Stimulus characteristics of a novel air-based multiple stimulus aesthesiometer.

PURPOSE: To identify the stimulus airflow characteristics and confirm the consistency of a novel air jet-based aesthesiometer capable of producing and applying multiple stimuli separated either by time and/or by space. METHODS: A novel aesthesiometer (Dolphin Aesthesiometer) was designed around a micro-blower under software management. Two nozzle attachments assisted in airflow control (flexible tube 1.6 mm diameter; brass tube 0.5 mm diameter). Four studies that tested the characteristics of the airflow and stimulus consistency were completed: (i) airflow pattern/trajectory, (ii) airflow surface dispersion, (iii) force of airflow across a range of stimulus strengths and (iv) thermal effects on the ocular surface. RESULTS: Stimulus characteristic studies revealed: (i) airflow is coherent within the expected test distance range for the instrument, and spread rate is constant irrespective of stimulus strength; (ii) airflow dispersion occurs upon encountering a surface and dispersion increases with increasing airflow rate; (iii) a consistent and small force (10-4 N) is applied by the airflow and (iv) repeatable thermal effects occur in relation to the airflow, and the mode of stimulation of the Dolphin aesthesiometer is predominantly thermal in nature. CONCLUSIONS: These studies confirm the repeatability and consistency of the novel instrument. The device is suitable for measuring corneal sensitivity. The availability of additional air jets allows the application of multiple stimuli to facilitate corneal summation investigations.

Sensitivity of Phonation Onset Pressure to Vocal Fold Stiffness Distribution.

Phonation onset is characterized by the unstable growth of vocal fold (VF) vibrations that ultimately results in self-sustained oscillation and the production of modal voice. Motivated by histological studies, much research has focused on the role of the layered structure of the vocal folds in influencing phonation onset, wherein the outer "cover" layer is relatively soft and the inner "body" layer is relatively stiff. Recent research, however, suggests that the body-cover (BC) structure over-simplifies actual stiffness distributions by neglecting important spatial variations, such as inferior-superior (IS) and anterior-posterior gradients and smooth transitions in stiffness from one histological layer to another. Herein, we explore sensitivity of phonation onset to stiffness gradients and smoothness. By assuming no a priori stiffness distribution and considering a second-order Taylor series sensitivity analysis of phonation onset pressure with respect to stiffness, we find two general smooth stiffness distributions most strongly influence onset pressure: a smooth stiffness containing aspects of BC differences and IS gradients in the cover, which plays a role in minimizing onset pressure, and uniform increases in stiffness, which raise onset pressure and frequency. While the smooth stiffness change contains aspects qualitatively similar to layered BC distributions used in computational studies, smooth transitions in stiffness result in higher sensitivity of onset pressure than discrete layering. These two general stiffness distributions also provide a simple, low-dimensional, interpretation of how complex variations in VF stiffness affect onset pressure, enabling refined exploration of the effects of stiffness distributions on phonation onset.

Dipole- and vortex sheet-based models of fish swimming.

Elucidating the hydrodynamics of fish swimming is critical to identifying the processes underlying fish orientation and schooling. Due to their mathematical tractability, models based on potential flow are preferred in the study of bidirectional interactions of fish with their surroundings. Dipole-based models that assimilate fish to pairs of vortices are particularly enticing, but yet to be thoroughly validated. Here, we embark on a computational fluid dynamics (CFD) campaign informed by experimental data to validate the accuracy of dipole-based models. The locomotory patterns of a fish undergoing carangiform swimming are reconstructed from existing experimental data, which are used as inputs to CFD simulations of a fish swimming in a channel flow. We demonstrate that dipole-based models are accurate in capturing key features of the fluid flow, but cannot predict the elongated flow streamlines around the fish that are evident in CFD. To address this issue, we propose an alternative model that replaces each vortex in the pair with a sheet along the fish length. Using a pair of vortex sheets that span approximately 80% of the fish body length with a separation distance of approximately 50% of the body width, the model is successful in predicting the fluid flow around the swimming fish for a range of background flow speeds and channel widths. The proposed model shows improved accuracy at the cost of a mildly increased computational effort, thereby constituting an ideal basis for research on fish hydrodynamics.

Effect of nodule size and stiffness on phonation threshold and collision pressures in a synthetic hemilaryngeal vocal fold model.

