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.

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.

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 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 (f_o), 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 f_o 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 f_o 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.

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.

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.

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.

Could spatial heterogeneity in human vocal fold elastic properties improve the quality of phonation?

The physical mechanisms leading to the acoustic and perceptual qualities of voice are not well understood. This study examines the spatial distribution of biomechanical properties in human vocal folds and explores the consequences of these properties on phonation. Vocal fold lamina propria specimens isolated from nine excised human male larynges were tested in uniaxial tension (six from non-smokers, three from smokers). An optical method was employed to determine the local stretch, from which the elastic modulus of three segments in the anterior-posterior direction was calculated. Several specimens exhibited a significant heterogeneity in the modulus with the middle segment stiffer than the other segments. It was concluded that such modulus gradients are stronger in specimens from non-smokers than smokers. To understand the functional implications of a modulus gradient, the first eigenmode of vibration was calculated with a finite element model. With a modulus gradient, the vocal fold's eigenmode deflection was spread along the anterior-posterior length, whereas for a homogeneous modulus distribution, the deflection was more focused around the mid-coronal plane. Consequently, the strong modulus gradient may enable more complete glottal closure, which is important for normal phonation, while a more homogeneous modulus may be responsible for poor glottal closure and a perceived "breathy" voice.

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.

Injection of human mesenchymal stem cells improves healing of vocal folds after scar excision--a xenograft analysis

OBJECTIVES

Using a xenograft model the aim was to analyze if injection of human mesenchymal stem cells (hMSC) into the rabbit vocal fold (VF), after excision of an established scar, can improve the functional healing of the VF.

STUDY DESIGN

Prospective design with an experimental xenograft model.

METHODS

The VFs of 12 New Zealand rabbits were injured by a bilateral localized resection. After 9 weeks the scar after the resection was excised and hMSC were injected into the VFs. After another 10 weeks 10 VFs were dissected and stained for histology. Lamina propria thickness and relative content of collagen type I were measured. Viscoelasticity of 14 VFs at phonatory frequencies was quantified by a simple-shear rheometer. The hMSC survival was determined using a human DNA specific reference probe, that is, FISH analysis.

RESULTS

The viscoelastic measurements, that is, dynamic viscosity and elastic shear modulus for the hMSC-treated VFs, were found to be similar to those of normal controls and were significantly lower than those of untreated controls (P < .05). A significant reduction in lamina propria thickness was also shown for the hMSC treated VFs compared with the untreated VFs (P < .05). This histologic finding corresponded with the viscoelastic results. No hMSC survived 10 weeks after the injection.

CONCLUSIONS

Human mesenchymal stem cells injected into the rabbit VF following the excision of a chronic scar, were found to enhance the functional healing of the VF with reduced lamina propria thickness and restored viscoelastic shear properties.

Ventricular Fold Phonation: Viscoelastic Properties and HSDI

Objective: Determine the functional biomechanical properties of the human false vocal fold mucosa at phonatory frequencies, in comparison with those of the true vocal fold cover; and to quantify the vibration patterns of ventricular fold phonation with HSDI (high speed digital imaging).

Method: Viscoelastic shear properties of false fold specimens were quantified as functions of frequency, with measurements of elastic shear modulus (G′) and dynamic viscosity (h′) at up to 250 Hz using a simple-shear rheometer. Ventricular fold phonation of three subjects was analyzed by HSDI (high speed digital imaging) through kymography and laryngotopography.

Results: All specimens showed similar frequency dependence of their viscoelastic properties, with G′ gradually increasing with frequency and h′ monotonically decreasing with frequency. G′ and h′ of the false fold mucosa were generally higher than those of the true vocal fold cover, although the differences did not reach statistical significance. Kymographic and laryngotopographic analysis of high speed digital images revealed vibration of the false fold mucosa for subjects undergoing ventricular fold phonation. The vibratory frequencies were lower than typical fundamental frequencies for phonation.

Conclusion: These findings showed false folds could function as a secondary sound source. These preliminary data suggested that the false fold mucosa could serve as replacement material for patients with unrepairable vocal fold cover damage.

