Jack Jiang

VOCAL FOLD PHYSIOLOGY

This article examines the physiologic factors responsible for the production of phonation in humans. The article begins with an explanation of the control mechanisms of phonation and theories of vocal fold vibration. The physiologic concepts are based on the myoelastic-aerodynamic, body-cover, and mucosal wave theories. An evaluation of the cover-body theory is explained in terms of pitch control. The factors that regulate the vocal folds to produce pitch changes, intensity variation, and register effects are outlined. The changes in pitch, intensity, and voice qualities are related to the vocal fold mass, tension, subglottic pressure, and airflow generated by the phonatory systems. A brief summary of abnormal voice production is given in terms of disordered physiology and the emerging theory of chaos.

Measurement of vocal fold intraglottal pressure and impact stress

Intraglottal pressure was measured according to a previously described hemilarynx procedure. Three phases were identified for intraglottal pressure: an impact phase, in which the vocal folds come into contact and produce a sharp pressure pulse; a preopen phase, in which there is a progressive pressure buildup due to increased exposure of the vocal fold surfaces to subglottal pressure; and an open phase, in which intraglottal pressure becomes aerodynamic and drops gradually from opening to closing. Impact pressure peaks were positively related to subglottal pressure, elongation, and adduction of the vocal folds. The midpoint of the membranous vocal fold received the maximum impact stress. The experimental results match well with analytical predictions and support a current theory of mechanical trauma leading to vocal nodules.

A methodological study of hemilaryngeal phonation

An excised hemilarynx setup was developed. The phonatory characteristics of nine excised canine larynges were examined. The left vocal fold of each larynx was then removed and substituted with a vertical plexiglass plate. The larynges were phonated again. Recordings were made of phonation threshold pressure, sound pressure level, average glottal flow, fundamental frequency, and amplitude of vocal fold vibration as observed with a video stroboscope. Measurements were made over a range of subglottal pressures. For the hemilarynx, simultaneous recordings of intraglottal pressure and vocal fold contact area were also made. It was found that amplitude and frequency of vocal fold vibration of the hemilarynx, as well as rates of change of amplitude and frequency as a function of subglottal pressure, were similar to those of the full larynx. Also similar were phonation threshold pressures and ranges of subglottal pressure over which the larynges phonated. The average airflow of the hemilarynx was approximately half that of the full larynx, and the sound pressure level, under similar conditions, was one fourth (about 6 dB less) in the hemilarynx.

Diagnosis and management of chronic laryngitis associated with reflux

Chronic laryngitis symptoms are commonly seen in otherwise healthy people. This article reviews recent progress in our understanding and effective treatment of chronic laryngitis. Clinical experience and prospective treatment and outcome studies have demonstrated objective evidence of the efficacy of treating patients with chronic laryngitis symptoms with nocturnal antireflux precautions and acid-suppressing medications. The role of pH testing and most common errors in treatment are reviewed.

Glottographic Measures Before and After Levodopa Treatment in Parkinson's Disease†

Objectives: Investigate the usefulness of acoustic and glottographic measures for detecting effects of levodopa (L‐dopa) treatment on vocal function of individuals with idiopathic Parkinsons disease.

Phonation threshold pressure measurements during phonation by airflow interruption

Objective/Hypothesis: Most methods to measure phonation threshold pressure (PTP) are clinically impractical because they are invasive. This report concerns an airflow interruption system developed to allow noninvasive estimation of (PTP) at different levels of vocal intensity. An estimation of PTP was made for normal subjects with normal larynges and no voice complaints and for individuals who had dysphonia associated with vocal polyps to compare the estimated minimal pressure across the glottis that was required to sustain phonation in the two conditions. Study Design: This was a methodological study designed to measure an unanticipated PTP from a subject. Methods: Subjects sustained a constant tone and the airflow was directed into a section of pipe with an airtight mask over the mouth and nose. The airflow, intramask pressure, and intensity of the acoustic output were recorded. A PTP was predicted from a difference between an estimate of the subglottal pressure and the vocal tract pressure at the point that phonation ceased after interruption of airflow. Eleven control subjects and 13 patients with vocal fold polyps were studied. In each population there were eight men and five women. The individuals in the group with vocal fold polyps averaged 39 years of age, and the control subject group averaged 49 years of age. Normal subjects produced a steady vowel /a/ at 75, 80, and 85 dB. Patients with polyps were unable to sustain phonation at these levels but were able to produce phonation at 65, 70, and 75 dB. The validity of the system was tested using a laryngeal model and in a patient with a normal larynx and voice who had a tracheotomy (placed for sleep apnea syndrome) which allowed direct measurement of subglottal pressure. Results: The measured mean PTP levels (with standard deviation [SD]) for the control subjects were 2.38 (1.273), 2.67 (1.879), and 2.98 (2.23) cm H2O at 75, 80, and 85 dB, respectively. The measured mean PTP levels (with SD) for the patients with polyps were 4.79 (2.67), 5.85 (2.34), and 7.37 (3.26) cm H2O at 75, 80, and 85 dB, respectively. The differences in mean PTP between groups at 75, 80, and 85 dB were significant at P = .013, P = .017, and P = .010, respectively. Conclusions: The estimations of PTP for patients with vocal fold polyps were significantly higher than for the control subjects at three phonation levels.

