Laryngeal Configuration Associated With Glottography

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Am J Otolarynsol 9:173-179, 1988 Laryngeal Configuration Associated With Glottography BRUCE R. GERRATT, PHD, DAVID G. HANSON, MD, AND GERALD S.

1 Am J Otolarynsol 9: , 1988 Laryngeal Configuration Associated With Glottography BRUCE R. GERRATT, PHD, DAVID G. HANSON, MD, AND GERALD S. BERKE, MD This report describes a method for testing and confirming the relationship of glottography to the vibratory movements of the vocal folds. According to this method, vocal fold movement is monitored by photoglottography (PGG) and electroglottography (EGG) as photographs are taken using a 80-1~sec flash provided by a laryngostroboscope. The flash is recorded as an impulse on the PGG waveform, indicating the location on the giottographic signals of the corresponding single frame photograph. We then present a test case, in which various vocal fold configurations are documented, demonstrating that the timing of glottal events can be correlated to glottographic signals by this method. AM J OTOLARYNGOL 9: by W.B. Saunders Company. Key words: glottography, photoglottography, electroglottography, laryngostroboscopy, stroboscopy, voice, laryngeal photography, vocal fold movement. The study of voice disorders is facilitated by a multifaceted approach, combining physiologic, acoustic, and perceptual measurement, Physiologic measurement provides the most direct data concerning pathophysiology underlying voice abnormality. Analysis of abnormal oscillatory movements of the vocal folds can assist in understanding the effects of anatomic deviations and neuromuscular disturbances. Direct observation of the vibratory patterns of the vocal folds is important for a basic understanding of how the normal voice is produced. Historically, high-speed cinematography has been used to study 1'2 movement of the vocal folds, Frame by frame analyses of these films can provide measures of glottal area 3-S and allow the study of the excursion of selected points on the surface of the folds, e Although a few laboratories use high-speed photography, it is both expensive and technically complex. Stroboscopy offers another means to view vocal fold vibration. A light source flashed in se- Received February 22, 1988, from the VA Medical Center, West Los Angeles, and UCLA School of Medicine, Los Angeles. Accepted for publication March 6, Supported by Public Health Service grant no. ReINS from the National Institute of Neurological and Communicative Disorders and Stroke. Address correspondence and reprint requests to Bruce R. Gerratt, PhD, VA Medical Center, Audiology & Speech Pathology (126), Wilshire & Sawtelle Blvds, Los Angeles, CA by W.B. Saunders Company /88/ /0 quence to the fundamental frequency creates a slow motion image of the vibratory motion by producing a composite sequence of images from many glottal cycles. It does not yield the fine details characteristic of cinematography, but rather provides a discernible view of vocal fold movement sampled from a series of glottal cycles. In recent years, glottography has been used as an alternative to high-speed filming for examining glottal movement, Photoglottography (PGG) monitors the amount of light transmitted through the vocal folds during phonation. A light source is positioned above or below the glottis and the photosensor is placed on the other side. 7 Concurrent analysis of high-speed films and PGG has demonstrated that light intensity, measured by the photosensor, is proportional to the cross-sectional area of the glottal aperture during phonation. 5'8 Another technique, electroglottography (EGG), monitors the change in electrical impedance across the neck in the vicinity of the vocal folds. Laryngeal modeling and comparison with high-speed filming have provided evidence that the EGG signal is proportional to the vocal fold contact area PGG provides more information when the glottis is open, and EGG indicates glottal contact during the closing phase. These measurement techniques are often used in combination, providing complementary data to the clinician. 14 Although glottographic techniques have been used in the laboratory, few reports of their clinical use have been published. One explanation 173

VOCAL FOLD MOVEMENT may be that the relationship between giottographic signals and underlying pathophysiology in various laryngeal pathologies is not well understood.

Although the glottographic signals were deviant for all subjects studied, the abnormal waveforms were not directly associated with documented pathologic changes in vocal fold movement.

