Effects of transglottal pressure change on fundamental frequency of phonation: preliminary evaluation of the effect of intraoral pressure change

Numerical Analysis of Effects of Transglottal Pressure Change on Fundamental Frequency of Phonation

Objectives:

In humans, a decrease in transglottal pressure ( Pt) causes an increase in the fundamental frequency of phonation ( F0) only at a specific voice pitch within the modal register, the mechanism of which remains unclear.

Methods:

In the present study, numerical analyses were performed to investigate the mechanism of the voice pitch-dependent positive change of F0 due to Pt decrease. The airflow and the airway, including the vocal folds, were modeled in terms of mechanics of fluid and structure.

Results:

Simulations of phonation using the numerical model indicated that Pt affects both the average position and the average amplitude magnitude of vocal fold self-excited oscillation in a non-monotonous manner. This effect results in voice pitch-dependent responses of F0 to Ft decreases, including the positive response of F0 as actually observed in humans.

Conclusions:

The findings of the present study highlight the importance of considering self-excited oscillation of the vocal folds in elucidation of the phonation mechanism.

On pressure-frequency relations in the excised larynx

The purpose of this study was to find relationships between subglottal pressure (P(s)) and fundamental frequency (F(0)) of phonation in excised larynx models. This included also the relation between F(0) and its rate of change with pressure (dFdP). 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. The pressure-frequency relation was obtained through a series of pressure-flow sweep experiments that were conducted for eight excised canine larynges. It was found that, at set adduction and elongation levels, the pressure-frequency relation is nonlinear, and is highly influenced by the adduction and elongation. The results indicated that for the lower phonation mode, the average rate of change of frequency with pressure was 2.9+/-0.7 Hzcm H(2)O, and for the higher mode was 5.3+/-0.5 Hzcm H(2)O for adduction changes and 8.2+/-4.4 Hzcm H(2)O for elongation changes. The results suggest that during speech and singing, the dFdP relationships are taken into account.

Effect of Artificially Lengthened Vocal Tract on Vocal Fold Oscillation's Fundamental Frequency

The fundamental frequency of vocal fold oscillation (F(0)) is controlled by laryngeal mechanics and aerodynamic properties. F(0) change per unit change of transglottal pressure (dF/dP) using a shutter valve has been studied and found to have nonlinear, V-shaped relationship with F(0). On the other hand, the vocal tract is also known to affect vocal fold oscillation. This study examined the effect of artificially lengthened vocal tract length on dF/dP. dF/dP was measured in six men using two mouthpieces of different lengths.

RESULTS

The dF/dP graph for the longer vocal tract was shifted leftward relative to the shorter one.

CONCLUSION

Using the one-mass model, the nadir of the "V" on the dF/dP graph was strongly influenced by the resonance around the first formant frequency. However, a more precise model is needed to account for the effects of viscosity and turbulence.

Relationship between transglottal pressure and fundamental frequency of phonation, with effects of dehydration produced by atropine, in healthy volunteers

We investigated the effects of the intravenous injection of atropine sulfate on the relationship between the fundamental frequency of phonation (F0) and the magnitude of F0 change per unit change in transglottal pressure (dF/dP) in 4 healthy male volunteers. Before the injection of atropine, we observed a nonlinear or V-shaped relationship between dF/dP and F0. After the injection, the values for dF/dP were reduced at a lower F0, whereas the values were unchanged at a higher F0. The results support our hypothesis that the relationship between dF/dP and F0 reflects adjustments in the length and depth of the vocal folds in controlling F0.

Effects of length and depth of vibration of the vocal folds on the relationship between transglottal pressure and fundamental frequency of phonation in canine larynges

The relationship between fundamental frequency of phonation (F0) and the change in F0 per unit change of transglottal pressure (dF/dP) was investigated in 3 excised canine larynges. The effects of the length and depth of vocal fold vibration on the relationship between dF/dP and F0 were evaluated. A positive correlation between dF/dP and F0 was observed when an increase in F0 was accompanied by a decrease in the depth of vibration while the length of vibration reached a plateau. Although a negative correlation between dF/dP and F0 was observed in only 1 case, this relationship seemed relevant to the length of vibration. These results help to clarify the adjustments of length and depth of vibration involved in regulating F0.

The effect of cricothyroid muscle action on the relation between subglottal pressure and fundamental frequency in an in vivo canine model

The relation between subglottal pressure (Ps) and fundamental frequency (F0) in phonation was investigated with an in vivo canine model. Direct muscle stimulation was used in addition to brain stimulation. This allowed the Ps-F0 slope to be quantified in terms of cricothyroid muscle activity. Results showed that, for ranges of 0-2 mA constant current stimulation of the cricothyroid muscle, the Ps-F0 slope ranged from 10 Hz/kPa to 60 Hz/kPa. These results were compared to similar slopes obtained in a previous study on excised larynges in which the vocal fold length was varied instead of cricothyroid activation. A physical interpretation of the Ps-F0 slope is that the amplitude-to-length ratio of the vocal folds decreases with CT activity, resulting in a smaller time-varying stiffness. In other words, there is less dependence of F0 on amplitude of vibration when the vocal folds are long instead of short.

Effects of transglottal pressure on fundamental frequency of phonation: study with a rubber model

The fundamental frequency of phonation (F0) change per unit change in transglottal pressure (dF/dP) was studied at different extension lengths and masses of the vibrating part of a rubber model. The dF/dP was decreased when the vibrating part was extended, and also when the mass of the vibrating part was increased. In the former, the F0 was increased, and in the latter, the F0 was decreased. In humans, we have noticed that when the F0 was increased, the dF/dP first decreased and then increased, taking a V-shaped curve as a function of the F0. The present study reveals the mechanism underlying the V-shaped curve observed in humans.