Vocal Range Variations Elicited With a Standard Mandarin Reading Passage in Individuals With Voice Disorders.

PURPOSE: This study examined whether the "Three Bears Passage" (TB), a standard Mandarin reading passage, could elicit significant vocal range variations in individuals with voice disorders. Relative sensitivity of TB versus another existing standard reading passage, "Passage in Mandarin" (PM), for differentiating between individuals with and without voice disorders was also evaluated. METHOD: Forty-two individuals with normal voice and 30 individuals with voice disorders participated in the study. Maximum fundamental frequency (f0), minimum f0, mean f0, f0 range, maximum vocal intensity, minimum intensity, mean intensity, and intensity range of all participants reading aloud the two passages were measured with Praat to construct speech range profiles (SRPs). RESULTS: Significantly larger vocal range was found for TB than for PM in individuals with voice disorders, including significantly higher maximum f0, mean f0, maximum intensity, mean intensity, and significantly larger f0 range and intensity range. Significantly more limited vocal range was observed in individuals with voice disorders than those without, with more obviously restricted SRPs while reading aloud TB compared to PM. Receiver operating characteristic analysis suggested that TB was more sensitive than PM in distinguishing between individuals with and without voice disorders. CONCLUSIONS: Our findings supported the potential of TB as a standard clinical assessment tool for evaluating pathological changes in vocal range. Future studies should explore if therapeutic approaches based on the passage or variations of it could be developed for overcoming functional limitations and restrictions in vocal range for specific voice disorders.

Mandarin Chinese version of the Aging Voice Index.

Objectives: This study developed the Mandarin Chinese version of the Aging Voice Index (AVI), with preliminary validation of the scale for potential clinical applications. Study Design: Scale development. Methods: The experimental procedure involved: (1) cross-cultural adaptation of the original AVI into the Mandarin Chinese version (CAVI); (2) evaluation by expert panel; (3) back translation; (4) pilot testing; (5) development of the final CAVI; (6) scale validation with 68 older adults of 60-89 years old (29 females and 39 males), 34 with voice disorders and 34 age-matched with normal voice. Internal consistency reliability, test-retest reliability, content validity, criterion-related validity, and discriminatory ability (diagnostic accuracy) of the CAVI were evaluated. Results: There were high internal consistency (Cronbach's alpha = 0.9733), high test-retest reliability (intraclass correlation coefficient = 0.9578, p < 0.01), high content validity (content validity index = 0.9710), high criterion-related validity (Pearson's r = 0.9439, p < 0.01 between CAVI and Voice Handicap Index-10; r = 0.8070, p < 0.01 between CAVI and voice-related quality of life [V-RQOL]), and significant difference in CAVI scores between the two groups with huge effect size (t(34.69) = -11.59, Cohen's d = 2.81, p < 0.001). Receiver operating characteristic analysis revealed a high diagnostic accuracy of the CAVI, with an area under the curve of 0.9974 (p < 0.001) and a cut-off score of 12.0 with 100% sensitivity and 97.1% specificity. Conclusion: Our findings suggested that the CAVI could be a reliable and valid standardized self-assessment questionnaire tool for clinical evaluation of the impact of voice problems specifically for Mandarin-speaking older adults. Further studies should explore a full-scale validation of the CAVI for being a standard clinical tool, including for older adults in Mainland China. Level of evidence: 3b (case-control study).

A 4-Week Straw Phonation in Water Exercise Program for Aging-Related Vocal Fold Atrophy.

