Emily Lin

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.

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.

The dynamics of length change in canine vocal folds

The time courses of vocal fold elongation and contraction have been measured as a function of intrinsic laryngeal muscle activity. The superior and recurrent laryngeal nerves of anesthetized canines were stimulated supramaximally (on-off in all combinations) while the vocal folds were surgically exposed and illuminated for conventional and higher speed (300 frames per second) video recording. Microsutures were placed on various points on the vocal folds to measure elongation and contraction. Vocal fold strain, defined as elongation divided by rest length, ranged from -17% to +45%. The typical time constant for exponential increase or decrease in strain was about 30 ms. This reflects primarily the intrinsic muscle activation times rather than a passive (inertial or viscoelastic) response of cricothyroid joint rotation or translation.

Evaluating iPhone Recordings for Acoustic Voice Assessment

Aims: This study examined the viability of using iPhone recordings for acoustic measurements of voice quality. Methods: Acoustic measures were compared between voice signals simultaneously recorded from 11 normal speakers (6 females and 5 males) through an iPhone (model A1303, Apple, USA) and a comparison recording system. Comparisons were also conducted between the pre- and post-operative voices recorded from 10 voice patients (4 females and 6 males) through the iPhone. Participants aged between 27 and 79 years. Results: Measures from iPhone and comparison signals were found to be highly correlated. Findings of the effects of vowel type on the selected measures were consistent between the two recording systems and congruent with previous findings. Analysis of the patient data revealed that a selection of acoustic measures, such as vowel space area and voice perturbation measures, consistently demonstrated a positive change following phonosurgery. Conclusion: The present findings indicated that the iPhone device tested was useful for tracking voice changes for clinical management. Preliminary findings regarding factors such as gender and type of pathology suggest that intra-subject, instead of norm-referenced, comparisons of acoustic measures would be more useful in monitoring the progression of a voice disorder or tracking the treatment effect.

Effects of head extension and tongue protrusion on voice perturbation measures.

Head extension with protruded tongue is the position for videolaryngoscopy and simultaneous glottographic recordings including photoglottographic signals. This study investigated the effect of head extension and tongue protrusion on the measures of fundamental frequency, frequency perturbation (jitter), and amplitude perturbation (shimmer). Acoustic signals recorded during sustained vowels were obtained from 49 women and 66 men with no speech or voice disorders in different head-tongue positions. Head extension was associated with increased fundamental frequency and decreased shimmer. In men, head extension did not appear to affect jitter. When the tongue was protruded, head extension tended to lower jitter. For both genders, tongue protrusion was associated with decreased fundamental frequency with head extension. In the men, tongue protrusion tended to increase shimmer when the head was in the neutral position. In the women, tongue protrusion was associated with increased jitter and increased shimmer and was most evident in the head-neutral position. These findings supported a physical linkage hypothesis of the relationship between vocal tract configuration and vocal fold vibration, suggesting that head-tongue position must be taken into account when comparing voice measures.

Effects of simulated source of tremor on acoustic and airflow voice measures.

To test the effects of different sources of tremor on the voice, tremor was simulated by external rhythmic perturbation of structures at the subglottal, glottal, and supraglottal levels in 10 healthy subjects. The acoustic and airflow signals simultaneously recorded during sustained phonation in the normal and the 3 simulated tremor conditions were analyzed and compared. Voice measures included: fundamental frequency, 2 short-term perturbation measures (jitter and shimmer), and 3 long-term tremor measures (prominence ratios of the spectral peaks of the acoustic frequency contour, acoustic amplitude contour, and airflow contour). Measures of fundamental frequency and percent shimmer were not significantly affected by the simulated tremors. Measures of percent jitter and the amplitudes of the long-term frequency and amplitude modulations were most prominently increased when respiratory drive was perturbed by simulated tremor. Spectral analysis of the acoustic amplitude contour was most useful in distinguishing the 3 sites of simulated tremor.

