|Year : 2015 | Volume
| Issue : 1 | Page : 7-10
Vowel harmonic amplitude differences in individuals with unilateral vocal fold paralysis
B Radish Kumar, Jayashree S Bhat, Jasna Usman
Department of Audiology and Speech Language Pathology, Kasturba Medical College (Manipal University), Mangalore, Karnataka, India
|Date of Web Publication||17-Dec-2015|
B Radish Kumar
Department of Audiology and Speech Language Pathology, Kasturba Medical College (Manipal University), Mangalore - 575 001, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Background: The studies reviewed suggest the potential clinical applications of vowel harmonic amplitude differences. In this study, it was hypothesized that there would be abnormal reduction of higher harmonic amplitudes relative to the amplitude of the first harmonics in individuals with unilateral vocal fold paralysis (UVFP) as they are characterized by breathy voice due to inadequate closure of vocal folds. Method: A total of 80 participants were divided into clinical group and control group. They were instructed to phonate/a/at their most comfortable pitch and loudness. Fourier transformation of the recorded acoustic signal was first performed to create a spectrum. Amplitudes were measured for the first and second harmonics as well as the harmonics at the first, second, and third formants using the Computerized Speech Science Lab. Results: Independent t-test was employed to compare the significant differences between the clinical and the control group in both males and females. The results revealed significant differences across the two groups and gender at P < 0.05. The obtained results were discussed with respect to the underlying pathophysiology. Conclusion: Spectral deviations in the clinical group are explained due to the presence of phonatory gap due to the UVFP.
Keywords: Vagus nerve, vocal fold paralysis, vowel harmonic amplitude differences
|How to cite this article:|
Kumar B R, Bhat JS, Usman J. Vowel harmonic amplitude differences in individuals with unilateral vocal fold paralysis. J Laryngol Voice 2015;5:7-10
| Introduction|| |
Unilateral vocal fold paralysis (UVFP) occurs due to the paralysis of the vagus nerve innervating the larynx on one side which may result in a breathy voice, dysphagia, a weak cough, and shortness of breath. , When the recurrent laryngeal nerve (RLN) is paralzsed on one side, the laryngeal adductor muscles such as the lateral cricoarytenoid and interarytenoids are unable to perform their adductory role and the cricothyroid muscle which is innervated by superior laryngeal nerve (SLN) remains still intact. This muscle when performes its adductory role never comes back to the abducted position due to the paralysis of posterior cricoarytenoid muscle, thereby causing abductor paralysis. Thus, the paralyzed vocal folds remain in paramedian position during breathing and phonation. In contrast, when both SLN and RLN get damaged on one side, all the muscles innervated by these nerves are not able to perform their adductory and abductory function leading to unilateral adductor paralysis.
One aspect of voice evaluation, which is difficult to assess perceptually is the amount of vocal fold closure during phonation. This information is valuable since UVFP reflect abnormalities in vocal fold closure. These informations are often predicted through computer based acoustic analysis. One of the acoustic analysis procedures, which have recently attracted the voice researchers, is the use of spectrum.
Spectrum is one of the efficient methods of acoustic voice analysis, which gives information about voice source and formant characteristics. Spectrum is generated out of fast Fourier transformation method which provides information on voice timber. The vowel spectra is reported to be a strong predictor of weak, breathy, and hoarse voice production in voice disorders. , The differences in the amplitude of the first harmonic (H1) and the second harmonic (H2) is an indicator of open quotient in a glottal signal. The differences in the amplitude of the H1 and the first formant (A1) reflects the first formant bandwidth that is, formant bandwidths in general increases with the increase in the size of the glottal chink. Similarly, the differences in the amplitude of t H1 and the second formant (A2) and third formant (A3) are an indicator of spectral tilt at the mid and high frequencies, respectively. These vowel harmonic amplitude differences increase in breathy voices and decrease in creaky voices. 