Optical measurements of vocal fold tensile properties: implications for phonatory mechanics

In voice research, in vitro tensile stretch experiments of vocal fold tissues are commonly employed to determine the tissue biomechanical properties. In the standard stretch-release protocol, tissue deformation is computed from displacements applied to sutures inserted through the thyroid and arytenoid cartilages, with the cartilages assumed to be rigid. Here, a non-contact optical method was employed to determine the actual tissue deformation of vocal fold lamina propria specimens from three excised human larynges in uniaxial tensile tests. Specimen deformation was found to consist not only of deformation of the tissue itself, but also deformation of the cartilages, as well as suture alignment and tightening. Stress-stretch curves of a representative load cycle were characterized by an incompressible Ogden model. The initial longitudinal elastic modulus was found to be considerably higher if determined based on optical displacement measurements than typical values reported in the literature. The present findings could change the understanding of the mechanics underlying vocal fold vibration. Given the high longitudinal elastic modulus the lamina propria appeared to demonstrate a substantial level of anisotropy. Consequently, transverse shear could play a significant role in vocal fold vibration, and fundamental frequencies of phonation should be predicted by beam theories accounting for such effects.

Viscoelastic properties of fresh human lenses under 40 years of age: implications for the aetiology of presbyopia

AIM

To determine the viscoelastic properties of fresh human lenses obtained from cadavers under 40 years of age.

METHODS

52 intact clear, human lenses were obtained from 26 donors (mean age of 27.5 ± 9.2 years) within 9 ± 4 h of death. The viscoelastic properties of the lens nuclei and 16 of the lens cortices were quantified within 42 ± 10 h of death using a controlled-strain, linear, simple-shear rheometer.

RESULTS

The means (± SD) of the viscoelastic properties of the lens nuclei at a frequency of 75 Hz were: elastic shear modulus, G'=11.00 ± 4.67 Pa, viscous shear modulus, G''=24.91 ± 10.98 Pa, magnitude of the complex shear modulus, |G*|=27.23 Pa, dynamic viscosity, η'=0.33 Pa.s, damping ratio, ζ=2.26 and phase shift, δ=66.17°. There was no statistical difference in these measures between the lens cortices and their respective lens nuclei. There was a small age-related statistically significant increase in G', p=0.003, but not G'' or |G*|.

CONCLUSIONS

The observed age-related increase in tissue stiffness of the lens nucleus, ~0.4 Pa/year, is too small to account for the 10 dioptre decline in accommodative amplitude in this age group.

Controlled release of hepatocyte growth factor from a bovine acellular scaffold for vocal fold reconstruction

A bovine acellular scaffold was found to facilitate tissue remodeling in a rat model of vocal fold injury, whereas hepatocyte growth factor (HGF) has been shown to have an antiscarring effect in the larynx. This study examined the loading and release kinetics of HGF in vitro, and the potential of the acellular scaffold as a timed-release system for the delivery of HGF in vivo. Bilateral wounds were created in the posterior vocal folds of 20 rats, with HGF-loaded acellular scaffolds implanted into the wounds unilaterally, and scaffolds without HGF implanted into the contralateral vocal folds as control. The rats were humanely sacrificed after 3, 7, 30, and 90 days and their larynges were examined histologically and immunohistochemically. Expressions of key matrix proteins in the vocal fold coronal sections were quantified by digital image analysis. Results demonstrated a gradual, sustained release of HGF for at least 7 days in vitro, consistent with the detection of glycosaminoglycans inherent of the scaffold. In rat vocal folds implanted with HGF-loaded scaffolds, apparently fewer inflammatory cells were observed 3 days after surgery when compared to the control. The mean relative densities of collagen III and hyaluronic acid were significantly lower than those of the control 7 days after surgery. Scaffold implants were apparently degraded by 3 months in all animals, with no evidence of fibrosis or calcification. These data suggested that the bovine acellular scaffold could be promising for the exogenous delivery of select growth factors in vivo.

Rheometric properties of canine vocal fold tissues: variation with anatomic location

OBJECTIVE

To evaluate the in vitro rheometric properties of the canine vocal fold lamina propria and muscle at phonatory frequencies, and their changes with anatomic location.

METHODS

Six canine larynges were harvested immediately postmortem. Viscoelastic shear properties of anterior, middle, and posterior portions of the vocal fold cover (lamina propria) as well as those of the medial thyroarytenoid (TA) muscle (vocalis muscle) were quantified by a linear, controlled-strain simple-shear rheometer. Measurements of elastic shear modulus (G') and dynamic viscosity (η') of the specimens were conducted with small-amplitude sinusoidal shear deformation over a frequency range of 1-250Hz.

