Trilayered Hydrogel Scaffold for Vocal Fold Tissue Engineering.

The lamina propria within the vocal fold (VF) is a complex multilayered tissue that increases in stiffness from the superficial to deep layer, where this characteristic is crucial for VF sound production. Tissue-engineered scaffolds designed for VF repair must mimic the biophysical nature of the native vocal fold and promote cell viability, cell spreading, and vibration with air flow. In this study, we present a unique trilayered, partially degradable hydrogel scaffold that mimics the multilayered structure of the VF lamina propria. Using thiol-norbornene photochemistry, trilayered hydrogel scaffolds were fabricated via layer-by-layer stacking with increasing polymer concentration from the top to middle to deep layer. Mechanical analysis confirmed that hydrogel modulus increased with increasing polymer concentration. Partially degradable hydrogels promoted high cell viability and cell spreading in three dimensions as assessed via live/dead and cytoskeleton staining, respectively. Importantly, partially degradable hydrogels maintained some degree of the three dimensional polymer network following protease exposure, while still enabling encapsulated cells to remodel their local environment via protease secretion. Finally, the trilayered hydrogel scaffold successfully vibrated and produced sound in proof-of-concept air flow studies. This work represents a critical first step toward the design of a multilayered, hydrogel scaffold for vocal fold tissue engineering.

A Tissue Engineered Construct for Laryngeal Regeneration: A Proof-of-Concept Device Design Study.

OBJECTIVES/HYPOTHESIS: Develop a patient-specific tissue engineered construct for laryngeal reconstruction following a partial laryngectomy. STUDY DESIGN: Bench and animal research. METHODS: A construct made from a porous polyethylene scaffold shaped in a canine-specific configuration and seeded with autologous canine adipose-derived stem cells in fibrin glue was implanted in a canine following a partial laryngectomy. After 1 year, the construct was first evaluated in vivo with high-speed imaging and acoustic-aerodynamic measures. It was then explanted and evaluated histologically. RESULTS: The canine study at 1 year revealed the construct provided voicing (barking) with acoustic and aerodynamic measures within normal ranges. The canine was able to eat and breathe normally without long-term support. The construct was integrated with epithelialization of all areas except the medial portion of the vocal fold structure. No anti-infective agents were needed after the standard perioperative medications were completed. CONCLUSION: This study provided a successful first step toward developing a patient-specific composite construct for patients undergoing partial laryngectomies. LEVEL OF EVIDENCE: NA Laryngoscope, 132:S1-S11, 2022.

High Speed Video Observations of Vocal Fold Kinematics While Playing a Clarinet.

INTRODUCTION: In this pilot study, flexible high-speed video (HSV) technology with synchronized audio is used to visualize vocal fold behavior in a wind instrumentalist. Specifically, this study aims to contribute to describing the vocal fold behavior of a professional clarinet musician playing varying tones and melodies. METHOD: Vocal folds of a healthy 26-year-old professional clarinet musician were recorded utilizing a HSV camera coupled to a flexible endoscope, which allowed the synchronous recording of audio with vocal fold movement at the onset, playing, and offset of playing. Two raters experienced with analyzing vocal folds described vocal fold motion of each sample. Samples were processed through a software model to determine the vocal fold movement relative to their position at rest. Digital kymograms (DKGs) were additionally obtained to visualize vocal fold micromovements throughout each sample. RESULTS: At the onset of playing, the raters observed the vocal folds moving to a paramedian position. Vocal fold adduction varied according to the task performed and ranged from 58% to 77% of the original resting glottis width. The calculated changes in glottis width and DKGs were consistent with the descriptions by the raters. CONCLUSION: This study demonstrates the utility of flexible HSV in observing vocal fold motion before, during, and after events other than sustained phonation. The incomplete adducted vocal fold postures observed while playing the clarinet not only differ from phonation but also differ depending on task. These various postures may contribute to voice fatigue in wind instrumentalists or to various disorders experienced during their careers.

Hydration mechanism of partially amorphized ß-tricalcium phosphate.