The differences in amplitude at harmonic (H1) and harmonic (H2) and formant frequencies (F1, F2, and F3) in the voice spectrum of individuals with UVFP have not been investigated so far. In the literature, these vowel harmonic amplitude measures were reported to provide to the degree of glottal abduction and adduction in weak and breathy voices. ,,,,, Larger vowel harmonic amplitude differences are frequently associated with longer open quotients (breathy voices) and smaller differences with shorter open quotients (creaky voices). Higher amplitude at H1 is positively correlated with perceptual voice quality of breathiness in the dysphonic voice samples. , Thus, it can be expected that there would be a decrease in the amplitudes at higher harmonics in relation to the amplitude at first harmonics in UVFP individuals. For this reason, in this study, it was hypothesized that there would be an increase in the vowel harmonic amplitude differences in individuals with UVFP and hence this study was attempted to explore the differences if any in the vowel harmonic amplitude differences in individuals with UVFP and normal controls.
| Method|| |
Participants were divided into clinical group and control group. Clinical group consisted of 40 males in the age range of 20-40 years diagnosed as having UVFP by an experienced laryngologist through indirect laryngoscopy. Laryngological findings did reveal the paramedian position of the paralyzed fold in all the participants with the presence of phonatory gap. Though the phonatory gap was evidenced, it was not quantified due to the lack of instruments. Electromyographic measurements were also not carried out as it was not available in our institution.
All the participants in the clinical group had mild to moderate breathy voice as evaluated through grade, roughness, breathiness, asthenia, strain. None of these participants had initiated medical treatments when the study was attempted. Control group comprised 40 age and gender-matched individuals. All these participants had normal vocal fold structure and function as evaluated through indirect laryngoscopy and perceptual voice evaluation. Etiologies such as vocal abuse/misuse, smoking, reflux symptoms, and hormonal dysfunction were ruled out through detailed case history in both the group of participants.
Computerized Speech Lab (CSL model 4150) (Kay Pentax, Lincoln Park, NJ, USA) was utilized for the purpose of measuring vowel harmonic amplitude differences in the study participants.
All the voice samples were recorded using a dynamic microphone in the Computerized Speech Lab (CSL model 4150). All the participants were instructed to phonate vowel/a/at their most comfortable pitch and loudness for at least 5 s. The recordings were repeated when required by providing adequate instructions for better clarification. The recordings were also repeated depending on the participant's performance at their comfortable pitch and loudness. Phonation of vowel/a/was recorded three times from each participant, and the middle 3 s segment was considered for the analysis. All the three samples were averaged for the mean value and considered for the analysis.
Fast Fourier transformation was first performed on the recorded voice samples to create a power spectrum. Amplitudes were calculated for the first and second harmonics, as well as the harmonics at the first, second, and third formants and the following measurements, were made.
H1-H2: The differences in the amplitude of the first harmonic (HI) compared to the amplitude of the second harmonic.
HI-A1: The differences in the amplitude of the first harmonic (H1) compared to the strongest harmonic in the first formant.
H1-A2: The differences in the amplitude of the first harmonic (H1) compared to the amplitude of the strongest harmonic in the second formant.
H1-A3: The differences in the amplitude of the first harmonic (H1) compared to the amplitude of the strongest harmonic in the third formant.
Statistical analysis was carried out with SPSS 10.0 (SPSS Corporation, Chicago, IL, USA). The mean and standard deviation (SD) for each measure was obtained for both the group of participants. Independent t-test was conducted to explore the significant difference between the means of vowel harmonic amplitude differences for both the groups.
| Results|| |
The present study explored the deviations if any in vowel harmonic amplitude differences in individuals with UVFP and the controls. The results of mean and SD is shown in [Table 1].
|Table 1: Mean and SD values of vowel harmonic amplitude differences in individuals with UVFP and the control group|
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From the Table, it is observed that the vowel harmonic amplitude differences are increased in the clinical group when compared with the control group. The results of independent t-test revealed statistically significant differences between the means of two groups across all the measures considered in the study at P < 0.05.
| Discussion|| |
Vowel harmonic amplitude differences provide an objective guide to the degree of vocal fold closure in dysphonic voice samples. ,,,] In the present study, it was assumed that there would be an increase in the vowel harmonic amplitude differences in individuals with UVFP due to the presence of hoarse and breathy voice quality in their voices. Hence, the present study explored vocal deviations in individuals with UVFP using vowel harmonic amplitude differences.