Synthetic vocal fold (VF) replicas were used to explore the role of nodule size and stiffness on kinematic, aerodynamic, and acoustic measures of voiced speech production. Emphasis was placed on determining how changes in collision pressure may contribute to the development of phonotrauma. This was performed by adding spherical beads with different sizes and moduli of elasticity at the middle of the medial surface of synthetic silicone VF models, representing nodules of varying size and stiffness. The VF models were incorporated into a hemilaryngeal flow facility. For each case, self-sustained oscillations were investigated at the phonation threshold pressure. It was found that increasing the nodule diameter increased the open quotient, phonation threshold pressure, and phonation threshold flow rate. However, these values did not change considerably as a function of the modulus of elasticity of the nodule. Nevertheless, the ratio of collision pressure to subglottal pressure increased significantly for both increasing nodule size and stiffness. This suggests that over time, both growth in size and fibrosis of nodules will lead to an increasing cycle of compensatory vocal hyperfunction that accelerates phonotrauma.

Modeling the influence of COVID-19 protective measures on the mechanics of phonation.

In an effort to mitigate the 2019 novel coronavirus disease pandemic, mask wearing and social distancing have become standard practices. While effective in fighting the spread of the virus, these protective measures have been shown to deteriorate speech perception and sound intensity, which necessitates speaking louder to compensate. The goal of this paper is to investigate via numerical simulations how compensating for mask wearing and social distancing affects measures associated with vocal health. A three-mass body-cover model of the vocal folds (VFs) coupled with the sub- and supraglottal acoustic tracts is modified to incorporate mask and distance dependent acoustic pressure models. The results indicate that sustaining target levels of intelligibility and/or sound intensity while using these protective measures may necessitate increased subglottal pressure, leading to higher VF collision and, thus, potentially inducing a state of vocal hyperfunction, a progenitor to voice pathologies.

Triangular body-cover model of the vocal folds with coordinated activation of the five intrinsic laryngeal muscles.

Poor laryngeal muscle coordination that results in abnormal glottal posturing is believed to be a primary etiologic factor in common voice disorders such as non-phonotraumatic vocal hyperfunction. Abnormal activity of antagonistic laryngeal muscles is hypothesized to play a key role in the alteration of normal vocal fold biomechanics that results in the dysphonia associated with such disorders. Current low-order models of the vocal folds are unsatisfactory to test this hypothesis since they do not capture the co-contraction of antagonist laryngeal muscle pairs. To address this limitation, a self-sustained triangular body-cover model with full intrinsic muscle control is introduced. The proposed scheme shows good agreement with prior studies using finite element models, excised larynges, and clinical studies in sustained and time-varying vocal gestures. Simulations of vocal fold posturing obtained with distinct antagonistic muscle activation yield clear differences in kinematic, aerodynamic, and acoustic measures. The proposed tool is deemed sufficiently accurate and flexible for future comprehensive investigations of non-phonotraumatic vocal hyperfunction and other laryngeal motor control disorders.

Physics of phonation offset: Towards understanding relative fundamental frequency observations.

Relative fundamental frequency (RFF) is a promising assessment technique for vocal pathologies. Herein, we explore the underlying laryngeal factors dictating RFF behaviours during phonation offset. To gain physical insights, we analyze a simple impact oscillator model and follow that with a numerical study using the well-established body-cover model of the vocal folds (VFs). Study of the impact oscillator suggests that the observed decrease in fundamental frequency during offset is due, at least in part, to the increase in the neutral gap between the VFs during abduction and the concomitant decrease in collision forces. Moreover, the impact oscillator elucidates a correlation between sharper drops in RFF and increased stiffness of the VFs, supporting experimental RFF studies. The body-cover model study further emphasizes the correlation between the drops in RFF and collision forces. The numerical analysis also illustrates the sensitivity of RFF to abduction initiation time relative to the phase of the phonation cycle, and the abduction period length. In addition, the numerical simulations display the potential role of the cricothyroid muscle to mitigate the RFF reduction. Last, simplified models of phonotraumatic vocal hyperfunction are explored, demonstrating that the observed sharper drops in RFF are associated with increased pre-offset collision forces.

Vocal fold dynamics in a synthetic self-oscillating model: Contact pressure and dissipated-energy dose.

