methods for measuring aerodynamic parameters has been hindered by relatively high intrasubject variability. To improve the intrasubject reliability, we evaluated the effect of auditory and visual feedback on subject performance when measuring aerodynamic parameters with the airflow interrupter.

METHODS

Eleven subjects performed four sets of 10 trials with the airflow interrupter: no feedback (control); auditory feedback (tone matching subject's F0 played over headphones); visual feedback (real-time feedback of sound pressure level, frequency, and airflow); and combined auditory and visual feedback. Task order was varied across subjects. The effect of each feedback method on mean and coefficient of variation (CV) of subglottal pressure (Ps), mean flow rate (MFR), and laryngeal airway resistance (RL; Ps/MFR) compared with that of the control trials was determined using paired t tests. Feedback methods were compared against each other using one-way repeated measures analysis of variance.

RESULTS

Each feedback method significantly decreased CV of RL compared with that of the control trials (auditory feedback: P=0.005; visual feedback: P=0.008; and combined feedback: P<0.001). Auditory feedback (P=0.011) and combined feedback (P=0.026) also decreased CV of MFR. Mean MFR was significantly higher during trials with visual feedback compared with that of the auditory feedback.

CONCLUSIONS

Each feedback method improved the intrasubject consistency when measuring RL. Feedback appeared to have a greater effect on MFR than Ps. Although there is no clear optimal feedback method, each is preferable to not providing any feedback during trials. Evaluating new methods of visual feedback to further improve MFR and thus RL measurement would be valuable.

Classification of glottic insufficiency and tension asymmetry using a multilayer perceptron

OBJECTIVE

Laryngeal function can be evaluated from multiple perspectives, including aerodynamic input, acoustic output, and mucosal wave vibratory characteristics. To determine the classifying power of each of these, we used a multilayer perceptron artificial neural network (ANN) to classify data as normal, glottic insufficiency, or tension asymmetry.

STUDY DESIGN

Case series analyzing data obtained from excised larynges simulating different conditions.

METHODS

Aerodynamic, acoustic, and videokymographic data were collected from excised canine larynges simulating normal, glottic insufficiency, and tension asymmetry. Classification of samples was performed using a multilayer perceptron ANN.

RESULTS

A classification accuracy of 84% was achieved when including all parameters. Classification accuracy dropped below 75% when using only aerodynamic or acoustic parameters and below 65% when using only videokymographic parameters.

CONCLUSIONS

Samples were classified with the greatest accuracy when using a wide range of parameters. Decreased classification accuracies for individual groups of parameters demonstrate the importance of a comprehensive voice assessment when evaluating dysphonia.

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.

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.

Noninvasive monitoring of vocal fold vertical vibration using the acoustic Doppler effect

OBJECTIVES/HYPOTHESIS

To validate a proposed method of noninvasively monitoring vocal fold vertical vibration through utilization of the acoustic Doppler effect and the waveguide property of the vocal tract.

STUDY DESIGN

Validation case-control study.

METHODS

In this device, an ultrasound beam is generated and directed into the mouth. The vocal tract, acting as a natural waveguide, guides the ultrasound beam toward the vibrating vocal folds. The vertical velocity of vocal fold vibration is then recovered from the Doppler frequency of the reflected ultrasound. One subject (age 32, male) was studied and measurements were taken under three modes of vocal fold vibration: breathing (no vibration), whispering (irregular vibration), and normal phonation (regular vibration).

RESULTS

The peak-to-peak amplitude of the measured velocity of vocal fold vertical vibration was about 0.16 m/s, and the fundamental frequency was 172 Hz; the extracted velocity information showed a reasonable waveform and value in comparison with the previous studies. In all three modes of phonation, the Doppler frequencies derived from the reflected ultrasound corresponded with the vertical velocity of vocal fold vibration as expected.

CONCLUSIONS

The proposed method can accurately represent the characteristics of different phonation modes such as no phonation, whisper and normal phonation. The proposed device could be used in daily monitoring and assessment of vocal function and vocal fold vibration.

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.

