The effect of various imbalance of the vocal cords was investigated in dog through the use of a high speed camera. Within the limit of our experimental procedure, the two vocal cords asymmetrical in mass or tension vibrated at the same frequency. Experimental evidence and clinical experiences indicated that imbalance between the glottal condition and expiratory air flow could be an important factor in the etiology of functional dysphonia or aphonia

Isshiki, Nobuhiko

Kyoto University Research Information Repository

Title Imbalance of the Vocal Cords as a Factor for DysphoniaAuthor(s)Is hiki, NobuhikoCitation音声科学研究 = Studia phonologica (1972), 6: 38-44Issue Date1972URL http://hdl.handle.net/2433/52599RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversitySTUDIA PHONOLOGICA VI (1972)Imbalance of the Vocal Cords as a Factor for Dysphonia*Nobuhiko ISSHIKI, M.D.Dysphonia without apparent organic lesion is usually referred to as func-tional voice disorder. This implies that the definition of "functional" wouldchange with the development of diagnostic means. What appears normal onconventional indirect laryngoscopy may prove abnormal on further-advancedexamination.Indirect layngoscopy can reveal gross organic lesion of the vocal cords, butrheological changes of the vocal cord, for instance, would be rather difficult to findout by indirect laryngoscopy. Our clinical experience with the use of indirectlaryngoscopy indicates that dysphonia is usually associated with imperfect closureof the glottis during phonation.The factors contributory to hoarseness, other than the glottal gap, shouldbe reevaluated under the experimental conditions representing each of the pos-sible factors. The present paper particularly deals with tension and mass im-balance between the bilateral cords, and imbalance between glottal conditionand expiratory air flow. The vibratory pattern of the vocal cords under variedartificial conditions was studied in dog through the use of a high speed camera.EXPERIMENTAL PROCEDURESTwelve adult dogs and 96 rolls of high speed film were used for the experi-ment.The dogs were anesthesized by Thiamylal Natrium 15 mg/kg intraperitone-ously. Supraglottal laryngectomy was performed for better visualization. Voic-ing was elicited mostly by pain stimuli but on occasion when the above procedurefailed to induce vocalization, Hering-Breuer's reflex was utilized: artificial blow-ing through the tracheostoma leads to the glottal closure and voicing.1) Imbalance between the vocal cords.The artificial conditions imposed on the vocal cords include tension or massimbalance with or without glottal gap. Tension imbalance was produced eitherby section of the superior laryngeal nerve or by electronic stimulation of the uni-lateral cricothyroid muscle after section of the bilateral external branches of thesuperior nerve. The stimuli were 5 volt, 50 Hz and 5 msec in duration.Nobuhiko ISSHIKI (-151~~): Department of Otorhinolaryngology School of Medicine, KyotoUniversity (Director: Professor M. Morimoto)II< The outline of this paper was presented as a special lecture at the XVth International Congressof Logopedics and Phoniatrics August 1971, Buenos Aires•Imbalance of the Vocal Cords as a Factor for Dysphonia 39In extirpated larynx, tension imbalance was directly created by pulling theunilateral arytenoid cartilage posteriorly. Mass imbalance was made by plac-ing a tiny lead disc carefully upon the upper surface of the unilateral or bilateralvocal cord so as not to produce the glottal gap.2) Imbalance between the glottis and expiratory air flow.The conditions of too weak tension of the vocal cord versus too strong airflow was created by bilateral section of the external branch of the superior laryn-geal nerve and artificial blowing through tracheostoma. A reverse relation wasrealized by electrical stimulation of the bilateral external branches or cricothyroidmuscles during spontaneous phonation.For analysis of the vibratory pattern of the vocal cord, a high speed motionfilm was taken during phonation (Hycam Model K 2001 by Read Lake Lab Inc.,4000-6000 frames/sec). Timing marks were plotted on one side of the film at1 msec intervals. The films were analyzed frame by frame through the use ofa film analyzer (Nac Motion Analyzer Model 16-8).RESULTS AND DISCUSSION1. Tension imbalance between the two vocal cords.The laryngeal picture and vibratory pattern of the vocal cords in case ofunilateral section of the external branch of the superior laryngeal nerve were es-sentially identical with those in case of contralateral stimulation of the cricothyroidmuscle after bilateral nerve section. Unilateral contraction of the cricothyroidmuscle resulted in deviation of the posterior commissure of the glottis to theinactivated side and more elongation of the vocal cord on the active side than onthe inactive side (Fig. 1). Under the above condition of imbalanced elongationof the vocal cords, the two vocal cords vibrated at the same frequency. (Fig. 2)The vocal cord on the side of active cricothyroid muscle, however, always precededIFigure 1. The glottal axis deviates toward the side of non-active cricothyroidmuscle. Left nerve section or right stimulation.40 Nobuhiko ISSHIKIR10 MSECFigure 2. Vocal cord vibration after