The effects of rehydration on phonation in excised canine larynges

Experiments using excised canine larynges were conducted to study the restoration of vocal efficiency in dehydrated larynges. Excised larynges were dehydrated with warm, dry air to the point that airflow through the approximated vocal folds would not entrain the folds to produce phonation. The dehydrated vocal folds were then bathed in a saline solution. The rehydrated larynges were then remounted on the bench apparatus that enabled phonation with a constant humidified airflow, and measurements were made of phonation threshold pressure, glottal airflow, and amplitude. Hydration resulted in significantly increased efficiency and decrease in phonation threshold pressure. The findings confirm clinical impressions that hydration is critical in the physiology of normal phonation.

Quantitative color analysis of laryngeal erythemain chronic posterior laryngitis

The purpose of this study was to quantitatively analyze the degree of erythema visible in the larynges of normal subjects and of patients with symptoms of chronic posterior laryngitis. Video-documented examinations of laryngoscopy were digitized and then analyzed using computer image analysis software that allowed quantification of average color values, hue, saturation, and brightness from digitized color images. Documented laryngoscopic images from 7 normal subjects and 64 patients complaining of chronic laryngitis symptoms were examined, and additional patient examinations which were obtained and documented during treatment for reflux laryngitis were analyzed. Analysis was made of five different areas of each laryngeal image: the right and left vocal folds, the right and left vocal processes, and the posterior arytenoid mucosa. Data analysis showed that average color value ratings of redness for the patients with chronic laryngitis were significantly (p <0.0561) greater than the average values for normal subjects for the vocal folds. Color values for redness of the posterior laryngeal structures and vocal folds in the patients who were treated for reflux laryngitis were significantly (p <0.05) reduced over time and correlated with the clinical response to treatment. The data suggest that computer color analysis of documented video-laryngoscopic examinations can provide quantitative data on degree of erythema and may be useful as a quantitative means of diagnosis and documentation of treatment outcome for reflux laryngitis.

Vocal Fold Impact Stress Analysis

Vocal fold impact stress (force/area) has been implicated as a factor possibly contributing to the formation of nodules and polyps. The force of impact of a moving body is related to its acceleration. Since the mass of the folds is relatively constant, one expects impact force to be directly proportional to acceleration. A measure that reflects the relative displacement of the vocal folds is photoglottography (PGG). The velocity and acceleration of the folds are easily obtained by calculating the first and second derivatives of the PGG displacement waveform. This study, therefore, compared the second derivative of the PGG signal with simultaneously measured impact stress in an excised canine larynx model. Glottal transillumination (PGG) was measured with a subglottic transducer. A miniature force transducer placed in the midline between the vocal folds measured impact stress at the midglottal position. For nine different larynges, there was a positive and linear relationship between the second derivative of PGG and impact stress. The statistically significant results support the hypothesis that the second derivative of PGG m ay provide a use fulnoninvasive way to estimate relative vocal fold impact stress.

Quantitative Study of Mucosal Wave Via Videokymography in Canine Larynges

Objectives Vocal fold mucosal wave movements are thought to be important in determining voice characteristics and quality. To see these movements, high‐speed cinematography and videostroboscopy have been used clinically; however, these techniques have disadvantages that make them impractical for quantitative measurement of mucosal wave movements. This study explored the feasibility of using line‐scan cameras for mucosal wave analysis.