Patient Report

Yonago Acta medica 2016;59:241–247

Analysis of Direct Simultaneous Measurement of Glottal Airflow Velocity, Subglottal Pressure, and High-Speed Imaging Using Flexible Transnasal Endoscope in a
Human Subject
Hideyuki Kataoka,*† Shiro Arii,‡ Takahiro Fukuhara,† Kazunori Fujiwara,† Yasuomi Kunimoto,† Kensaku
Hasegawa§ and Hiromi Takeuchi†*Department of Adult and Elderly Nursing, School of Health Science, Tottori University Faculty of Medicine, Yonago 683-8503, Japan,†Division of Otolaryngology, Head and Neck Surgery, Department of Medicine of Sensory and Motor Organs, School of Medicine,
Tottori University Faculty of Medicine, Yonago 683-8503, Japan, ‡Department of Information and Knowledge Engineering, Graduate
School of Engineering, Tottori University, Tottori 680-8550, Japan and §Department of Otolaryngology-Head and Neck Surgery, Nippon Medical School Chiba Hokusoh Hospital, Inzai 270-1694, Japan

ABSTRACT
It is difficult to directly observe glottal airflow velocity
just above the glottis due to sensor size requirements
and limited accessibility. We developed a miniature hotwire probe and flexible fiberscopic high-speed imaging
system for human examinations. Simultaneous direct
measurement of glottal airflow velocity, subglottal pressure, and vocal fold vibration was achieved in a patient
who was treated with a T-tube for tracheal stenosis.
Airflow velocity changes at the anterior midline of the
vocal folds were synchronized with subglottal pressurechanges during each phonation cycle. The velocity at theanterior midline of the vocal folds showed a rhythmic
pattern of sharp, high peaks. The result of fast Fourier transform analysis indicated that glottal velocity at
the anterior midline of the vocal folds had abundant
high-frequency components that were not affected byresonance of the vocal tract. Airflow velocity was variable and diminished except at the anterior midline of the
vocal folds.

by the fact that their movements are difficult to observe
directly. Thus computer simulation models3 and experiments with excised canine larynges4, 5 can be powerfultools in lieu of direct in vivo human study.
To the knowledge of the authors, no studies havecombined measures of subglottal pressure and glottal
airflow velocity with simultaneous high-speed recordingof vocal fold movements in human phonation. Vocal
fold movements are likely to have an impact on therelationship between subglottal pressure and glottal airflow velocity. Such laryngeal aerodynamic studies arenecessary for a basic understanding of the mechanics ofphonation. We developed an extremely small, flexible
hot-wire probe that is inserted into a flexible transnasal
endoscope.6 Glottal velocities were measured in a single
subject after expansion of subglottic stenosis and before
stomal closure. We demonstrated the realistic evaluationof glottal velocity in a human in different phases of thephonation cycle. Subglottal pressure and glottal velocity
were recorded concurrently with the observation of vocal fold vibrations using a high-speed imaging system.

Key words

glottal velocity; high-speed imaging; subglottal pressure; transnasal endoscope

PATIENT REPORTPatient

Laryngeal aerodynamic parameters represent valuable
information about the mechanical characteristics ofhuman phonation. Simultaneous analysis of multiple
parameters is important to evaluate the relationships
between glottal flow, subglottal pressure, and vocal foldvibration.1 Alipour et al. reported that it is conceivablethat measuring airflow velocity at the laryngeal level inhumans will be feasible in the future when accessibility
and sensor size requirements are met.2 Currently, studying the human vocal folds is significantly complicatedA 53-year-old man was treated with a silicone T-tube
for tracheal stenosis. He suffered from life-threatening
heat stroke on a very hot summer day and was therefore
intubated. After he recovered from heat stroke–induced
brain damage, he was referred to Tottori University
Hospital for the treatment of post intubation tracheal
stenosis. We removed endotracheal granulation andscarred tissue using an XPS microdebrider (Medtronic
Xomed, Jacksonville, FL) and a silicone T-tube stentwas placed for tracheal expansion in the area of tracheal
stenosis. The patient was evaluated 3 months after the
expansion. Endoscopic evaluation found that vocal focal
fold movements were normal and endotracheal stenosis
was thought to be cured. He provided informed consent
using a procedure approved by the ethics committee ofCorresponding author: Hideyuki Kataoka, MD, PhD
hkataoka@med.tottori-u.ac.jp
Received 2016 May 30
Accepted 2016 June 20
Abbreviation: FFT, fast Fourier transform241

H. Kataoka et al.

Fig. 1. A miniature hot-wire probe. A: A hot-wire tip was connected to a coaxial cable, which passed through the wire commonly used
for clinical biopsy. B: The hot-wire tip was inserted into the channel of the flexible transnasal endoscope. The tip of the probe had an active length of 1.6 mm.