PURPOSE: This study evaluated the efficacy of a 4-week straw phonation in water (SPW) exercise program on aging-related vocal fold atrophy (VFA), with a secondary objective to examine the immediate effects of SPW exercises. METHOD: Thirty-eight older adults aged 60 years and above formally diagnosed with aging-related VFA were randomly assigned into an experimental group undergoing SPW exercises with an 8-cm depth of straw submersion into water for 4 weeks plus vocal hygiene practice (n = 20), and a control group with only vocal hygiene practice (n = 18). Outcome measures included laryngeal endoscopic measures of glottal gap, auditory-perceptual ratings of voice quality, acoustic measures, aerodynamic measures, and standardized self-assessment questionnaire scores. An additional round of acoustic and aerodynamic assessment following 20 min of SPW exercises was conducted to examine the immediate effects. RESULTS: Significant improvements in normalized glottal gap area, perceptual rating of breathiness, smoothed cepstral peak prominence, harmonics-to-noise ratio (HNR), mean oral airflow, subglottal pressure and laryngeal airway resistance at comfortable loudness, Voice-related Quality of Life scores, and Chinese Vocal Fatigue Index Factor 3 scores were observed in the experimental group relative to the control group. There were also significant immediate effects for HNR, mean oral airflow, subglottal pressure, and laryngeal airway resistance. CONCLUSIONS: These findings suggested significant immediate improvements in vocal function following SPW exercises, with additional significant improvements in vocal function as well as significant improvements in quality of life following the 4-week SPW exercise program. Further studies with more long-term follow-up are recommended to better understand the efficacy of SPW exercises with deep levels of straw submersion into water as an effective clinical option for the management of hypofunctional dysphonia associated with aging-related VFA.

A Vocal Hygiene Program for Mitigating the Effects of Occupational Vocal Demand in Primary School Teachers.

PURPOSE: Teachers are occupational voice users with significant vocal demand. This study examined if a vocal hygiene program could mitigate the effects of occupational vocal demand in primary school teachers across 1 month. METHOD: Sixty female teachers participated, with 30 in an experimental group receiving vocal hygiene education plus daily home practice for 1 month and 30 in a control group with no intervention. Their vocal changes across the month were quantified with (a) acoustic measures on fundamental frequency (fo), vocal intensity, jitter and shimmer, harmonics-to-noise ratio, and smoothed cepstral peak prominence and (b) Voice Handicap Index (VHI-10) and Vocal Fatigue Index (VFI) scores. RESULTS: Analysis of covariance showed significantly larger changes (significant decreases) in conversational fo and in jitter for the experimental group relative to the control group. Post hoc pairwise comparisons following repeated-measures analysis of variance showed significant decreases in conversational fo and in jitter across the month for the experimental group. No significant differences in VHI-10 and VFI scores were found between the groups. CONCLUSIONS: Vocal demand-related changes in acoustic measures could be partially mitigated with the vocal hygiene program. Future studies with a more refined intervention program and more long-term follow-up are recommended to better understand the long-term benefits of vocal hygiene programs on primary school teachers.

The Reliability and Validity of the Mandarin Chinese Version of the Vocal Fatigue Index: Preliminary Validation.

PURPOSE: This study attempted to develop and to preliminarily validate the Mandarin Chinese version of the Vocal Fatigue Index (VFI) as a standardized self-assessment questionnaire tool for potential clinical applications. METHOD: The experimental procedure involved (a) cross-cultural adaptation of the VFI into the Mandarin Chinese version (CVFI), (b) evaluation by an expert panel, (c) back translation, (d) pilot testing, and (e) validation of the questionnaire by three participant groups: 50 with voice disorders, 50 occupational voice users (at-risk group), and 50 with normal voice (control group). Internal consistency, test-retest reliability, content validity, and convergent validity of the CVFI were examined, and discriminatory ability (diagnostic accuracy) for distinguishing between the groups was evaluated. RESULTS: Results showed high internal consistency (Cronbach's alpha ≥ .8817 for the total CVFI scores for all groups), high test-retest reliability (intraclass correlation coefficients ≥ .9072, p < .001 for the total CVFI scores for all groups), high content validity (total content validity index = 0.9368), and high convergent validity (Pearson r ≥ .8155, p < .001 between the total CVFI scores and Factors 1 and 2 scores). Significant differences between the three groups were found in all scores. Receiver operating characteristic analysis revealed a high diagnostic accuracy for distinguishing between the disorders group and the normal group (area under the curve ≥ 0.927, p < .001 for the total CVFI scores and Factors 1 and 2 scores), with cutoff scores of ≥ 36 (total CVFI score), ≥ 23.5 (Factor 1 score), ≥ 7.5 (Factor 2 score), and ≤ 6.5 (Factor 3 score). CONCLUSIONS: These findings suggested that the CVFI could be a reliable and valid self-assessment tool for the clinical evaluation of vocal fatigue in Mandarin Chinese-speaking populations. A full-scale validation study of the CVFI is recommended to verify these results.

