Glottal opening in patients with vocal fold tissue changes

Journalof Voice

Vol. 5, No. 3, pp. 239-246 © 1991Raven Press, Ltd., New York

Glottal Opening in Patients with Vocal Fold Tissue Changes Michael P. Karnell, Ligang Li, and William R. Panje The Center for Speech and Swallowing Disorders, Otolaryngology-Head and Neck Surgery, Pritzker School of Medicine, The University of Chicago, Chicago, Illinois, U.S.A.

Summary: Synchronized videostroboscopy and electroglottography were applied to the measurement of anterior-to-posterior open glottal length in four groups of patients; two with no clinically significant voice disorder, one with vocal fold polyps, and one with vocal fold nodules. The data showed that the groups did not differ significantly when open glottal length was measured at the time of minimum glottal opening. The pathological groups had significantly lower open glottal length measurements, however, when measurements were obtained at the time that vocal fold contact was initiated during the glottal cycle. The findings are preliminary evidence that vocal fold neoplasms may not have the effect of reducing glottal closure, as previously suggested in the literature. The data also highlight the importance of examining differential effects of vocal fold neoplasms at various points throughout the glottal cycle. Key Words: L a r y n x - - G l o t t i s - - S t r o b o s c o p y - - E l e c t r o g l o t t o g r a p h y - - N o d ules--Polyps.

Changes in vocal fold tissue characteristics are commonly associated with voice disorders. Such changes may be due to growths such as nodules, polyps, and cancer (1-6), or may be the result of vocal fold trauma (7). They may also be iatrogenic consequences of surgical resection of such growths (8,9). Any change in the viscoelastic characteristics of vocal fold tissue, normal or otherwise, can alter vocal fold vibratory function (10-12). Changes that are the result of pathologic processes frequently produce perceptible changes in voice quality that may be considered abnormal and/or pathological. Considerable interest has been focused on identifying in detail how tissue changes alter the specific physiologic parameters of vocal fold vibration, many of which involve glottal valving. Normal vocal fold vibration involves rapid, quasiperiodic

valving of the breath stream at the glottis (13). This valving can be altered by changes in the mass and/ or elasticity of vocal fold tissue (14). For example, Leonard et al. (9) found that surgical stripping and laser excision of vocal fold mucosa in cats resulted in epithelial and nerve abnormalities in regenerated mucosa, although the effects of laser appeared somewhat less severe than stripping. Crockett et al. (8) reported stroboscopic observations from a group of 12 patients with laryngeal papilloma during remission. They found that these patients tended to exhibit asymmetrical vocal fold vibration, incomplete glottal closure, decreased amplitude of vocal fold vibration, and absence of mucosal waves. All such findings were attributed to increased vocal fold stiffness and mass. Peppard et al. (15) reported stroboscopic observations that individuals with nodules are likely to exhibit an "hourglass" closure pattern due to incomplete glottal closure around the site of the nodule. Scherer et'al. (16) observed that changes in vocal fold tissue, such as nodules, may be less likely to result in abnormal frequency perturbation

Address correspondence and reprint requests to Michael P. Karnell, Ph.D., Otol.-Head and Neck Surgery, Pritzker School of Medicine, University of Chicago Hospitals, 5841 S. Maryland Ave., Box 412, Chicago, IL 60637, U.S.A.

239

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M. P. K A R N E L L E T A L .