The energy dissipated during vocal fold (VF) contact is a predictor of phonotrauma. Difficulty measuring contact pressure has forced prior energy dissipation estimates to rely upon generalized approximations of the contact dynamics. To address this shortcoming, contact pressure was measured in a self-oscillating synthetic VF model with high spatiotemporal resolution using a hemilaryngeal configuration. The approach yields a temporal resolution of less than 0.26 ms and a spatial resolution of 0.254 mm in the inferior-superior direction. The average contact pressure was found to be 32% of the peak contact pressure, 60% higher than the ratio estimated in prior studies. It was found that 52% of the total power was dissipated due to collision. The power dissipated during contact was an order of magnitude higher than the power dissipated due to internal friction during the non-contact phase of oscillation. Both the contact pressure magnitude and dissipated power were found to be maximums at the mid anterior-posterior position, supporting the idea that collision is responsible for the formation of benign lesions, which normally appear at the middle third of the VF.

Vocal fold dynamics in a synthetic self-oscillating model: Intraglottal aerodynamic pressure and energy.

Self-sustained oscillations of the vocal folds (VFs) during phonation are the result of the energy exchange between the airflow and VF tissue. Understanding this mechanism requires accurate investigation of the aerodynamic pressures acting on the VF surface during oscillation. A self-oscillating silicone VF model was used in a hemilaryngeal flow facility to measure the time-varying pressure distribution along the inferior-superior thickness of the VF and at four discrete locations in the anterior-posterior direction. It was found that the intraglottal pressures during the opening and closing phases of the glottis are highly dependent on three-dimensional and unsteady flow behaviors. The measured aerodynamic pressures and estimates of the medial surface velocity were used to compute the intraglottal energy transfer from the airflow to the VFs. The energy was greatest at the anterior-posterior midline and decreased significantly toward the anterior/posterior endpoints. The findings provide insight into the dynamics of the VF oscillation and potential causes of some VF disorders.

Continuous forearm cooling attenuates gastrointestinal temperature increase during cycling.

Hot environmental conditions can challenge thermoregulation resulting in exacerbated heat strain. This study evaluated the influence of continuous inner forearm cooling on gastrointestinal temperature (TGI) and physiological responses to exercise in hot (30°C) and humid (relative humidity: 70%) conditions. Eleven trained cyclists (seven male age: 37±12 years; four female age: 41±15 years; mean±standard deviation) performed two experimental trials, cycling at 66% of their self-reported functional threshold power (average work rate over an hour of maximum effort cycling; 175±34W) for 45 minutes in an environmental chamber. One trial employed continuous inner forearm cooling (COOL) with 5°C water passing through aluminum heat exchangers, while the other had no cooling (CONTROL). Heat was removed from the body at an average rate of 30.3±6.6W during the COOL trial resulting in an attenuation of TGI rise (CONTROL: 2.46±0.70, COOL: 2.03±0.63°C·h-1; p=0.002). The change in heart rate from the 10th minute to the end of exercise, as an indicator of cardiovascular drift, was reduced (CONTROL: 20±7, COOL: 17±6beats·min-1; p=0.050) and end-exercise thermal comfort was improved in the COOL trial with a trend for reduced rating of perceived exertion (p=0.055). Findings suggest that continuous cooling of the inner forearms can attenuate the rise of TGI and help mitigate the risk of heat injury during exercise in hot and humid conditions.

Bayesian estimation of vocal function measures using laryngeal high-speed videoendoscopy and glottal airflow estimates: An in vivo case study.

This study introduces the in vivo application of a Bayesian framework to estimate subglottal pressure, laryngeal muscle activation, and vocal fold contact pressure from calibrated transnasal high-speed videoendoscopy and oral airflow data. A subject-specific, lumped-element vocal fold model is estimated using an extended Kalman filter and two observation models involving glottal area and glottal airflow. Model-based inferences using data from a vocally healthy male individual are compared with empirical estimates of subglottal pressure and reference values for muscle activation and contact pressure in the literature, thus providing baseline error metrics for future clinical investigations.

Comparison of pulse contour, aortic Doppler ultrasound and bioelectrical impedance estimates of stroke volume during rapid changes in blood pressure.