Glottographic Signal Perturbation in Biomechanically Different Types of Dysphonia

Glottographic signals may be superior to acoustic signals for tracking glottal source perturbations, since supraglottal vocal tract effects on glottographic signals are relatively minimal compared with the acoustic signal as measured beyond the lips. This study compared the ability of differing signals to differentiate among normal voices and abnormal voices that were due to two categories of biomechanical disease. Acoustic, electroglottographic, and photoglottographic signals recorded during vowel phonation sustained by 26 normal subjects and 65 patients were measured for perturbations of frequency and amplitude. One‐way analysis of variance (ANOVA) revealed that amplitude perturbation measures from photoglottographic signals significantly differentiated neuromuscular from mass lesion sources of dysphonia. Acoustic and electroglottographic signal perturbations differentiated between normal and abnormal voices but did not distinguish between the dysphonic characteristics of neuromuscular disorders and those of mass lesions of the vocal folds.

Photoglottographic measures in parkinson's disease*

This study examines the usefulness of photoglottographic measures in reflecting the phonatory effect of Parkinsons disease. In the first experiment, data obtained by photoglottography were compared between 15 male patients with Parkinsons disease and 15 normal male speakers of similar age. Six photoglottographic parameters, mean open quotient (OQ), mean speed quotient (SQ), perturbation of open quotient (POQ), perturbation of speed quotient (PSQ), frequency perturbation ratio (FPR), and amplitude perturbation ratio (APR), in sustained vowel phonation were investigated. Increased SQ (t = -2.731, df = 28, P = 0.011) and POQ (t = -2.584, df = 28, P = 0.015) were significantly associated with data from patients in comparison to normal speakers. The FPR, APR, and OQ were not significantly different between normal subjects and patients. A follow-up experiment, including 12 female and 19 male patients with Parkinsons disease, was designed to evaluate the sensitivity of SQ and POQ in detecting vocal dysfunction. The sensitivity of SQ was found to be relatively high (93.5%), while that of POQ was low (45.2%). Methodological issues regarding the effects of gender, age, stage of the disease, and treatment on photoglottographic measures in Parkinsons disease were discussed.

Glottographic phase difference in recurrent nerve paralysis

Phase measures with simultaneously recorded electroglottography (EGG) and photoglottography (PGG) signals have been studied in canine models and found to be sensitive to the effect of recurrent laryngeal nerve (RLN) paralysis on vocal fold vibration. This study examined the usefulness of this type of measure in clinical application. The combined glottographic signals were obtained from 5 men with a diagnosis of unilateral RLN paralysis and 5 age-matched controls. In the patient group, EGG waveforms were found to have a consistent phase delay in relation to PGG. A measure of the overall glottographic phase difference (GPD) was found to significantly distinguish the control group (mean GPD = 0.2371 ms) from the patient group (mean GPD = −0.2765 ms). A validity analysis performed on 19 subjects with or without unilateral RLN paralysis confirmed that the GPD test had a relatively high efficiency (91.7%) in detecting unilateral RLN paralysis in the male population.

Correlation between Glottal Area and Photoglottographic Signal in Normal Subjects

Photoglottography (PGG) is an established technique for depicting the vibratory patterns of the vocal folds. The present study investigates the correlation between the glottal area and the corresponding PGG signal. Six normal (five male, one female) subjects who did not use their voices professionally were investigated during constantly sustained phonation at spontaneous pitches. Laryngostroboscopy was performed in combination with PGG. The simultaneously recorded laryngostroboscopic images and PGG signals were directly digitized and stored on a computer. The correlation between the glottal area and the corresponding PGG amplitudes across each vibratory cycle of the vocal folds was calculated and they were found to be highly and positively correlated (r=0.973, p<0.001). The PGG signal reflects changes in the glottal area during the vibration cycle of the vocal folds. The proposed simultaneous laryngostroboscopic and PGG technique has proved to be useful for facilitating the interpretation of changes in glottal area.Photoglottography (PGG) is an established technique for depicting the vibratory patterns of the vocal folds. The present study investigates the correlation between the glottal area and the corresponding PGG signal. Six normal (five male, one female) subjects who did not use their voices professionally were investigated during constantly sustained phonation at spontaneous pitches. Laryngostroboscopy was performed in combination with PGG. The simultaneously recorded laryngostroboscopic images and PGG signals were directly digitized and stored on a computer. The correlation between the glottal area and the corresponding PGG amplitudes across each vibratory cycle of the vocal folds was calculated and they were found to be highly and positively correlated (r = 0.973, p < 0.001). The PGG signal reflects changes in the glottal area during the vibration cycle of the vocal folds. The proposed simultaneous laryngostroboscopic and PGG technique has proved to be useful for facilitating the interpretation of changes in glottal area.