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Biomedical subjects

I R Titze

Publications and source records attributed to I R Titze.

At least 91 records · Page 5Linked to original sources
PubMed1990

Unification of perturbation measures in speech signals.

Voice perturbation measures, formerly defined in a somewhat ad hoc fashion, are discussed within the framework of signal theory. An attempt is made to unify a variety of existing jitter, shimmer, and noise measures on the basis of common underlying perturbation functions and their derivatives. Some simple modulations (sinusoid, Gaussian noise, linear trend) are imposed on cyclic parameters in phonation (e.g., amplitude and fundamental frequency) to test the ability of perturbation measures to detect or reject these types of modulations. It is expected that this systematic approach to perturbation analysis will be helpful in identifying the sources of irregularity in the voice and, thereby, in the detection of laryngeal disorders.

Humans↗
PubMed1989

Tetanic contraction in vocal fold muscle.

Active properties of canine vocalis muscle tissue were investigated through a series of experiments conducted in vitro. Samples of the vocalis muscle were dissected from dog larynges excised a few minutes before death and kept in Krebs solution at a temperature of 37 +/- 1 degree C and a pH of 7.4 +/- 0.05. Isometric and isotonic tetanic responses of the vocalis muscle were obtained electronically with a Dual Servo System (ergometer). Isometric tension was recorded at various levels of elongation and stimulation rate. Isotonic shortening was recorded at various levels of force, and shortening velocity was obtained by numerical analysis of recorded data. It was found that fused tetanus occurred at stimulation rates of about 90 Hz, where the isometric tetanic force saturates. Repeated stimulation of the muscle in vitro not only caused nonrecoverable fatigue in the tissue, but also decreased its passive tension. The combined active and passive isometric tension increased with elongation of the muscle. Results of isometric active responses were normalized with respect to average passive response. This normalization allowed for better comparison between tetanic contraction and twitch contraction. It was found that maximum tetanic contraction was 6.4 times greater than maximum twitch contraction obtained in a previous study. A tetanic contraction period was defined and investigated for eight samples of vocalis muscle tissue from different dogs. The tetanic contraction period showed a linear increasing trend with strain.

Animals↗
PubMed1989

On the relation between subglottal pressure and fundamental frequency in phonation.

The change in fundamental frequency with subglottal pressure in phonation is quantified on the basis of the ratio between vibrational amplitude and vocal fold length. This ratio is typically very small in stringed instruments, but becomes quite appreciable in vocal fold vibration. Tension in vocal fold tissues is, therefore, not constant over the vibratory cycle, and a dynamic tension gives rise to amplitude-frequency dependence. It is shown that the typical 2-6 Hz/cm H2O rise in fundamental frequency with subglottal pressure observed in human and canine larynges is a direct and predictable consequence of this amplitude-frequency dependence. Results are presently limited to phonation in the chest register.

Animals↗
PubMed1989

Physiologic and acoustic differences between male and female voices.

Comparison is drawn between male and female larynges on the basis of overall size, vocal fold membranous length, elastic properties of tissue, and prephonatory glottal shape. Two scale factors are proposed that are useful for explaining differences in fundamental frequency, sound power, mean airflow, and glottal efficiency. Fundamental frequency is scaled primarily according to the membranous length of the vocal folds (scale factor of 1.6), whereas mean airflow, sound power, glottal efficiency, and amplitude of vibration include another scale factor (1.2) that relates to overall larynx size. Some explanations are given for observed sex differences in glottographic waveforms. In particular, the simulated (computer-modeled) vocal fold contact area is used to infer male-female differences in the shape of the glottis. The female glottis appears to converge more linearly (from bottom to top) than the male glottis, primarily because of medial surface bulging of the male vocal folds.

Female↗
PubMed1989

Phonosurgical studies: fat-graft reconstruction of injured canine vocal cords.

Damage to the vocal cords can result in scarring and impaired vibration and can manifest clinically as hoarseness and loss of vocal power. If the vibratory characteristics could be restored in these scarred vocal cords, the vocal intensity and efficiency of phonation also should improve. In an effort to enhance the vibration of damaged vocal cords, we implanted a submucosal fat autograft within the injured vocal cord cover layer of dogs 6 weeks after unilateral mucosal excision had been performed. Three months postoperatively these animals were compared to normal dogs and those with mucosal excision but no fat-grafting. Acoustic and biomechanical measures of phonation were collected from an excised larynx preparation. We found that the fat-augmented vocal cords had lower threshold pressures for phonation, greater vocal intensity, and more efficient acoustic output than injured vocal cords without the fat-grafting. These results provide a foundation for further research on reconstructive surgery of damaged vocal cords.

Adipose Tissue↗
PubMed1988

Development of an in vitro technique for measuring elastic properties of vocal fold tissue.