Acoustic Analysis of Taiwanese Tones in Esophageal Speech and Pneumatic Artificial Laryngeal Speech.

PURPOSE: This study examined the acoustic properties of Taiwanese (Southern Min) lexical tones produced in esophageal speech (ES) and pneumatic artificial laryngeal speech (PAL), including onset fundamental frequency (F0), slope of F0 contour, duration, and amplitude (intensity) of the vowel portion of syllables carrying seven Taiwanese tones. METHOD: Seven ES speakers, seven PAL speakers, and 18 normal laryngeal (NL) speakers (all male) read aloud target syllables carrying the tones in monosyllables, disyllables, and sentences. Acoustic features were measured with Praat. RESULTS: Acoustic analysis revealed (a) no significant effects of linguistic level on acoustic parameters except for duration, which generally significantly decreased from monosyllables to disyllables to sentences for Tones 1 and 5; (b) significant differences across the speaker groups in onset F0 (PAL > ES > NL), duration (PAL > NL and PAL > ES for all tones), and mean amplitude (PAL > NL > ES); and (c) no significant difference in mean slope of F0 contour across the speaker groups. CONCLUSIONS: These preliminary data on acoustic properties of Taiwanese tones produced by ES and PAL speakers could facilitate the design of therapeutic strategies for improving the intelligibility of alaryngeal lexical tones. Further studies are recommended to examine the relative perceptual importance of the acoustic parameters.

A Mandarin Chinese Reading Passage for Eliciting Significant Vocal Range Variations.

Purpose There is a lack of standardized Mandarin reading text material that could potentially elicit significant variations in fundamental frequency (F0) and in vocal intensity for clinical voice evaluation. In this study, a phonetically balanced "Three Bears Passage" was developed based on the classical "Goldilocks" story for this purpose. The hypothesis was that the vocal range (F0 range and Intensity range) elicited while reading aloud the passage could be similar to that of the voice range profile (VRP) obtained with sustained vowel production and significantly different from that while reading an existing standard Mandarin passage. Method One hundred twenty young adults (60 men and 60 women, aged 25.22 ± 3.74 years) without vocal pathologies and vocal training participated in the study. Vocal range data, including F0-related measures and intensity-related measures, were obtained with Praat in order to construct VRPs for the sustained /a/ and to construct speech range profiles for passage reading. Results F0 range and intensity range for the new passage were significantly larger than those for the existing Mandarin passage for both male and female participants. In particular, the F0 range for the passage was not significantly different from that of the VRP for male participants. Conclusions These findings suggested that the new passage could allow individuals without vocal training to demonstrate a large vocal range in both F0 and vocal intensity, in a passage reading setting in a relatively short time. Further studies should be pursued with the passage to investigate the vocal range and vocal potential of individuals with voice disorders.

Effect of Training With Anchors on Auditory-Perceptual Evaluation of Dysphonia in Speech-Language Pathology Students.

Purpose Auditory-perceptual evaluation is essential for the clinical assessment of voice disorders. Unstable perceptual voice evaluation has been shown for inexperienced listeners as compared to expert listeners. We examined the effects of perceptual training with external auditory anchors with and without immediate feedback on the evaluation of roughness and breathiness of natural, nonsynthesized speech stimuli (reading of a standard passage) in speech-language pathology students. Method Perceptual voice evaluation and training with anchors using a visual analog scale was implemented with a computer software. Forty-eight speech-language pathology students were randomly assigned into three groups, feedback group (Group F), no feedback group (Group NF), and control group (Group C), attending one training session and four assessment sessions (before training, immediately after training, and 1 and 7 weeks after training). Group F received training with anchors with immediate feedback, Group NF received training without immediate feedback, and Group C received sham training (exposure session). Results Training with anchors significantly increased the rating accuracy (agreement with expert ratings) on both roughness and breathiness for Group F, with the effects lasting for 7 weeks. No significant changes in rating accuracy with training were observed for Group NF and Group C. No improvements in intra- and interrater reliability as well as intrarater agreement were observed in all three groups, whereas interrater agreement on breathiness (but not roughness) significantly increased for all groups, with the effect lasting for 7 weeks only for Group F. Conclusions These findings suggested that perceptual training with external auditory anchors and the use of immediate feedback could be effective for facilitating the development of perceptual voice evaluation skills in speech-language pathology students. Further studies involving more extensive training with stimuli covering a full range of dysphonia severity categories and improvements in design of the training protocol are recommended to verify these results.