Calcium phosphate cements (CPCs) are applied as bone cements due to their excellent biocompatibility. In the present study, the quantitative phase content development during hydration of partially amorphized ß-tricalcium phosphate (ß-TCP) within the first 24h was investigated by in-situ X-ray diffraction (XRD) combined with the G-factor method, an external standard method. The quantity of amorphous phase (ATCP) in the powders was determined by the G-factor method. The hydration model established for partially amorphized ß-TCP indicates that ATCP reacted first, followed by the hydration of a small fraction of crystalline ß-TCP starting after some h. Consequently, hydration resulted in biphasic samples composed of calcium deficient hydroxyapatite (CDHA) and crystalline ß-TCP. The ratio wt%(CDHA)/wt%(ß-TCP) after 24h hydration was adjustable by the initial ATCP content. The crystallinity of CDHA was nearly independent of the ATCP content. Since the biological degradability of CDHA and ß-TCP differ, the degradation performance of the set cements is expected to be adjustable by varying the ATCP content. The present study provided a basic understanding of the hydration mechanism of partially amorphized ß-TCP, which is the prerequisite for the development of applicable CPC formulations. STATEMENT OF SIGNIFICANCE: Calcium phosphate cements (CPCs) are medically applied for bone repair due to their excellent biocompatibility. ß-Tricalcium phosphate (ß-TCP), which is hardly reactive in water in its crystalline state, was previously shown to be activatable by partial amorphization. This provides potential for the development of new CPCs setting to biphasic samples composed of ß-TCP and calcium deficient hydroxyapatite (CDHA). The degradation performance of these cements is expected to be adjustable by varying the ratio of CDHA to ß-TCP. In the present study, the so far unknown setting mechanism of partially amorphized ß-TCP was investigated in detail. The results contribute to the basic understanding of the hydration of partially amorphized ß-TCP, which is important for the targeted development of new cement formulations.

Reaction kinetics of dual setting α-tricalcium phosphate cements.

Addition of ductile polymers to calcium-deficient hydroxyapatite (CDHA)-forming bone cements based on α-tricalcium phosphate (α-TCP) is a promising approach to improve the mechanical performance of α-TCP cements and extend their application to load-bearing defects, which is else impeded by the brittleness of the hardened cement. One suitable polymer is poly-(2-hydroxyethylmethacrylate) (p-HEMA), which forms during cement setting by radical polymerisation of the monomer. In this study the hydration kinetics and the mechanical performance of α-TCP cements modified with addition of different HEMA concentrations (0-50 wt% in the cement liquid) was investigated by quantitative in situ XRD and four-point bending tests. Morphology of CDHA crystals was monitored by scanning electron microscopy. The hydration of α-TCP to CDHA was increasingly impeded and the visible crystal size of CDHA increasingly reduced with increasing HEMA concentration. Modification of the cements by adding 50 wt% HEMA to the cement liquid changed the brittle performance of the hardened cement to a pseudoplastic behaviour, reduced the flexural modulus and increased the work of fracture, while lower HEMA concentrations had no significant effect on these parameters. In such a composite, the extent of CDHA formation was considerably reduced (34.0 ± 1.8 wt% CDHA with 50 % HEMA compared to 54.1 ± 2.4 wt% CDHA in the reference formed after 48 h), while the general reaction kinetics were not changed. In conclusion, while the extent of CDHA formation was decreased, the mechanical properties were noticeably improved by addition of HEMA. Hence, α-TCP/HEMA composites might be suitable for application in some load-bearing defects and have adequate properties for mechanical treatment after implantation, like insertion of screws.

Differential roles for the thyroarytenoid and lateral cricoarytenoid muscles in phonation.

OBJECTIVES/HYPOTHESIS: Laryngeal adductor muscle dysfunction is a common cause of voice disorders. Reconstitution of adductor muscle function is often the target of therapy, but the effects of these muscles on voice production remain to be fully understood. This study investigated the differential roles of thyroarytenoid (TA) and lateral cricoarytenoid (LCA) muscles on voice production. STUDY DESIGN: Basic science study using an in vivo canine model of phonation. METHODS: The TA and LCA muscle nerve branches were stimulated to obtain seven graded levels of muscle activation, from threshold to maximal contraction. The effects of LCA muscle activation alone, TA muscle activation alone, and combined TA and LCA muscle activation on phonation onset parameters were investigated. Phonatory posture, phonation onset type, fundamental frequency (F0), phonation onset pressure, and airflow were evaluated. RESULTS: LCA muscle activation closed the posterior glottis, but the midmembranous gap remained. TA muscle activation closed the membranous glottis, but the posterior gap remained. Complete glottal closure was obtained only with combined TA and LCA muscle activation. Phonation onset with the LCA muscle alone was characterized by multiple modes (soft, aperiodic, periodic), whereas with the TA muscle alone it was abrupt and periodic but had significant baseline noise. Combined muscle activation led to elimination of baseline noise with stable abrupt periodic onset of phonation. Combined muscle activation was also necessary for F0 variation. The LCA muscle assisted the TA muscle in increasing subglottal pressure while concurrently reducing phonation onset airflow. CONCLUSIONS: The TA muscle is necessary for F0 variation, stable onset phonation, and increased subglottal pressure, but needs the LCA muscle for optimal effectiveness and to reduce airflow requirements with increased activation. LEVEL OF EVIDENCE: NA.