Effects of consonant manner and vowel height on intraoral pressure and articulatory contact at voicing offset and onset for voiceless obstruents

In obstruent consonants, a major constriction in the upper vocal tract yields an increase in intraoral pressure (P(io)). Phonation requires that subglottal pressure (P(sub)) exceed P(io) by a threshold value, so as the transglottal pressure reaches the threshold, phonation will cease. This work investigates how P(io) levels at phonation offset and onset vary before and after different German voiceless obstruents (stop, fricative, affricates, clusters), and with following high vs low vowels. Articulatory contacts, measured using electropalatography, were recorded simultaneously with P(io) to clarify how supraglottal constrictions affect P(io). Effects of consonant type on phonation thresholds could be explained mainly in terms of the magnitude and timing of vocal-fold abduction. Phonation offset occurred at lower values of P(io) before fricative-initial sequences than stop-initial sequences, and onset occurred at higher levels of P(io) following the unaspirated stops of clusters compared to fricatives, affricates, and aspirated stops. The vowel effects were somewhat surprising: High vowels had an inhibitory effect at voicing offset (phonation ceasing at lower values of P(io)) in short-duration consonant sequences, but a facilitating effect on phonation onset that was consistent across consonantal contexts. The vowel influences appear to reflect a combination of vocal-fold characteristics and vocal-tract impedance.

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.

Differentiating between adductor and abductor spasmodic dysphonia using airflow interruption

OBJECTIVES/HYPOTHESIS

To measure the laryngeal resistance (R(L)), subglottal pressure (P(s)), and mean flow rate (MFR) of adductor (ADSD) and abductor (ABSD) spasmodic dysphonia patients using the airflow interrupter.

METHODS

The R(L) of six ABSD and seven ADSD patients was measured using the airflow interrupter, a noninvasive device designed to measure MFR and P(s) via mechanical balloon valve interruption. Subjects performed 10 trials at each of two intensity levels, with each trial consisting of a sustained /a/ during which phonation was interrupted for 500 ms. Laryngeal resistance was calculated as subglottal pressure divided by airflow.

RESULTS

Mean R(L) for the ADSD and ABSD subtypes at 65 dB were 24.78 cmH(2)O/L/s and 14.51 cmH(2)O/L/s, respectively (P = .04). Mean R(L) at 70 dB were 40.02 cmH(2)O/L/s and 15.84 cmH(2)O/L/s (P = .014). P(s) for the ADSD and ABSD subtypes at 65 dB were 10.23 cmH(2)O and 8.32 cmH(2)O, respectively (P = .582). At the 70 dB level, P(s) were 12.39 cmH(2)O and 11.78 cmH(2)O (P = .886). MFR for the ADSD and ABSD subtypes at 65 dB were 435 mL/s and 746 mL/s (P = .205). Mean MFR at 70 dB were 518 mL/s and 848 mL/s (P = .198).

CONCLUSIONS

Noninvasive measurements of R(L) may be useful for differentiating between ADSD and ABSD. This simple objective test, which produces a quantitative output, could be used to evaluate laryngeal function in patients with spasmodic dysphonia.

Comparison of labial and mechanical interruption for measurement of aerodynamic parameters

OBJECTIVES/HYPOTHESIS

To directly compare the mechanical and labial interruption techniques of measuring subglottal pressure (P(s)), mean flow rate (MFR), and laryngeal resistance (R(L)).

METHODS

Thirty-four subjects performed 10 trials with both mechanical and labial interruption. P(s) and MFR were recorded, whereas R(L) was calculated by dividing P(s) by MFR. Coefficients of variation were calculated to compare intrasubject precision. A subset of 10 subjects performed the tasks twice with 30 minutes between sessions. Bland-Altman plots were used to determine intrasubject repeatability for each of the methods.

RESULTS

Mechanical interruption produced coefficients of variation for P(s), MFR, and R(L) of 0.0995, 0.127, and 0.129, respectively. Labial interruption produced coefficients of variation of 0.102, 0.147, and 0.169, respectively. P values were 0.824 for P(s), 0.159 for MFR, and 0.043 for R(L). The Bland-Altman plots revealed comparable repeatability between the two methods. The 95% confidence intervals of the Bland-Altman plots for mechanical interruption were (-0.050, 0.072), (-0.543, 1.832), and (-2.498, 10.528) for MFR, P(s), and R(L). Confidence intervals for labial interruption were (-0.018, 0.031), (0.057, 2.442), and (-3.267, 10.595) for MFR, P(s,) and R(L).

CONCLUSIONS

Mechanical interruption produced higher precision when measuring R(L) because of more reliable airflow measurements. Mechanical and labial interruption showed comparable repeatability. Further research into using mechanical interruption clinically is warranted.

Phonation threshold pressure estimation using electroglottography in an airflow redirection system

OBJECTIVES/HYPOTHESIS

The present study proposed to estimate phonation threshold pressure (PTP) noninvasively using airflow redirection into a pneumatic capacitance system.