2 VOCAL FOLD MOVEMENT may be that the relationship between giottographic signals and underlying pathophysiology in various laryngeal pathologies is not well understood. For example, Gerratt et ap 5 used PGG and EGG to study vocal fold movement in patients with Parkinson's disease and recurrent and superior laryngeal nerve paralysis. Although the glottographic signals were deviant for all subjects studied, the abnormal waveforms were not directly associated with documented pathologic changes in vocal fold movement. Certain inferences regarding the relationship of glottography and laryngeal configuration can be made. For example, to calculate some traditional measures of vocal fold movement, it is necessary to select points on the waveform corresponding to the beginning of glottal opening, the moment of glottal closing, and the moment of maximal glottal separation. Both the speed quotient (the ratio of time the vocal folds spend in lateral excursion to the duration of medial excursion) and the open quotient (the ratio of time the glottis is open to total cycle duration) both require knowledge of all three points on the waveform. Gerratt et al as used the positive and negative peaks in the third derivative of the PGG signal to define the location of glottal opening and closing. Similarly, Childers and Krishnamurthy a~ used positive and negative peaks of the first derivative of the EGG signal. Although there are good theoretical bases for these definitions, confirmation of vocal fold configuration at these points is desirable and may be necessary w h e n studying glottographic signals from patients with abnormal laryngeal function. A few investigators have combined stroboscopy and glottography to aid in the interpretation of glottographic signals recorded in the excised human larynx 16 and in the living canine larynx. 17 The purpose of this report is to describe a related, clinically feasible method to confirm the correlation between glottography and vocal fold movement in the living human larynx. METHODS Subjects Two adult men with normal laryngeal structure and function took part in the study. Data Acquisition Glottography Vocal fold movement was monitored by two methods: Figure I. A photograph of the larynx taken during the closed portion of the glottal cycle. American Journal of Otolaryngology 174

GERRATT ET AL LIJ......... T... r... I... 1-... I... (D C~ 6'3 od C9 C9 O_ ttj 8 S I 0 I 5 28 2S 38 3S iisec Figure 2.

The instant of time when the photographic flash for this picture was registered is represented by the left vertical face of the wide, clipped peak near the right border. Electroglottography.

3 GERRATT ET AL LIJ T... r... I I... (D C~ 6'3 od C9 C9 O_ ttj 8 S I 0 I S 38 3S iisec Figure 2. The PGG and EGG (increasing impedance toward the top of the figurej signals that were recorded during the time when the photograph in Fig I was taken. The instant of time when the photographic flash for this picture was registered is represented by the left vertical face of the wide, clipped peak near the right border. Electroglottography. The two electrodes of an EGG (Synchrovoice, Briarcliff Manor, NY) were placed on either side of the thyroid alae with a ground electrode on the side of the neck, held in place by an elastic collar. The unit provided a signal proportional to the impedance between the two electrodes in the vicinity of the glottis. Photoglottograpy. We used a custom-made, single-element, photo-voltaic detector (Centronic, OSD 50) with an active area of 50 mm 2 which was encapsulated in plastic and electromagnetically shielded. The photodetector was placed on the skin of the neck at the level of the cricothyroid membrane and held in place by hand. The position of the photodetector was adjusted to obtain maximum PGG signal intensity, and was maintained in that position for the duration of the study. The larynx was illuminated for PGG through the mouth using a 70-degree, telescopic nasopharyngoscope (Karl Storz Endoscopy, Culver City, CA; model 7100C) connected to a 350-watt xenon light source (Storz model 487C). The glottographic signals and the acoustic signal transduced by a microphone [Bruel & Kjaer Instruments, Marlborough, MA; model 4144) were recorded on the FM channels of an instrumentation recorder (Tandberg, model 115D). The glottographic signals of interest were then low-pass filtered at 1,500 Hz and digitized at 20,000 samples per second. Stroboscopic Photography. The larynx was sighted with a 90-degree telescopic laryngoscope, with a documentation type light sheath placed through the mouth into the oropharynx. The nasopharyngoscope used to illuminate the Figure 3. A photograph of the larynx taken immediately after the opening of the upper margins of the vocal folds. Volume 9 NumSer 4 July

VOCAL FOLD MOVEMENT W rn C3 n~ h- n o LtJ 0 S I e I 5 20 2S 38 35 P1SEC Figure 4. The PGG and EGG signals recorded during the time when the photograph in Fig 3 was taken.

larynx for PGG was strapped to the laryngoscope with the end of the nasopharyngoscope 5 mm from the end of the laryngoscope, directed toward the larynx.

4 VOCAL FOLD MOVEMENT W rn C3 n~ h- n o LtJ 0 S I e I S P1SEC Figure 4. The PGG and EGG signals recorded during the time when the photograph in Fig 3 was taken. The photographic flash occurred as the amount of transillumination and electrical impedance began to increase after the baseline portion of the signals. larynx for PGG was strapped to the laryngoscope with the end of the nasopharyngoscope 5 mm from the end of the laryngoscope, directed toward the larynx. The eyepiece of the laryngoscope was attached to an OM2-N Olympus 35- mm camera with a 50-mm lens (Olympus, New Hyde Park, NY). A laryngostroboscope (Bruel & Kjaer, model 4914) provided illumination for the "-r- I single-frame photographs. The stroboscopic unit was synchronized to the fundamental frequency (Fo) of phonation by a frequency detection circuit that monitored the acoustic voice signal transduced by a contact microphone placed on the side of the neck near the glottis. The subject was instructed to sustain the vowel /i/ at a comfortable pitch and loudness level. This vowel was selected to decrease the likelihood of supraglottic light obstruction by the epiglottis. To visualize different portions of the glottal cycle, a foot pedal was used to change the timing of the strobe flash relative to a trigger signal produced by the Fo detection circuit. When a particular glottal configuration was selected, the experimenter depressed the camera shutter release, simultaneously triggering a special photographic flash of 80 ~sec at 24 klux intensity, which is a feature of this stroboscope. The shutter speed of the camera was set at 1/8o of a second and the aperture at f 2.0. Film exposure was determined by the duration of the flash and the aperture at the eyepiece of the laryngoscope. Color slide film (Scotch 3M, St Paul, MN; 1,000 ISO) was used and processed at 4,000 ISO. Even though a low level of xenon light constantly il- Figure 5. A photograph of the larynx taken when the vocal folds have just separated completely, with a few mucous strands still bridging the glottis. Americon Journol of Otoloryngology 176