section of the external branch of thesuperior laryngeal nerve on the left. The frequency are equal onboth sides. Note the phase shift between the two cords: moretense side (r) precedes the opposite member in opening and closingthe glottis.the mate in vibratory cycle. These findings were quite consistent among differentmaterials. As to the amplitude'of vibration, the findings were rather diverse. In4 of 9 cases, no essential differences in amplitude were noted between the twocords. In the other 5 cases, the amplitude of vibration on the crico-thyroid ac-tive side was slightly greater than the ncm-active side.On the extirpated larynx, where the cricothyroid distance was manuallyapproximated on one side, the frequency of vibration was same on both sides andthe tense cord preceded the opposite cord in vibratory cycle just as in the non-extirpated larynx.When one vocal cord' of the extirpated larynx was strongly stretched by directpull of the arytenoid posteriorly, the tense cord vibrated with much less amplitude.First, it should be noted that the effect of tension imbalance induced by uni-lateral contraction of the cricothyroid muscle isentire1y different from that in-duced by direct stretching of one vocal cord. In other words, contraction ofthe unilateral cricothyroid muscle produces not only tension imbalance: but alsoshift of the glottal axis, which in turn may cause imbalance in the air-pressureforce exterted against each subglottal plane. Of clinical· interest is the findingthat the vocal cord on the side of the inactivated cricothyroid muscle is stretchedremarkably, (2 mm for 12 cm vocal cord) by the contraction of the opposite cri-cothyroid muscle, though less than the active side (3 mm). Within the limitationof the experimental materials used, it should be emphasized that the effect ofcontraction of cricothyroid muscle on the vocal cord tension is not sharply sepa-rable between both sides.The phase shift between the bilatetal vocal cords, which was consistentlyfound in case of unilateral action of the cricothyroid muscle, is difficult to explainat present. There is no knowing yet whether the phase shift is due to the slightdifference in tension or due to the shift of glottal axis or both.When the glottal gap was combined with tension imbalance, the vibratorypattern became irregular. The number of vibratory cycle were sometimes differ-ent and sometimes not, although counting the number 9f vibration itself was diffi-cult.Imbalance of the Vocal Cords as a Factor for Dysphonia 412. Mass imbalance between the two vocal cordsIn general, the weighted vocal cord vibrated with smaller amplitude butthe frequency of vibration was identical on both sides. The voice was loweredin pitch but not hoarse. Increase in mass of the vocal cord resulted in increaseof the glottal resistance, and stronger subglottal blowing was required for voiceproduction. If the glottis was not completely closed at rest, the vibration of theboth cords became irregular and unloaded vocal cord frequently corssed the mid-line in closed phase (Figure 3). In summary, our experimental results indicatethat if there is no glottal gap, tension or mass imbalance of· the two cords doesnot produce independent vibrations at different frequencies.Smith and Moore, utilizing the Smith's vocal cord model, demonstratedthat the weighted cord vibrates with less amplitude but at the same frequencyas the opposite cord. As to the clinical cases, von "Leden, Moore, and Timckereported that no measurable difference in the fundamental frequencies of the twovocal cords was observed even in the presence of pronounced unilateral diseases.L10 MSECFigure 3. Weighting one vocal cord (1) and glottal gap. The vibration ofthe weighted cord is irregular and the unloaded cord frequentlycrosses t he midline in closed phase.Figure 4. Glottal vibration during cough. The posterior wall of the glottisvibrates synchronously with the vocal cords.42 Nobuhiko ISSHIKIDunkel and Schlosshauer, and Jeschek reported on cases of recurrent laryngealnerve paralysis in which the two cords vibrate at the same frequency.Figure 4 illustrates the vibratory pattern of the vocal cord during cough.It is very interesting that the posterior wall (Marked C) vibrates synchronouslywith the vocal cords (Marked A). Under the condition of high velocity of airflow and consequent great Bernoulli effect at the glottis, the posterior wall ofthe glottis is assumed to be driven into vibration synchronously with the vocalcord.The above example seems to indicate that any tissue on the same level atthe glottis, regardless of slig?