Biomedical subjects

F Alipour

Publications and source records attributed to F Alipour.

12 recordsLinked to original sources

PubMed2001

Effects of oscillation of a mechanical hemilarynx model on mean transglottal pressures and flows.

This study introduces a mechanical model of the larynx for investigating dynamic aerodynamic effects of phonation. The model mimics the hemilarynx. The tracheal inlet section was rectangular (25-mm width, 20-mm height). The vocal fold was fabricated with precision machinery from hard plastic with an attached oscillating plunger. A speaker assembly and audio amplifier drove the plunger, mimicking one-dimensional vocal-fold motion toward a flat wall. The glottal shape was rectangular. The glottal diameter was well specified or dynamically followed with a laser system. The air was sucked through the channel using a vacuum with controlled speed. Frequency and amplitude of the glottis were varied. The mean pressure and mean flow data were recorded. For steady-flow conditions, the glottal gap ranged from 0.39 to 2.58 mm. The pressure coefficient for steady flow had a range of 3.1 to 1.3 for Reynolds numbers between 300 and 9000. For oscillation conditions (a) the frequency was varied from 75 to 150 Hz while the amplitude was held relatively constant, and (b) the amplitude was varied to 0.3 mm for a fixed frequency of 100 Hz. The results indicate that the hemilarynx model provides mean pressure-flow data similar in form to other models with two vocal folds. Furthermore, the dimensional and non-dimensional pressure coefficient is sensitive to variations in glottal gap and glottal amplitude, but relatively insensitive to the frequency of oscillation.

Glottis↗

PubMed2001

Aerodynamic profiles of a hemilarynx with a vocal tract.

The pressure-flow relationship was examined in excised canine and human larynges with and without a vocal tract. Canine and human larynges were prepared and cut in the midsagittal plane from the top to about 10 mm below the vocal folds. The right half was removed and replaced with an acrylic plate. The vocal tract was simulated initially with a 15-cm plastic tube and later with a vocal tract model with an area function resembling "ah." Simultaneous recordings were made of the glottal pressure, mean subglottal pressure, and average airflow at various levels of adduction. Preliminary data indicated that the pressure-flow relationships were similar to those of a full larynx and were almost linear. The addition of the vocal tract increased the glottal resistance by moving these pressure-flow lines to the lower-flow and higher-pressure region. The human larynx appears to phonate more easily than the canine larynx on the laboratory bench and has lower phonation threshold pressures.

Air Pressure↗

PubMed2000

Dynamic glottal pressures in an excised hemilarynx model.

During phonation, air pressures act upon the vocal folds to help maintain their oscillation. The air pressures vary dynamically along the medial surface of the vocal folds, although no live human or excised studies have shown how those pressure profiles vary in time. The purpose of this study was to examine time-dependent glottal pressure profiles using a canine hemilarynx approach. The larynx tissue was cut in the midsaggital plane from the top to about 5 mm below the vocal folds. The right half was replaced with a Plexiglas pane with imbedded pressure taps. Simultaneous recordings were made of glottal pressure signals, subglottal pressure, particle velocity, and average airflow at various levels of adduction. The data indicate that the pressures in the glottis (on the Plexiglas) vary both vertically and longitudinally throughout the phonatory cycle. Pressures vary most widely near the location of maximum vibratory amplitude, and can include negative pressures during a portion of the cycle. Pressures anterior and posterior to the maximum amplitude location may have less variation and may remain positive throughout the cycle, giving rise to a new concept called dynamic bidirectional pressure gradients in the glottis. This is an important concept that may relate strongly to tissue health as well as basic oscillatory mechanics.

Animals↗

PubMed2000

Vocal fold bulging effects on phonation using a biophysical computer model.

Glottal adduction is a primary laryngeal variable that helps to determine glottal configuration and phonatory output. Greater adduction of the vocal folds can be produced by narrowing the gap between the vocal processes or by bulging the medial surface of the vocal folds. This study examined phonatory effects due to changing the degree of bulging using a computational model. Bulging was modeled as a quadratic surface and was related to active muscle stress. Results indicated that bulging had a significant effect on glottal flow resistance, maximum glottal width and area, and mean glottal volume velocity. The results are discussed relative to clinical issues of hyperfunction.

Biophysical Phenomena↗

PubMed2000

A finite-element model of vocal-fold vibration.

A finite-element model of the vocal fold is developed from basic laws of continuum mechanics to obtain the oscillatory characteristics of the vocal folds. The model is capable of accommodating inhomogeneous, anisotropic material properties and irregular geometry of the boundaries. It has provisions for asymmetry across the midplane, both from the geometric and tension point of view, which enables one to simulate certain kinds of voice disorders due to vocal-fold paralysis. It employs the measured viscoelastic properties of the vocal-fold tissues. The detailed construction of the matrix differential equations of motion is presented followed by the solution scheme. Finally, typical results are presented and validated using an eigenvalue method and a commercial finite-element package (ABAQUS).

Computer Simulation↗

PubMed2000

Biomechanical and histologic observations of vocal fold fibrous proteins.

This article discusses the molecular composition of the vocal fold and the relationship of fibrous molecules to the biomechanical and physiological performance of the tissue. The components of the extracellular matrix may be divided into fibrous proteins and interstitial proteins. The fibrous proteins, consisting of collagens and elastins, are the focus of this report. Elastin concentration varies by tissue depth in the vocal folds. Variation of elastin by age is reported, but some controversy exists. The biomechanical terms of stress and strain (and stress-strain curves of human vocal folds) are related to the fibrous proteins of the vocal folds. The fibrous proteins, their role in stress, and their effect on the dynamic range of vocal pitch are presented.

Aging↗

PubMed1999

Active and passive characteristics of the canine cricothyroid muscles.