According to Hanson, H1-H2 amplitude difference is a marker for the open quotient.  In the present study, H1-H2 amplitude differences were increased in individuals with UVFP. This could be due to the presence of phonatory gap in their voices. This is in agreement with the previous studies which have reported reduced energy at the harmonics due to the noise in the in the spectrum ,,,, . Similar findings are also reported in the voice spectrum of individuals with vocal nodules. 
Increased H1-A1 amplitude differences in individuals with UVFP point towards the larger first formant bandwidth (i.e. reduced energy at F1). The first formant bandwidths increase with increasing open quotient.  Since the UVFP individuals present with phonatory gap, they exhibited an increased H1-A1 amplitude difference. This is again supported by the findings of reduced energy at F1 due to the presence of the phonatory gap. ,,,,,,,
The amplitude of the first harmonic (H1) compared to the amplitude of the second formant (A2) and the third formant (A3) represents the spectral tilt at mid and high frequencies, respectively. In a normal voice spectrum, amplitudes at harmonics decreased at the rate of − 6 dB/octave across the spectrums. However, this rate is increased in individuals with UVFP as determined through these measures. This finding is also supported by the past studies on voice disorders. ,,,,, Similar findings are observed in individuals with vocal nodules too. 
Increased vowel harmonic amplitude differences in individual with UVFP can be explained due to the presence of phonatory gap in their voice samples. Thus, the present findings emphasize that the voice of an individual with UVFP can be best described by vowel harmonic amplitude measures. This measure can be utilized to compare the efficacy of voice treatment in these individuals.
| Conclusion|| |
The present study examined the vowel harmonic amplitude differences in individuals with UVFP and the results reveal increased vowel harmonic amplitude differences in individuals with UVFP in comparison to control group. These findings suggest the potential use of these measures in the routine assessment of individuals with voice disorders. Further, the future research should target obtaining normative data using this particular measure in the Indian population.
| References|| |
Hirano M, Bless DM. Videostoboscopic Examination of the Larynx. San Diego, CA: Singular; 1993.
McFarlane SC, Watterson TL, von Berg S. Behavioral intervention in the pesence of unilateral vocal fold paralysis: Indications, diagnosis, techniques, and interpetation. Phonoscope 1999;2:203-15.
Hanson HM. Glottal characteristics of female speakers: Acoustic correlates. J Acoust Soc Am 1997;101:466-81.
Radish Kumar B, Bhat JS, Mukhi P. Vowel harmonic amplitude differences in persons with vocal nodules. J Voice 2011;25:559-61.
de Krom G. Some spectral correlates of pathological breathy and rough voice quality for different types of vowel fragments. J Speech Hear Res 1995;38:794-811.
Hanson HM, Chuang ES. Glottal characteristics of male speakers: Acoustic correlates and comparison with female data. J Acoust Soc Am 1999;106:1064-77.
Ní Chasaide A, Gobl C. Voice source variation. In: Hardcastle WJ, Laver J, editors. The Handbook of Phonetic Sciences. Oxford: Blackwell Publishers Ltd.; 1997.
Hanson HM, Stevens KN, Kuo HJ, Chen MY, Slifka J. Towards models of phonation. J Phon 2001;29:451-80.
Arnold KS, Emanuel FW. Spectral noise levels and roughness severity ratings for vowels produced by male children. J Speech Hear Res 1979;22:613-26.
Yanagihara N. Significance of harmonic changes and noise components in hoarseness. J Speech Hear Res 1967;10:531-41.