The purpose of this investigation was to develop an in vitro technique for measurement of elastic properties of isolated vocal fold tissue. Larynges were excised from anesthetized dogs, immediately submerged in a Krebs-Ringer solution, and aerated with 95% oxygen and 5% carbon dioxide. The tissue was maintained in the aerated electrolyte solution throughout the experiment. The vocalis muscle was carefully dissected, with attachments to the arytenoid and thyroid cartilages maintained. The preparation was then subjected to isometric (constant length) force-elongation measures, which were converted to stress-strain values. Stage I of the investigation identified the dog model with the least intrastudy variability relative to the age, sex, and breed of the research animal, as well as to the effects of curare. Stage II investigated the effects of different instrumentation, definitions of reference length, methods of elongation, and effects of electrical stimulation. Once the procedure had been refined, the effects of age and sex were retested. There was a significant interaction between sex and strain and between age and strain. The least variability was obtained with curarized tissue from one sex of young, mixed-breed dogs, where an arbitrary 1 gram of initial force was the criterion for establishing "zero" strain. Problems associated with determination of reference length and various approaches to this problem are discussed.

Aging↗
PubMed1988

The physics of small-amplitude oscillation of the vocal folds.

A theory of vocal fold oscillation is developed on the basis of the body-cover hypothesis. The cover is represented by a distributed surface layer that can propagate a mucosal surface wave. Linearization of the surface-wave displacement and velocity, and further small-amplitude approximations, yields closed-form expressions for conditions of oscillation. The theory predicts that the lung pressure required to sustain oscillation, i.e., the oscillation threshold pressure, is reduced by reducing the mucosal wave velocity, by bringing the vocal folds closer together and by reducing the convergence angle in the glottis. The effect of vocal tract acoustic loading is included. It is shown that vocal tract inertance reduces the oscillation threshold pressure, whereas vocal tract resistance increases it. The treatment, which is applicable to falsetto and breathy voice, as well as onset or release of phonation in the absence of vocal fold collision, is harmonized with former treatments based on two-mass models and collapsible tubes.

Biophysical Phenomena↗
PubMed1987

Some technical considerations in voice perturbation measurements.

The maximum theoretical quantization noise (shimmer and jitter) for digital recording systems is estimated and compared with normal vocal shimmer and jitter. Nine bits of resolution and 500 samples per cycle are needed to minimize the contaminating sampling noise without interpolation between samples. With interpolation, however, fewer than 100 samples per cycle can resolve jitter down to 0.1%. Low-pass filtering is not harmful unless peak-picking strategies are used, and the peaks are severely broadened by the low-pass filter. A window of at least 20 cycles is suggested, and multiple tokens of an utterance are necessary to obtain a stable mean for perturbation measures.

Humans↗
PubMed1987

Twitch response in the canine vocalis muscle.

The twitch response of the canine vocalis muscle was investigated through a series of experiments conducted in vitro. Samples of vocalis muscle were dissected and prepared from canine larynges a few minutes before death and kept in Krebs solution at a temperature of 37 +/- 1 degrees C and pH of 7.4 +/- 0.05. Field stimulation with parallel-plate silver electrodes was applied to study the twitch response of muscle samples. The peak tension and time course of isometric contraction of isolated muscle samples were measured electronically with a Cambridge Technology Dual Servo System (ergometer). Contraction time and 50% relaxation time of this muscle were measured for seven samples at various levels of strain. It was found that contraction time ranged between 22 and 32 ms and 50% relaxation time ranged between 17 and 37 ms. Results indicate that the vocalis muscle is a fast muscle capable of performing rapid maneuvers in support of changes in fundamental frequency.

Animals↗
PubMed1985

Generation and dissipation of heat in vocal fold tissue.

The power dissipated in the vocal folds during phonation results from viscous loss in the fold tissues and can be estimated on the basis of a simplified representation of the geometry and movement of the folds. Assuming this power is converted into heat, it combines with the effects of muscle contraction, blood perfusion, and thermal conduction to the surface of the folds to determine fold temperature. To isolate the thermomechanical source of heat, the vocal folds of excised larynges were vibrated vertically over a range of frequencies and amplitudes, while the temperature rise in them was measured by inserted fine-wire thermocouples. The temperature rise observed was somewhat smaller than that predicted. This may be partly accounted for by convective and evaporative cooling of the vocal fold as it moved relative to the ambient air. Future studies should consider the time course of heating and vocal fold geometry in more detail.

Animals↗
PubMed1985

Viscoelastic modeling of canine vocalis muscle in relaxation.

Analysis of vocal fold vibration requires information on the viscoelastic properties of the vocalis muscle. The force response of two canine vocalis muscles was measured in one-dimensional, stepwise elongation of the tissue as a function of time with a computer-controlled ergometer. The viscoelastic behavior of the muscle in its passive state was demonstrated through the relaxation test. A quasilinear viscoelastic model was used to parametrize the relaxation function, and results are reported for various levels of strain. Furthermore, a model was used to obtain theoretical time-dependent stress-strain curves to compare with experimental data.

Animals↗
PubMed1984

Elasticity of canine vocal fold tissue.

Stress-strain curves were obtained from vocalis muscle tissue that was kept viable in an aerated Krebs-Ringer solution after excision of the larynx from live dogs. Results are compared to similar curves obtained from dead tissue and suggest that vocal fold elasticity depends on the level of strain, the elapsed time after elongation, the condition of the tissue, and the choice of rest length for strain computation. Tables of Young's moduli for various conditions are given.