(jitter) values but more likely to result in abnormal amplitude perturbation (shimmer) values. They suggested that this was due to variations in tissue and movement asymmetries between the right and left folds. Data such as those reported by Crockett et al. (8) and Peppard et al. (15) suggest that vocal fold neoplasms have the effect of reducing glottal closure (or, inversely, increasing the amount of glottal opening) because of localized increased mass and stiffness of the vocal fold. However, no measurements were provided about glottal closure in those reports, and no specifics were provided regarding the point within the vibratory cycle from which the observations were obtained. It seems likely that a speaker may attempt to compensate for the presence of increased load on the vocal folds associated with nodules by increasing adductor contraction. The effects of nodules on laryngeal mechanics and control may be more complex than previously believed. For example, questions remain about whether changes in vocal fold tissue influence glottal closure throughout the vibratory cycle or only at specific points during the glottic cycle. Clearly, additional data are needed. The purpose of this research was to compare measurements of glottal opening at three specific points in the vocal fold vibratory cycle among four groups of adults: two groups with vocal fold tissue changes (nodules and polyps) and two groups of individuals who had no evidence of vocal fold tissue changes. It was expected that the patients with tissue changes would be found to have larger glottal opening measurements than would the two groups of normal patients. Moreover, it was expected that these findings would be consistent at all three points during the vibratory cycle that were tested.

METHODS Synchronized videostroboscopy and electroglottography were performed for each subject at the University of Chicago Hospital, using techniques and instrumentation described previously (17,18). Instrumentation

A split-screen synchronized videostroboscopic and electroglottographic procedure was employed. Briefly, a Bruel and Kjaer Model 4914 stroboscopic light source was used to perform two functions simultaneously. A schematic representation of the inJournal of Voice, Vol. 5, No. 3, 1991

strumentation arrangement is provided in Fig. 1. Videostroboscopic images of vocal fold movements during phonation were recorded using the stroboscopic light source with an Olympus E N F P-2 fiberoptic endoscope coupled to a Medical Dynamics 5410 video camera. The camera output was coupled to a Meade Electronics model U240th time code generator, which produced a digital time display on the video image to the nearest centisecond. The stroboscopic light source also served to trigger a Tektronix type 502-l dual screen oscilloscope, which was used to display an electroglottographic (EGG) signal from a Synchrovoice Research electroglottograph. No filtering of the electroglottographic waveform was used, in order to avoid phase distortion between the videostroboscopic images and the EGG waveform. For the purposes of this study, baseline stabilization with low-pass filtering was unnecessary because our interest was in examining relationships between EGG waveform characteristics and glottal morphology. Measurement of absolute amplitude of the EGG waveform was not necessary for this project. A video image of the EGG oscilloscope screen was produced by focusing on the oscilloscope display an Ikegami model ITCC-46 video camera. The video outputs from this camera and the videostroboscopic camera were displayed simultaneously on a Sony model KX-1211 HG video monitor via RCA video splitter. The result was a split-screen image showing the stroboscopic image at the middle of the monitor screen and the triggered EGG image near the bottom of the screen (Fig. 2). The video images were recorded on 3/4" Fuji videotape with a Sony VO-5800 videocassette recorder. Procedure After initial examination by an otolaryngologist, patients were referred to the speech-language pathologist for voice and videostroboscopic evaluation. A topical anesthetic (4% Lidocaine) and a vasoconstrictor (2% neosynephrine)were applied to the anterior nasal passage using a standard atomizer. Perceived aspects of vocal function were then recorded including maximum phonation time, severity and quality of vocal dysfunction, and appropriateness of habitual pitch and pitch range. The contact electrodes used for EGG assessment of vocal fold contact were then fixed to the subject's neck at the level of the thyroid lamina with a foam rubber collar, t~GG output was monitored during positioning, and electrode position was ad-

GLOTTAL OPENING A N D VOCAL FOLD TISSUE CHANGES

Video Camera

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justed until the optimal signal was obtained. The contact microphone used to detect laryngeal pulses during phonation was positioned under the EGG collar lateral to the EGG contact electrodes. The subject was instructed to phonate in order to test the adequacy of the EGG waveform display and the triggering of the stroboscope. The flexible fiberoptic endoscope coupled to the video camera was then inserted through the anesthetized nasal passage. The tip of the insertion tube was passed through the velopharyngeal port and was positioned in the oropharynx. At that time, the subject was instructed to produce a sustained /i/ sound. If the production was judged by the examiner to be nonrepresentative of habitual pitch and loudness, the subject was given additional instructions (count to three and sustain the final vowel in "three") and asked to repeat the production. During each production, the examiner passed the tip of the insertion tube into the laryngeal vestibule and the stroboscopic light source was engaged. Additional minor adjustments in endoscopic lens position were performed until a stable stroboscopic im-

