|Year : 2013 | Volume
| Issue : 1 | Page : 10-13
Laryngeal aerodynamic analysis of vocal nodules
Department of Speech Language Pathology, All India Institute of Speech and Hearing, Manasagangotri, Mysore, Karnataka, India
|Date of Web Publication||24-Sep-2013|
Research officer, Department of Speech Language Pathology, All India Institute of Speech and Hearing, Manasagangotri, Mysore 570 006, Karnataka
Source of Support: None, Conflict of Interest: None
| Abstract|| |
The present study is aimed to investigate the effects of vocal nodules on the aerodynamic analysis of the voice. The study included twelve females with normal laryngeal and respiratory functions and twelve age, gender and language matched females with bilateral vocal nodules within the age group of 18-40 years. All participants were subjected to non-invasive aerodynamic analysis using Aeroview 1.4.4 version (Glottal Enterprises Inc, USA). The participants were instructed to produce the CV syllable train "papapapa" into the circumvented mask at comfortable pitch and loudness. The recorded stimuli were analyzed to obtain laryngeal aerodynamic measures such as estimated subglottic pressure, mean airflow rate, laryngeal airway resistance, and laryngeal airway conductance. Mean and standard deviation for all the four laryngeal aerodynamic measures were calculated separately for both control and clinical groups. The results revealed significant effect of voice on laryngeal measures such as estimated subglottic pressure and mean airflow rate. Thus, results suggest that indirect measurement of laryngeal aerodynamic parameters are effective and essential investigative tools in assessment of vocal nodules.
Keywords: Sub-glottic pressure, laryngeal airway conductance, laryngeal airway resistance, mean air flow rate, vocal nodule
|How to cite this article:|
Sheela S. Laryngeal aerodynamic analysis of vocal nodules. J Laryngol Voice 2013;3:10-3
| Introduction|| |
Vocal nodules, also called as nodes, singer's nodes, screamer's nodes are localized benign masses, located within the superficial layer of the lamina propria. They typically occur at the midpoint of the membranous vocal folds at the junction of the anterior third and posterior two-thirds of the full length of the vocal fold  with an excessive deposit of collagen IV and fibronectin. ,
Vocal nodules are caused by repeated trauma to the vocal folds during talking or singing. The midpoint of the membranous vocal folds, where the extra mass growths occur, receives the maximum impact during production of voice. Other factors such as the presence of dehydration, respiratory infections, inflammatory factors (smoking, alcohol use, caffeine intake, drug effects, allergies, exposure to noxious chemicals, laryngopharyngeal reflux) may be predisposing or aggravating factors for nodules development. 
In adults, vocal nodules are more frequent in women (94.5%) than in men. , Specifically, lesions occur most frequently in women between the ages of 20-40 years.  Small extra mass growths that develop at the site of the trauma are usually known as "soft nodules." They interfere with the adduction and vibration of the vocal folds. If soft nodules are ignored, persistent damage may begin to produce fibrous scar tissue, referred to as "hard nodules." Vocal nodules cause a minimal disruption of the mucosal wave on stroboscopy. 
Patients with vocal fold nodules usually complain of dysphonia. Vocal fatigue is common. Perceptually, the voice usually has a strained/leaky quality. Often, the voice also includes perceptual features that indicate irregularities in vocal fold vibrations, such as roughness (irregular voice) as well as vocal fry. , Due to the increased mass of the vocal folds, fundamental frequency (f 0 ) tends to be lower than normal.  Problems with the upper vocal pitch range are often the first symptom noticed by individuals with vocal nodule. Furthermore, the quality of the voice worsens with use, particularly if there is extensive, loud, pressed voice use. 
Assessment of voice production routinely includes perceptual evaluation of voice quality and measures of laryngeal function using acoustic, aerodynamic and video-stroboscopic instrumentation. Aerodynamics is a branch of science that is concerned with the study of gas motion in objects and the forces that are created. Laryngeal aerodynamics (LA) is a specific field within this branch of science that studies the airflow and pressure changes that are produced within the larynx. LA analysis is based on the fact that voice production is essentially an aerodynamic phenomenon, whereby the glottis transforms aerodynamic power into acoustic power. For phonation to take place, both a suitable quantity of air and a suitable air pressure are needed. The aerodynamic forces working at the glottis seem to be responsible for the creation of the sustained vibration of the vocal folds. , LA analysis assess the interaction of both respiratory and laryngeal functions,  which provides information related to the valving efficiency of the glottis during phonation.
LA measures include mean air flow rate (MAFR), estimated sub-glottal pressure (ESGP), laryngeal airway resistance (LAR) and laryngeal airway conductance (LAC), etc. These measures are briefly explained below.