Calorimetry investigations of milled α-tricalcium phosphate (α-TCP) powders to determine the formation enthalpies of α-TCP and X-ray amorphous tricalcium phosphate.

One α-tricalcium phosphate (α-TCP) powder was either calcined at 500°C to obtain fully crystalline α-TCP or milled for different durations to obtain α-TCP powders containing various amounts of X-ray amorphous tricalcium phosphate (ATCP). These powders containing between 0 and 71wt.% ATCP and up to 2.0±0.1wt.% ß-TCP as minor phase were then hydrated in 0.1M Na2HPO4 aqueous solution and the resulting heat flows were measured by isothermal calorimetry. Additionally, the evolution of the phase composition during hydration was determined by in situ XRD combined with the G-factor method, an external standard method which facilitates the indirect quantification of amorphous phases. Maximum ATCP hydration was reached after about 1h, while that of crystalline α-TCP hydration occurred between 4 and 11h, depending on the ATCP content. An enthalpy of formation of -4065±6kJ/mol (T=23°C) was calculated for ATCP (Ca3(PO4)2), while for crystalline α-TCP (α-Ca3(PO4)2) a value of -4113±6kJ/mol (T=23°C) was determined.

Influence and interactions of laryngeal adductors and cricothyroid muscles on fundamental frequency and glottal posture control.

The interactions of the intrinsic laryngeal muscles (ILMs) in controlling fundamental frequency (F0) and glottal posture remain unclear. In an in vivo canine model, three sets of intrinsic laryngeal muscles-the thyroarytenoid (TA), cricothyroid (CT), and lateral cricoarytenoid plus interarytenoid (LCA/IA) muscle complex-were independently and accurately stimulated in a graded manner using distal laryngeal nerve stimulation. Graded neuromuscular stimulation was used to independently activate these paired intrinsic laryngeal muscles over a range from threshold to maximal activation, to produce 320 distinct laryngeal phonatory postures. At phonation onset these activation conditions were evaluated in terms of their vocal fold strain, glottal width at the vocal processes, fundamental frequency (F0), subglottic pressure, and airflow. F0 ranged from 69 to 772 Hz and clustered into chest-like and falsetto-like groups. CT activation was always required to raise F0, but could also lower F0 at low TA and LCA/IA activation levels. Increasing TA activation first increased then decreased F0 in all CT and LCA/IA activation conditions. Increasing TA activation also facilitated production of high F0 at a lower onset pressure. Independent control of membranous (TA) and cartilaginous (LCA/IA) glottal closure enabled multiple pathways for F0 control via changes in glottal posture.

Phonatory effects of type I thyroplasty implant shape and depth of medialization in unilateral vocal fold paralysis.

OBJECTIVES/HYPOTHESIS: Medialization thyroplasty (MT) is commonly used to treat glottic insufficiency. In this study, we investigated the phonatory effects of MT implant medialization depth and medial surface shape. METHODS: Recurrent laryngeal nerve (RLN) and vagal paralysis were simulated in an in vivo canine. A type 1 MT was performed using a silicone elastomer implant with variable medialization depths and medial surface shapes: rectangular, V-shaped, divergent, and convergent. The effects on phonation onset flow/pressure relationships and acoustics were measured. RESULTS: Increasing depth of medialization led to improvements in fundamental frequency (F0) range and normalization of the slope of pressure/flow relationship toward baseline activation conditions. The effects of implant medial shape also depended on depth of medialization. Outcome measures were similar among the implants at smaller medialization depths. With large medialization depths and vagal paralysis conditions, the divergent implant maintained pressure/flow relationship closer to baseline. The vagal paralysis conditions also demonstrated decreased fundamental frequency range and worse flow/pressure relationship compared to RLN paralysis. CONCLUSIONS: The depth and medial shape of a medialization laryngoplasty (ML) implant significantly affect both the F0 range and aerodynamic power required for phonation. These effects become more notable with increasing depth of medialization. The study also illustrates that ML is less effective in vagal paralysis compared to RLN paralysis. LEVEL OF EVIDENCE: N/A.

