Eileen M. Finnegan

Effects of a Semioccluded Vocal Tract on Laryngeal Muscle Activity and Glottal Adduction in a Single Female Subject

Voice training exploits semiocclusives, which increase vocal tract interaction with the source. Modeling results suggest that vocal economy (maximum flow declination rate divided by maximum area declination rate, MADR) is improved by matching the glottal and vocal tract impedances. Changes in MADR may be correlated with thyroarytenoid (TA) muscle activity. Here the effects of impedance matching are studied for laryngeal muscle activity and glottal resistance. One female repeated [pa:p:a] before and immediately after (a) phonation into different-sized tubes and (b) voiced bilabial fricative [β:]. To allow estimation of subglottic pressure from the oral pressure, [p] was inserted also in the repetitions of the semiocclusions. Airflow was registered using a flow mask. EMG was registered from TA, cricothyroid (CT) and lateral cricoarytenoid (LCA) muscles. Phonation was simulated using a 7 × 5 × 5 point-mass model of the vocal folds, allowing inputs of simulated laryngeal muscle activation. The variables were TA, CT and LCA activities. Increased vocal tract impedance caused the subject to raise TA activity compared to CT and LCA activities. Computer simulation showed that higher glottal economy and efficiency (oral radiated power divided by aerodynamic power) were obtained with a higher TA/CT ratio when LCA activity was tuned for ideal adduction.

A preliminary study of the prognostic role of electromyography in laryngeal paralysis

Confidence in the reliability of laryngeal electromyography to predict recovery is critical if this tool is to be used to select the type and timing of surgical intervention. The characteristics of electromyography of 14 patients with unilateral vocal fold paralysis were assessed to determine which factor or combination of factors would be most useful in determining prognosis. We examined the duration, amplitude, waveform morphology, root-mean-square, and time interval from onset to electromyography recording. The results supported the concept that electromyography recordings are valuable in determining prognosis if performed before 6 months and preferably within 6 weeks of onset of laryngeal paralysis. A positive prognosis for laryngeal recovery was indicated when the following electromyography features were present in the immobile vocal fold: (1) normal motor unit waveform morphology. (2) overall electromyography activity characterized by a root-mean-square value greater than 40 μV in any one task, and (3) no electrical silence during voluntary tasks. On the basis of this criteria our overall correct prognostic rate was 89%.

Pressure-flow relationships during phonation as afunction 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.

Aerodynamic and Acoustic Effects of False Vocal Folds and Epiglottis in Excised Larynx Models

Objectives: The purpose of this study was to examine the aerodynamic and acoustic effects of the false vocal folds and the epiglottis on excised larynx phonation. Methods: Several canine larynges were prepared and mounted over a tapered tube that supplied pressurized, heated, and humidified air. Glottal adduction was accomplished either by using two-pronged probes to press the arytenoids together or by passing a suture to simulate lateral cricoarytenoid muscle activation. First, the excised larynx with false vocal folds and epiglottis intact was subjected to a series of pressure-flow experiments with longitudinal tension and adduction as major control parameters. Then, the epiglottis and finally the false vocal folds were removed and the experiment was repeated. The subglottal pressure and the electroglottographic, flow rate, audio, and sound pressure signals were recorded during each experiment. Glottal flow resistance was calculated from the pressure and flow signals. The electroglottographic signal was used to extract the fundamental frequency. Results: It was found that the false vocal folds and the epiglottis offer a positive contribution to the glottal resistance and sound intensity of the larynx. Also, vocal fold elongation and glottal medial compression caused an increase in glottal resistance. The pressure-flow relationships were approximately linear regardless of the structure. Conclusions: The addition of the supraglottic laryngeal structures has a significant impact on both aerodynamic and acoustic characteristics of excised larynges.

Increased Stability of Airflow Following Botulinum Toxin Injection

Objectives: The purpose of this study was to determine whether stability of airflow, as well as mean airflow, increased following botulinum toxin injection to laryngeal and extralaryngeal muscles in persons with spasmodic dysphonia (SD), some with associated vocal tremor (VT).