STUDY DESIGN

Prospective study.

METHODS

Subjects phonated into the device, which interrupts airflow mechanically and redirects the flow into a pneumatic capacitor. Five interruptions were effected per trial. PTP was estimated as the difference between subglottal pressure (SGP) and transglottal pressure at phonation offset. The novel method was tested for consistency in 20 normal human subjects at low (75 dB) and high (85 dB) sound pressure levels. The device was tested for validity on a tracheotomy patient.

RESULTS

Mean SGP was 9.02 +/- 3.27 cm H(2)O, and mean PTP was 3.68 +/- 1.41 cm H(2)O. Intrasubject coefficient of variation, a measure of intrasubject consistency, was 0.33 +/- 0.23. Statistically significant differences existed between the means of SGP but not PTP at 75 dB and 85 dB. The correlation coefficient between accepted and experimental SGP in a tracheotomy patient was 0.947 (P < .001).

CONCLUSIONS

Measurements corresponded well to previously reported values, and intrasubject variability was low, indicating the device was consistent. Testing on a tracheotomy patient demonstrated validity. More research is needed to determine the sensitivity and specificity of the device in differentiating between normal and pathological voices. This device may have clinical application as a noninvasive and reliable method of estimating PTP and indicating that laryngeal health is likely abnormal.

Phonation threshold pressure measurement with a semi-occluded vocal tract

PURPOSE

The purpose of this article was to determine if a semi-occluded vocal tract could be used to measure phonation threshold pressure. This is in contrast to the shutter technique, where an alternation between a fully occluded tract and an unoccluded tract is used.

METHOD

Five male and 5 female volunteers phonated through a thin straw held between the lips. Oral pressure behind the lips was measured. Mathematical predictions of phonation threshold pressures were compared to the measured ones over a range of frequencies.

RESULTS

It was shown that, for a 2.5-mm diameter straw, phonation threshold pressures were obtainable over a 2-octave range of fundamental frequency by all volunteers. In magnitude, the pressures agreed with the 0.2-0.5 kPa values obtained in previous investigations. Sensitivity to viscoelastic and geometric properties of the vocal folds was generally not compromised with greater oral impedance, but some differences were predicted theoretically in contrast to an open mouth configuration.

CONCLUSION

Because phonation threshold pressure is always dependent on vocal tract interaction, it may be advantageous to choose an exact and fixed oral semi-occlusion for the measurement and interpret the results in light of the known acoustic load.

Effects of mucosal loading on vocal fold vibration

A chain model was proposed in this study to examine the effects of mucosal loading on vocal fold vibration. Mucosal loading was defined as the loading caused by the interaction between the vocal folds and the surrounding tissue. In the proposed model, the vocal folds and the surrounding tissue were represented by a series of oscillators connected by a coupling spring. The lumped masses, springs, and dampers of the oscillators modeled the tissue properties of mass, stiffness, and viscosity, respectively. The coupling spring exemplified the tissue interactions. By numerically solving this chain model, the effects of mucosal loading on the phonation threshold pressure, phonation instability pressure, and energy distribution in a voice production system were studied. It was found that when mucosal loading is small, phonation threshold pressure increases with the damping constant R(r), the mass constant R(m), and the coupling constant R(mu) of mucosal loading but decreases with the stiffness constant R(k). Phonation instability pressure is also related to mucosal loading. It was found that phonation instability pressure increases with the coupling constant R(mu) but decreases with the stiffness constant R(k) of mucosal loading. Therefore, it was concluded that mucosal loading directly affects voice production.

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.

Indirect estimation of laryngeal resistance via airflow redirection

OBJECTIVES

Our aim was to estimate aerodynamic parameters of laryngeal resistance (RL) and aerodynamic power indirectly from a subglottal pressure (Ps) data trace obtained with the airflow redirection system.

METHODS

During airflow interruption, the airflow redirection tank fills capacitively with pressure until it reaches the subject's Ps. Therefore, a time constant, tau, can be extracted from the data trace and used to calculate RL. The validity of applying this method to the estimation of RL was demonstrated with a computer model. Estimations were made for values of 10, 20, 30, 40, and 50 cm H2O per liter per second (L/s). Twenty subjects performed 10 trials on the experimental system designed to measure Ps. The values of RL and aerodynamic power were then calculated.

RESULTS

The computer model simulation yielded a maximum measurement error of 3.00% and a mean error of 1.78%. In human subject testing, the mean +/- SD laryngeal resistance was 22.61 +/- 8.65 cm H2O per L/s, the mean Ps was 6.91 +/- 1.94 cm H2O, and the mean aerodynamic power was 0.247 +/- 0.170 kPa x (L/s).

