The effect of vocal fold adduction on the acoustic quality of phonation: ex vivo investigations

Abstract

Objectives: The purpose of this study was to investigate the effect of vocal fold adduction on voice quality in an ex vivo larynx model.

Study design: Prospective, repeated-measures experiments.

Methods: Ten excised canine larynges were mounted on an excised larynx phonation system and measurements were recorded for three different vocal fold adduction levels. Acoustic perturbation measurements of jitter, shimmer, and signal-to-noise ratio (SNR) were calculated from recorded radiated sound histories.

Results: Ex vivo experiments indicated that statistically significant increases in the means of jitter (P=0.005), shimmer (P=0.002), and SNR (P=0.011) measures decreased with respect to vocal fold adduction as the independent variable. Theoretical results showed that the direct current (DC) and alternating current (AC) component of glottal area increased monotonically with prephonatory glottal area.

Conclusions: Acoustic perturbation increased with the degree of vocal fold abduction. Ex vivo larynx measurements suggested that a hyperadducted state may be acoustically best. This may be explained theoretically by an increase in DC/AC ratio as the prephonatory area is increased.

Figure 1

(a) DC and AC components of glottal area as a function of the prephonatory glottal area. (b) DC/AC glottal area ratio as a function of the prephonatory glottal area.

Figure 1

(a) DC and AC components of glottal area as a function of the prephonatory glottal area. (b) DC/AC glottal area ratio as a function of the prephonatory glottal area.

Figure 2

The excised larynx phonation system. Pressurized airflow from a building source (A) was routed through a manometer (B) and two heater-humidifiers in series (C). A pseudolung (D) below the larynx (E, not shown) simulates the volumetric and capacitive characteristics of human lungs. An anterior micromanipulator (F) precisely controlled vocal fold elongation and lateral micromanipulators (G) controlled arytenoid adduction. A microphone (H) and digital pre-amplifier (I) recorded acoustics while a pneumotachometer (J) recorded air pressure. A digital camera (K) was used to document larynx position.

Figure 3

The three prephonatory glottal configurations used in the ex vivo laryngeal experiments. Illustrated (not to scale) are the abducted arytenoids configuration from (a) superior and (d) coronal views, the adducted arytenoids configuration from (b) superior and (e) coronal views, and the hyperadducted arytenoids configuration from (c) superior and (f) coronal views.

Figure 3

The three prephonatory glottal configurations used in the ex vivo laryngeal experiments. Illustrated (not to scale) are the abducted arytenoids configuration from (a) superior and (d) coronal views, the adducted arytenoids configuration from (b) superior and (e) coronal views, and the hyperadducted arytenoids configuration from (c) superior and (f) coronal views.

Figure 3

The three prephonatory glottal configurations used in the ex vivo laryngeal experiments. Illustrated (not to scale) are the abducted arytenoids configuration from (a) superior and (d) coronal views, the adducted arytenoids configuration from (b) superior and (e) coronal views, and the hyperadducted arytenoids configuration from (c) superior and (f) coronal views.

Figure 3

The three prephonatory glottal configurations used in the ex vivo laryngeal experiments. Illustrated (not to scale) are the abducted arytenoids configuration from (a) superior and (d) coronal views, the adducted arytenoids configuration from (b) superior and (e) coronal views, and the hyperadducted arytenoids configuration from (c) superior and (f) coronal views.

Figure 3

The three prephonatory glottal configurations used in the ex vivo laryngeal experiments. Illustrated (not to scale) are the abducted arytenoids configuration from (a) superior and (d) coronal views, the adducted arytenoids configuration from (b) superior and (e) coronal views, and the hyperadducted arytenoids configuration from (c) superior and (f) coronal views.

Figure 3

The three prephonatory glottal configurations used in the ex vivo laryngeal experiments. Illustrated (not to scale) are the abducted arytenoids configuration from (a) superior and (d) coronal views, the adducted arytenoids configuration from (b) superior and (e) coronal views, and the hyperadducted arytenoids configuration from (c) superior and (f) coronal views.

Figure 4

Mean transglottal flows during phonation with differing vocal fold adduction configurations under target subglottal pressures of (a) 15 cm H₂O, (b) 20 cm H₂O, and (c) 25 cm H₂O. The true mean subglottal pressures for each group were 14.93±0.15 cm H₂O, 20.01±0.24 cm H₂O, and 24.94±0.24 cm H₂O. The upper and lower edges of the box represent the 75th and 25th percentile, respectively, and a line within each box marks the median transglottal flow for the given adduction level. Whiskers above and below each box represent the 90th and 10th percentiles, respectively. Statistical outliers are graphed as points.

Figure 4

Mean transglottal flows during phonation with differing vocal fold adduction configurations under target subglottal pressures of (a) 15 cm H₂O, (b) 20 cm H₂O, and (c) 25 cm H₂O. The true mean subglottal pressures for each group were 14.93±0.15 cm H₂O, 20.01±0.24 cm H₂O, and 24.94±0.24 cm H₂O. The upper and lower edges of the box represent the 75th and 25th percentile, respectively, and a line within each box marks the median transglottal flow for the given adduction level. Whiskers above and below each box represent the 90th and 10th percentiles, respectively. Statistical outliers are graphed as points.

Figure 4

Mean transglottal flows during phonation with differing vocal fold adduction configurations under target subglottal pressures of (a) 15 cm H₂O, (b) 20 cm H₂O, and (c) 25 cm H₂O. The true mean subglottal pressures for each group were 14.93±0.15 cm H₂O, 20.01±0.24 cm H₂O, and 24.94±0.24 cm H₂O. The upper and lower edges of the box represent the 75th and 25th percentile, respectively, and a line within each box marks the median transglottal flow for the given adduction level. Whiskers above and below each box represent the 90th and 10th percentiles, respectively. Statistical outliers are graphed as points.

Figure 5

(a) Jitter, (b) Shimmer, and (c) SNR data from the sample population. The upper and lower edges of the box represent the 75th and 25th percentile, respectively, and a line within each box marks the median measurement value for the given vocal fold adduction level. Whiskers above and below each box represent the 90th and 10th percentiles, respectively. Statistical outliers are graphed as points. The results of one-way repeated measures ANOVA are indicated in the upper right corner.

Figure 5

(a) Jitter, (b) Shimmer, and (c) SNR data from the sample population. The upper and lower edges of the box represent the 75th and 25th percentile, respectively, and a line within each box marks the median measurement value for the given vocal fold adduction level. Whiskers above and below each box represent the 90th and 10th percentiles, respectively. Statistical outliers are graphed as points. The results of one-way repeated measures ANOVA are indicated in the upper right corner.

Figure 5

(a) Jitter, (b) Shimmer, and (c) SNR data from the sample population. The upper and lower edges of the box represent the 75th and 25th percentile, respectively, and a line within each box marks the median measurement value for the given vocal fold adduction level. Whiskers above and below each box represent the 90th and 10th percentiles, respectively. Statistical outliers are graphed as points. The results of one-way repeated measures ANOVA are indicated in the upper right corner.