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

Size: px

Start display at page:

Download "Effects of transglottal pressure on fundamental frequency of phonation: Study with a rubber model"

Belinda Robertson
5 years ago
Views:

Effects of transglottal pressure on fundamental frequency of phonation: Study with a rubber model Kazutomo Kitajima, Hideyuki Kataoka, Shigehiro Owaki Department of Otolaryngology, Shiga University

1 Effects of transglottal pressure on fundamental frequency of phonation: Study with a rubber model Kazutomo Kitajima, Hideyuki Kataoka, Shigehiro Owaki Department of Otolaryngology, Shiga University of Medical Science, Seta, Otsu, Japan ISCA Archive Abstract Transglottal pressure affects fundamental frequency of phonation (Fo). When we plot Fo-change per unit change of transglottal pressure (df/dp) as function of Fo, the values for df/dp showed a non-linear or V-shaped relationship against Fo. In this study, we calculated the values for df/dp with a rubber model under various condition of length and weight of the vibrating part, aiming to reproduce a similar relationship between df/dp and Fo that has been observed in humans. The results showed that an increase in the length decreased df/dp, and increased Fo. An increase in the weight decreased df/dp, and decreased Fo as well. Using selected data, we were able to reproduce a V-shaped relationship between df/dp and Fo, which is similar to that observed in humans. Based on the results, we speculate that, in humans, length-change of the vocal folds determines Fo at a lower Fo, and weight-change determines Fo at a higher Fo. Key words: fundamental frequency of phonation, model experiment, transglottal pressure 1. Introduction The transglottal pressure influences the fundamental frequency of phonation (Fo). We have investigated the magnitude of Fo-change per unit change of transglottal pressure (abbreviated as df/dp) in humans. Figure 1 shows the relationship between df/dp and Fo that was reported in our previous paper [1]. Square-symbols represent the values for df/dp at modal register, while + symbols represent the values at falsetto register. It is noted that the values for df/dp vary with Fo, making a letter-v shape within the modal register. It is also noted that the values of falsetto register are larger than of modal register in general. Titze has described that the values for df/dp decrease with Fo, based on the theoretical and experimental studies [2]. The left half of the letter-v relationship observed in our previous study (Figure 1) could be explained by it. The right half of the letter-v, however, needs another explanation. The values for df/dp of falsetto register are larger than of modal register as is noted in Figure 1. At falsetto register, the vibration is restricted to the edge of the vocal fold. We speculate that the vibrating mass or weight of the vocal fold would be relevant to the right half of the letter V relationship because of the following reasons. The first one is that the vibrating mass or weight of the vocal fold is getting smaller with Fo [3] even within the modal register. The second one is the length of the vocal folds reaches a plateau at higher Fo-region of modal register [4]. In this study we aimed to reconstruct a letter V-shaped relationship between df/dp and Fo with a rubber model of the vocal folds. 2. Rubber model Figure 2 shows the rubber model. A thin rubber tube was cut out from the finger part of the surgical glove. The one end of the rubber tube was attached to the rigid pipe (19.5mm in outer diameter). The other end of the rubber tube was folded back on itself, and then was expanded and flattened by two needles (0.5mm in diameter) that were inserted into it. Two pockets were created at both sides of the flattened rubber tube. The air was insufflated into the rigid pipe, inducing vibration of the rubber tube including two pockets. During vibration, a hole for pressure regulation (4mm in diameter) was quickly opened, which leads to a quick reduction of the air-pressure inside the rigid pipe. We recorded the air-pressure (cmh2o) and flow rate (ml/sec) inside the rigid pipe. 3. Experimental procedures Incremental change in weight We increased the weight of the pockets by placing paste (Therasol; WR Medical Electronics Co. Still Water, Min) in them. The specific gravity of the paste was The incremental changes in weight were expressed in terms of paste volume (ml). MAVEBA 2001, Firenze, Italy 21