Influence of asymmetric recurrent laryngeal nerve stimulation on vibration, acoustics, and aerodynamics.

OBJECTIVES/HYPOTHESIS: Evaluate the influence of asymmetric recurrent laryngeal nerve (RLN) stimulation on the vibratory phase, acoustics and aerodynamics of phonation. STUDY DESIGN: Basic science study using an in vivo canine model. METHODS: The RLNs were symmetrically and asymmetrically stimulated over eight graded levels to test a range of vocal fold activation conditions from subtle paresis to paralysis. Vibratory phase, fundamental frequency (F0 ), subglottal pressure, and airflow were noted at phonation onset. The evaluations were repeated for three levels of symmetric superior laryngeal nerve (SLN) stimulation. RESULTS: Asymmetric laryngeal adductor activation from asymmetric left-right RLN stimulation led to a consistent pattern of vibratory phase asymmetry, with the more activated vocal fold leading in the opening phase of the glottal cycle and in mucosal wave amplitude. Vibratory amplitude asymmetry was also observed, with more lateral excursion of the glottis of the less activated side. Onset fundamental frequency was higher with asymmetric activation because the two RLNs were synergistic in decreasing F0 , glottal width, and strain. Phonation onset pressure increased and airflow decreased with symmetric RLN activation. CONCLUSION: Asymmetric laryngeal activation from RLN paresis and paralysis has consistent effects on vocal fold vibration, acoustics, and aerodynamics. This information may be useful in diagnosis and management of vocal fold paresis. LEVEL OF EVIDENCE: N/A.

Posterior cricoarytenoid muscle dynamics in canines and humans.

OBJECTIVES/HYPOTHESIS: The posterior cricoarytenoid (PCA) muscle is the sole abductor of the glottis and serves important functions during respiration, phonation, cough, and sniff. The present study examines vocal fold abduction dynamics during PCA muscle activation. STUDY DESIGN: Basic science study using an in vivo canine model and human subjects. METHODS: In four canines and five healthy humans vocal fold abduction time was measured using high-speed video recording. In the canines, PCA muscle activation was achieved using graded stimulation of the PCA nerve branch. The human subjects performed coughing and sniffing tasks. High-speed video and audio signals were concurrently recorded. RESULTS: In the canines, the vocal fold moved posteriorly, laterally, and superiorly during abduction. Average time to reach 10%, 50%, and 90% abduction was 23, 50, and 100 ms with low stimulation; 24, 58, and 129 ms with medium stimulation; and 21, 49, and 117 ms with high-level stimulation, respectively. In the humans, 100% abduction times for coughing and sniffing tasks were 79 and 193 ms, respectively. CONCLUSIONS: The PCA abduction times in canines are within the range in humans. The results also further support the notion that PCA muscles are fully active during cough.

Effect of amorphous phases during the hydraulic conversion of α-TCP into calcium-deficient hydroxyapatite.

Powders of α-tricalcium phosphate (α-TCP), which readily react with water to form calcium-deficient hydroxyapatite (CDHA), are frequently used in bone cements. As, for clinical applications, it is important to adjust the setting reaction of the cements to a reasonable reaction time, exact knowledge of the hydration mechanism is essential. It is known that prolonged milling results in partial amorphization of α-TCP powders and that dissolution of the amorphous phase significantly accelerates the hydration, but it is not clear yet when the amorphous phase reacts in comparison to the crystalline α-TCP. Therefore the aim of this study was to investigate the development of quantitative phase content of α-TCP samples during hydration. For this purpose, three α-TCP powders, containing 0, 16 and 71wt.% of amorphous phase (ATCP), were mixed with either deionized water or a 0.1M Na2HPO4 aqueous solution. The crystalline evolution of the paste was assessed quantitatively during the first 48h of hydration at 23°C by G-factor quantification. The present investigations demonstrate that ATCP reacted earlier than crystalline α-TCP. The results also suggest the formation of an X-ray amorphous phase during the hydraulic conversion formation of α-TCP into CDHA.

Effects of asymmetric superior laryngeal nerve stimulation on glottic posture, acoustics, vibration.