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.

Effects of a 6-Week Straw Phonation in Water Exercise Program on the Aging Voice.

Purpose Semi-occluded vocal tract (SOVT) exercises with tubes or straws have been widely used for a variety of voice disorders. Yet, the effects of longer periods of SOVT exercises (lasting for weeks) on the aging voice are not well understood. This study investigated the effects of a 6-week straw phonation in water (SPW) exercise program. Method Thirty-seven elderly subjects with self-perceived voice problems were assigned into two groups: (a) SPW exercises with six weekly sessions and home practice (experimental group) and (b) vocal hygiene education (control group). Before and after intervention (2 weeks after the completion of the exercise program), acoustic analysis, auditory-perceptual evaluation, and self-assessment of vocal impairment were conducted. Results Analysis of covariance revealed significant differences between the two groups in smoothed cepstral peak prominence measures, harmonics-to-noise ratio, the auditory-perceptual parameter of breathiness, and Voice Handicap Index-10 scores postintervention. No significant differences between the two groups were found for other measures. Conclusions Our results supported the positive effects of SOVT exercises for the aging voice, with a 6-week SPW exercise program being a clinical option. Future studies should involve long-term follow-up and additional outcome measures to better understand the efficacy of SOVT exercises, particularly SPW exercises, for the aging voice.

Ovine Vocal Fold Tissue Fatigue Response to Accumulated, Large-Amplitude Vibration Exposure at Phonatory Frequencies.

Purpose The contribution of tissue mechanical response to vocal fatigue is poorly understood. This study investigated the fatigue response of vocal fold tissues to large-amplitude vibration exposure at phonatory frequencies, using an ex vivo ovine model. Method Twelve sheep vocal fold mucosal specimens were subjected to sinusoidal, simple-shear deformation for prolonged cycles, under a large but physiological shear strain (46%) in a frequency range of 100-230 Hz. The duration of shear varied from a critical vibration exposure limit of 1,040 s to 4 times the limit (4,160 s). Tissue viscoelastic response was quantified by the elastic shear modulus (G'), viscous shear modulus (G″), and damping ratio (G″/G'). Results Distinct response patterns were observed at different frequencies. G' and G″ generally decreased with vibration exposure at 100 Hz, whereas they generally increased with vibration exposure at 200 and 230 Hz. Statistically significant differences were found for G″ increasing with vibration exposure at 200 Hz and damping ratio decreasing with vibration exposure at 200 Hz. Significant increases with frequency were also found for all viscoelastic functions. Results suggested that the contribution of tissue viscoelastic response to vocal fatigue could be highly frequency dependent. In particular, increases in G″ with vibration exposure could lead to high phonation threshold pressures and difficulty sustaining phonation at higher frequencies following prolonged vocalization. Conclusion These preliminary findings may help us better understand vocal fatigue and recovery and should be corroborated by studies with human vocal fold tissues.

Nonlinear viscoelastic characterization of human vocal fold tissues under large-amplitude oscillatory shear (LAOS).

Viscoelastic shear properties of human vocal fold tissues were previously quantified by the shear moduli (G' and G″). Yet these small-strain linear measures were unable to describe any nonlinear tissue behavior. This study attempted to characterize the nonlinear viscoelastic response of the vocal fold lamina propria under large-amplitude oscillatory shear (LAOS) with a stress decomposition approach. Human vocal fold cover and vocal ligament specimens from eight subjects were subjected to LAOS rheometric testing with a simple-shear rheometer. The empirical total stress response was decomposed into elastic and viscous stress components, based on odd-integer harmonic decomposition approach with Fourier transform. Nonlinear viscoelastic measures derived from the decomposition were plotted in Pipkin space and as rheological fingerprints to observe the onset of nonlinearity and the type of nonlinear behavior. Results showed that both the vocal fold cover and the vocal ligament experienced intercycle strain softening, intracycle strain stiffening, as well as shear thinning both intercycle and intracycle. The vocal ligament appeared to demonstrate an earlier onset of nonlinearity at phonatory frequencies, and higher sensitivity to changes in frequency and strain. In summary, the stress decomposition approach provided much better insights into the nonlinear viscoelastic behavior of the vocal fold lamina propria than the traditional linear measures.