2 3. 2. Incremental change in length An incremental increase in the length was obtained by expanding the distance between two needles. 3.3 Study design The procedures of the study are shown in Figure 3. The initial length was 25.1mm. There was no paste in the pockets at this length. With a 1ml syringe, 0.05ml of paste was placed into each pocket (0.1ml total). The air was insufflated into the rigid pipe (air insufflation test). When the regular vibration of the rubber tube was observed, we quickly opened the hole for pressure regulation. The air-pressure inside the rigid pipe (abbreviated as Pt), the vibration-sound and the flow rate through the pipe were recorded during this procedure. Figure 4 shows a sample of the data display. Pt decreased quickly after opening the hole for pressure regulation, which was indicated by a vertical arrow. The length was increased in 0.5mm steps, and the air insufflation test was repeated until no vibration was observed. Then the length was reduced to the initial one (25.1mm), and another 0.1ml of paste was added to the pockets. The cycle of length-increase was repeated at each step of paste till 0.8 ml Calculation of df/dp The df/dp was calculated from the data display (Figure 4) with the following formula. df/dp = (Fo1-Fo2) / (Pt1-Pt2) Fo1 (Hz) is the frequency of the sound before reduction of air-pressure measured in a 300 ms-window (indicated by two dotted lines). Fo2 is frequency of the sound after reduction of air-pressure in a 300 ms-window. Pt1 (cm H2O) is the air pressure averaged during 300 ms-window, corresponding to Fo1 measurement before Pt reduction. Pt2 (cm H2O) is the air pressure averaged during 300 ms, corresponding to Fo2 measurement after Pt reduction. 4. Results Table 1 lists the values for the length (mm), paste volume (ml), frequency (Hz), df/dp, Pt1 (cm H2O) and flow rate (ml/sec). We group these data by paste volumes. The values for df/dp as function of Fo are plotted in Figure 5 and Figure 6. Figure 5 shows the values for df/dp with various pastevolume at each length. When the length is not changed, the increase of paste volume decreased the df/dp and also Fo, although each value for paste volume was not displayed in the figure. The correlation coefficients were calculated for the relationship between df/dp and Fo at each length, and between df/dp and paste volume at each length (Table 2). A positive relation was noticed at the former except for two conditions (26.6 and 28.6mm), and negative correlation was noted in the latter except for two conditions (26.6 and 28.6mm) Figure 6 shows the values for df/dp as a function of Fo with various lengths at each paste volume. When the paste volume is not changed, the increase of length decreased df/ dp, and raised Fo. The correlation coefficients were calculated for the relationship between df/dp and Fo at each paste volume, and between df/dp and length at each paste volume (Table 3). A negative correlation was observed at the former, except for three conditions (0.1, 0.4, and 0.5ml). The df/dp decreased with length, although meaningful correlations were observed only in two conditions (0.2 and 0.3ml). In humans, we believe the length-change of the vocal folds determines the left half of letter-v, based on Titze s study [2]. Regarding the right half the letter-v, we expected that the mass-reduction is responsible to it, as was described in the introduction. If these mechanisms were indeed responsible for the V-shaped relation, we could reproduce that relation with the selected data from Table 1. By means of this construct, we increase the length of the rubber model from 25.1mm to 27.1mm at a paste volume of 0.8ml, and then reduced the paste volume from 0.8ml to 0.1ml keeping the length of 27.1 mm. Figure 7 shows the result. Although the left half of the letter V is rather short, the general shape resembles the relation noted in Figure Discussion The letter V shape reproduced (Figure 7) showed three major differences from the shape observed in humans (Figure 1). The first one is the left half of the letter V is shorter than the right one, which would mean that the effects of the length was not well expressed with the rubber model. The second one is that there were no minus values for df/ dp. The third one is that the values for df/dp are lager in general than of humans. In our study for the Figure 1, we changed the transglottal pressure with a sudden increase of intra-oral pressure during phonation, which is contrary to the rubber model. Previous papers have shown that the sensitivity of fundamental frequency to the transglottal pressure is smallest in highpitched modal register, intermediate in the low-pitched modal register, and largest in falsetto register, despite different method of pressure-change applied in each study, that is, supraglottaly or subglottaly [2,5,6]. Thus, this difference in pressure-change is not relevant to the difference between MAVEBA 2001, Firenze, Italy 22