OBJECTIVES/HYPOTHESIS: Evaluate the effects of asymmetric superior laryngeal nerve stimulation on the vibratory phase, laryngeal posture, and acoustics. STUDY DESIGN: Basic science study using an in vivo canine model. METHODS: The superior laryngeal nerves were symmetrically and asymmetrically stimulated over eight activation levels to mimic laryngeal asymmetries representing various levels of superior laryngeal nerve paresis and paralysis conditions. Glottal posture change, vocal fold speed, and vibration of these 64 distinct laryngeal-activation conditions were evaluated by high speed video and concurrent acoustic and aerodynamic recordings. Assessments were made at phonation onset. RESULTS: Vibratory phase was symmetric in all symmetric activation conditions, but consistent phase asymmetry toward the vocal fold with higher superior laryngeal-nerve activation was observed. Superior laryngeal nerve paresis and paralysis conditions had reduced vocal fold strain and fundamental frequency. Superior laryngeal nerve activation increased vocal fold closure speed, but this effect was more pronounced for the ipsilateral vocal fold. Increasing asymmetry led to aperiodic and chaotic vibration. CONCLUSIONS: This study directly links vocal-fold tension asymmetry with vibratory phase asymmetry, in particular the side with greater tension leads in the opening phase. The clinical observations of vocal fold lag, reduced vocal range, and aperiodic voice in superior laryngeal paresis and paralysis is also supported.

Development of a glottal area index that integrates glottal gap size and open quotient.

Because voice signals result from vocal fold vibration, perceptually meaningful vibratory measures should quantify those aspects of vibration that correspond to differences in voice quality. In this study, glottal area waveforms were extracted from high-speed videoendoscopy of the vocal folds. Principal component analysis was applied to these waveforms to investigate the factors that vary with voice quality. Results showed that the first principal component derived from tokens without glottal gaps was significantly (p < 0.01) associated with the open quotient (OQ). The alternating-current (AC) measure had a significant effect (p < 0.01) on the first principal component among tokens exhibiting glottal gaps. A measure AC/OQ, defined as the ratio of AC to OQ, was proposed to combine both amplitude and temporal characteristics of the glottal area waveform for both complete and incomplete glottal closures. Analyses of "glide" phonations in which quality varied continuously from breathy to pressed showed that the AC/OQ measure was able to characterize the corresponding continuum of glottal area waveform variation, regardless of the presence or absence of glottal gaps.

Variability in the relationships among voice quality, harmonic amplitudes, open quotient, and glottal area waveform shape in sustained phonation.

Increases in open quotient are widely assumed to cause changes in the amplitude of the first harmonic relative to the second (H1*-H2*), which in turn correspond to increases in perceived vocal breathiness. Empirical support for these assumptions is rather limited, and reported relationships among these three descriptive levels have been variable. This study examined the empirical relationship among H1*-H2*, the glottal open quotient (OQ), and glottal area waveform skewness, measured synchronously from audio recordings and high-speed video images of the larynges of six phonetically knowledgeable, vocally healthy speakers who varied fundamental frequency and voice qualities quasi-orthogonally. Across speakers and voice qualities, OQ, the asymmetry coefficient, and fundamental frequency accounted for an average of 74% of the variance in H1*-H2*. However, analyses of individual speakers showed large differences in the strategies used to produce the same intended voice qualities. Thus, H1*-H2* can be predicted with good overall accuracy, but its relationship to phonatory characteristics appears to be speaker dependent.

Neuromuscular control of fundamental frequency and glottal posture at phonation onset.

The laryngeal neuromuscular mechanisms for modulating glottal posture and fundamental frequency are of interest in understanding normal laryngeal physiology and treating vocal pathology. The intrinsic laryngeal muscles in an in vivo canine model were electrically activated in a graded fashion to investigate their effects on onset frequency, phonation onset pressure, vocal fold strain, and glottal distance at the vocal processes. Muscle activation plots for these laryngeal parameters were evaluated for the interaction of following pairs of muscle activation conditions: (1) cricothyroid (CT) versus all laryngeal adductors (TA/LCA/IA), (2) CT versus LCA/IA, (3) CT versus thyroarytenoid (TA) and, (4) TA versus LCA/IA (LCA: lateral cricoarytenoid muscle, IA: interarytenoid). Increases in onset frequency and strain were primarily affected by CT activation. Onset pressure correlated with activation of all adductors in activation condition 1, but primarily with CT activation in conditions 2 and 3. TA and CT were antagonistic for strain. LCA/IA activation primarily closed the cartilaginous glottis while TA activation closed the mid-membranous glottis.