RESULTS

All specimens showed similar frequency dependence of the viscoelastic functions, with G' gradually increasing with frequency and η' decreasing with frequency monotonically. G' and η' of the canine vocalis muscle were significantly higher than those of the canine vocal fold cover, and η' of the canine vocal fold cover was significantly higher than that of the human vocal fold cover. There were no significant differences in G' and in η' between different portions of the canine vocal fold cover.

CONCLUSION

These preliminary data based on the canine model suggested that the vocalis muscle, while in a relaxed state in vitro, is significantly stiffer and more viscous than the vocal fold cover during vibration at phonatory frequencies. For large-amplitude vocal fold vibration involving the medial portion of the TA muscle, such distinct differences in viscoelastic properties of different layers of the vocal fold should be taken into account in multi-layered biomechanical models of phonation.

Biomechanics of fundamental frequency regulation: Constitutive modeling of the vocal fold lamina propria

Accurate characterization of biomechanical characteristics of the vocal fold is critical for understanding the regulation of vocal fundamental frequency (F(0)), which depends on the active control of the intrinsic laryngeal muscles as well as the passive biomechanical response of the vocal fold lamina propria. Specifically, the tissue stress-strain response and viscoelastic properties under cyclic tensile deformation are relevant, when the vocal folds are subjected to length and tension changes due to posturing. This paper describes a constitutive modeling approach quantifying the relationship between vocal fold stress and strain (or stretch), and establishes predictions of F(0) with the string model of phonation based on the constitutive parameters. Results indicated that transient and time-dependent changes in F(0), including global declinations in declarative sentences, as well as local F(0) overshoots and undershoots, can be partially attributed to the time-dependent viscoplastic response of the vocal fold cover.

Spatially varying properties of the vocal ligament contribute to its eigenfrequency response

The vocal ligament is known to have nonlinear variation in geometry, yet this is rarely considered in empirical or computational studies. This paper investigates the effects of a nonlinear variation of the anterior-to-posterior geometry and the corresponding spatial variation in elastic modulus on the fundamental frequency of vibration for the vocal ligament. Uniaxial tensile tests were performed on a vocal ligament specimen dissected from an excised 60-year-old male larynx. Digital image correlation (DIC) was used to obtain the spatial deformation field for the entire ligament specimen. DIC results revealed that the tensile deformation was very heterogeneous, with the least amount of deformation occurring in the region of smallest cross-sectional area. The elastic modulus was calculated locally and was found to be approximately 10 times higher at the midpoint of the vocal ligament than in the anterior and posterior macula flavae regions. Based on the spatially varying material properties obtained, finite element models (isotropic and transversely isotropic) were created to investigate how the effects of varying cross-section, heterogeneous stiffness, and anisotropy could affect the fundamental frequency of vibration. It was found that the spatial cross-section variation and the spatially varying anisotropy (i.e. modulus ratio) are significant to predictions of the vibration characteristics. Fundamental frequencies predicted with a finite element model are discussed in view of rotatory inertia and contribution of transverse shear deformation.

Collagen injection for correcting vocal fold asymmetry: high-speed imaging

OBJECTIVES

We hypothesized that high-speed digital imaging with videokymographic and laryngotopographic analysis would provide a quantitative method to evaluate the effect of collagen injection for the correction of asymmetric and irregular vocal fold vibration in unilateral vocal fold paralysis.

METHODS

Videokymographic and laryngotopographic analysis was performed for high-speed digital recordings of vocal fold vibration for visualizing the glottal vibratory patterns, and for quantifying the frequency of vibration of each vocal fold, respectively, including comparisons between the paralyzed and normal vocal folds before and after surgery. This included prospective observations of 11 subjects with unilateral vocal fold paralysis (4 male, 7 female; mean +/- SD age, 67.1 +/- 12.0 years) using high-speed digital image analysis before and after collagen injection.

RESULTS

Analysis of the laryngotopographs revealed 2 distinct frequencies of vibration for the paralyzed and contralateral vocal folds for 8 of the 11 subjects before surgery. After collagen injection, the vibration frequencies became identical, despite asymmetric vibration amplitudes. Asymmetric vibration amplitudes were also observed in the other 3 subjects before surgery, but the amplitudes became symmetric after collagen injection, despite a persistent phase shift.