Tottori University (Record Number 2614). The examination was performed a few days before the operation of
the T-tube removal and stomal closure.

the silicone T-tube. A schematic diagram is shown in
Fig. 2.
This procedure had a barely obvious influence onphonation, as normal spontaneous phonation was possible even with the T-tube in place because tracheal stenosis had been fully treated on the day of the examination.
The pressure transducer was placed in the subject’s
trachea about half an hour in advance; this minimized
temperature and moisture differences between the transducer and the environment and therefore increased theaccuracy of detecting pressure changes.

Velocity measurement system

Glottal airflow velocity was measured with a miniature
hot-wire anemometer that was attached to the tip of thewire commonly used for clinical biopsy (Fig. 1A). The
hot-wire tip was inserted into the channel of a flexible
transnasal endoscope ENF Type3 (Olympus, Tokyo, Japan) (Fig. 1B). Calibration curves were obtained for all
hot-wire probes. The high-speed camera system was run
at a frame rate of 1000 images per second with an image
resolution of 512 × 512 pixels. In previous articles, we
described a method for calibrating the hot-wire probe
and high-speed recording system.6 A flexible transnasal
endoscope was inserted into the nose and the sensor
probe remained inside the channel until it crossed overthe epiglottis. The sensor probe then protruded from theendoscope channel and the position of the tip was carefully checked on a monitor. Glottal airflow velocity wasmeasured at different positions as the probe approached
the vocal folds.

Data analysis

Transnasal fiberscopic examination was performed toenable observation of vocal fold vibrations. The subject
was asked to produce steady phonation of the vowel /e/within the modal register and in a comfortable manner.
The signal from the pressure converter was input
to a control unit (TCB-500, Millar, Houston, TX), andthe output from the control unit was displayed on an
oscilloscope (SS -7602, Iwatsu, Tokyo, Japan) and synchronized with the glottal velocity measurement results
using a 4-track, 16-bit analog to digital conversion board(CBI-320416, Interface Corporation, Hiroshima, Japan)
in a personal computer.
The glottal velocity was measured by means of the
hot-wire probe while the patient maintained continuous
phonation of /e/ in a comfortable manner. The tip of thePressure measurement system

In order to obtain the waveform of the pressure below
the vocal folds, pressure recording should be performedin the trachea. A pressure transducer was placed inside
242

Glottal velocity in a human subject

OLYMPUS ENF Type T3

High Speed Digital Camera
FASTCAM-MAX 120K
Constant Temperature
Anemometer
KANOMAX MODEL 1011
Personal
ComputerA/D Interface
CBI-320416

pressure transducer
hot-wire probe

Pressure Control Unit
Millar TCB-500

dental impression paste

Fig. 2. Schematic diagram of the measurement system.

probe was gradually advanced toward the vocal folds
during a single sustained vowel sound, then graduallyslid over the vocal fold surface to the false vocal foldsurface.
Figure 3 shows examples of airflow velocity at different sensor positions; inside the upper edge of the epiglottis (about 20 mm above the glottis) in the top graph A,
at the anterior midline of the vocal folds (about 10 mmabove the glottis) in the second graph B, and at the lateral shift on the false vocal folds in the third graph C. In
graphs A and C, the airflow velocity fluctuates irregularly with no discernible peaks, and is diminished overall.
In graph B, the velocity at the anterior midline of the vocal folds shows a rhythmic pattern of sharp, high peaks.
Figure 4 shows subglottal pressure (dotted line) andairflow velocity (solid line) measured at the anterior midline about 10 mm above the glottis. Maximum airflow
velocity higher than 30 m/s was found at the anterior
midline of the vocal folds. The airflow velocity showedsharp fluctuations corresponding with the phonation cycle. Subglottal pressure was measured relative to atmospheric pressure, and thus 0 kPa in Fig. 4 is equivalent toatmospheric pressure. The fundamental frequency wasalmost 155 Hz. Glottal velocity changes at the anterior
midline of the vocal folds were synchronized with subglottal pressure changes during each phonation cycle.
Peak glottal airflow velocities seemed to occur slightly

