DIGITS

Objective: During phonation, energy is transferred from the subglottal airflow through the air/mucosa interface which results in the propagation of the mucosal wave in the vocal fold. The vocal fold is soft, and the subglottal mucosa is stiff. We hypothesize that it is highly improbable that there is a rigid boundary between the tissue structures, with a sudden drop in stiffness; and that a gradual change would be more likely to support the efficient transfer of energy from the air-flow to the mucosal wave. Our objective is to test this hypothesis by quantifying the change in mucosa stiffness with respect to anatomical position.

The aim of this study was to measure the shear modulus of the vocal fold in a human hemilarynx, such that the data can be related to direction of applied stress and anatomical context. Dynamic spring rate data were collected using a modified linear skin rheometer using human hemilarynges, and converted to estimated shear modulus via application of a simple shear model. The measurement probe was attached to the epithelial layer of the vocal fold cover using suction. A sinusoidal force of 3 g was applied to the epithelium, and the resultant displacement logged at a rate of 1 kHz. Force measurement accuracy was 20 mg and position measurement accuracy was 4 mm. The force was applied in a transverse direction at the midmembranous point between the vocal process and the anterior commissure. The shear modulus of the three female vocal folds ranged from 814 to 1232 Pa. The shear modulus of the three male vocal folds ranged from 1021 to 1796 Pa. These data demonstrate that it is possible to obtain estimates for the shear modulus of the vocal fold while preserving anatomical context. The modulus values reported here are higher than those reported using parallel plate rheometry. This is to be expected as the tissue is attached to surrounding structures, and is under natural tension.

The characterization of vocal fold scar is advancing on the molecular and clinical levels. As the number of possible interventions for vocal fold scar grows and with the advancement of mathematical modeling to help predict oscillation, greater accuracy and precision in the measurement of vocal fold pliability will become essential. Although indirect pliability measures of pliability have been used with successfully, direct measurement of tissue pliability is essential. Indirect measurement with Pparallel plate technology has proven useful in this regard but is limited in its utililimitationsty; i. It requires the vocal fold to be removed fromrequires the tissue to be removed from the surrounding framework, allows no does not measure site-specificity pliability, and offers no future for in-situ vivo use in animals or humans.

The shear modulus of the vocal fold is an essential parameter required to enhance our understanding of how the vocal fold operates, to develop mathematical models of phonatation, and to provide benchmarks to quantify the effectiveness of surgical procedures. The authors announced the successful deployment of an instrument to measure vocal fold elasticity in-vivo last year, and now present the data taken from 8 patients in-vivo. The shear modulus was measured at the mid-membranous point, in a transverse direction with respect to the axis drawn between the anterior commissure and vocal process. The range of mean shear modulus results is 701 to 2225 Pascals, with a mean value of 1371 Pascals.

Quantification of the elastic properties of the human vocal fold provides invaluable data for researchers deriving mathematical models of phonation, developing tissue engineering therapies, and as normative data for comparison between healthy and scarred tissue. This study measured the shear modulus of excised cadaver vocal folds from 20 subjects. Twenty freshly excised human larynxes were evaluated less than four days post-mortem. They were split along the saggital plane and mounted without tension. Shear modulus was obtained by two different methods. For method 1 cyclical shear stress was applied transversely to the mid-membranous portion of the vocal fold, and shear modulus derived by applying a simple shear model. For method 2 the apparatus was configured as an indentometer, and shear modulus obtained from the stress/strain data by applying an established analytical technique. Method 1 shear model for male larynxes yielded a range from 246 to 3,356 Pa, with a mean value of 1,008 and SD of 380. The range for female larynxes was 286-3,332 Pa, with a mean value of 1,237 and SD of 768. Method 2 indentometer model for male larynxes yielded a range from 552 to 2,741 Pa, with a mean value of 1,000 and SD of 460. The range for female larynxes was 509-1,989 Pa, with a mean value of 1,332 and SD of 428. We have successfully demonstrated two methodologies that are capable of directly measuring the shear modulus of the human vocal fold, without dissecting out the vocal fold cover tissue. The sample size of nine female and 11 male larynxes is too small to validate a general conclusion. The high degree of variability in this small cohort of subjects indicates that factors such as age, health status, and post-mortem delay may be significant; and that there is range of 'normality' for vocal fold tissue.