NEW FINDINGS: What is the central question of this study? Pulse contour analysis of the finger arterial pressure by Windkessel modelling is commonly used to estimate stroke volume continuously. But is it valid during dynamic changes in blood pressure? What is the main finding and its importance? Second-by-second analysis revealed that pulse contour analysis underestimated stroke volume by up to 25% after standing from a squat, and 16% after standing thigh-cuff release, when compared with aortic Doppler ultrasound estimates. These results reveal that pulse contour analysis of stroke volume should be interpreted with caution during rapid changes in physiological state. ABSTRACT: Dynamic measurements of stroke volume (SV) and cardiac output provide an index of central haemodynamics during transitional states, such as postural changes and onset of exercise. The most widely used method to assess dynamic fluctuations in SV is the Modelflow method, which uses the arterial blood pressure waveform along with age- and sex-specific aortic properties to compute beat-to-beat estimates of aortic flow. Modelflow has been validated against more direct methods in steady-state conditions, but not during dynamic changes in physiological state, such as active orthostatic stress testing. In the present study, we compared the dynamic SV responses from Modelflow (SVMF ), aortic Doppler ultrasound (SVU/S ) and bioelectrical impedance analysis (SVBIA ) during two different orthostatic stress tests, a squat-to-stand (S-S) transition and a standing bilateral thigh-cuff release (TCR), in 15 adults (six females). Second-by-second analysis revealed that when compared with estimates of SV by aortic Doppler ultrasound, Modelflow underestimated SV by up to 25% from 3 to 11 s after standing from the squat position and by up to 16% from 3 to 7 s after TCR (P < 0.05). The SVMF and SVBIA were similar during the first minute of the S-S transition, but were different 3 s after TCR and at intermittent time points between 34 and 44 s (P < 0.05). These findings indicate that the physiological conditions elicited by orthostatic stress testing violate some of the inherent assumptions of Modelflow and challenge models used to interpret bioelectrical impedance responses, resulting in an underestimation in SV during rapid changes in physiological state.

Haemodynamic and cerebrovascular effects of intermittent lower-leg compression as countermeasure to orthostatic stress.

NEW FINDINGS: What is the central question of this study? Does smartly timed intermittent compression of the lower legs alter cerebral blood velocity and oxygenation during acute orthostatic challenges? What is the main finding and its importance? Intermittent compression timed to the local diastolic phase increased the blood flux through the legs and heart after two different orthostatic stress tests. Cerebral blood velocity improved during the first minute of recovery, and indices of cerebral tissue oxygenation remained elevated for 2 min. These results provide promise for the use of lower-leg active compression as a therapeutic tool for individuals vulnerable to initial orthostatic hypotension and orthostatic stress. ABSTRACT: Intermittent compression of the lower legs provides the possibility of improving orthostatic tolerance by actively promoting venous return and improving central haemodynamics. We tested the hypothesis that intermittent compression of 65 mmHg timed to occur only within the local diastolic phase of each cardiac cycle would attenuate the decrease in blood pressure and improve cerebral haemodynamics during the first minute of recovery from two different orthostatic stress tests. Fourteen subjects (seven female) performed four squat-to-stand transitions and four repeats of standing bilateral thigh-cuff occlusion and release (TCR), with intermittent compression of the lower legs applied in half of the trials. Blood flow in the superficial femoral artery, mean arterial pressure, Doppler ultrasound cardiac output, total peripheral resistance, middle cerebral artery blood velocity (MCAv) and cerebral tissue saturation index (TSI%) were monitored. With both orthostatic stress tests, there was a significant compression × time interaction for superficial femoral artery flow (P < 0.001). The hypotensive state was attenuated with intermittent compression despite decreased total peripheral resistance (squat-to-stand, compression × time interaction, P < 0.001; TCR, compression × time interaction, P = 0.002) as a consequence of elevated cardiac output in both tests (P < 0.001). Intermittent compression also increased MCAv (P = 0.001) and TSI% (P < 0.001) during the squat-to-stand transition and during TCR (MCAv and TSI%, compression × time interaction, P < 0.001). Intermittent compression of the lower legs during quiet standing after an active orthostatic challenge augmented local, central and cerebral haemodynamics, providing potential as a therapeutic tool for individuals vulnerable to orthostatic stress.

The effect of high-speed videoendoscopy configuration on reduced-order model parameter estimates by Bayesian inference.

Bayesian inference has been previously demonstrated as a viable inverse analysis tool for estimating subject-specific reduced-order model parameters and uncertainties. However, previous studies have relied upon simulated glottal area waveforms with superimposed random noise as the measurement. In practice, high-speed videoendoscopy is used to measure glottal area, which introduces practical imaging effects not captured in simulated data, such as viewing angle, frame rate, and camera resolution. Herein, high-speed videos of the vocal folds were approximated by recording the trajectories of physical vocal fold models controlled by a symmetric body-cover model. Twenty videos were recorded, varying subglottal pressure, cricothyroid activation, and viewing angle, with frame rate and video resolution varied by digital video manipulation. Bayesian inference was used to estimate subglottal pressure and cricothyroid activation from glottal area waveforms extracted from the videos. The resulting estimates show off-axis viewing of 10° can lead to a 10% bias in the estimated subglottal pressure. A viewing model is introduced such that viewing angle can be included as an estimated parameter, which alleviates estimate bias. Frame rate and pixel resolution were found to primarily affect uncertainty of parameter estimates up to a limit where spatial and temporal resolutions were too poor to resolve the glottal area. Since many high-speed cameras have the ability to sacrifice spatial for temporal resolution, the findings herein suggest that Bayesian inference studies employing high-speed video should increase temporal resolutions at the expense of spatial resolution for reduced estimate uncertainties.