Viscoelastic properties of human aryepiglottic fold and ventricular fold tissues at phonatory frequencies.

OBJECTIVE: The purpose of this study was to quantify the viscoelastic shear properties of the human ventricular fold (or false vocal fold) mucosa and aryepiglottic fold mucosa at frequencies of phonation. METHODS: Linear viscoelastic shear properties of the mucosa of false vocal fold and aryepiglottic fold specimens from seven cadaveric subjects were determined as functions of frequency (5-250 Hz) and compared to those of the true vocal fold cover. Measurements of elastic shear modulus (G') and dynamic viscosity (η') were made with a controlled-strain simple-shear rheometer. Linear least-squares regression was conducted to curve-fit log G' and log η' versus log frequency, and statistical analysis was performed with one-way analysis of variance. RESULTS: All specimens showed similar frequency dependence of the viscoelastic functions G' and η', with G' gradually increasing with frequency and η' monotonically decreasing with frequency. The magnitudes of G' and η' of the false fold mucosa were generally higher than those of the aryepiglottic fold mucosa and true vocal fold cover, but there were no significant differences in G' and η' among the false fold, aryepiglottic fold, and true vocal fold. CONCLUSION: The false vocal fold and aryepiglottic fold mucosa showed similar frequency dependence and a similar range of tissue viscoelastic behavior as the true vocal fold. These preliminary findings suggested that such tissues could become candidates for the replacement of the true vocal fold lamina propria in patients with significant tissue loss and deficiencies, for those requiring laryngeal reconstruction following partial laryngectomy or airway reconstruction. LEVEL OF EVIDENCE: NA. Laryngoscope, E296-E301, 2018.

A mixed-effects model approach for the statistical analysis of vocal fold viscoelastic shear properties.

A mixed-effects model approach was introduced in this study for the statistical analysis of rheological data of vocal fold tissues, in order to account for the data correlation caused by multiple measurements of each tissue sample across the test frequency range. Such data correlation had often been overlooked in previous studies in the past decades. The viscoelastic shear properties of the vocal fold lamina propria of two commonly used laryngeal research animal species (i.e. rabbit, porcine) were measured by a linear, controlled-strain simple-shear rheometer. Along with published canine and human rheological data, the vocal fold viscoelastic shear moduli of these animal species were compared to those of human over a frequency range of 1-250Hz using the mixed-effects models. Our results indicated that tissues of the rabbit, canine and porcine vocal fold lamina propria were significantly stiffer and more viscous than those of human. Mixed-effects models were shown to be able to more accurately analyze rheological data generated from repeated measurements.

Strain modulations as a mechanism to reduce stress relaxation in laryngeal tissues.

Vocal fold tissues in animal and human species undergo deformation processes at several types of loading rates: a slow strain involved in vocal fold posturing (on the order of 1 Hz or so), cyclic and faster posturing often found in speech tasks or vocal embellishment (1-10 Hz), and shear strain associated with vocal fold vibration during phonation (100 Hz and higher). Relevant to these deformation patterns are the viscous properties of laryngeal tissues, which exhibit non-linear stress relaxation and recovery. In the current study, a large strain time-dependent constitutive model of human vocal fold tissue is used to investigate effects of phonatory posturing cyclic strain in the range of 1 Hz to 10 Hz. Tissue data for two subjects are considered and used to contrast the potential effects of age. Results suggest that modulation frequency and extent (amplitude), as well as the amount of vocal fold overall strain, all affect the change in stress relaxation with modulation added. Generally, the vocal fold cover reduces the rate of relaxation while the opposite is true for the vocal ligament. Further, higher modulation frequencies appear to reduce the rate of relaxation, primarily affecting the ligament. The potential benefits of cyclic strain, often found in vibrato (around 5 Hz modulation) and intonational inflection, are discussed in terms of vocal effort and vocal pitch maintenance. Additionally, elderly tissue appears to not exhibit these benefits to modulation. The exacerbating effect such modulations may have on certain voice disorders, such as muscle tension dysphonia, are explored.