241

Video Camera

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Video Clock Video Tape Recorder

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age of the entire vocal fold length was recorded. The scope was removed to the oropharynx just prior to or during termination of phonation. This procedure was repeated until the examiner judged that additional recording would not further contribute to evaluation of vocal fold vibratory function. Data measurement and analysis Measurements of open glottal anterior-to-posterior length were obtained from the video records as follows. For each subject, 10 cycles (not necessarily consecutive) of simultaneous videostroboscopic and electroglottographic recordings of vocal fold vibration were measured. These cycles were identified by inspection of the videotape records and selection of segments that contained stable segments of vocal fold vibratory activity. Each segment was then carefully scanned for video fields that contained vocal fold configuration at each of the following points as displayed on the EGG waveform: maximum glottal opening (A); baseline offset, the major upward deflection of the waveform associated with beginning of vocal fold contact (B); the

FIG. 2. Example of videostroboscopic image of laryngeal posture at time of maximum glottal opening with synchronized electroglottographic (EGG) waveform. T, trigger onset point of the EGG waveform that corresponds to the laryngeal posture in the image.

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M. P. K A R N E L L E T A L .

C

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1J A

D

Time FIG. 3. The points on the electroglottographic (EGG) waveform where anterior-posterior open glottal length measurements were obtained. A: Maximum glottal opening. B: EGG baseline offset. C: EGG peak. D: EGG baseline onset.

point of p e a k waveform amplitude associated with maximum vocal fold contact (C); and baseline onset, the point where the waveform returns to baseline associated with the termination of vocal fold contact (D). These points are shown on an idealized EGG waveform in Fig. 3. Points B, C, and D, described here as offset, peak, and onset, are the points during the vocal fold contact portion of the vibratory cycle that are of major interest in this study. The videotape image was stabilized in stop action while linear measurements of open glottal length were obtained in arbitrary units (millimeters). These measurements were obtained from I0 glottal cycles. The open glottal length measurements from points B (offset), C (peak), and D (onset) were normalized to the maximum open glottal length mea-

surement at point A (maximum glottal opening). This resulted in data representing the percentage of maximum length of glottal opening at each of the three primary points of interest when vocal fold contact occurs (points B, C, and D). An example of the measurements obtained at each point throughout a representative EGG waveform cycle in a woman with nodules is presented in Fig. 4.

Subjects Twenty-four subjects were examined by a head and neck surgeon and a certified speech-language pathologist. Twelve of the 24 subjects had voice quality that was considered within normal limits and no identifiable laryngeal disorder at the time of evaluation. Six of these were normal volunteers with no evidence of vocal pathology. Six were patients who sought medical attention but were considered to have normal voice quality at the time of data collection. Twelve additional subjects had laryngeal disorders at the time of evaluation. Six were diagnosed as having vocal nodules. The size of the nodules was variable in these patients. The nodules were considered small in four subjects and large in two subjects. The remaining six had received surgery for removal of vocal fold polyps or polypoid masses. These patients ranged from minimal postoperative abnormality to clear evidence of vocal fold stiffening secondary to scarring. Age and gender data for each group is provided in Table 1. Table 2 contains ratings of voice quality for the nodules and postoperative polyps groups.

FIG. 4. Examples of a n t e r i o r - p o s t e r i o r open glottal length measurements obtained from a patient with nodules at each of the four points throughout the vibratory cycle. Normalized measurements for points B, C, and D were obtained by dividing each by the measurement at point A.