earlier than peak subglottal pressures.
The glottal airflow velocity at the anterior midline of the vocal folds was analyzed by fast Fouriertransform (FFT) algorithm (Fig. 5). The waveform had
abundant high-frequency components, but otherwise did
not demonstrate the typical amplitude reduction of theconsecutive harmonic components throughout the tract.
These results suggest that the glottal airflow velocity at
the anterior midline just above the glottis was not affected by vocal tract resonance filters.
Figure 6 shows a detailed analysis of the vibration
during a single phonation cycle, and illustrates eight
sequential high-speed images during the open and closing phases of the vocal folds. The upper portion of the
figure shows subglottal pressure (dotted line) and airflow
velocity (solid line) measured at the anterior midlineof the vocal folds. The lower portion shows high-speed
images captured at 1000 frames per second during thephonation cycle phase, and illustrations of vocal foldmovements at each downward-pointing arrow on thesolid line indicating airflow velocity.
The highest subglottal pressure was almost 3 kPa(between phases 4 and 5), and the maximum glottal velocity profiles were highest during the late closing phase(phase 4). Maximum velocities occurred slightly earlier
than maximum subglottal pressures.
243

H. Kataoka et al.

Velocity m/s

50
0

A

40
30
20
10
0

1

1.05

1.1

Time sVelocity m/s

50
0

B

40
30
20
10
0

2.6

2.65

2.7

Time sVelocity m/s

50
0

C

40
30
20
10
0

5.7

5.75

5.8

Time sFig. 3. Airflow velocity recorded at different positions. A: inside the upper edge of the epiglottis. B: at the anterior midline of the vocal folds. C: lateral to the false vocal folds.
4

Airflow Velocity
Subglottal Pressure

Velocity m/s

40

3

30
2
20
1

10

0

Pressure kPa

50

3.2

3.25

Time s3.3

0Fig. 4. Typical subglottal pressure and glottal airflow velocity signal recordings at the anterior midline of the
vocal folds.

244

Glottal velocity in a human subject

Amplitude spectrum m/s

101

100

10

-1

10-2

0

5
Frequency kHz

10Fig. 5. FFT amplitude spectrum of glottal airflow velocity at the anterior midline of the vocal folds.
FFT, fast Fourier transform.

Airflow Velocity

Velocity m/s

Pressure kPa

Subglottal Pressure

TimeTime ss
Phase

Fig. 6. The correlations among vocal fold movement, glottal airflow velocity, and subglottal pressure. Dotted line: subglottal pressure;solid line: glottal airflow velocity measured at the midline immediately above the glottis. The lower photographs and illustrations show
the phases of the phonation cycle at each downward-pointing arrow on the solid line (glottal airflow velocity).

245

H. Kataoka et al.

DISCUSSION
In this report we present an evaluation of glottal airflow
velocity above the glottis in a single subject who had undergone expansion for subglottal stenosis and was treated with a T-tube. The subject’s phonation was performed
in natural manner during high-speed image recording
performed via insertion of a flexible transnasal endoscope.
The flexible transnasal endoscope appears to offer better potential than the rigid transoral endoscopein terms of simultaneously acquiring additional vocal
function measures, because the insertion path of thetransnasal endoscope results in less interference with thenormal function of the vocal tract during voice production. In a transoral rigid telescope study, phonation was
unnatural due to the common practice of protruding andholding the tongue outside of the mouth during the examination.7
Hot-wire anemometer measurements have become
accepted for use in phonation studies.8, 9 Experimental
characterization of glottal jet velocity measurements
above the glottis has been reported in canine models.
Velocities obtained from hot-wire anemometry during
phonation have been described in the in vivo canine larynx10, 11 and the excised canine larynx.2 Teager12 reported the first direct flow measurements of the vocal tract
using a hot-wire anemometer, but the probe was inserted
through the mouth and positioned near the tongue andbelow the hard palate.
In this report we measured glottal airflow velocity
above the glottis using a miniature hot-wire probe that
was advanced as closely as possible to the vocal folds.
A detailed analysis of the vocal fold vibration of thephonation cycle showed that glottal airflow velocity was
maximum just before closure of the vocal folds, and subglottal pressure substantially increased at the moment ofclosure of the lower edges of the vocal folds. The amplitude of the velocity fluctuated sharply.
Several reports have suggested that airflow throughthe vocal folds may produce additional sound sources
due to the rotational motion of the flow.13–15 Khosla etal.16 suggested that intraglottal vortices, occurring during
the latter phase of vocal fold closing, play an importantrole in rapid vocal fold closing and flow reduction. Triepet al.17 constructed a mechanical glottal cam model thatsimulated glottal motion with silicone membranes, andvisualized the fluid dynamics that are relevant for glottal
jet flow.
In our report, airflow velocity was lower and morevariable lateral to the midline than at the midline itself.
It is possible that variable airflow indicates the formationof vortices. Our report also found that glottal airflow