An extended Kalman filter approach to non-stationary Bayesian estimation of reduced-order vocal fold model parameters.

The Bayesian framework for parameter inference provides a basis from which subject-specific reduced-order vocal fold models can be generated. Previously, it has been shown that a particle filter technique is capable of producing estimates and associated credibility intervals of time-varying reduced-order vocal fold model parameters. However, the particle filter approach is difficult to implement and has a high computational cost, which can be barriers to clinical adoption. This work presents an alternative estimation strategy based upon Kalman filtering aimed at reducing the computational cost of subject-specific model development. The robustness of this approach to Gaussian and non-Gaussian noise is discussed. The extended Kalman filter (EKF) approach is found to perform very well in comparison with the particle filter technique at dramatically lower computational cost. Based upon the test cases explored, the EKF is comparable in terms of accuracy to the particle filter technique when greater than 6000 particles are employed; if less particles are employed, the EKF actually performs better. For comparable levels of accuracy, the solution time is reduced by 2 orders of magnitude when employing the EKF. By virtue of the approximations used in the EKF, however, the credibility intervals tend to be slightly underpredicted.

Investigating the impact of passive external lower limb compression on central and peripheral hemodynamics during exercise.

PURPOSE: The objective of this study was to assess the effectiveness of graduated compression socks (GCS) on enhancing muscle blood flow and oxygenation during exercise and recovery in healthy subjects. METHODS: Twelve healthy volunteers completed a protocol involving baseline, exercise, and recovery periods with and without GCS. Each test was repeated twice to assess repeatability of the results. The applied sock pressure was measured prior to experimentation using a custom pressure sensing system, and modified as necessary using tensor bandages to control the applied load. During each of the experimental phases, blood velocity in the popliteal artery, calf muscle tissue oxygenation, muscle activity, heart rate, blood pressure, cardiac output, and applied pressure from the sock were measured. Popliteal artery diameter was measured during baseline and recovery periods. RESULTS: The GCS significantly reduced deoxyhemoglobin (HHb) in the leg during baseline (HHb, p = 0.001) and total blood volume and HHb in the leg during exercise (total hemoglobin, p = 0.01; HHb, p = 0.02). However, there were no differences in leg muscle blood flow velocity or any other variables with and without GCS at baseline, exercise, or recovery. Interestingly, it was found that the local applied sock pressure was very sensitive to the sock application process and, furthermore, the pressure varied considerably during exercise. CONCLUSIONS: No significant changes were observed in measures reflecting oxygen delivery for healthy subjects using GCS during exercise and recovery. Applied sock pressure was carefully controlled, thus eliminating the sock application process as a variable.

Non-stationary Bayesian estimation of parameters from a body cover model of the vocal folds.

The evolution of reduced-order vocal fold models into clinically useful tools for subject-specific diagnosis and treatment hinges upon successfully and accurately representing an individual patient in the modeling framework. This, in turn, requires inference of model parameters from clinical measurements in order to tune a model to the given individual. Bayesian analysis is a powerful tool for estimating model parameter probabilities based upon a set of observed data. In this work, a Bayesian particle filter sampling technique capable of estimating time-varying model parameters, as occur in complex vocal gestures, is introduced. The technique is compared with time-invariant Bayesian estimation and least squares methods for determining both stationary and non-stationary parameters. The current technique accurately estimates the time-varying unknown model parameter and maintains tight credibility bounds. The credibility bounds are particularly relevant from a clinical perspective, as they provide insight into the confidence a clinician should have in the model predictions.

The effect of hydroxyquinoline-based gel on pessary-associated bacterial vaginosis: a multicenter randomized controlled trial.

