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Table of Contents
ORIGINAL ARTICLE
Year : 2016  |  Volume : 6  |  Issue : 2  |  Page : 36-43

Configuration of vocal folds during and after tube phonation in patients with voice disorders: A computerized tomographic study


1 Department of Communication Sciences, University of Chile; Department of Otolaryngology, Las Condes Clinic, Santiago, Chile
2 Department ofRadiology, University of Chile Hospital, Santiago, Chile
3 Department of Otolaryngology, University of Chile, Santiago, Chile
4 Department of Communication Sciences, University of Chile, Santiago, Chile
5 Department of Otolaryngology, University of Chile Hospital, Santiago, Chile, Chile

Date of Web Publication13-Oct-2017

Correspondence Address:
Marco Guzman
Department of Communication Sciences, University of Chile, Santiago, Chile. Department of Otolaryngology, Las Condes Clinic, Av Independencia 1027, Santiago
Chile
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jlv.JLV_16_16

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   Abstract 

Purpose: The study aims to observe whether any systematic change in vocal fold configuration occurs during and after phonation into a tube using computerized tomography (CT). Materials and Methods: Ten participants diagnosed with functional dysphonia were included in the study. CT was performed when participants produced the sound (a:), phonated into a drinking straw and when repeating (a:) after the exercise. Similar procedure was performed with a stirring straw after 20 min of vocal rest. Anatomic variables included: (1) glottal area, (2) glottal width, (3) vertical vocal fold thickness, (4) vocal fold area, and (5) vocal fold length. Each vocal fold was separately analyzed. Results: Only glottal area for stirring straw was statistically different throughout the three time points. This variable increased during tube phonation compared to conditions pre- and post-tube. Discussion: Since vocal fold length did not change during tube phonation, the increment in glottal area was likely due to increased amplitude of vibration. Increased vibratory amplitude has been found in previous studies with high-speed imaging, suggesting an increased subglottic pressure. From the physiologic point of view, transglottal pressure plays an important role in vocal fold amplitude of vibration. Conclusions: Tube phonation seems to cause increased glottal area during exercise. This change is more prominent during exercise with a higher degree of airflow resistance. Therefore, the degree of flow resistance is an important clinical variable to be considered when choosing the right voice exercises regarding the voice status/phonatory pattern of patients during voice therapy.

Keywords: Computerized tomography, semioccluded exercises, straw phonation, tube phonation, vocal folds, voice therapy


How to cite this article:
Guzman M, Miranda G, Muñoz D, Jara R, Pino J, Olavarria C, Madrid S. Configuration of vocal folds during and after tube phonation in patients with voice disorders: A computerized tomographic study. J Laryngol Voice 2016;6:36-43

How to cite this URL:
Guzman M, Miranda G, Muñoz D, Jara R, Pino J, Olavarria C, Madrid S. Configuration of vocal folds during and after tube phonation in patients with voice disorders: A computerized tomographic study. J Laryngol Voice [serial online] 2016 [cited 2017 Nov 24];6:36-43. Available from: http://www.laryngologyandvoice.org/text.asp?2016/6/2/36/216703


   Introduction Top


Tube phonation is a semioccluded vocal tract exercise (exercises with partial occlusion or artificial lengthening of the vocal tract), a common method used in voice therapy. The free end of the tube can be open to the air or placed in water. Several effects attributed to tube phonation have been linked to an increase in vocal tract acoustic impedance, specifically changes in the inertive reactance,[1],[2],[3] which may favorably affect the vocal fold vibration.[1],[2],[3],[4],[5]

Several recent studies have demonstrated that tube phonation produces changes in air pressure measures during vocalization.[6],[7],[8],[9],[10],[11],[12] Both tube phonation into air and water increase subglottic and oral pressure compared to vowel phonation.[7],[9],[12] In general, phonation into a tube below the water surface produced the highest values for both pressure measures.[7],[9],[12] These studies have suggested that the increased subglottic pressure could be a way to compensate for increased oral pressure, which in turn, is caused by the high degree of airflow resistance offered by semiocclusions. This airflow resistance varies depending on the diameter and length of the tube in air and the depth of immersion when the tube is placed into the water.[7],[12] Vocal tract shape has also been examined during tube phonation.[9],[13],[14],[15],[16] Main findings reported are a lower laryngeal position, wider hypopharyngeal area, a tighter closure between the velum and the nasal passage, expansion of the cross-sectional area of the oropharynx and in the oral cavity, and a larger total volume of vocal tract compared to vowel phonation before exercises.[9],[13],[14],[15],[16]