CONCLUSIONS

The proposed method of data analysis enables a clinician to estimate RL and aerodynamic power from a single experimental trial designed to measure Ps. This technique provides the clinician with an aerodynamic function report that can be used to analyze patient health and treatment efficacy.

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.

Estimating subglottal pressure via airflow interruption with auditory masking

Current noninvasive measurement of subglottal pressure using airflow interruption often produces inconsistent results due to the elicitation of audio-laryngeal reflexes. Auditory feedback could be considered as a means of ensuring measurement accuracy and precision. The purpose of this study was to determine if auditory masking could be used with the airflow interruption system to improve intrasubject consistency. A prerecorded sample of subject phonation was played on a loop over headphones during the trials with auditory masking. This provided subjects with a target pitch and blocked out distracting ambient noise created by the airflow interrupter. Subglottal pressure was noninvasively measured using the airflow interruption system. Thirty subjects, divided into two equal groups, performed 10 trials without auditory masking and 10 trials with auditory masking. Group one performed the normal trials first, followed by the trials with auditory masking. Group two performed the auditory masking trials first, followed by the normal trials. Intrasubject consistency was improved by adding auditory masking, resulting in a decrease in average intrasubject standard deviation from 0.93+/-0.51 to 0.47+/-0.22 cm H(2)O (P < 0.001). Auditory masking can be used effectively to combat audio-laryngeal reflexes and aid subjects in maintaining constant glottal configuration and frequency, thereby increasing intrasubject consistency when measuring subglottal pressure. By considering auditory feedback, a more reliable method of measurement was developed. This method could be used by clinicians, as reliable, immediately available values of subglottal pressure are useful in evaluating laryngeal health and monitoring treatment progress.

Reliable time to estimate subglottal pressure

Measuring subglottal pressure (P(s)) with complete interruption can be problematic due to unsteady plateaus in supraglottal pressure data traces during balloon valve interruption. Subjectively determining when the graph plateaus neglect the effects of laryngeal, auditory, and other physical reflexes may alter patient effort and glottal configuration. If the P(s) estimation was made at a consistent time before the onset of reflexes, the recorded pressure would not be dependent on subjective analysis by a clinician, and intrasubject data would be more precise. Previously collected data using the airflow interruption system have shown consistency at approximately 150 milliseconds after balloon valve inflation. To evaluate the validity of estimating P(s) at this point, a theoretical and a physical model were applied. A theoretical ideal gas model of capacitance calculated the time necessary for supraglottal pressure to equilibrate with P(s). Using a mechanical pseudolung which served as a constant pressure source, known subresistor pressures were compared to the pressure measured by the interruption device. Both models confirmed the validity of measuring P(s) consistently at 150 milliseconds into the 500-millisecond interruption. In human trials testing 25 subjects, mean intrasubject standard deviation using this optimal time constant was 0.66+/-0.37cm H(2)O, and 1.11+/-0.48cm H(2)O when performing plateau analysis (P<0.0005). This novel modification to the clinically feasible interruption model for P(s) estimation demonstrates a marked improvement in the reliability of balloon valve interruption while maintaining the validity demonstrated in previous studies.

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.

Estimating subglottal pressure via airflow redirection

Subglottal pressure (SGP) is a valuable parameter in the research and clinical assessment of laryngeal function. The lungs serve as a constant pressure source during sustained phonation, and that pressure, SGP, can be used to determine the efficiency with which the larynx converts aerodynamic power to acoustic power. As the larynx serves as an aerodynamic transducer, the vocal efficiency (Ve) coefficient, defined as acoustic power (dB) divided by aerodynamic power (SGP x glottal airflow) has been shown to reliably reflect vocal health. However, current SGP measurement techniques are hesitantly used because of either an invasive nature or the requirement of intensive patient training. This study tests a novel device that has been designed to noninvasively estimate SGP through mechanical airflow redirection, producing a numeric output on completion of the trial, which lasts only a few seconds. The novelty of this design lies in the ease of use for both the patient and the clinician. Multiple mechanical airflow redirections occlude the airway for only 135 ms, which is predicted to limit the effect of confounding laryngeal reflexes that may occur during the trials. Additionally, the airflow redirection into a retention device allows for the pneumatic in-trial comparison of the estimated SGP with the pressure achieved by the patient, providing a numeric output to the clinician on completion.