[Current methods for modelling voice production]. / Aktuelle Methoden zur Modellierung des Stimmgebungsprozesses.

BACKGROUND: Many details of the phonatory process are not yet fully understood. Besides observational research, scientists have long since been trying to explain the physical fundamentals of voicing using simulations. This approach is commonly called modeling. However, the knowledge gained often failed to find its way to professionals working with the voice, such as singing teachers, voice therapists, and voice coaches, and sometimes also to otorhinolaryngologists and phoniatricians. The reason for this is that scientific publications on this topic mostly contain very detailed mathematical and physical descriptions, which are often hard to understand. OBJECTIVE: A simplified presentation and explanation of current methods for modeling the phonatory process, which have contributed greatly to uncovering and understanding the relationships involved in voicing during recent years. METHODS: The presented methods cover a wide spectrum, ranging from numerically rather simple to mathematically highly complex models. Experimental models are based on self-oscillating silicon or static vocal folds. Cadaver models have the advantage of being representative of the natural phonation process. RESULTS: An overview of different kinds of models is given to show the diversity of modeling approaches without going into mathematical or physical details. CONCLUSION: Numerical and experimental models for simulating the phonatory process enable causalities and correlations to be uncovered, which can be used in the future to adapt conservative and surgical voice therapies, or even to suggest entire new treatment strategies.

Investigation of prescribed movement in fluid-structure interaction simulation for the human phonation process.

In a partitioned approach for computational fluid-structure interaction (FSI) the coupling between fluid and structure causes substantial computational resources. Therefore, a convenient alternative is to reduce the problem to a pure flow simulation with preset movement and applying appropriate boundary conditions. This work investigates the impact of replacing the fully-coupled interface condition with a one-way coupling. To continue to capture structural movement and its effect onto the flow field, prescribed wall movements from separate simulations and/or measurements are used. As an appropriate test case, we apply the different coupling strategies to the human phonation process, which is a highly complex interaction of airflow through the larynx and structural vibration of the vocal folds (VF). We obtain vocal fold vibrations from a fully-coupled simulation and use them as input data for the simplified simulation, i.e. just solving the fluid flow. All computations are performed with our research code CFS++, which is based on the finite element (FE) method. The presented results show that a pure fluid simulation with prescribed structural movement can substitute the fully-coupled approach. However, caution must be used to ensure accurate boundary conditions on the interface, and we found that only a pressure driven flow correctly responds to the physical effects when using specified motion.

Measurement of the elasticity modulus of soft tissues.

A measurement setup combined with a Finite Element (FE) simulation is presented to determine the elasticity modulus of soft materials as a function of frequency. The longterm goal of this work is to measure in vitro the elasticity modulus of human vocal folds over a frequency range that coincides with the range of human phonation. The results will assist numerical simulations modeling the phonation process by providing correct material parameters. Furthermore, the measurements are locally applied, enabling to determine spatial differences along the surface of the material. In this work the method will be presented and validated by applying it to silicones with similar characteristics as human vocal folds. Three silicone samples with different consistency were tested over a frequency range of 20-250 Hz. The results of the pipette aspiration method revealed a strong frequency dependency of the elasticity modulus, especially below 100 Hz. In this frequency range the elasticity moduli of the samples varied between 5 and 27 kPa.

Finite element simulation of nonlinear wave propagation in thermoviscous fluids including dissipation.

A recently developed finite element method (FEM) for the numerical simulation of nonlinear sound wave propagation in thermoviscous fluids is presented. Based on the nonlinear wave equation as derived by Kuznetsov, typical effects associated with nonlinear acoustics, such as generation of higher harmonics and dissipation resulting from the propagation of a finite amplitude wave through a thermoviscous medium, are covered. An efficient time-stepping algorithm based on a modification of the standard Newmark method is used for solving the non-linear semidiscrete equation system. The method is verified by comparison with the well-known Fubini and Fay solutions for plane wave problems, where good agreement is found. As a practical application, a high intensity focused ultrasound (HIFU) source is considered. Impedance simulations of the piezoelectric transducer and the complete HIFU source loaded with air and water are performed and compared with measured data. Measurements of radiated low and high amplitude pressure pulses are compared with corresponding simulation results. The obtained good agreement demonstrates validity and applicability of the nonlinear FEM.

The HLA-DQB alleles and amino acid variants of the vitamin D-binding protein in diabetic patients in Alsace.

BACKGROUND: The HLA-DQB1 chain, in particular the amino acid in position 57, and genetic variants of the vitamin D-binding protein (DBP) have been reported to be associated with type 1 diabetes. There are two known polymorphisms in exon 11 of the DBP gene resulting in amino acid variants: codons 416 GAT --> GAG (Asp --> Glu) and 420 ACG --> AAG (Thr --> Lys). We compared distribution of DQB1 alleles and amino acid variants of DBP in type 1 diabetic patients (n = 44) in the Alsacian population and in healthy controls (n = 58). METHODS: The second exon of the DQB1 gene and exon 11 of DBP were analyzed by restriction mapping after polymerase chain reaction. RESULTS: A significant enrichment in DQB1 alleles encoding for an amino acid different from Asp in position 57 (NA) was observed in diabetic subjects as compared to controls (94.3 vs. 32.8%; p < 0.001). Combinations other than Ala/Ala carried the highest relative risk (OR = 52; p < 0.001). The analysis of the polymorphism in exon 11 of DBP showed a significant difference in the allele frequency of the HaeIII site, but not of the StyI site between patients and controls. Allele frequencies of HaeIII in diabetic subjects were 36% and 64% for Asp and Glu respectively (p < 0.001; chi(2) = 29.5). The frequency of Asp/Asp and Glu/Glu genotypes was increased in controls and diabetic subjects respectively. DBP alleles in individuals carrying the DQB1 NA combination revealed that 46.6% of diabetics were DBP Asp/Glu, but this was not statistically significant using the Fisher exact test (16/31 vs. 0/3; p = 0.23). CONCLUSIONS: The study of the DQB1 chain confirmed the value of alleles encoding for an amino acid different from Asp in position 57 (NA) in the susceptibility to type 1 diabetes. The allele frequency of the HaeIII site, but not of the StyI site, differed between patients and controls (HaeIII p < 0.001; StyI p > 0.05).