Biomedical subjects

R C Scherer

Publications and source records attributed to R C Scherer.

18 recordsLinked to original sources

PubMed2001

Intraglottal pressure profiles for a symmetric and oblique glottis with a divergence angle of 10 degrees.

Human phonation does not always involve symmetric motions of the two vocal folds. Asymmetric motions can create slanted or oblique glottal angles. This study reports intraglottal pressure profiles for a Plexiglas model of the larynx with a glottis having a 10-degree divergence angle and either a symmetric orientation or an oblique angle of 15 degrees. For the oblique glottis, one side was divergent and the other convergent. The vocal fold surfaces had 14 pressure taps. The minimal glottal diameter was held constant at 0.04 cm. Results indicated that for either the symmetric or oblique case, the pressure profiles were different on the two sides of the glottis except for the symmetric geometry for a transglottal pressure of 3 cm H2O. For the symmetric case, flow separation created lower pressures on the side where the flow stayed attached to the wall, and the largest pressure differences between the two sides of the channel were 5%-6% of the transglottal pressure. For the oblique case, pressures were lower on the divergent glottal side near the glottal entry and exit, and the cross-channel pressures at the glottis entrance differed by 27% of the transglottal pressure. The empirical pressure distributions were supported by computational results. The observed aerodynamic asymmetries could be a factor contributing to normal jitter values and differences in vocal fold phasing.

Glottis↗

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

The effect of exit radii on intraglottal pressure distributions in the convergent glottis.

Explore the source record for details and available documents.

Airway Resistance↗

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↗

PubMed1999

Electroglottographic tracking of phonatory response to Botox.

Botox injection into the thyroarytenoid muscle is thought to alter the glottal competence and laryngeal adduction of patients with adductor spasmodic dysphonia (ADSD). Hypofunctional responses to treatment have been rated subjectively and inferred from postinjection breathy voice, aphonia, midline glottal gap, or subclinical aspiration. Clinical experience suggests that temporary hypofunction varies in duration and severity among patients. This study used electroglottographic measures to examine changes over time in glottal competence during the relatively stable phonation produced by 5 patients with ADSD. Hierarchical linear modeling was used to test 3 hypotheses: (a) that reduced laryngeal adduction would occur during the first 3 weeks postinjection, followed by a reversal; (b) that patients' hypofunctional response curves would differ one from another; and (c) that changes in adduction, if present, would be related to changes in severity ratings of ADSD symptoms. For 3 participants, significant hypoadduction occurred after injection and reversed toward preinjection level over an 8-week period. Two participants demonstrated a flat or increasing vocal fold contact response curve during the early postinjection period. Observations were consistent with the previously reported differences and possibly complex relation between the resolution of breathy hypofunction and ultimate return of ADSD symptoms.

Adult↗

PubMed1998

Just noticeable differences for glottal flow waveform characteristics.

This study was primarily motivated by the need to establish the correspondence between auditory abilities and laryngeal function. Just noticeable differences (JNDs) were obtained for the open quotient and speed quotient of the glottal flow waveform. The quotients were synthesized for both the glottal flow alone, and for the output pressure signal after the glottal flow signal was applied to the synthesis vocal tract for the vowel /a/. Six adult men and five adult women, all teachers of singing, participated as listeners. An adaptive auditory listening procedure was used to estimate JNDs for the four types of stimuli. The group average JND values were as follows. For the standard open quotient value of .6000, JND = 0.0264 (SD = .010) for the glottal flow and JND = 0.0344 (SD = .020) for the output pressure. For the open quotient, there was no statistically significant difference between genders or between the types of signals. For the standard speed quotient value of 2.000, JND = 0.154 (SD = .043) for the glottal flow and JND = 0.319 (SD = .167) for the output pressure. For the speed quotient, there was no statistically significant difference between genders, but the difference between types of stimulus (glottal flow versus output pressure) was significant (p < .006). The variance among the JND values was significantly larger for the output pressure stimuli compared to the glottal flow stimuli for both the open quotient and the speed quotient.

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

Longitudinal phonatory characteristics after botulinum toxin type A injection.

Following Botulinum Toxin Type A injection, glottal competency of an adductor spasmodic dysphonia patient is thought to vary over a wide range. This study quantifies variability in laryngeal adduction for one such patient over a 10-week period. Analyses of kinematic and aerodynamic measures were used to track the voice weekly. The measures included the electroglottographic waveform width (EGGW50), nondimensional electroglottographic slope quotient (SLQ), glottal flow open quotient (FOQ), dc glottal flow, and nondimensional glottal flow peak quotient (FPQ). The results suggested that change in degree of glottal adduction over time can be observed even when vocal instability is present within each recording session. Perceptual ratings of vocal quality (breathy to pressed) were related to the laryngeal measures. The coefficient of variation for EGGW50 and the percentage of dichrotic phonations reached minima during sessions with predominantly breathy and hypoadducted phonation. The methods used in this study show potential to aid decisions about dose level and sources of perceptual adductor spasmodic dysphonia symptoms for a given patient.