MAFR is the volume of air flow across the vocal folds during the phonation in 1 s. It is generally measured in liters or milliliters or cubic centimeters per second (l/s or ml/s or cc/s). ESGP is one of the LA parameters that has been proposed to be measured for voice evaluation.  It is the amount of pressure exerted on the vocal folds during adduction and is measured in cm H 2 O.
LAR and LAC are derived parameters. LAR is the ratio of ESGP to MAFR.  It is the quotient of peak intraoral pressure (estimated from production of an unvoiced plosive/p/) divided by the peak flow rate (measured from production of a vowel/i/) as produced in a repeated train of/pi/syllables. This measurement is intended to reflect the overall resistance of the glottis and by extension serves as an estimate of the valving characteristic, whether too tight (hyperfunctional), too loose (hypofunctional) or normal. Laryngeal resistance has been used in experimental settings to further analyze the covarying relationship between pressure and flow in vocal fold vibration. A word of caution is useful, however, because derived measures pose some limits to interpretability. The magnitude of a particular derived value is not meaningful without examining the separate contributions of pressure and flow. For example, a measure of increased LAR values might be attributable to excessive ESGP, insufficient transglottal flow or both. LAC is the ratio of MAFR to the ESGP. It is the converse of LAR and reflects the conductance for airflow at the level of glottis.
Early investigators have found that aerodynamic studies are helpful in etiological classification of voice disorders, , while later studies showed that the diagnostic value of aerodynamic measurements is low in identifying the exact etiology, but they may point to a tendency to the "hyperfunction" or "hypofunction" styles of vocal production. ,
However, the main purpose of aerodynamic measures is to evaluate the degree of some aspects of vocal function and to monitor the post-therapeutic changes. 
Tanaka and Gould  studied vocal efficiency in order to explain LA aspects in voice disorder. Vocal efficiency is defined as the ratio of sound power at the mouth opening (or the opening end of a tube if inserted in the mouth) to aerodynamic power calculated as mean flow rate times, mean ESGP.  They had selected ten normal adult subjects and variety of clients with unilateral and/or bilateral vocal nodule (small/large), unilateral and/or bilateral vocal polyp (small/large), Reinke's edema, recurrent laryngeal nerve (RLN) paralysis and glottal cancer. The body plethysmography was used to obtain LA measures such as ESGP (cm H 2 O) and MAFR (cc/s). Each subject sat in the airtight box with a mouthpiece and a clip placed on the nose. Then, the subject was instructed to sustain the vowel/a/for a few seconds at a comfortable loudness and pitch level. Specifically, in subjects with bilateral vocal nodules, MAFR values were 0.258 L/s and SGP 8.3 cm H 2 O. They suggested an aerodynamic-biochemical classification based on vocal fold lesion type associated with low vocal efficiency. Firstly, a large glottal chink (RLN paralysis) associated with high MAFR value. Secondly, mass on vocal folds (vocal nodule, vocal polyp and Reinke's edema), associated with a high level of MAFR and ESGP values. Thirdly, highly stiffened vocal fold (Glottal cancer), associated with high SGP value.
Sapienza and Stathopoulos  studied laryngeal measures in female subjects with bilateral vocal nodules. Their clinical group consisted of ten females with bilateral vocal nodule and control consisted consists of ten females with normal voice. The pneumotachograph (Glottal Enterprises, Model MS 100 A-2) was used to obtain SGP (cmH 2 O) LA measure. The subjects were instructed to produce a syllable string consisting of/pa/at their comfortable pitch and loudness at a rate of 1.5 syllables/s.  The ESGP value in females with bilateral vocal nodule was 8.05 cmH 2 O (±2.46) and in females with normal voice was 6.07 cmH 2 O (±1.07). The ESGP value was significantly higher in females with bilateral vocal nodule compared with females with normal voice production. The authors have attributed the increase in ESGP values in females with bilateral vocal nodules indicating that a greater amount of air is being transferred through the glottis during voice production and suggests the presence of glottal incompetence.
In summary, few studies showed that aerodynamic studies of the dysphonic voices of vocal fold nodules usually show statistically significant increased ESGP values ,, as well as statistically significant increased MAFR values  as an attempt to produce phonation in the presence of leaky glottis.
The aim of this study is to evaluate the effect of vocal nodules on aerodynamic analysis of the voice.
| Materials and Methods|| |
The control group consisted of twelve female subjects with normal laryngeal and respiratory system and functions in the age range of 18-40 years. The clinical group consisted of twelve age, sex and language matched subjects diagnosed as "bilateral vocal nodules" through stroboscopic evaluation.