CONCLUSIONS

Asymmetric vibration in vocal fold paralysis was exemplified by differences in vibration frequency and amplitude between the vocal folds. The present study showed that after collagen injection, these aspects of vibratory patterns improved toward symmetry. This surgical procedure could improve the functional symmetry of the larynx for phonation.

Arytenoid Adduction for Correcting Vocal Fold Asymmetry: High-Speed Imaging

Objectives

We hypothesized that high-speed digital imaging provides a quantitative method to evaluate the effect of arytenoid adduction for the correction of asymmetric and irregular vocal fold vibration in unilateral vocal fold paralysis.

Methods

Six subjects with unilateral vocal fold paralysis participated in the study (4 male, 2 female; mean [±SD] age, 52.5 ± 21.3 years). Videokymographic and laryngotopographic methods for image analysis were performed for highspeed recordings of vocal fold vibration for visualizing the glottal vibratory patterns, and for quantifying the frequency of vibration of each vocal fold, respectively. Comparisons of the paralyzed and the normal vocal folds were made before and after arytenoid adduction.

Results

Analysis of the laryngotopographs revealed 2 distinct frequencies of vibration for the paralyzed and the contralateral vocal folds for all subjects before surgery. After arytenoid adduction, the vibration frequencies became identical or nearly identical in all subjects.

Conclusions

Asymmetric vibration in vocal fold paralysis was exemplified by differences in vibration frequency between the vocal folds. The present data showed that after arytenoid adduction the vibration frequencies and the vibratory patterns of the contralateral vocal folds approached symmetry. This surgical procedure could improve the functional symmetry of the larynx for phonation.

Viscoelastic properties of phonosurgical biomaterials at phonatory frequencies

OBJECTIVES/HYPOTHESIS

The purpose of this study was to examine the functional biomechanical properties of several injectable biomaterials currently or potentially used for vocal fold augmentation.

STUDY DESIGN

Rheometric investigation of phonosurgical materials in vitro.

METHODS

Linear viscoelastic shear properties of 3% bovine collagen (atelocollagen), micronized AlloDerm (Cymetra; LifeCell Corp., Branchburg, NJ), calcium hydroxylapatite (CaHA) (Radiesse; BioForm Medical, San Mateo, CA), and 2.4% cross-linked hyaluronic acid (HA) gel (Juvéderm; Allergan, Inc., Irvine, CA) were quantified as functions of frequency covering the phonatory range, and compared to those of the human vocal fold cover. Measurements of elastic shear modulus (G') and dynamic viscosity (eta') were made at up to 250 Hz with a controlled-strain simple-shear rheometer. Linear least-squares regression was conducted to curve-fit log G' and log eta' versus log frequency, and statistical analysis was performed with one-way analysis of variance.

RESULTS

Radiesse and Cymetra were found to be the stiffest and the most viscous materials, followed by Juvéderm and atelocollagen. There were significant differences in the magnitudes of G' and eta' among the phonosurgical materials and the normal human vocal fold cover (p < .001), whereas there was no significant difference in the frequency dependence of G' and eta' among the materials. Post hoc Tukey tests revealed significant differences (p < .05) in pairwise comparisons of the magnitudes of G' and eta' among all materials and the vocal fold cover.

CONCLUSIONS

These findings suggested that although these biomaterials may be injected lateral to the lamina propria for the treatment of glottic insufficiency, none of them are rheologically optimal for the functional reconstruction of the vocal fold lamina propria.

A bovine acellular scaffold for vocal fold reconstruction in a rat model

With a rat model of vocal fold injury, this study examined the in vivo host response to an acellular xenogeneic scaffold derived from the bovine vocal fold lamina propria, and the potential of the scaffold for constructive tissue remodeling. Bilateral wounds were created in the posterior vocal folds of 20 rats, and bovine acellular scaffolds were implanted into the wounds unilaterally, with the contralateral vocal folds as control. The rats were humanely sacrificed after 3 days, 7 days, 1 month, and 3 months, and the coronal sections of their larynges were examined histologically. Expressions of key matrix proteins including collagen I, collagen III, elastin, fibronectin, hyaluronic acid, and glycosaminoglycans (GAGs) were quantified with digital image analysis. Significant infiltration of host inflammatory cells and host fibroblasts in the scaffold implant was observed in the acute stage of wound repair (3 days and 7 days postsurgery). The mean relative densities of collagen I, collagen III, and GAGs in the implanted vocal folds were significantly higher than those in the control after 3 days, followed by gradual decreases over 3 months. Histological results showed that the scaffolds were apparently degraded by 3 months, with no fibrotic tissue formation or calcification. These preliminary findings suggested that the bovine acellular scaffold could be a potential xenograft for vocal fold regeneration.