Because of the recycle time of the flash unit in the laryngostroboscope, each photograph was produced during separate vowel productions. RESULTS AND DISCUSSION 0 S I 0 I 5 28 25 38 35 HSEC Figure 6.

5 GERRATT ET AL O O3 od (9 (D (_9 (9 h3 1 glottal configuration through the entire vocal cycle. The subject was asked to phonate, and the experimenter adjusted the strobe flash to a desired configuration and then took a photograph of the larynx. Because of the recycle time of the flash unit in the laryngostroboscope, each photograph was produced during separate vowel productions. RESULTS AND DISCUSSION 0 S I 0 I HSEC Figure 6. The PGG and EGG signals recorded during the time when the photograph in Fig 5 was taken. The photographic flash took place at the beginning of the open portion of the glottal cycle, when a substantial amount of transilluruination and electrical impedance was registered. luminated the larynx for PGG, the strobe flash for single frame photography was sufficiently greater in intensity to obtain sharp, undistorted images. Experimental Task Photographic images were taken during phonation at a fixed interval to provide samples of As we expected, based on their normal laryngeal function, the data from both subjects were similar. We will therefore present the data of only one experimental subject to support our conclusion. Figure i is a picture of the larynx in the middle of the closed portion of the vocal cycle and Fig 2 shows the PGG and EGG signals recorded during that event. The PGG signal demonstrates the periodic opening and closing of the vocal folds during phonation, with the narrow, clipped peaks of the stroboscopic flash superimposed on every other glottal cycle. Impedance is at a minimum in the EGG signal at the intersection of these clipped peaks, and there is a minimum of light flow in the PGG signal. At the right of Fig 2, Figure 7. A photograph of the larynx taken when the vocal folds were at the point of maximum separation. Volume 9 Number 4 July

VOCAL FOLD MOVEMENT 133 -, --- p... O IX. I'CO I t i m S 10 I 5 20 25 30 35 NSEC Figure 8. The PGG and EGG signals recorded during the time when the photograph in Fig 7 was taken.

6 VOCAL FOLD MOVEMENT 133 -, --- p... O IX. I'CO I t i m S 10 I NSEC Figure 8. The PGG and EGG signals recorded during the time when the photograph in Fig 7 was taken. The photographic flash occurred at the point of maximum transillumination and electrical impedance. a wider clipped peak represents the more intense stroboscopic flash triggered by the 35-mm camera shutter release which recorded Fig 1, The left border of this strobe flash represents the beginning of the exposure of that photograph, but the duration of the flash was considerably shorter than the wide, clipped peak shown in Fig 2, which reflects the delayed recovery of the photosensor after exposure to extremely intense light. In fact, the left border of this peak in the PGG signal can be considered the point at which the picture of the larynx shown in Fig 1 was taken, that is, during the least amount of transillumination in the PGG signal, representing minimal glottal area. Minimal electrical impedance in the EGG signal indicates maximum vocal fold contact. Figure 3 shows a picture of the larynx when a small space between the anterior third of the vocal folds can be seen. The corresponding giottographic signals in Fig 4 shows that this laryngeal configuration occurred as light intensity began to increase, rising above the baseline, and just after the point of minimum impedance in the EGG signal. The vocal folds had begun to thin progressively from the lower portion to the upper, thereby decreasing the amount of vocal fold contact. In Fig 5, the vocal folds appear to have just achieved complete separation, with the exception of a few persistent strands of mucous bridging the glottis. The glottographic signals displayed in Fig 6 show that the photograph was taken just after a substantial increase in transillumination occurred in the PGG tracing. The larynx is pictured in Fig 7 at the point at Figure 9. A photograph of the larynx taken during the closing phase, when the vocal folds were still separated but returning to midline. American Journal of Otolaryngology 178