Perception of Vocal Tremor During Sustained Phonation Compared With Sentence Context

OBJECTIVES/HYPOTHESIS Vocal tremor is an acoustical phenomenon characterized by relatively periodic modulations in fundamental frequency and intensity. Although vocal tremor is considered easier to perceive during sustained phonation than during connected speech, systematic comparison between these speech contexts has not been investigated. This investigation compared vocal tremor perception during sustained phonation and connected speech contexts. STUDY DESIGN This is a prospective, controlled study with randomized conditions. METHODS Audio recordings from five speakers diagnosed with essential vocal tremor were used for this study. Twenty-four naive adult listeners rated the overall severity (ie, aberrance) of the voice and the degree of shakiness (ie, tremor) during sustained phonation of /i/. A different group of 21 naive adult listeners rated sentence stimuli consisting of two different sentences, one loaded with voiced and the other with voiceless speech sounds. RESULTS All speakers were rated by listeners to have similar levels of shakiness and overall severity during sustained phonation. However, significantly higher levels of shakiness and overall severity were perceived during sustained phonation than during sentence context. A nonsignificant trend was shown for higher average ratings for shakiness and overall severity on voice-loaded compared with voiceless-loaded sentences. CONCLUSIONS This study demonstrated that vocal tremor is perceived as significantly more severe during sustained phonation than during connected speech. More importantly, individual speakers differed in their ability to reduce vocal tremor perception during connected speech. Thus, sustained phonation does not necessarily offer a valid estimation of the impact of a vocal tremor on an individuals connected speech.

VFS Interjudge Reliability Using a Free and Directed Search

Reports in the literature suggest that clinicians demonstrate poor reliability in rating videofluoroscopic swallow (VFS) variables. Contemporary perception theories suggest that the methods used in VFS reliability studies constrain subjects to make judgments in an abnormal way. The purpose of this study was to determine whether a directed search or a free search approach to rating swallow studies results in better interjudge reliability. Ten speech pathologists served as judges. Five clinical judges were assigned to the directed search group (use checklist) and five to the free search group (unguided observations). Clinical judges interpreted 20 VFS examinations of swallowing. Interjudge reliability of ratings of dysphagia severity, affected stage of swallow, dysphagia symptoms, and attributes identified by clinical judges using a directed search was compared with that using a free search approach. Interjudge reliability for rating the presence of aspiration and penetration was significantly better using a free search (“substantial” to “almost perfect” agreement) compared to a directed search (“moderate” agreement). Reliability of dysphagia severity ratings ranged from “moderate” to “almost perfect” agreement for both methods of search. Reliability for reporting all other symptoms and attributes of dysphagia was variable and was not significantly different between the groups.

Phonatory characteristics of the excised human larynx in comparison to other species.

OBJECTIVE The purpose of this study was to determine the conditions needed to elicit phonation from excised human larynges and the resultant range of phonations produced; compare that with similar information previously obtained from canine, pig, sheep, and cow; and relate those findings to previously reported information about viscoelastic properties of the vocal fold tissue (ie, stress-strain curves and Youngs modulus). METHODS Six human larynges of the geriatric group (age range, 70-89) were mounted on the bench without supraglottic structures, and phonation was achieved with the flow of heated and humidified air through the tracheal tube. Using various sutures to mimic the function of the laryngeal muscles, the larynges were put through a series of sustained oscillations with adduction as a control parameter. RESULTS The human larynges oscillated with an average frequency that was close to the canine larynges, but the oscillation behavior and wide frequency range were similar to those of pig larynges. The similarity of the wide vibration frequency ranges of human and pig larynges may be because of the nonlinear behavior of their elasticity, which is related to the high collagen content of the vocal folds. On the contrary, other species with limited frequency ranges showed almost linear stress-strain curves because of the higher elastin and lower collagen contents. CONCLUSIONS The physiological differences in the linearity and ranges of oscillation of excised larynges reported in this study and previous studies are reflective of the tissue composition and mechanics.

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.

Measures of Spectral Slope Using an Excised Larynx Model

Spectral measures of the glottal source were investigated using an excised canine larynx (CL) model for various aerodynamic and phonatory conditions. These measures included spectral harmonic difference H1-H2 and spectral slope that are highly correlated with voice quality but not reported in a systematic manner using an excised larynx model. It was hypothesized that the acoustic spectra of the glottal source were significantly influenced by the subglottal pressure, glottal adduction, and vocal fold elongation, as well as the resulting vibration pattern. CLs were prepared, mounted on the bench with and without false vocal folds, and made to oscillate with a flow of heated and humidified air. Major control parameters were subglottal pressure, adduction, and elongation. Electroglottograph, subglottal pressure, flow rate, and audio signals were analyzed using custom software. Results suggest that an increase in subglottal pressure and glottal adduction may change the energy balance between harmonics by increasing the spectral energy of the first few harmonics in an unpredictable manner. It is suggested that changes in the dynamics of vocal fold motion may be responsible for different spectral patterns. The finding that the spectral harmonics do not conform to previous findings was demonstrated through various cases. Results of this study may shed light on phonatory spectral control when the larynx is part of a complete vocal tract system.