Measurement of Young's modulus of vocal folds by indentation.

OBJECTIVES: To assess the accuracy of the indentation method for stiffness measurements and to estimate the Young's modulus of the vocal fold using this technique. STUDY DESIGN: Basic science. METHODS: Indentation tests were performed using a range of indenter diameters and indentation depths on single- and double-layer silicone rubber models with various cover-layer thicknesses with known geometry and Young's moduli. Measurements were repeated on intact vocal folds and isolated muscle and cover-layer samples from three cadaveric human larynges. RESULTS: Indentation on single-layer rubber models yielded Young's moduli with acceptable accuracy when the indentation depth was equal to or smaller than the indenter diameter, and both were smaller than the physical dimensions of the material sample. On two-layer models, the stiffness estimation was similarly influenced by indenter diameter and indentation depth, and acceptable accuracy was reached when indentation depth was much smaller than the height of the top cover layer. Measurements on midmembranous vocal fold tissue revealed location-dependent Young's moduli (in kPa) as follows: intact hemilarynx, 8.6 (range=5.3-13.1); isolated inferior medial surface cover, 7.5 (range=7-7.9); isolated medial surface cover, 4.8 (range=3.9-5.7); isolated superior surface cover, 2.9 (range=2.7-3.2); and isolated thyroarytenoid muscle, 2.0 (range=1.3-2.7). CONCLUSIONS: Indenter diameter, indentation depth, and material thickness are important parameters in the measurement of vocal fold stiffness using the indentation technique. Measurements on human larynges showed location-dependent differences in stiffness. The stiffness of the vocal folds was also found to be higher when the vocal fold structure was still attached to the laryngeal framework compared with that when the vocal fold was separated from the framework.

Graded activation of the intrinsic laryngeal muscles for vocal fold posturing.

Previous investigations using in vivo models to study the role of intrinsic laryngeal muscles in phonation have used neuromuscular stimulation to study voice parameters. However, these studies used coarse stimulation techniques using limited levels of neuromuscular stimulation. In the current investigation, a technique for fine control of laryngeal posturing was developed using graded stimulation of the laryngeal nerves. Vocal fold strain history to graded stimulation and a methodology for establishing symmetric laryngeal activation is presented. This methodology has immediate applications for the study of laryngeal paralysis and paresis, as well as general questions of neuromuscular control of the larynx.

Functional testing of a tissue-engineered vocal fold cover replacement.

OBJECTIVES: Tissue engineering may provide a treatment for severe vocal fold scars. This study quantifies mechanical properties and demonstrates vibration of a tissue-engineered vocal fold cover replacement. METHODS: Tissue-engineered constructs were produced from fibrin and adipose-derived stem cells. Optimized bilayered constructs contained epithelial and mesenchymal cell phenotypes in a stratified geometry. For comparison, homogeneous constructs did not have epithelial differentiation. Elastic modulus was determined using indentation. Immunohistochemical labeling for type I collagen was performed. A bilayered construct was also tested in phonation in an excised larynx model. RESULTS: Bilayered vocal fold cover replacements had indentation moduli similar to human vocal fold covers (mean construct modulus 6.8 kPa). Collagen deposition occurred in the middle of the construct. Homogeneous constructs had a mean modulus of 8.3 kPa, and collagen was concentrated at the surface. An excised larynx with unilateral vocal fold cover replacement phonated and exhibited mucosal waves at physiologic airflow. CONCLUSION: Bilayered tissue-engineered constructs were produced that exhibited indentation modulus, microstructure, and vibration similar to that exhibited by human vocal fold covers.

On the acoustical relevance of supraglottal flow structures to low-frequency voice production.

The supraglottal flow exhibits many complex phenomena such as recirculation, jet instabilities, jet attachment to one vocal fold wall, jet flapping, and transition to turbulence. The acoustical relevance of these flow structures to low-frequency voice production was evaluated by disturbing the supraglottal flow field using a cylinder and observing the consequence on the resulting sound pressure field. Despite a significantly altered supraglottal flow field due to the presence of the cylinder, only small changes in sound pressure amplitude and spectral shape were observed. The implications of the results on our understanding of phonation physics and modeling of phonation are discussed.