7 GERRATT ET AL (D CE O3 ~d (.9 ryngeal dysfunction produce EGG and PGG tracings that deviate considerably from the norm. High-speed, single-frame photography has improved our ability to clarify and substantiate our interpretation of such irregular PGG and EGG waveforms. Acknowledgment. We wish to thank Kristin Precoda for her assistance in data collection. S 1 0 I S 21~ 25 31~ 35 HSEC Figure 10. The PGG and EGG signals recorded during the time when the photograph in Fig 9 was taken. The photographic flash occurred slightly more than half way down the closing slope of the PGG signal, and close to the abrupt change in slope after the plateau in the EEG signal. which the folds are maximally open. Figure 8 shows that this photograph was taken at the point of maximum transillumination of the PGG signal and near the peak of maximum impedance of the EGG signal, representing minimum vocal fold contact, Figure 9 shows the vocal folds returning to midline. There was a noticeable reduction in glottal area compared with the configuration shown in Fig 7. As expected, Fig 9 shows the lower margins leading the upper margins during glottal closure. The superior surface of the upper margins is outlined by glistening highlights. Figure 10 positions this event on the descending slope of the PGG signal, and near the end of the plateau of maximal impedance in the EGG signals. APPLICATIONS The methods we have described can be used to provide information on the moments of glottal opening and closing for use in obtaining measures such as the speed quotient and open quotient. One potential problem in generalizing the results to a number of glottal cycles could be posed by a significant perturbation among the cycles. In most cases, however, the position of these events is essentially unchanged from cycle to cycle. Because the technique is simple and the necessary instruments are often readily available, this method could help make the use and interpretation of glottography more clinically feasible. We are currently using this technique to investigate laryngeal disorders in patients with varied neuromotor disorders. Patients with la- References 1. Farnsworth D: High speed motion pictures of the human vocal cords. Bell Telephone Lab Rec 1940; 18: Pressman J: Physiology of the vocal cords in phonation and respiration. Arch Otolaryngol 1942; 35: Timcke R, Von Leden H, Moore P: Laryngeal vibrations: Measurement of the glottic wave. Part 1. The normal vibratory cycle. Arch Otolaryngol 1958; 68: Timcke R, Von Leden H, Moore P: Laryngeal vibrations: Measurement of the glottic wave. Part 2. Physiologic variations. Arch Otolaryngol 1959; 69: Harden J: Comparison of glottal area changes as measured from ultra high-speed photographs and photoelectric glottographs. J Speech Hear Res 1975; 18: Boer T: Investigation of the phonatory mechanism, in Ludlaw CL, O'Connell M (eds): Proceedings of the Conference on the Assessment of Vocal Pathology. Rockville, MD, ASHA Reports 11, 1979, pp Sonneson B: On the anatomy and vibratory pattern of the human vocal folds. Acta Otolaryngol 1960; 156:35-80 (suppl) 8. Boer T, Lofqvist A, McGarr N: Laryngeal vibrations: A comparison between high speed filming glottographic techniques. J Acoust Soc Am 1983; 73: Feurcin AJ: Laryngograpbic examination of vocal fold vibration, in B Wyke [ed): Ventilatory and Phonatory Control Mechanisms. Oxford, Oxford University, 1975, pp Childers DG, Krishnamnrthy AK: A critical review of eleetroglottography. Crit Rev Biomed Eng 1985; 12: Childers DG, Hicks DM, Moore GP, et ah A model for vocal fold vibratory motion, contact area, and the electroglottogram. ] Acoust Soc Am 1986; 80: Titze IR, Talkin D: Simulation and interpretation of glottegraphic waveforms, in Ludlow CL, Hart Me (eds): Proceedings of the Conference on the Assessment of Vocal Pathology. Washington DC, American Speech and Hearing Association, 1981, pp Gilbert HR, Potter CR, Hoodin R'. Laryngograph as a measure of vocal fold contact area. J Speech Hear Res 1984; 27: Baer T, Titze I, Yoshioka H: Multiple simultaneous measures of vocal activity, in Bless D, Abbs J (eds): Vocal Fold Physiology: Contemporary Research and Clinical Issues. San Diego, College Hill, 1983, pp Gerratt BR, Hanson DG, Berke GS: Glottographic measures of laryngeal function in individuals with abnormal motor control, in Harris C, Boer T (eds): Vocal Fold Physiology: Laryngeal Function in Phonation and Respiration. San Diego, College Hill, 1987, pp Lecluse FLE, Brocaar MP, Verschuure I: The electroglottography and its relation to glottal activity. Folia PhoniaLr (Basel) 1975; 27: Berke GS, Moore DM, Hanson DG, et ah Laryngeal modeling: Theoretical, in vitro, in vivo. Laryngoscope 1987; 97: Volume 9 Number 4 July

Photoglottography: A Clinical Synopsis

Journal of Voice Vol. 5, No. 2, pp. 98-105 1991 Raven Press, Ltd., New York Photoglottography: A Clinical Synopsis Bruce R. Gerratt, *David G. Hanson, Gerald S. Berke, and Kristin Precoda Veterans Administration