Journal of Voice, Vol. 5, N 9. 3, 1991

GLOTTAL OPENING AND VOCAL FOLD TISSUE CHANGES

TABLE 1. Summary of patient group by gender and age a Gender

Age (years)

Pearson R

Group

Male

Female

Mean

Range

Mean

Range

NV NP N P

3 2 2 1

3 4 4 5

30.7 46.7 32.5 48.7

24--39 25-75 13-51 30--61

0.965 0.963 0.943 0.975

0.91-0.99 0.93-0.98 0.90-0.98 0.93-0.99

resulted in measurement of 30 to 40 video fields for each subject. The same video fields were measured a second time no sooner than 24 h after the first measurements were completed. Pearson correlation coefficients were calculated between the two sets of measurements for each subject and are presented in Table 1. Based on these data, the reliability of the measurements was considered acceptable.

Patient groups are as follows: NV, normal volunteers; NP, normal patients; N, nodules; P, polyps. Also included are Pearson R correlation coefficient summary data for measurement reliability for each group.

Both men and women were included in this study. We anticipated that effects of the vocal fold tissue changes on glottal closure would not be influenced significantly by gender. Overall, there were 16 women and eight men subjects. The proportion of women in the nodules and polyps groups (nine of 12) was slightly greater than the proportion of women in the two normal groups (seven of 12).

Measurement reliability Identification of EGG events (baseline offset, peak, baseline onset) was accomplished by visual identification of these events on the videotape records. Reliability of event identification was examined by identifying a second time the video field in which occurred one of each of the events for each subject. This resulted in a total of 72 repeated event identifications. Overall mean difference between original and repeated event identifications was less than one video field (SD = 2.4 fields). Reliability of open glottal length measurements was tested by measuring field-by-field open glottal length during a complete stroboscopic cycle of vocal fold vibratory movement for each subject. This TABLE 2. Judgments of voice quality at the time of data collection a Nodules

Postoperative polyps

Subject

Perceived quality

Subject

Perceived quality

JK JM BP WG FP RK

GIRoBIAoSo GoRoBoAoSo GoRoBoAoS0 G2R2B2AoSo G~RIBoAoS 0 G2R2B lAoSo

RM MG CC MH JG JK

G2R2BoAoS0 GIR1B 1AoS 1 GoRoBoAoS0 G2R2BoAoS0 GIRIBoAoS 1 G1RIBoAoS 0

a Ratings from 0 (normal) to 3 (severe) were provided regarding Grade, Roughness, Breathiness, Asthenia, and Strained aspects of voice quality.

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RESULTS Means and standard deviations of the normalized glottal opening data are presented in Table 3. Graphic comparisons of the means are presented in Fig. 5. Analyses of variance showed significant differences among means at the time of waveform baseline offset (p < 0.01) and waveform baseline onset (p < 0.01). Differences among means at the time of peak vocal fold contact area were not significant. Post hoc t-tests performed for the waveform baseline offset data showed that mean relative length of glottal opening was significantly greater (p < 0.05) for the normal volunteers and the normal patients compared to the patients with nodules and polyps. No significant differences were found, however, between the normal patients and the normal volunteers or between the patients with nodules and the patients with polyps. Post hoc t tests performed for the baseline onset data showed that significant differences (p < 0.05) existed for all comparisons except normal patients and patients with polyps. Mean relative open glottal length was greatest for the normal volunteer group and least for the nodule group. The means for the normal patient group and TABLE 3. Summary statistics (mean and SD) for normalized open glottal length measures at each event Group Offset Normal Normal patients Nodules Polyps Peak Normal Normal patients Nodules Polyps Onset Normal Normal patients " Nodules Polyps

n

Mean

SD

60 60 60 60

0.84 0.86 0.79 0.77

0.10 0.09 0.15 0.13

60 60 60 60

0.11 0.09 0.12 0.10

0.11 0.10 0.17 0.17

60 60 60 60

0.88 0.84 0.74 0.81

0.08 0.14 0.16 0.16

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M. P. K A R N E L L E T AL.