The human umbilical vein with Wharton's jelly as an allogeneic, acellular construct for vocal fold restoration

This study investigated the potential of the decellularized human umbilical vein (HUV) as an allogeneic, acellular extracellular matrix (ECM) scaffold for engineering the vocal fold lamina propria in vitro. HUV specimens with Wharton's jelly on the abluminal surface were uniformly dissected from native umbilical cords using an automated procedure and subjected to a novel saline-based decellularization treatment for removal of potentially antigenic epitopes. Human vocal fold fibroblasts from primary culture were seeded onto the resulting acellular constructs and cultured for 21 days. The structures of decellularized and fibroblast-repopulated HUV constructs and the attachment, proliferation, and infiltration of fibroblasts were examined with light microscopy and scanning electron microscopy. Changes in the relative densities of collagen in the constructs associated with decellularization and recellularization were quantified using digital image analysis. In addition, fibroblasts infiltrating the scaffolds were released by cell recovery and quantified by counting. Viscoelastic properties of the scaffolds were measured using a linear, simple-shear rheometer at phonatory frequencies. Results showed that an acellular ECM construct with an intact three-dimensional structure of Wharton's jelly was fabricated. Vocal fold fibroblasts readily attached on the abluminal surface of the construct with high viability, with significant cellular infiltration up to approximately 600 microm deep into the construct. A significant increase in collagen expression was observed with recellularization. The elastic modulus and dynamic viscosity of the fibroblast-repopulated scaffolds were comparable to those of the human vocal fold lamina propria. These findings supported the potential of the construct as a possible surgical allograft for vocal fold restoration and reconstruction.

Modeling of the transient responses of the vocal fold lamina propria

The human voice is produced by flow-induced self-sustained oscillation of the vocal fold lamina propria. The mechanical properties of vocal fold tissues are important for understanding phonation, including the time-dependent and transient changes in fundamental frequency (F(0)). Cyclic uniaxial tensile tests were conducted on a group of specimens of the vocal fold lamina propria, including the superficial layer (vocal fold cover) (5 male, 5 female) and the deeper layers (vocal ligament) (6 male, 6 female). Results showed that the vocal fold lamina propria, like many other soft tissues, exhibits both elastic and viscous behavior. Specifically, the transient mechanical responses of cyclic stress relaxation and creep were observed. A three-network constitutive model composed of a hyperelastic equilibrium network in parallel with two viscoplastic time-dependent networks proves effective in characterizing the cyclic stress relaxation and creep behavior. For male vocal folds at a stretch of 1.4, significantly higher peak stress was found in the vocal ligament than in the vocal fold cover. Also, the male vocal ligament was significantly stiffer than the female vocal ligament. Our findings may help explain the mechanisms of some widely observed transient phenomena in F(0) regulation during phonation, such as the global declination in F(0) during the production of declarative sentences, and local F(0) changes such as overshoot and undershoot.

A simple-shear rheometer for linear viscoelastic characterization of vocal fold tissues at phonatory frequencies

Previous studies reporting the linear viscoelastic shear properties of the human vocal fold cover or mucosa have been based on torsional rheometry, with measurements limited to low audio frequencies, up to around 80 Hz. This paper describes the design and validation of a custom-built, controlled-strain, linear, simple-shear rheometer system capable of direct empirical measurements of viscoelastic shear properties at phonatory frequencies. A tissue specimen was subjected to simple shear between two parallel, rigid acrylic plates, with a linear motor creating a translational sinusoidal displacement of the specimen via the upper plate, and the lower plate transmitting the harmonic shear force resulting from the viscoelastic response of the specimen. The displacement of the specimen was measured by a linear variable differential transformer whereas the shear force was detected by a piezoelectric transducer. The frequency response characteristics of these system components were assessed by vibration experiments with accelerometers. Measurements of the viscoelastic shear moduli (G' and G") of a standard ANSI S2.21 polyurethane material and those of human vocal fold cover specimens were made, along with estimation of the system signal and noise levels. Preliminary results showed that the rheometer can provide valid and reliable rheometric data of vocal fold lamina propria specimens at frequencies of up to around 250 Hz, well into the phonatory range.