Collagen microstructure in the vocal ligament: initial results on the potential effects of smoking.

OBJECTIVES/HYPOTHESIS: This investigation quantitatively characterizes the collagenous microstructure of human vocal ligament specimens excised postmortem from nonsmokers and smokers. STUDY DESIGN: Retrospective cohort study. METHODS: Second harmonic generation (SHG) imaging was performed at three anatomical locations of vocal ligament specimens: anterior, mid-membranous, and posterior regions. Two microstructural parameters were extracted from the SHG images: (1) normalized fiber density, and (2) fiber dispersion coefficient, quantifying the degree of collagen fiber dispersion about a preferred direction. RESULTS: For both the nonsmoker and smoker subjects, the fiber dispersion coefficient was heterogeneous. Differences in the collagenous structure of nonsmokers and smoker subjects were pronounced at the mid-membranous location. However, the directionality of the heterogeneity in the smoker subjects was opposite to that in the nonsmoker subjects. Specifically, the fiber dispersion coefficient in the nonsmoker subjects was lower in the mid-membranous region (indicating more fiber alignment) than at the anterior/posterior regions, but for the smoker subjects the fiber dispersion coefficient was higher at the mid-membranous region. The normalized fiber density was near constant in the nonsmoker subjects, but the smoker subjects had fewer fibers in the mid-membranous region than at the anterior/posterior regions. CONCLUSION: Spatial microstructural variations may exist in the vocal fold ligament both in nonsmokers and smokers. Smoking appears to influence the degree and direction of microstructure heterogeneity in the vocal fold ligament.

The anisotropic hyperelastic biomechanical response of the vocal ligament and implications for frequency regulation: a case study.

One of the primary mechanisms to vary one's vocal frequency is through vocal fold length changes. As stress and deformation are linked to each other, it is hypothesized that the anisotropy in the biomechanical properties of the vocal fold tissue would affect the phonation characteristics. A biomechanical model of vibrational frequency rise during vocal fold elongation is developed which combines an advanced biomechanical characterization protocol of the vocal fold tissue with continuum beam models. Biomechanical response of the tissue is related to a microstructurally informed, anisotropic, nonlinear hyperelastic constitutive model. A microstructural characteristic (the dispersion of collagen) was represented through a statistical orientation function acquired from a second harmonic generation image of the vocal ligament. Continuum models of vibration were constructed based upon Euler-Bernoulli and Timoshenko beam theories, and applied to the study of the vibration of a vocal ligament specimen. From the natural frequency predictions in dependence of elongation, two competing processes in frequency control emerged, i.e., the applied tension raises the frequency while simultaneously shear deformation lowers the frequency. Shear becomes much more substantial at higher modes of vibration and for highly anisotropic tissues. The analysis was developed as a case study based on a human vocal ligament specimen.

Empirical measurements of biomechanical anisotropy of the human vocal fold lamina propria.

The vocal folds are known to be mechanically anisotropic due to the microstructural arrangement of fibrous proteins such as collagen and elastin in the lamina propria. Even though this has been known for many years, the biomechanical anisotropic properties have rarely been experimentally studied. We propose that an indentation procedure can be used with uniaxial tension in order to obtain an estimate of the biomechanical anisotropy within a single specimen. Experiments were performed on the lamina propria of three male and three female human vocal folds dissected from excised larynges. Two experiments were conducted: each specimen was subjected to cyclic uniaxial tensile loading in the longitudinal (i.e., anterior-posterior) direction, and then to cyclic indentation loading in the transverse (i.e., medial-lateral) direction. The indentation experiment was modeled as contact on a transversely isotropic half-space using the Barnett-Lothe tensors. The longitudinal elastic modulus E(L) was computed from the tensile test, and the transverse elastic modulus E(T) and longitudinal shear modulus G(L) were obtained by inverse analysis of the indentation force-displacement response. It was discovered that the average of E(L) /E(T) was 14 for the vocal ligament and 39 for the vocal fold cover specimens. Also, the average of E(L)/G(L), a parameter important for models of phonation, was 28 for the vocal ligament and 54 for the vocal fold cover specimens. These measurements of anisotropy could contribute to more accurate models of fundamental frequency regulation and provide potentially better insights into the mechanics of vocal fold vibration.

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.