EGG BASELINE OFFSET

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FIG. 5. Mean relative open glottal length for each group at electroglottographic (EGG) baseline offset, EGG peak, and EGG baseline onset.

the polyp group fell between the volunteer and nodule groups. If gender were a significant variable, the nodules and polyps groups (the two groups with the larger proportion of women) may have been expected to have a greater proportion of glottal opening than the two normal groups. In fact, the opposite was true. This lends some support to our assumption that gender may not be an important variable when considering the.effects of vocal fold neoplasms on glottal closure. Journal of Voice, Vol. 5, No. 3, 1991

The data reported here are in conflict with previously reported findings by Crockett et al. (8) and Peppard et al. (15), which indicated that vocal fold neoplasms have the effect of reducing glottal closure. Although some nodules may have that effect, other nodules may serve to increase glottal closure. In the current study, mean relative anteriorposterior (A-P) length of glottal opening was found to be smaller at the time of EGG waveform baseline offset, which signals the beginning of vocal fold contact, and at the time of EGG waveform baseline onset, which signals the termination of vocal fold contact. Smaller length of glottal opening reflects an increase in length of vocal fold contact and, consequently, increased glottal closure. Mean relative length of glottal opening for the group with vocal fold polyps was similar to that for the group with nodules at the time of waveform baseline offset. The two groups differed, however, at the time of waveform baseline onset, with the nodules group exhibiting lower mean relative glottal opening. The two groups with no observable vocal fold pathology were not significantly different at the time of waveform baseline offset, but those groups did differ at the time of waveform baseline onset. In this case, the normal patient group exhibited lower mean relative glottal opening. No differences were found among the groups compared here at the time of maximum vocal fold contact as reflected by peak EGG waveform output. This finding was somewhat surprising because it seemed reasonable that if vocal fold neoplasms do have the effect of reducing glottal closure, that effect would be most noticeable at the time of maximum glottal closure. This was not the case among the groups tested here. The results reported here indicate that vocal fold neoplasms may have the effect of contributing to glottal closure, rather than inhibiting glottal closure as previously reported. Also, these findings show that vocal fold neoplasms may influence vocal fold vibratory function and glottal valving differentially throughout the vibratory cycle. The effects of such neoplasms may be most clearly observed, relative to normal vocal fold function, at the beginning of vocal fold contact. It seems reasonable, therefore, to expect that the earliest effects of such neoplasms may be best identified at that time as well. However, the data also indicate that patients who come to the clinic with complaints about vocal dis-

GLOTTAL OPENING A N D VOCAL FOLD TISSUE CHANGES

turbance, but who show no abnormality upon examination, may be discriminated from normal individuals by an increase in glottal closure (decrease in mean relative length of glottal opening) at the termination of vocal fold contact (the time of EGG waveform baseline onset). It is possible that these patients are noticing the effects of a nascent or unseen neoplasm. Indeed, mean relative length of glottal opening for the normal patient group measured at the termination of vocal fold contact (waveform baseline onset) was not significantly different from that measure in the group of patients who have vocal fold polyps. Therefore, examination of this point in the glottal cycle, rather than the point at waveform baseline offset, may be particularly valuable for patients who sound and look normal but report some change in vocal function. When the findings are considered as a group, they support the general conclusion that vocal fold pathology may be best identified during the closing or opening phases of the vibratory cycle, rather than during the closed phase. Additional research is needed to confirm these suggestions, however. Decreased relative glottal opening for the nodules and postoperative polyp groups at the time of waveform baseline offset may be due to the mechanical effects of a relatively large increase in tissue contact as stiff masses of tissue (such as nodules or scarred tissue) come in contact over an relatively large area at the beginning of the closing phase of the vibratory cycle. However, a more active, motor control process may also be involved. The data appear to be consistent with a theory that compensatory laryngeal adjustments in response to vocal fold neoplasms may serve to increase laryngeal adductor muscle activity. Such adjustments may be attempted in order to maintain glottal resistance and subglottal pressure at some acceptable level in spite of the presence of mechanical opposition to closure that vocal fold neoplasms may introduce. This type 0f model has been suggested by Warren (19) regarding airway regulation for speech as it pertains to speakers with velopharyngeal insufficiency. Warren (19) suggested "for speech aerodynamics, subglottal pressure is kept relatively constant by checking or enhancing elastic forces and by compensating for sudden changes in respiratory load" (p. 252). Moreover, Warren (19) suggested that the speech motor control program may initiate compensatory adjustments to the detriment of speech quality. Such adjustments at the level of the glottis in response to mechanical interference with glottal clo-

