Name: hemi-laryngeal setup for studying vocal fold vibration in three dimensions
Uploaded: 2017-11-25T13:00:00
Description: Watch this Scientific Journal Video about Hemi-laryngeal Setup for Studying Vocal Fold Vibration in Three Dimensions at JoVE.com

This work was supported by an APART grant of the Austrian Academy of Sciences (CTH), the Technology Agency of the Czech Republic project no. TA04010877 (CTH, VH and JGS), and the Czech Science Foundation (GACR) project no GA16-01246S (to JGS). We thank W. Tecumseh Fitch for his suggestion to use denture fixative cream, and Ing. P. Liska from the Czech Army Forest Service for his help in acquiring the excised deer larynges.

The animal specimens analyzed in this paper were treated in accordance with the standard ethical requirements of the Palacky University in Olomouc, Czech Republic. They stem from red deer living wildly in forests, which were hunted by the Czech Army Forest Service during a regular hunting season.
1. Preparation of the Hemi-larynx Specimen
Note: Only properly prepared specimens should be used, as indicated in4 . Quick freezing of the larynx<sup ...

The hemi-larynx preparation shares the advantages of the &#34;conventional&#34; (full) excised larynx setup: In such an experimental approach, physical and physiological boundary conditions and parameters (such as subglottal pressure or vocal fold elongation) can be controlled fairly well. The behavior of the hemilarynx is homologous to that of a full larynx with a perfect lateral symmetry, with the exception that magnitudes of some parameters (e.g., air flow rate, sound pressure) are reduced by approximately 50...

Voice is typically created by vibrating laryngeal tissue (mainly the vocal folds), which converts a steady airflow, supplied by the lungs, into a sequence of airflow pulses. The acoustic pressure waveform (i.e., the primary sound) emerging from this sequence of flow pulses acoustically excites the vocal tract which filters them, and the resulting sound is radiated from the mouth and (to a certain degree) from the nose1. The spectral composition of the generated sound is largely influenced by the quality of vocal fold vibration, governed by laryngeal biomechanics and interactions with the tracheal airflow2. Both in a clinical and a research context, documentation and assessment of vocal fold vibration is thus of foremost interest when studying voice production.
In humans, direct endoscopic investigation of the larynx during sound production in vivo is challenging, and it is virtually impossible in nonhuman mammals, given current technological means. Therefore, and in order to guarantee carefully controlled physical and/or physiological experimental boundary conditions, the use of excised larynges3,4 is in many cases an adequate substitution for investigation of in vivo voice production mechanisms.
Vocal fold vibration is a complex three-dimensional phenomenon5. While conventional investigation methods like laryngeal endoscopy (in vivo) or excised larynx preparations typically provide only a superior view of the vibrating vocal folds6, they do not allow for complete three-dimensional analysis of vocal fold motion. In particular, in the superior view the lower (caudal) margins of the vocal folds are invisible during a major portion of the vibratory cycle. This is due to the phase delay between the inferior (caudal) and the superior (cranial) edge of the vocal folds, a phenomenon which is typically seen during vocal fold oscillation5. As direct empirical evidence for backing up findings from mathematical and physical models is scarce, knowledge of the geometry and motion of the lower vocal fold edge7, and thus the geometry of the subglottal channel8,9,10 is crucial for better understanding the interaction between laryngeal airflow, vocal fold tissue, and the resulting forces and pressures11,12. Another aspect of vocal fold vibration that is hidden from the customary superior view is the vertical (caudo-cranial) depth of the contact between the two vocal folds. The vertical contact depth is related to the vertical thickness of the vocal folds, which is a potential indicator of the vocal register used in singing (&#34;chest&#34; vs. &#34;falsetto&#34; register)13,14.
In order to overcome the shortcomings of conventional (full) excised larynx preparations, a so-called hemi-larynx setup can be utilized, where one half of the larynx is removed, thus facilitating the assessment of the vibratory characteristics of the remaining vocal fold in three dimensions. Surprisingly, since the introduction of this setup in the 1960s15 and an initial validation of the concept in 199316, not many laboratories have performed experiments with this promising experimental approach17,18,19,20,21,22,23. An explanation for this might be found in the difficulties of creating a viable hemi-larynx preparation. While the conventional excised (full) larynx preparation is well documented4, no such in-depth instructions are as yet available for creating a hemi-larynx setup. It is therefore the purpose of this paper to provide a tutorial for establishing a reliably reproducible hemi-larynx setup, supplemented by experimental results from red deer specimens.
A hemi-larynx setup shares many features with a &#34;conventional&#34; excised larynx setup, such as measurement equipment, high-speed or other imaging technology to adequately document the vibrations of the laryngeal structures during sound generation, or proper supply of heated, humidified air. These general setup considerations are described in detail in both a book chapter4 and a technical report from the National Center of Voice and Speech24. Reiteration of these instructions would be beyond the scope of this manuscript. Here, only the specialized directives for generating a hemi-larynx setup are presented.