The Gas Bearing Electrodynamometer (GBE)(1) has been used for the last 20 years to obtain sensitive measurements of the stratum corneum. A new instrument for measuring the mechanical properties of the stratum corneum incorporates all of the measurement principles of the GBE but none of its components. A force-controlled miniature d.c. servo, gearing and leadscrew replace the magnet / solenoid arrangement of the GBE. Error resulting from conversion of an electrical signal to a mechanical force is automatically compensated. Consequently, this control renders the need for a friction-free bearing redundant. The original Linear Variable Differential Transformer (LVDT) has been replaced with a unit with a sensitivity of 0.01% and force is now measured by a calibrated 50g load beam. The function generator, signal conditioner and storage oscilloscope have been replaced by user-friendly software run by a small portable computer. The new design offers greater inherent accuracy than the GBE and requires minimal servicing. The new instrument (Linear Skin Rheometer, "LSR" ) has been shown to provide sensitive measurements of stratum corneum mechanics and was used to measure the mechanical responses of the stratum corneum to two topical moisturising treatments of differing relative hydration performance (as determined by impedance measurements using the Nova™ DPM9003). The relative performance of the two products as measured by the LSR compared favourably with corresponding impedance data, indicating the ability of the LSR to differentiate varying degrees of stratum corneum plasticisation in response to hydration.

Problem: Hyaluronan has been shown to improve the viscoelastic properties after injections in normal rabbit vocal folds and in patients with unilateral paresis and vocal fold atrophy. Viscoelasticity is important to the vocal fold vibratory capacity. The aim of the study was to analyze the short-term viscoelastic properties after the injection of hyaluronan in scarred rabbit vocal folds.Methods: Vocal folds of New Zealand rabbits were scarred and after 2 months one group received injections with crosslinked hyaluronan and another group was injected with saline. After 2 more months (4 months after scarring) both groups and a third group of control animals with normal vocal folds were euthanized. The larynges were dissected out, 16 vocal folds were frozen in -20 C for viscoelastic measurements, whereas 16 vocal folds were prepared and stained for histological analysis including measurements from digitized slides. Two methods were used for the viscoelastic analysis: (1) analyses were made on intact vocal folds with a linear skin rheometer (LSR) adapted to laryngeal measurements, and (2) the vocal folds were dissected and analyzed in a parallel-plate rheometer.Results: Measurements on the digitized slides showed a thickened lamina propria of the scarred samples as compared to the normal vocal folds (P < 0.05). The viscoelastic LSR analysis on intact vocal folds showed a tendency to stiffening of the scarred vocal folds as compared to the normal group (P = 0.05). The parallel plate rheometry on the same samples after dissection showed a decreased dynamic viscocity of the scarred samples injected with hyaluronan (Hylaform) as compared to the normals and to the scarred group that received no hyaluronan (P < 0.01 and P < 0.05, respectively).Conclusion: Injection of scarred rabbit vocal folds with hyaluronan in the short term rendered improved viscoelastic parameters.Significance: Hyaluroan may prove useful for treating vocal fold scarring.Support: None reported.

The process of integration is the combining of the independently tested software and hardware modules to produce a prototype system. Invariably the integrated system does not work, precipitating the pointed index finger phase of design procedure whereby the hardware and software engineers simultaneously raise their index figures to each other and exclaim" It is your fault".-they are course both correct.

Microprocessor based instrumentation can be placed in two groups: either the instrument is intended for mass production, or its one of a small production batch of between 1 and 100 units. The project planning of the development of any microprocessor-based instrument is primarily determined by the category to which the final product belongs.

Abstract: Characterisation of the bio-mechanical properties of the human vocal fold is an essential aid to understanding vocal fold oscillation, as an aid to diagnosis, and to support surgical as well as tissue engineering therapies. The authors will present preliminary results of an extensive study that has examined 20 excised human larynxes, and obtained data from 8 volunteer patients in-vivo during surgery under general anaesthesia.

Objective: To verify the anisotropic nature of the vocal folds by reproducing an experiment led by Rholfs that measured vocal fold elasticity in the transverse and longitudinal directions. To present a physiological explanation of the measured phenomena using immunochemical results.

Objective. This study mapped the variation in tissue elasticity of the subglottic mucosa, applied these data to provide initial models of the likely deformation of the mucosa during the myoelastic cycle, and hypothesized as to the impact on the process of phonation. Study Design. Six donor human larynges were dissected along the sagittal plane to expose the vocal folds and sub-glottic mucosa. A linear skin rheometer was used to apply a controlled shear force, and the resultant displacement was measured. These data provided a measure of the stress/strain characteristics of the tissue at each anatomic point. A series of measurements were taken at 2-mm interval inferior of the vocal folds, and the change in elasticity was determined. Results. It was found that the elasticity of the mucosa in the subglottic region increased linearly with distance from the vocal folds in all 12 samples. A simple deformation model indicated that under low pressure conditions the sub-glottic mucosa will deform to form a cone, which could result in a higher velocity, thus amplifying the low pressure effect resulting from the Venturi principle, and could assist in maintaining laminar flow. Conclusions. This study indicated that the deformation of the subglottic mucosa could play a significant role in the delivery of a low pressure airflow over the vocal folds. A large scale study will now be undertaken to secure more data to evaluate this hypothesis, and using computational fluid dynamics based on actual three-dimensional structure obtained from computed tomography scans the aerodynamics of this region will be investigated.