Changes in the glottal source during tube phonation have also been investigated. The increased vocal tract impedance (mentioned above) during semiocclusions appeared to change the glottal flow amplitude and pulse shape.[1],[4] Furthermore, the oscillation threshold pressure is reduced by increased vocal tract inertance.[4] Story et al.[1] stated that this occurs when fundamental frequency approaches the first formant frequency. Hence, phonating at a frequency at or near the first formant (which happens during tube phonation) may allow for an efficient voice production that could possibly be associated with lower effort. Moreover, several studies related to glottal source modifications have reported a change in electroglottographic closed quotient when tube phonation is compared to vowel phonation.[9],[12],[17],[18],[19],[20],[21] Muscle activity using electromyography has also been assessed.[22] Authors found that the ratio of thyroarytenoid (TA) muscle versus cricothyroid muscle activity increased during phonation into a tube. In addition, changes in vocal fold vibration and glottal area variables have been observed by high-speed digital imaging (HSDI) during tube phonation.[23],[24],[25] Furthermore, a recent double-case study was carried out to observe whether there are systematic changes in the vocal fold adjustment during and after tube phonation using computerized tomography (CT).[26] No clear common trends in vocal fold configuration were found in either participant.

To date, most data related to glottal source function during tube phonation has been obtained from vocally healthy participants. The present study aimed to observe whether any systematic change in vocal fold configuration occurs during and immediately after phonation into a tube using CT in a group of participants diagnosed with functional dysphonia.


   Materials and Methods Top


Participants

Ten participants were included in the present study (six females and four males). The average age of the participants was 26 years, with a range of 21–43. Inclusion criteria included: (1) age range of 20–45 years, (2) laryngoscopic diagnosis of mild hyperfunctional dysphonia, and (3) no previous voice training or therapy. None of the participants reported previous experience using tube phonation or other semiocclusions as vocal training or warm-up exercises. Participants did not report any known hearing pathology at the time of the experiment. The procedures followed the present study were in accordance with the ethical standards of the responsible committee on human experimentation and with the Helsinki Declaration of 1975, as revised in 2000. This study was reviewed and approved by the Review Board (reference number: 5417.10.13). Informed consent was obtained from all participants.

Laryngoscopic assessment

All participants were asked to undergo flexible laryngoscopy (Olympus ENF type p4; Olympus, Center Valley, PA, USA) to confirm the presence of functional dysphonia. Endoscopic laryngeal examinations were performed by one laryngologist who is coauthors of the present study. Intranasal topical anesthesia was used during transnasal endoscopy for all participants.

Computerized tomography scanning

The CT images were acquired using a Somatom Sensation 64 (Siemens, Germany) CT machine. The CT imaging parameters used to provide images of the vocal tract were: voltage 100 kV, time of the rotation 0, 4 s, and slice thickness 1, 2 mm. In supine position inside the CT machine, participants were asked to produce the following phonatory tasks: (1) to sustain vowel [a:] (baseline, condition pre), (2) to phonate a sustained vowel-like sound into a drinking straw (tube 1) (5 mm of inner diameter and 25.8 cm in length) for 15 minutes, immediately after that, (3) to produce another sustained vowel (a:) (condition post). After 20 min of complete silence (vocal rest), participants performed phonation into a plastic stirring straw (tube 2) (2.7 mm of inner diameter and 10.7 cm in length) for 15 min. Participants were immediately asked to produce another sustained vowel [a:] (postcondition). All phonations were carried out at habitual loudness level and speaking pitch. Pitch was kept constant during all phonatory tasks, and it was perceptually controlled by one of the experimenters using an electronic keyboard. Participants were required to produce a stable sound with good lip closure, feel vibratory sensations as strong as possible on the alveolar ridge, face and head areas, and produce an easy voice during tube phonation. Each participant was scanned once while producing each phonatory task. No additional repetitions were performed due to the limitations of maximum allowed radiation exposure. Participants were asked to adopt a relaxed posture in the CT scanner and exactly the same body and head position were kept during the entire CT procedure. The head position was mechanically fixed in a frame during all experiments.

Computerized tomography image analysis

Most of CT variables and measures included in the present study were based on previous research.[26]

Anatomic variables calculated from all participants included: (1) total glottal area, (2) glottal width, (3) vertical vocal fold thickness, (4) vocal fold area, and (5) vocal fold length. Each vocal fold was separately analyzed in each participant.