Active and passive characteristics of the canine cricothyroid muscle were investigated through a series of experiments conducted in vitro and compared with their counterparts in the thyroarytenoid muscle. Samples from separate portions of canine cricothyroid muscle, namely, the pars recta and pars obliqua, were dissected from dog larynges excised a few minutes before death and kept in Krebs-Ringer solution at a temperature of 37 degrees C +/- 1 degrees C and a pH of 7.4+/-0.05. Active tetanic stress was obtained in isometric and isotonic conditions by applying field stimulation to the muscle samples through a pair of parallel-plate platinum electrodes and using a train of square pulses of 0.1-ms duration and 85-V amplitude. Force and elongation of the samples were obtained electronically with a dual-servo system (ergometer). The results indicate that the dynamic response of the canine cricothyroid muscle is almost twice as slow as that of the thyroarytenoid muscle. The average 50% tetanic contraction times for pars recta and pars obliqua were 84 ms and 109 ms, respectively, in comparison to 50 ms for thyroarytenoid. The examination of force-velocity response of this muscle indicates a maximum shortening velocity of 2 to 3 times its length per second, which is about half of the thyroarytenoid shortening speed. The passive properties of the pars recta and pars obliqua portions are similar to those of thyroarytenoid muscle.

Animals↗

PubMed1999

Geometric structure of the human and canine cricothyroid and thyroarytenoid muscles for biomechanical applications.

The geometric structure of the cricothyroid (CT) muscle and thyroarytenoid (TA) muscle was quantified in 6 human and 3 canine larynges. Each muscle was divided into a series of fiber bundles. With a 3-dimensional micrometer probe, the coordinates of the origin and insertion of each bundle were measured before dissection. It was found that the mass of the CT muscle in the dog was 1.463+/-0.280 g, which was significantly greater than the 0.9423+/-0.123 g found in the human. This was a result of the cross-sectional area of the canine CT muscle being 105.3+/-11.6 mm2 instead of the 73.8+/-7.4 mm2 found for the human. However, the ratios of CT/TA mass and cross-sectional area between the two groups were not significantly different, suggesting that the two muscles grow proportionally.

Adult↗

PubMed1997

The membranous contact quotient: a new phonatory measure of glottal competence.

The membranous contact quotient (MCQ) is introduced as a measure of dynamic glottal competence. It is defined as the ratio of the membranous contact glottis (the anterior-posterior length of contact between the two membranous vocal folds) and the membranous vocal fold length. An elliptical approximation to the vocal fold contour during phonation was used to predict MCQ values as a function of vocal process gap (adduction), maximum glottal width, and membranous glottal length. MCQ is highly dependent on the vocal process gap and the maximum glottal width, but not on vocal fold length. Five excised larynges were used to obtain MCQ data for a wide range of vocal process gaps and maximum glottal widths. Predicted and measured MCQ values had a correlation of 0.93, with an average absolute difference of 9.6% (SD = 10.5%). The model is better at higher values of MCQ. The theory for MCQ is also expressed as a function of vocal process gap and subglottal pressure to suggest production control potential. The MCQ measure is obtainable with the use of stroboscopy and appears to be a potentially useful clinical measure.

Animals↗

PubMed1997

Pressure-flow relationships during phonation as a function of adduction.

Pressure-flow relationships were obtained for five excised canine larynges. Simultaneous recordings were made of average subglottal pressure, average air flow, and the electroglottograph at various levels of adduction and vocal fold lengths. The level of adduction was controlled by positioning the arytenoid cartilages via laterally imbedded three-prong attachments and by the use of intra-arytenoid shims. Adduction was quantified by measuring the vocal process gap. Results indicated a linear pressure-flow relationship within the experimental range of phonation for each level of adduction. Differential glottal resistance increased as the vocal process gap was reduced. A model is presented for the differential resistance as a hyperbolic function of vocal process gap. The pressure-flow relationship and the model can be used in computer simulations of speech production and for clinical insight into the aerodynamic function of the human larynx.

Animals↗

PubMed1996

Velocity distributions in glottal models.

Velocity distributions within three models of the human larynx, namely, a rigid plexiglas model, an excised canine larynx, and a computational model are investigated with experimental and theoretical analyses. A plexiglas wind tunnel with interchangeable glottal constrictions was used as a two-dimensional steady-flow model to measure velocity and pressure for various glottal shapes. A canine excised larynx was used as a prototype pulsatile flow model to study pressure and velocity variations during phonation. Results of the plexiglas modelling indicated a parabolic laminar velocity profiles upstream of the glottal constriction and turbulent and asymmetric velocity profile downstream of the glottal constriction. The time-averaged velocities of the excised larynx had similarities with the plexiglas model results, and instabilities and asymmetries were also demonstrated by the computational method.

Animals↗

PubMed1995

Pulsatile airflow during phonation: an excised larynx model.

Pulsatile airflow in the excised larynx was investigated with simultaneous recordings of air velocity, subglottal pressure, volume flow, and the electroglottograph signal for various conditions of the larynx. Canine larynges were mounted on a bench with sutures attached to cartilages to mimic the function of laryngeal muscles. Sustained oscillations were established and maintained with the flow of heated and humidified air through the trachea. The instantaneous air velocity above the glottis, which is the summation of a periodic velocity and the turbulent component, was measured with a constant temperature hot-wire probe at various locations. The phase-averaged velocity was used to construct the patterns of jet flow at selected time frames of the oscillation cycle. Results suggest that supraglottal air velocity is highly spatially and temporally dependent. Cycles of local air velocity with double peaks were not uncommon and a case is provided. For one phase-averaged phonatory cycle, a 9 x 13 velocity measurement grid demonstrated strongly nonuniform velocity surfaces for eight phases of the cycle, with greater velocities located anteriorly.

Animals↗