3 Figure 1and Figure 7. In humans, the cricothyroid (CT) and thyroarytenoid (TA) muscles mainly determine Fo. Although the length of the rubber model simulates the action of CT muscles, the model lacks complicated actions of TA muscles, which has been described by Titze [7]. If simulation of TA was incorporated, we would be able to minimize the difference between Figure1 and Figure Conclusion The results showed that an increase in the length of the rubber model decreased df/dp, and increased Fo. An increase in the weight decreased df/dp, and decreased Fo. Using selected data, we were able to reproduce a V-shaped relationship between df/dp and Fo, similar to that observed in humans. The rubber model supports our hypothesis for Fo regulation of modal register, that is, the length of the vocal folds determines Fo at a lower region, and weight or mass determines Fo at a higher region. References [1] Tanaka K, Kitajima K, Kataoka H. Effects of transglottal pressure changes on fundamental frequency of phonation: preliminary evaluation of the effect of intraoral pressure change. Folia Phoniatr Logop 1997;49: [2] Titze IR: On the relation between subglottal pressure and fundamental frequency in phonation. J Acoust Soc Am 1989; [3] Hollien H. On vocal registers. J Phonetics 1974;2: [4] Nshizawa N, Sawashima M, Yonemoto K. Vocal fold length in vocal pitch change. Vocal Physiology: Voice production, Mechanism and function, Fujimura O ed. Raven Press, Ltd., New York 1988; [5] Hixon TJ, Klatt DH, Mead J. Influence of forced transglottal pressure changes on vocal fundamental frequency. J Acoust Soc Am 1971;49:105(A). [6] Baer T. Reflex activation of laryngeal muscles by sudden induced subglottal pressure change. J Acoust Soc Am 1979;65(5): [7] Titze IR, Luchei ES, Hirano M:Role of the thyroarytenoid muscle in regulation of fundamental frequency. J Voice 1989;3: MAVEBA 2001, Firenze, Italy 23

4 Figure 1. Changes in fundamental frequency of phonation (Fo) per unit change of transglottal pressure (df/ dp) are plotted as function of Fo. Square-symbols represent the values of modal register, while +symbols represent those of falsetto register. Air Pressure Regulation Hole Rigid Pipe Pressure Flow Figure 2. The cut end of the thin rubber tube was folded back on itself, making two pockets at the bottom end of the tube. The two needles inserted into the tube expanded Rubber the bottom. Rubber Pocket Needle Needle start initial length add 0.1 ml of paste Figure 3. Flow chart of experimental procedures. quit yes paste >0.8ml no air insufflation test length increase 0.5 mm no regular vibration yes collection of data MAVEBA 2001, Firenze, Italy 24

5 Figure 4. Data display on computer screen. From top to the bottom, sound, Pt (cmh2o) and Flow (ml/sec). Vertical arrow indicates the place where Pt was decreased. The time distance between two dotted vertical lines is 300msec. length paste Fo df/dp Pt1 flow volume (mm) (ml) (Hz) (cmh2o) (ml/sec) length paste Fo df/dp Pt1 flow volume (mm) (ml) (Hz) (cmh2o) (ml/sec) length paste Fo df/dp Pt1 flow volume (mm) (ml) (Hz) (cmh2o) (ml/sec) Table 1. The values for length, paste volume, Fo, df/dp, Pt1and Flow. The data were grouped by the amount of paste volume. MAVEBA 2001, Firenze, Italy 25

6 df/dp (Hz/cm H2O) Fo Hz length (mm) Table2. Correlation coefficients by length df/dp and Fo df/dp and paste volume Length(mm) r p r p * * * * * * * * * * * * * statistically significant (p<.05) Figure 5. The values for df/dp as a function of Fo, with various paste-volume at each length. df/dp (Hz/cm H2O) F0 Hz paste volume (ml) Table3. Correlation coefficients by paste volume df/dp and Fo df/dp and length Paste volume(ml) r p r p * * * * * * * * statistically significant (p<.05) Figure 6. The values for df/dp as a function of Fo, with various length at each paste volume. df/dp (Hz/cm H2O) paste volume (ml) Hz Fo Figure 7. The df/dp vs. Fo characteristics reproduced from selected data. MAVEBA 2001, Firenze, Italy 26

Speech Communication Seminar Stockholm. Aug. 1-3, Abstract

Speech Communication Seminar Stockholm. Aug. 1-3, 1974 A MATHEMATICAL MODEL OF SPEECH AERODYNAMICS John J. Ohala Phonology Laboratory, Department of Linguistics, University of California, Berkeley, California