Animals↗
PubMed1984

Parameterization of the glottal area, glottal flow, and vocal fold contact area.

A new set of parameters is described for analysis and synthesis of glottal area, vocal fold contact area, and glottal volume flow. Parameters are all nondimensionalized and consist of an abduction quotient, a shape quotient, a phase quotient, and a load quotient in addition to fundamental frequency and vibrational amplitude. The parameters show promise in interpretation of electroglottographic, photoglottographic, and inverse filtered volume velocity waveforms in terms of the glottal configuration. Some comparisons between modeled and measured glottographic waveforms are made.

Glottis↗
PubMed1983

Pressure-flow relationships in two models of the larynx having rectangular glottal shapes.

The pressure-flow equations used in computer simulation studies of phonation lack experimental validation. Two polyester resin models of the laryngeal airway with rectangular glottal ducts were constructed in order to obtain the relationships between translaryngeal pressure drop and volume flow through the airway. The results are in disagreement with the early estimates of Wegel [Bell Syst. Tech. J. 9, 207-227 (1930)], but match the predictions given by Ishizaka and Matsudaira [SCRL Monograph No. 8 (1972)] to within approximately +/- 10% for typical translaryngeal pressures for speech, with larger discrepancies being found for the model with the larger glottal diameter. The equation given by van den Berg et al. [J. Acoust. Soc. Am. 29, 626-631 (1957)] may not be properly compared because their supraglottal pressure hole location may have been different from that used in the present study. The data from the two models also are compared to recent empirical studies using an enlarged model of the larynx [J. Gauffin et al., Conference on Vocal Fold Physiology, Madison (1981)].

Biomechanical Phenomena↗
PubMed1980

Comments on the myoelastic - aerodynamic theory of phonation.

The myoelastic-aerodynamic theory of phonation has been quantified and tested with mathematical models. The models suggest that vocal fold oscillation is produced as a result of asymmetric forcing functions over closing and opening portions of the glottal cycle. For nearly uniform tissue displacements, as in falsetto voice, the asymmetry in the driving forces can result from the inertia of the air moving through the glottis. This inertia can in turn be enhanced or suppressed by supraglottal or subglottal vocal tract coupling. More obvious and pronounced asymmetries in the driving forces are associated with non-uniform vocal fold tissue displacements. These are combinations of normal tissue modes, and can result in vertical and horizontal phase differences along the surfaces, as observed in chest voice. The ranges of oscillation increase among various models as more freedom in the simulated tissue movement is incorporated. Of particular significance in initiating and maintaining oscillation are the vertical motions that facilitate coupling of aerodynamic energy into the tissues and allow tissue deformations under conditions of incompressibility. Vertical displacements also can have a significant on vocal tract excitation. Control of fundamental frequency of oscillation (FO) is basically myoelastic, partially as a result of deliberate or reflex adjustments of laryngeal muscles, and partially as a result of nonlinear tissue strain over the vibrational cycle. This places limits on the control of FO by subglottal pressure, and forces such control to be inseparably connected with vibrational amplitude, or less directly, with vocal intensity.

Biomechanical Phenomena↗
PubMed1979

A theoretical study of the effects of various laryngeal configurations on the acoustics of phonation.

Simulation of glottal volume flow and vocal fold tissue movement was accomplished by numerical solution of a time-dependent boundary value problem, in which nonuniform, orthotropic, linear, incompressible vocal fold tissue media were surrounded by irregularly shaped boundaries, which were either fixed or subject to aerodynamic stresses. Spatial nonuniformity of the tissues was of the layered type, including a mucosal layer, a ligamental layer, and muscular layers. Orthotropy was required to stabilized the vocal folds longitudinally and to accomodate large variations in muscular stress. Incompressibility and vertical motions at the golttis played an important role in producing and sustaining phonation. A nominal configuration for male fundamental speaking pitches was selected, and the regulation of fundamental frequency, intensity, average volume flow, and vocal efficiency was investigated in terms of variations around this nominal configuration. Parameters which were varied consisted of geometrical factors such as length, thickness, and depth, factors for shaping the glottis, as well as tissue elasticities, tissue viscosities, and subglottal pressure. Since nonlinear stress-strain properties were not included, subglottal pressure did not produce a pronounced effect upon fundamental frequency under these somewhat edealized conditions F0 rasing correlated strongly with increased tension in the ligament, and somewhat with increasing tension in the vocalis. F0 lowering correlated with increase in vocal fold length when the tensions were held constant, but not with increase in vocal fold thickness. Vocal intensity and efficiency are shown to have local maxima as the configurational parameters are varied one at a time. It appears that oral acoustic power output and vocal efficiency can be maximized by proper adjustments of longitudinal tension of nonmuscular (mucosal and ligamental) tissue layers in relation to muscular layers. Quantitative verification of the "body-cover" theory is therefore suggested, and several further implications with regard to control of the human larynx are considered.

Acoustics↗