Removing undersampling artifacts in DCE-MRI studies using independent components analysis

In breast MRI mammography both high temporal resolution and high spatial resolution have been shown to be important in improving specificity. Adaptive methods such as projection reconstruction time-resolved imaging of contrast kinetics (PR-TRICKS) allow images to be reconstructed at various temporal and spatial resolutions from the same data set. The main disadvantage is that the undersampling, which is necessary to produce high temporal resolution images, leads to the presence of streak artifacts in the images. We present a novel method of removing these artifacts using independent components analysis (ICA) and demonstrate that this results in a significant improvement in image quality for both simulation studies and for patient dynamic contrast-enhanced (DCE)-MRI images. We also investigate the effect of artifacts on two quantitative measures of contrast enhancement. Using simulation studies we demonstrate that streak artifacts lead to pronounced periodic oscillations in pixel concentration curves which, in turn, lead to increased errors and introduce bias into heuristic measurements. ICA filtering significantly reduces this bias and improves accuracy. Pharmacokinetic modeling was more robust and there was no evidence of bias due to the presence of streak artifacts. ICA filtering did not significantly reduce the errors in the estimated pharmacokinetic parameters; however, the chi-squared error was greatly reduced after ICA filtering.

Collagen Injection as a Supplement to Arytenoid Adduction for Vocal Fold Paralysis

Objectives:

Dysphonia associated with vocal fold paralysis can persist even after successful medialization procedures, including arytenoid adduction. It is hypothesized that laryngeal collagen injection could improve phonation following arytenoid adduction in selected patients. Our objective was to evaluate how collagen injection could result in measurable improvements in vocal function and voice quality.

Methods:

Forty patients with unilateral vocal fold paralysis who had undergone arytenoid adduction underwent transoral injection of non—cross-linked bovine dermal collagen by means of indirect laryngoscopy and a curved injection device. A control group of 40 patients underwent arytenoid adduction but not collagen injection. The patients' voice quality was assessed perceptually with the GRBAS scale, and vocal function was assessed by acoustic and aerodynamic measures (maximum phonation time and transglottal DC flow). The relative glottal area was also assessed by videostroboscopy.

Results:

Significant improvements in vocal function and voice quality were observed with collagen injection for those patients who did not achieve satisfactory glottal competence with arytenoid adduction alone. Glottal area measurements revealed that glottic insufficiency was significantly reduced after arytenoid adduction as well as after collagen injection.

Conclusions:

The findings suggest that collagen injection could be an effective supplementary treatment for improving voice following arytenoid adduction. It has the advantage of being a minimally invasive outpatient office procedure. The long-term efficacy of the procedure should be explored.

Predictions of fundamental frequency changes during phonation based on a biomechanical model of the vocal fold lamina propria

This study examines the local and global changes of fundamental frequency (F(0)) during phonation and proposes a biomechanical model of predictions of F(0) contours based on the mechanics of vibration of vocal fold lamina propria. The biomechanical model integrates the constitutive description of the tissue mechanical response with a structural model of beam vibration. The constitutive model accounts for the nonlinear and time-dependent response of the vocal fold cover and the vocal ligament. The structural model of the vocal fold lamina propria is based on a composite beam model with axial stress. Results show that local fluctuations such as F(0) overshoots and undershoots can be characterized by the biomechanical model and might be related to the processes of stress relaxation of vocal fold tissues during length changes. The global changes of F(0) declination in declarative sentence production can also be characterized by the model. Such F(0) declination is partially attributed to the peak stress decay associated with stress relaxation of the vocal fold lamina propria and partially to neuromuscular control of the vocal fold length.

A two-layer composite model of the vocal fold lamina propria for fundamental frequency regulation

The mechanical properties of the vocal fold lamina propria, including the vocal fold cover and the vocal ligament, play an important role in regulating the fundamental frequency of human phonation. This study examines the equilibrium hyperelastic tensile deformation behavior of cover and ligament specimens isolated from excised human larynges. Ogden's hyperelastic model is used to characterize the tensile stress-stretch behaviors at equilibrium. Several statistically significant differences in the mechanical response differentiating cover and ligament, as well as gender are found. Fundamental frequencies are predicted from a string model and a beam model, both accounting for the cover and the ligament. The beam model predicts nonzero F(0) for the unstretched state of the vocal fold. It is demonstrated that bending stiffness significantly contributes to the predicted F(0), with the ligament contributing to a higher F(0), especially in females. Despite the availability of only a small data set, the model predicts an age dependence of F(0) in males in agreement with experimental findings. Accounting for two mechanisms of fundamental frequency regulation--vocal fold posturing (stretching) and extended clamping--brings predicted F(0) close to the lower bound of the human phonatory range. Advantages and limitations of the current model are discussed.