OBJECTIVE: Pessaries are important options for women with pelvic floor disorders, but many pessary users experience bacterial vaginosis (BV). The aim of this study was to evaluate the effect of TrimoSan gel (Milex Pessaries, Cooper Surgical, Trumbull, CT) on BV prevalence among pessary users. STUDY DESIGN: Women presenting for a pessary fitting completed questionnaires on vaginal symptoms and hormone therapy use and underwent a BV BLUE test and slide collection for BV analysis by Nugent's criteria. Following pessary fitting, women were randomized to either standard pessary care with the use of TrimoSan placed vaginally twice weekly or to standard pessary care without TrimoSan gel. Women returned 2 weeks and 3 months later for a repeat slide collection for Gram stain, BV BLUE testing, and completion of questionnaires on vaginal symptoms and desire to continue the pessary. RESULTS: There were 184 women randomized after successful fitting (92 to the TrimoSan group), and 147 (79%) presented for 3-month follow up. Mean age was 56 ± 16 years; patients were mostly white (57%) or Hispanic (23%), and 36% were using hormone therapy. The groups did not differ in the prevalence of BV by Nugent's criteria at 2 weeks (20% TrimoSan vs 26% no gel, P = .46) or 3 months (24% TrimoSan vs 23% no gel, P = .82), nor did they differ in BV by BV BLUE testing at 2 weeks (0% TrimoSan vs 4% no gel, P = .12) or 3 months (3% TrimoSan vs 0% no gel, P = .15). The prevalence of at least one vaginal symptom did not differ between groups at 2 weeks (44% TrimoSan vs 45% no gel, P = .98) or 3 months (42% TrimoSan vs 32% no gel, P = .30). The TrimoSan group was equally likely to want to continue their pessary use compared with the standard care group at 2 weeks (90% vs 86%, P = .64) and 3 months (63% vs 60%, P = .76). CONCLUSION: TrimoSan gel in the first 3 months of pessary use does not decrease the prevalence of BV or vaginal symptoms and does not alter the likelihood of a woman desiring to continue pessary use.

Numerical investigation of fluid flow in a chandler loop.

The Chandler loop is an artificial circulatory platform for in vitro hemodynamic experiments. In most experiments, the working fluid is subjected to a strain rate field via rotation of the Chandler loop, which, in turn, induces biochemical responses of the suspended cells. For low rotation rates, the strain rate field can be approximated using laminar flow in a straight tube. However, as the rotation rate increases, the effect of the tube curvature causes significant deviation from the laminar straight tube approximation. In this manuscript, we investigate the flow and associated strain rate field of an incompressible Newtonian fluid in a Chandler loop as a function of the governing nondimensional parameters. Analytical estimates of the strain rate from a perturbation solution for pressure driven steady flow in a curved tube suggest that the strain rate should increase with Dean number, which is proportional to the tangential velocity of the rotating tube, and the radius to radius of curvature ratio of the loop. Parametrically varying the rotation rate, tube geometry, and fill ratio of the loop show that strain rate can actually decrease with Dean number. We show that this is due to the nonlinear relationship between the tube rotation rate and height difference between the two menisci in the rotating tube, which provides the driving pressure gradient. An alternative Dean number is presented to naturally incorporate the fill ratio and collapse the numerical data. Using this modified Dean number, we propose an empirical formula for predicting the average fluid strain rate magnitude that is valid over a much wider parameter range than the more restrictive straight tube-based prediction.

Modeling the effects of a posterior glottal opening on vocal fold dynamics with implications for vocal hyperfunction.

Despite the frequent observation of a persistent opening in the posterior cartilaginous glottis in normal and pathological phonation, its influence on the self-sustained oscillations of the vocal folds is not well understood. The effects of a posterior gap on the vocal fold tissue dynamics and resulting acoustics were numerically investigated using a specially designed flow solver and a reduced-order model of human phonation. The inclusion of posterior gap areas of 0.03-0.1 cm(2) reduced the energy transfer from the fluid to the vocal folds by more than 42%-80% and the radiated sound pressure level by 6-14 dB, respectively. The model was used to simulate vocal hyperfucntion, i.e., patterns of vocal misuse/abuse associated with many of the most common voice disorders. In this first approximation, vocal hyperfunction was modeled by introducing a compensatory increase in lung air pressure to regain the vocal loudness level that was produced prior to introducing a large glottal gap. This resulted in a significant increase in maximum flow declination rate and amplitude of unsteady flow, thereby mimicking clinical studies. The amplitude of unsteady flow was found to be linearly correlated with collision forces, thus being an indicative measure of vocal hyperfunction.