From the source CT image, a reconstruction of the vocal folds was performed. A transverse and parallel plane to the upper surface of the vocal folds was drawn in the starting sagittal image [Figure 1]a. Then, the transverse plane was moved down to reach the midline of the vocal folds in an anterior-posterior direction. In the resulting axial image [Figure 1]b, the plane was used to create an axis connecting both anterior and posterior commissures. The anterior part of the axis was placed in the apex of the anterior commissure. The posterior part of the axis intersected the middle of the distance between the vocal processes. In the middle point between anterior commissure and vocal processes (mid-membranous part of the vocal folds), a perpendicular line to the anterior-posterior axis was created. In the coronal view [Figure 1]c, this line determined the plane (perpendicular to the vocal fold surface).
Figure 1: The sagittal (a), axial (b), and coronal (c) slices showing how the reconstruction of the vocal folds was performed from each computerized tomographic sample. Three planes can be observed: Transverse plane (t), coronal plane (c), and sagittal plane (s)

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Glottal area was calculated from the axial image considering both membranous and cartilaginous glottis [Figure 2]. Glottal width, vocal fold areas, and vocal fold thicknesses were measured in the coronal plane perpendicularly to the vocal fold surface. Measurements of the vocal fold thicknesses were performed at 1 and 2 mm distances from the glottis [Figure 3]. Cross-sectional vocal fold areas were calculated following the vocal fold contours and lines that previously determined vocal fold thicknesses [Figure 3]. Glottal width was measured as the distance between the most medial parts of the vocal folds [Figure 3]. All CT distance and area measurements were performed using the software OsiriX version 5.0.2 64 bit (Pixmeo SARL, Bernex, Switzerland).
Figure 2: Measurement of glottal area from the axial image considering both membranous and cartilaginous glottis

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Figure 3: Measurement of glottal width, vocal fold areas (A1 and A2), and vocal fold thicknesses (T1 and T2) from the coronal plane

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Statistical analysis

Numerical variables were described by median and interquartile range (IQR) and compared through Wilcoxon test. A generalized estimating equation model was fitted to assess differences between pre-, during, and post-tube use as well as differences between tubes. All analyses were performed using Stata ® 13.1 (StataCorp, College Station, TX, USA), P < 0.05 was considered to be statistically significant, and all reported P values were two-sided.


   Results Top


[Table 1] shows median and IQR from vocal fold variables for both sequences (tube 1 and tube 2). In general, it is possible to observe that no significant differences were found for any parameter, except for glottal area in tube 2 sequence, when comparing pre, during, and after tube phonation conditions [Figure 4]. [Figure 5],[Figure 6],[Figure 7] display trends observed for all vocal fold variables for both tube 1 and tube 2 sequences. Moreover, when comparing tube 1 and tube 2 sequences, no significant differences were found. Similarly, no significant differences were found between right and left vocal folds for both tube 1 and tube 2 sequences.
Table 1: Median and interquartile range from vocal fold variables for both sequences (tube 1 and tube 2)

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Figure 4: Glottal area before tube phonation (left), during tube phonation (middle), and after tube phonation (right)

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Figure 5: Observed trends for vocal fold length, glottal area, and glottal width

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Figure 6: Observed trends for vocal fold thickness 1 and 2

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Figure 7: Observed trends for vocal fold area 1 and 2

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   Discussion Top


The present study aimed to observe possible systematic change in configuration of the vocal folds during and after tube phonation using CT in a group of participants diagnosed with functional dysphonia. Inspection of results showed that only glottal area for tube 2 (stirring straw) was statistically different throughout the three time points (pre, during, and after tube). This variable increased during tube phonation compared to conditions pre- and post-tube. A similar trend was observed for tube 1 (drinking straw), but no significant differences were found [Figure 5].{Figure 5}

All variables used in our investigation were the same as variables used in the previously cited study by Hampala et al.[27] except glottal area (obtained from CT samples) which was first included in the present research. Therefore, no direct comparison is possible regarding this variable. Nevertheless, since vocal fold length did not change during tube phonation, the increment in glottal area was likely due to increased amplitude of vibration. Laukkanen et al.[23] in a HSDI study whose purpose was to investigate the effects of tube phonation, assessed the amplitude-to-dynamic length (A-DL) ratio. An increased A-DL ratio was found for the longest tube, which according to authors, may suggest a greater vocal effort (increased subglottic pressure).[23] Similar findings were reported by Castro et al.[28] in a videokymography investigation performed with participants diagnosed with unilateral vocal fold paralysis. An increase in the mean displacement and maximum displacement of the vibratory amplitude of the nonparalyzed vocal fold was observed after tube phonation into water. Differently, in a recent HSDI study, Guzman et al.[25] found that the amplitude-to-length ratio (A-LR) was in most cases lower during phonation into water, for all immersion depths. From the physiologic point of view, transglottal pressure (difference between subglottic and oral pressures) is expected to play an important role in vocal fold amplitude of vibration. A decreased A-LR may reflect a decreased transglottal pressure (Ptrans) during increased vocal tract loading while an increase in A-LR could be expected when Ptrans increases.