velocity may consist of high frequency components andmay include vortices around the vocal fold vibration.
Our results do not contradict those of a variety of canine
larynx experiments or computer models. The laryngeal
aerodynamic parameters discussed in this study showedthat direct measurements of subglottal pressure andglottal airflow velocity above the glottis, with simultaneous recording of vocal fold movement, are feasible andcontribute to understanding the energy source of voice
production.
The authors declare no conflicts of interest.

REFERENCES
1 Hertegård S, Gauffin J. Glottal area and vibratory patterns
studied with simultaneous stroboscopy, flow glottography,
and electroglottography. J Speech Hear Res. 1995;38:85-100.
PMID: 7731222.
2 Alipour F, Scherer RC. Characterizing glottal jet turbulence. J
Acoust Soc Am. 2006;119:1063-73. PMID: 16521768.
3 Alipour F, Scherer RC. Time-dependent pressure and flow
behavior of a self-oscillating laryngeal model with ventricularfolds. J Voice. 2015;29:649-59. PMID: 25873541.
4 Alipour F, Karnell M. Aerodynamic and acoustic effects ofventricular gap. J Voice. 2014;28:154-60. PMID: 24321590.
5 Oren L, Khosla S, Gutmark E. Intraglottal geometry andvelocity measurements in canine larynges. J Acoust Soc Am.
2014;135:380-8. PMID: 24437778.
6 Kataoka H, Arii S, Ochiai Y, Suzuki T, Hasegawa K, Kitano H.
Analysis of human glottal velocity using hot-wire anemometry and high-speed imaging. Ann Otol Rhinol Laryngol.
2007;116:342-8. PMID: 17561762.
7 Kobler JB, Hillman RE, Zeitels SM, Kuo J. Assessment of
vocal function using simultaneous aerodynamic and calibrated videostroboscopic measures. Ann Otol Rhinol Laryngol.
1998;107:477-85. PMID: 9635457.
8 Kitajima K, Isshiki N, Tanabe M. Use of a hot-wire flow
meter in the study of laryngeal function. Studia Phonologica. 1978;12:25-30. Available from: http://hdl.handle.
net/2433/52565.
9 Kitajima K. Airflow study of pathologic larynges using a hot
wire flowmeter. Ann Otol Rhinol Laryngol. 1985;94:195-7.
PMID: 3158263.
10 Berke GS, Moore DM, Monkewitz PA, Hanson DG,
Geratt BR. A preliminary study of particle velocity during
phonation in an in vivo canine model. J Voice. 1989;3:306-13.
DOI: 10.1016/S0892-1997(89)80052-9.
11 Bielamowicz S, Berke GS, Kreiman J, Genatt BR. Exit jet
particle velocity in the in vivo canine laryngeal model withvariable nerve stimulation. J Voice. 1999;13:153-60. PMID:
10442746.
12 Teager HM. Some observations on oral air flow during phonation. IEEE Transactions on Acoustics, Speech, and Signal
Processing. 1980;28:599-601.
13 Kucinschi BR, Scherer RC, DeWitt KJ, Ng TTM. Flowvisualization and acoustic consequences of the air moving
through a static model of the human larynx. J Biomech Eng.
2006;128:380-90. PMID: 16706587.

246

Glottal velocity in a human subject
14 Barney A, Shadle CH, Davies POAL. Fluid flow in a dynamic
mechanical model of the vocal fold and tract. I. Measurements and theory. J Acoust Soc Am. 1999;105:444-455. DOI:
10.1121/1.424504.
15 Shadle CH, Barney A, Davies POAL. Fluid flow in a dynamic mechanical model of the vocal fold and tract. II. Implications for speech production studies. J Acoust Soc Am.
1999;105:456-66. DOI: 10.1121/1.424574.

16 Khosla S, Murugappan S, Paniello R, Ying J, Gutmark E.
Role of vortices in voice production: normal versus asymmetric tension. Laryngoscope. 2009;119:216-21. PMID: 19117305.
17 Triep M, Brücker C, Stingl M, Döllinger M. Optimized transformation of the glottal motion into a mechanical model. Med
Eng Phys. 2011;33:210-17. PMID: 21115384.

247