Relative contributions of collagen and elastin to elasticity of the vocal fold under tension

This study examined the contributions of collagen and elastin to the tensile elastic properties of the vocal fold lamina propria. Uniaxial stress-strain responses of vocal fold cover and vocal ligament specimens from 20 human larynges (12 males, 8 females) were quantified with sinusoidal stretch-release deformation in vitro. Mid-coronal sections of 12 specimens were examined histologically with Masson's trichrome and elastin van Gieson stain to quantify the relative densities of collagen and elastin fibers. Results showed that significantly higher levels of collagen were found in the male vocal fold than female, for both the cover and the ligament. For male there was a significantly higher level of elastin in the cover than in the ligament. On average, the elastic modulus of the male cover was about twice that of the female at high-tensile strain (35-40%), whereas the male ligament was 3-5 times stiffer than the female in the same range. The ligament was stiffer than the cover for male, but the opposite was observed for female. These findings suggested that collagen and elastin could contribute differentially to elasticity of the cover and the ligament. The data may provide guidance for surgical reconstruction and tissue engineering of different lamina propria layers.

A Biodegradable, Acellular Xenogeneic Scaffold for Regeneration of the Vocal Fold Lamina Propria

A novel method for preparing an acellular xenogeneic extracellular matrix scaffold for tissue engineering was developed. Bovine vocal fold lamina propria specimens were treated with high-concentration sodium chloride, nucleic acid digestion, and ethanol dehydration for decellularization and removal of immunogenic foreign epitopes. Human vocal fold fibroblasts from primary culture were seeded onto the acellular scaffolds and cultured for 21 days. The decellularized and the recellularized scaffolds were examined by light microscopy, fluorescent microscopy, and scanning electron microscopy. Collagen synthesis and release by fibroblasts were quantified by the Sircol assay, whereas the synthesis and release of hyaluronic acid, decorin, and fibronectin were assessed by enzyme-linked immunosorbent assays. Viscoelastic shear properties of the scaffolds were quantified by a simple-shear rheometer at frequencies of up to 250 Hz. Preliminary results showed that a biodegradable, acellular extracellular matrix scaffold with an intact basement membrane and 3-dimensional structure of the matrix proteins was engineered. Vocal fold fibroblasts readily attached to and infiltrated the scaffold with high viability and active protein synthesis, demonstrating the biocompatibility. The elastic shear modulus and dynamic viscosity of the acellular scaffold and the fibroblast-repopulated scaffold were comparable to those of the human vocal fold cover. These findings support the potential of the scaffold as a xenograft for vocal fold reconstruction and regeneration.

Viscoelastic shear properties of the fresh porcine lens

AIM

To determine the viscoelastic properties of the porcine lens

METHODS

Linear viscoelastic shear properties of the stroma of four porcine lenses were measured within 5 hours post-mortem, using sinusoidal oscillatory shear deformation. The elastic shear modulus, viscous shear modulus, dynamic viscosity, damping ratio, and phase shift of the lenses were quantified by a controlled-strain, linear simple-shear rheometer at frequencies of 10-50 Hz.

RESULTS

The mean viscoelastic properties and their standard deviations across the frequencies examined were: the elastic shear modulus, G' = 6.2+/-4.0 Pa, the viscous shear modulus, G'' = 19.2+/-2.5 Pa, the dynamic viscosity, eta' = 0.16+/-0.1 Pa x sec, the damping ratio zeta = 4.06+/-1.25, and the phase shift, delta = 76 degrees +/- 5.6 degrees.

CONCLUSIONS

The measured viscoelastic shear properties of the porcine lens reflect a low dynamic viscosity with a high damping ratio. The porcine lens is viscoelastic and is more viscous than elastic. The magnitude of the complex shear modulus of the porcine lens, |G*|, is similar to the shear modulus of the young human lens. Understanding these viscoelastic properties of the natural lens may provide guidance in developing a lens substitute capable of accommodation in the post cataract patient.