245

sure may be expected to have the result of increasing glottal closure in some patients with vocal fold nodules or other neoplasms, resulting in a somewhat hyperadducted condition. Similar effects may also be involved in patients who suffer vocal fold paralysis and compensate by hyperadducting the ventricular and/or aryepiglottic folds. Previous observations of incomplete closure due to nodules may have involved only select patients with very large nodules. However, errors of clinical judgment or imprecise definition of terms are possible also. For example, subjective judgments and categorization of closure patterns may be imprecise regarding the time at which the judgments are made. If nodules are most easily recognized when the vocal folds are not completely in contact, i.e., when they are in the process of opening or closing, j u d g m e n t s a b o u t " c l o s u r e p a t t e r n s " may be strongly influenced by observations made during those portions of the vibratory cycle. It seems likely that the nodules tend to contact one another more quickly at the beginning of the closing phase and separate more slowly at the end of the opening phase compared to surrounding tissue, resulting in the so-called hourglass-shaped glottal configuration. If such judgments contribute to categorical assignments, the criteria for such assignments of glottal configurations to closure patterns must be clarified. The data reported here are limited by the relatively small number of subjects in the groups compared. The use of length of glottal opening as the sole dependent variable is also a limiting factor. Clearly, the glottis is defined by the three-dimensional vocal fold geometry, and that structure may vary, within limits, along any of those dimensions. Additional studies employing larger groups of patients and a more complete array of measures of vocal fold function collected at multiple points along the glottal cycle are indicated to more clearly define how vocal fold neoplasms affect the vibratory function of the vocal folds. Another possible limiting factor was that the groups were not balanced by gender. Although there is no conclusive evidence that it would indeed have an effect, it is possible gender could have influenced the measurements, particularly at the time of maximum contact area, given the assumption that women may be more likely than men to have glottal opening at that" time. If this were an important factor in this study, however, the polyps group would have been expected to have the largest open Journal of Voice, Vol. 5, No. 3, 1991

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glottal length measures at that point because there was only one man in that group. This was not the case. Regardless, it seems advisable to balance groups by gender when possible. This research has implications for researchers who would attempt to model the effects of vocal fold neoplasms on vibratory function of the vocal folds and laryngeal motor control. Detailed studies of vocal fold vibratory function may also improve our clinical ability to identify the effects of a vocal fold neoplasm and possibly, to predict the type of neoplasm involved even before it can be directly observed. REFERENCES 1. Harrington-Hall BL, Lee L, Stemple JC, Niemi KR, McHone MM. Description of laryngeal pathologies by age, sex, and occupation in a treatment-seeking sample. J Speech Hear Disord 1988;53:57--64. 2. Harma R, Sonninen A, Vartiainen E, Haveri P, Vaisanen A. Vocal polyps and nodules. Folia Phoniatr 1975;27:19-25. 3. Hirano M, Durita S, Matsuoka H. Vocal function following hemilaryngectomy. Ann Otol Rhinol Laryngol 1987;86:586689. 4. Calcaterra TC. Bilateral omohyoid muscle flap reconstruction for anterior commissure cancer. Laryngoscope 1987; 87:810-3. 5. Woo P. Phonatory volume velocity recording by use of hot film anemometry and signal analysis. Otolaryngol Head Neck Surg 1986;95:312-9. 6. Prosek RA, Montgomery AA, Walden BE, Hawkins DB. An

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