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			<td >Surgical blades</td>
			<td >Surgeon</td>
			<td >Jai Surgical Ltd., New Delhi, India</td>
			<td ></td>
		</tr>
		<tr >
			<td >Saw</td>
			<td >Hand saw (Lux, 150 mm length)</td>
			<td >Lux, Wermelskirchen, Germany</td>
			<td ></td>
		</tr>
		<tr >
			<td >Thermometer</td>
			<td >Testo 922</td>
			<td >Testo Ltd., Hampshire, UK</td>
			<td >K-type Probe, Operating temperature -20 to +50 &#176;C</td>
		</tr>
		<tr >
			<td >Autoclave bags</td>
			<td >Autoclave bags</td>
			<td >vwr.com, VWR International s.r.o., Stribrna Skalice, Czech republic</td>
			<td ></td>
		</tr>
		<tr >
			<td >Conductive glass plates</td>
			<td >Custom made</td>
			<td >UPOL - Joint laboratory of Optics 
			Trida 17. listopadu 50A, 772 07 Olomouc, the Czech Rep.</td>
			<td ></td>
		</tr>
		<tr >
			<td >Fixative cream</td>
			<td >Denture fixative cream</td>
			<td >Blend-a-dent Natural</td>
			<td ></td>
		</tr>
		<tr >
			<td >Prongs and fastening system</td>
			<td >Customized Kanya Al eloxed profiles</td>
			<td >Distributor: VISIMPEX a.s.. Seifertova 33, 750 02 Prerov, the Czech Rep.;</td>
			<td >&#160;Combination of Kanya RVS and PVS fastening systems (http://www.kanya.cz/) + custom made prongs</td>
		</tr>
		<tr >
			<td >Mounting tube</td>
			<td >Custom made</td>
			<td >UPOL - Joint laboratory of Optics, 
			Trida 17. listopadu 50A, 772 07 Olomouc, the Czech Rep.</td>
			<td ></td>
		</tr>
		<tr >
			<td >LED Light</td>
			<td >Verbatim 52204 LED Lamp</td>
			<td >Mitsubishi Chemical Holdings Corporation, Tokyo, Japan</td>
			<td ></td>
		</tr>
		<tr >
			<td >Camera</td>
			<td >Canon EOS1100D</td>
			<td >Canon Inc.</td>
			<td >18-55 mm lens</td>
		</tr>
		<tr >
			<td >Airpump</td>
			<td >Resun LP100</td>
			<td >Resun</td>
			<td ></td>
		</tr>
		<tr >
			<td >Strobe light</td>
			<td >ELMED Helio-Strob micro2</td>
			<td >ELMED Dr. Ing. Mense GmbH, Heiligenhaus, Germany</td>
			<td ></td>
		</tr>
		<tr >
			<td >Humidifier</td>
			<td >Custom made</td>
			<td >Voice Research Lab, Dept. Biophysics, Faculty of Sciences, Palacky University Olomouc, Czech republic</td>
			<td ></td>
		</tr>
		<tr >
			<td >Subglottic tract</td>
			<td >Custom made adjustable subglottic tract</td>
			<td >Voice Research Lab, Dept. Biophysics, Faculty of Sciences, Palacky University Olomouc, Czech republic</td>
			<td >Hampala, V., Svec, Jan, Schovanek, P., and Mandat, D. Uzitny vzor c. 25585: Model subglotickeho traktu. [Utility model no. 25585: Model of subglottal tract] (In Czech) Soukup, P. 2013-27834(CZ 25505 U1), 1-7. 24-6-2013. Praha, Urad prumysloveho vlastnictvi</td>
		</tr>
	</tbody>
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hemi-laryngeal setup for studying vocal fold vibration in three dimensions

The voice of humans and most non-human mammals is generated in the larynx through self-sustaining oscillation of the vocal folds. Direct visual documentation of vocal fold vibration is challenging, particularly in non-human mammals. As an alternative, excised larynx experiments provide the opportunity to investigate vocal fold vibration under controlled physiological and physical conditions. However, the use of a full larynx merely provides a top view of the vocal folds, excluding crucial portions of the oscillating structures from observation during their interaction with aerodynamic forces. This limitation can be overcome by utilizing a hemi-larynx setup where one half of the larynx is mid-sagittally removed, providing both a superior and a lateral view of the remaining vocal fold during self-sustained oscillation.
Here, a step-by-step guide for the anatomical preparation of hemi-laryngeal structures and their mounting on the laboratory bench is given. Exemplary phonation of the hemi-larynx preparation is documented with high-speed video data captured by two synchronized cameras (superior and lateral views), showing three-dimensional vocal fold motion and corresponding time-varying contact area. The documentation of the hemi-larynx setup in this publication will facilitate application and reliable repeatability in experimental research, providing voice scientists with the potential to better understand the biomechanics of voice production.

Illustrations of the hemi-larynx preparation and its mounting on the air supply tube, as referenced in the previous section, are provided in Figure 1 and Figure 2, respectively.
Documentation of vocal fold vibration from two camera angles
Airflow-induced self-sustaining oscillation of the hemi...

Watch this Scientific Journal Video about Hemi-laryngeal Setup for Studying Vocal Fold Vibration in Three Dimensions at JoVE.com

Hemi-laryngeal Setup for Studying Vocal Fold Vibration in Three Dimensions

This paper introduces a protocol for the preparation of hemi-larynx specimens facilitating a multi-dimensional view of vocal fold vibration, in order to investigate various biophysical aspects of voice production in humans and non-human mammals.

The voice of humans and most non-human mammals is generated in the larynx through self-sustaining oscillation of the vocal folds. Direct visual ...

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