Previous studies have demonstrated that Ptrans changes during semioccluded vocal tract exercises.[6],[7],[9],[12] Titze et al.[6] stated that when a semiocclusion, such as tube phonation, is produced, there should be a reduction in the Ptrans (which is considered the force driving vocal fold vibration), unless the subglottic pressure is raised. Results from a single-case study by Guzman et al.[9] showed that Ptrans decreased during both traditional Finnish glass tube and stirring straw. Contrary, in a recent investigation performed in participants with different voice conditions, Ptrans was higher than baseline condition for all semioccluded exercises.[12] Radolf et al.[7] showed similar findings for both Finnish glass tube and stirring straw phonation. A compensatory adjustment to sustain the phonatory airflow during phonation could be a possible explanation for increase in Ptrans. Outcomes from the two later studies could imply that although both oral pressure (Poral) and subglottic pressure (Psub) increased, they do not change proportionally, i.e., Psub increases relatively more than Poral during semiocclusions. This could be a suitable explanation for the increased glottal area found during phonation into tube 2 in the present study. This change in Ptrans and glottal area associated to vibratory amplitude of vocal folds is most likely an unconscious compensation for varying supraglottic load and a manner of searching for the optimal match between glottal and supraglottal impedances (to avoid breathy and pressed phonation), as Laukkanen et al.[23] suggested.

Since we suggest that the increment in glottal area during tube 2 was likely caused by increased amplitude of vibration, an increase in glottal width (another variable included in the present study) should also be expected. Although this variable showed an increase during both tube 1 and tube 2, differences were not statistically significant when comparing the three time points (before, during, and after).

Hirano [29] and Yumoto et al.[30] have demonstrated that increased activity of TA muscle makes the vocal fold thicker and bulged. Moreover, Titze et al.[31] suggested that relatively high TA muscle activity (in relation to the activity of muscles that stiffen the vocal fold cover such as cricoarytenoid muscle) should lead to the greatest amplitude of vibration of vocal folds (which was observed during tube 2 in the present study). In this regard, Laukkanen et al.[23] suggested that phonation with a raised supraglottic load such as semioccluded voice exercises might offer a tool for training optimization of relative TA activity. Based on this assumption, Laukkanen et al.[22] in a single-case study explored laryngeal muscle activity before, during, and after different semioccluded exercises. Results showed that increased vocal tract load caused an increased TA/CT ratio during and after the use of the tube compared to before exercises. The TA/CT ratio increased in proportion to the degree of the semiocclusion. Stirring straw (the narrowest tube used in this study) showed the most prominent changes. Authors suggested that the increased TA activity is used in response to the increased intraglottal pressure resulting from the semiocclusion. If semiocclusions of the vocal tract really cause the vocal folds to thicken and bulge (due to higher TA activity), the measures in the present study for both vertical thickness and vocal fold area should be expected to increase. Nevertheless, no significant changes were observed for these variables in our data. Hampala et al.,[26] in a CT study, also reported no clear changes neither during nor after tube phonation. The absence of change in thickness and vocal fold area measures suggests that either the TA did not change considerably during tube phonation or the change could not be detected with this measurement method.

Since participants from the present study were required to keep the same pitch during the entire sequence, F0 and vocal fold length are not expected to be modified when comparing conditions pre, during, and after tube phonation. As previously mentioned, this assumption was confirmed in our data. No changes of vocal fold length were observed. Same results were reported by Hampala et al.[26] Earlier investigations have reported that tube phonation and other semioccluded postures may modify F0. However, no consistency has been observed.[6],[8],[16],[22],[31],[32],[33],[34],[35]


   Conclusion Top


Tube phonation seems to cause increased glottal area during exercise due to an increased transglottal pressure. This change is more prominent during exercise with a narrow stirring straw (higher degree of airflow resistance) than drinking straw (lower degree of airflow resistance than narrow straw). Modifications do not remain after exercises. Moreover, vocal fold geometry seems not to change due to a possible increased TA activity during semiocclusion. However, we acknowledge the possibility that CT measures are not the best method to detect this possible vocal fold modification.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
 
 
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