~ difference in mass or tension, would vibrate at thesame frequency, if the Bernoulli effect is great and the tissue is compliant. How-ever the present experiment also indicates that when the glottis is not completelyclosed, the number of vibration of the imbalanced two cords may not coincidewith each other.Recent reports on the vibratory pattern of the vocal cords, however, showthat the vocal cords could vibrate at different rate. Moore found that in caseof small localized edema on one vocal cord the two cords vibrated at different rates.Ward, Sanders, Goldman and Moore reported on a very interesting case of phy-siological diplophonia where the two vocal cords vibrated at different frequencies.In our experiment, so far we have not been able to elicit periodic and independ-ent vibration of the two vocal cords at different frequencies. The reported clini-cal cases of vibration of the two cords at different frequencies are rare conditionworthy of special report. On the other hand, our experiment is now only at thequalitative stage, and quantitative and more systematic investigation is neededfor explaining more varied type of vibration. Vocal cord vibration at differentfrequency for each side would take place only under very critical condition, ifit is possible.The effect of weighting one vocal cord is not so simple as may be expected.I t also depends on the tension of the vocal cords. The next exemplifies the com-plexity of the relations between the factors. The voice was originally very highand weak due to great tension of the vocal cord. Loading one vocal cord withtiny lead disc facilitated voice production: louder and lower voice was produced.Loading the two cords with heavier disc completely ceased vocalization.Vibratory features of the vocal cord is theoretically determined by threefactors: stiffness (tension) , mass of the vocal cord and subglottal air pressure.Therefore, more systematic and quantitative investigation as a function of thethree parameters is required as the next step for understanding the mechanismof hoarseness.3. Imbalance between the glottal condition and expiratory air flow.When the bilateral external branches of the superior laryngeal nerve werecut, the voice became very low and rough although the glottis was completelyImbalance of the Vocal Cords as a Factor for DysphoniaL10 MSECFigure 5. After bilateral section of the external branch of the superiorlaryngeal nerve.Although the glottis closes completely at rest, too flaccidvocal cords give rise to aperiodic vibration." 0'Figure 6. The curves from top to bottom indicate electronic stimulation tothe cricothyroid muscle, subglottal pressure and voice. Voiceceases while the stimuli arc given to the cricothyroid muscle,43closed at rest. High speed film demonstrated marked shift of the mucosa alongthe margin of the glottis indicating lax vocal cord and predominant Bernoullieffect at work, The vibration of the vocal cord is not very periodic, with theglottis sometimes closed and sometimes remaining open (Figure 5), As the ex-piratory air flow increases, the vibration of the vocal cords becomes more irregular,Briefly, too flaccid vocal cord can be responsible for dysphonia.Too tense vocal cord can also be responsible for aphonia or dysphonia. Fig-ure 6 demonstrates that voice can not be produced when the vocal cords are tootense: voice ceases while the electronic stimuli are given to the cricothyroid muscle,Clinically, a case of hyperfunctional dysphonia was much improved in voicetemporarily by 0.5% Xylocain injection into the cricothyroid muscle, Theseexperimental and clinical findings suggest the importance of rheological character-istics (stiffness) or the vocal cord in so-called functional dysphonia.44 Nobuhiko ISSHIKISUMMARYThe effect of various imbalance of the vocal cords was investigated in dogthrough the use of a high speed camera. Within the limit of our experimentalprocedure, the two vocal cords asymmetrical in mass or tension vibrated at thesame frequency'Experimental evidence and clinical experiences indicated that imbalancebetween the glottal condition and expiratory air flow could be an important factorin the etiology of functional dysphonia or aphonia.REFERENCES1. Dunker, E. & SC;hlosshauer, B.: Klinische und experimentelle Studien tiber Stimmlippen-schwingungen. Arch. Ohren- Nasen-Kehlkopfh. 172: 363, 1958.2. Dunker, E. and Schlosshauer, B.: Uber Anspannung und Schwingungsform der Stimmlippen.Arch. Ohren- Nasen- Kehlkopfh. 173: 492, 1958.3. Dohne, E.: Beobachtungen tiber cine periphere Lahmung des Nerves Laryngeus Superior.Arch. Sprach-Stimmheilk. 5, 157, 1941.4. Hiroto, 1.: Pathophysiology of the larynx as a vocal organ. Practica Otologica Kyoto 59(suppl.), 229, 1966.5. ]eschek,].: Das Schwingungsverhalten der Stimmbander bei Lahmung in Paramedian undIntermediarstellung. Zentralblatt f. H. N. O. Heilk. 64, 239, 1959.6. Moore, P. and von Leden, H.: Dynamic variations of the vibratory pattern in the normallarynx. Folia Phoniat. 10, 205, 1958.7. Moore, P.: Otolaryngology and Speech Pathology. Laryngoscope 78: 1500, 1968.8. Smith, S. :On Artificial Voice Production. Proceedings of the 4th International Congress ofPhoniatric Sciences. Helsinki 1961.9. Smith, S.: Remarks on the physiology of the vibrations of the vocal cords. Folia Phoniat. 6,166, 1954.10. von Leden, H., Moore, P. and Timcke, R.: Laryngeal vibrations: measurement of the glotticwave. Part III. The pathologic larynx. Arch. Otolaryng. 71: 16, 1960.11. von Leden, H. and Moore, P.: Vibratory pattern of the vocal cords in unilateral laryngealparalysis. Arch Otolaryng. 53: 493, 1961.12. Ward, P., Sanders,]., Goldman, R., and Moore, P.: Diplophonia. Annales of Otolog. 78: 771,1969.(Aug. 31, 1972, received)

Imbalance of the Vocal Cords as a Factor for Dysphonia

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Imbalance of the Vocal Cords as a Factor for Dysphonia

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