Aged↗

PubMed1995

Required number of tokens to determine representative voice perturbation values.

Acoustic perturbation analyses of prolonged vowels are used in determining phonatory stability characteristics. When a number of tokens are analyzed, the average perturbation values create a stability profile of the voice. How many tokens are needed to obtain a representative perturbation value? In this study, five perturbation measures were considered, namely, jitter, shimmer, harmonics-to-noise ratio, coefficient of variation for amplitude, and coefficient of variation for frequency. Subject groups were chosen on the basis of individual average perturbation values. Results indicate that, except for the harmonics-to-noise ratio, generally, the less stable the voice, the greater is the number of tokens needed to obtain representative averages. For highly stable voices, at least six tokens are suggested: for voices with normal to high levels of instability, at least 15 tokens are recommended. Regardless of vocal stability, at least 10 tokens are suggested for the harmonics-to-noise ratio measure.

Adult↗

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↗

PubMed1994

The integration of voice science, voice pathology, medicine, public speaking, acting, and singing.

The integration of voice science, voice pathology, medicine, public speaking, acting, and singing has been central to evolution in all fields. The Voice Foundation Symposia have played a seminal and central role in fostering integration among disciplines. The result has been an improvement in the knowledge and practice in each field. And the future promises to be even more informative and exciting.

Congresses as Topic↗

PubMed1993

Finite element simulation of glottal flow and pressure.

Computational studies of laryngeal aerodynamics should help clarify the relationships among configuration, air flow, surface pressure, and vocal fold movement within the larynx, and the acoustic consequences of the output glottal air flow. The penalty finite element method [S. W. Kim, Comput. Fluids 16(4), 429-444 (1988a); NASA CR-179357 (1988b); S. W. Kim and R. A. Decker, Int. J. Num. Meth. Fluids 9, 43-57 (1989)] was adopted to simulate steady air flow and air pressure through the larynx. A total of 133 conditions of different glottal configurations and inflow rates were studied. The computational results were compared to empirical data from earlier experiments. Two cases are reported (1) constant glottal divergence (42 degrees) but variable diameter and (2) constant glottal diameter (0.04 cm) but variable glottal angle. For case (1), the average discrepancy for translaryngeal pressure drop between the computational results and empirical data was 6.8% for pressures between 3 and 15 cm H2O. Flow separation occurred just downstream of the minimal glottal diameter. For case (2), the computational results for translaryngeal pressure drop differed from the empirically derived Scherer-Guo (S-G) equation predictions by an average of 8.9% for pressure between 3 and 13 cm H2O. Pressure recovery in the glottis suggested that the optimal glottal diffuser angle was near 10 degrees. Results suggest that the computational method should be sufficient to study glottal aerodynamics (assuming quasisteady flow).

Air Pressure↗

PubMed1990

Acoustic analysis of voice in amyotrophic lateral sclerosis: a longitudinal case study.

Acoustic measures of phonatory instability (coefficient of variation for amplitude, coefficient of variation for frequency, shimmer, jitter, and harmonics-to-noise ratio), phonatory limits (maximum fundamental frequency range and maximum duration of vowel phonation), and the nasal-oral amplitude ratio were measured five times throughout a 6-month period from the phonation of a 69-year-old male patient with amyotrophic lateral sclerosis (ALS), an age- and sex-matched control subject, and on one occasion from a 16-subject control group matched to the patient in age and sex. The patient was free of vocal symptoms at the initiation of the study. When compared to the other recording sessions, the final recording of the ALS patient was characterized by increased coefficient of variation for amplitude, increased coefficient of variation for frequency, increased shimmer, increased jitter, reduced harmonics-to-noise ratio, and reduced maximum vowel duration. These acoustic manifestations of increased phonatory instability and reduced phonatory limits over time were in contrast to the consistency observed in the phonation of the longitudinal control subject and were outside the range of plus or minus one standard deviation on most acoustic variables when compared to the control group. These findings support the potential use of acoustic analysis in reflecting progression of ALS and suggest the need for further studies to investigate the relationship between acoustic analysis of voice and manifestations of neurological disease.

Aged↗

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↗

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↗

PubMedDate not supplied

Acoustic analysis of voices of patients with neurologic disease: rationale and preliminary data.

This paper presents a rationale for acoustic analysis of voices of neurologically diseased patients, and reports preliminary data from patients with myotonic dystrophy, Huntington's disease, Parkinson's disease, and amyotrophic lateral sclerosis, as well as from individuals at risk for Huntington's disease. Noninvasive acoustic analysis may be of clinical value to the otolaryngologist, neurologist, and speech pathologist for early and differential diagnosis and for documenting disease progression in these various neurologic disorders.

Adolescent↗