The Aeroview 1.4.4 version (Glottal Enterprises Inc, USA) was used to collect aerodynamic data from each subject. The Aeroview is a computer-based system that measures the MAFR and ESGP pressure during the vowel production. The derived parameters such as LAR (ESGP/MAFR) and LAC (MAFR/ESGP) using an automated factory-optimized algorithm are also displayed. Other measures of voice such as the sound pressure level and the fundamental frequency of the measured vowel segment phonation can also be obtained. Before recording, the transducers for measuring airflow and air pressure were calibrated on a daily basis as per the guidelines provided by Glottal Enterprises.
The subjects were seated comfortably and the procedure was explained clearly. The subjects were instructed to hold the mask firmly against the face so that nose and mouth were covered with the intraoral tube placed between the lips and above the tongue. The examiner confirmed the correct placement of the transducer or ensured that the mask is firmly fitted. The participants were then instructed to produce the repetitions of consonant-vowel syllable/pa/6-7 times into the circumvented mask at a comfortable pitch and loudness to obtain six to seven stable peaks of intraoral pressure. The rate and style of production was demonstrated by the examiner and two practice runs were given before the actual recording. Following practice, the actual recordings were made. The recording with syllable production rate between 2.0 and 3.5/s (recommended by the manufacturer) and with appropriate pressure peak morphology was considered for the further analysis. Typical pressure peak and airflow wave morphology is shown in [Figure 1].
|Figure 1:Typical wave morphology of appropriate pressure peak and airflow|
Click here to view
The recorded waveform was analyzed by placing the cursors on flat portions of two adjacent pressure peaks. The application software analyzes the waveform and provides the values of ESGP (cmH 2 O), MAFR (ml/s), LAR (cmH 2 O/ml/s), LAC (ml/s/cmH 2 O) values. On obtaining three peak-to-peak measurements, the software automatically provides their average value. In order to facilitate comparison of MAFR values with earlier studies, MAFR which is obtained in ml/s was converted manually to L/s. Accordingly, derived parameters such as LAR and LAC obtained values were converted to (cmH 2 O/L/s) and (L/s/cmH 2 O) respectively.
Statistical Package for Social Sciences version 17.0 was used to obtain descriptive statistical measures such as mean and standard deviation (SD). For both groups, all four LA parameters were calculated separately.
| Results and Discussion|| |
The present study consisted of two groups. The control group consisted of twelve female subjects with normal laryngeal and respiratory system and functions and clinical group of 12 female subjects diagnosed as "bilateral vocal nodules" through stroboscopic evaluation. [Table 1] depicts the mean and SD and p values for LA measures such as ESGP, MAFR, LAR and LAC. The results show a significant difference between the control group and clinical group for laryngeal measures such as ESGP (P < 0.01) and MAFR (P < 0.01).
|Table 1: Mean and SD for laryngeal aerodynamic measures ESGP, MAFR, LAR, and LAC measures|
Click here to view
The ESGP and MAFR values were higher for clinical group compared with the control group. This can be attributed to the fact that ESGP represents the energy immediately available for the creation of the acoustic signals. Since vocal nodules hinder proper acoustic signals because of the glottal air leak, the subjects with vocal nodule try to "compensate" for this by increasing ESGP. This finding is consistent with previous reports from Isshiki and Ringel, 1964;  Stathopoulos and Weismer, 1985;  and Tanaka and Gould, 1985.  The phonatory glottal gap that results from vocal nodules leads to air leak as has been explained. This can explain the increase in MAFR values in the clinical group compared to control group. This finding is in consonance with previous reports from Tanaka and Gould, 1985. 
The high LAR value was obtained for the control group compared with the clinical group, but not statistically significant. However, decrease in LAR in the clinical group can be attributed to the phonatory glottal gap caused by vocal nodules, leading to a decrease in the resistance of the glottis. It can also be attributed to the possibility that the increase in MAFR was much higher than that of ESGP. The high LAC value was observed for clinical group compared with the control group, but not statistically significant. It reflects the conductance for airflow at the level of glottis. This parameter was not considered by any of the earlier reported studies.
| Conclusion|| |
The present study found statistically significant differences in ESGP and MAFR values in females with bilateral vocal nodules in comparison with females with normal laryngeal and respiratory system and functions. The LAR values were lesser in the clinical group compared with the control group, but not statistically significant. Non invasive LA measures such as ESGP and MAFR are effective and may be used as essential investigative tool in the assessment of vocal nodules.
| Acknowledgments|| |
I would like to express my sincere gratitude to Dr. S. R. Savitri, Director, AIISH, Mysore for providing me an opportunity to carry out this study.
| References|| |
|1.||Verdolini K, Rosen CA, Branski RC. Classification Manual for Voice Disorders-I. London: Lea Publishers; 2008. |
|2.||Gray SD, Pignatari SS, Harding P. Morphologic ultrastructure of anchoring fibers in normal vocal fold basement membrane zone. J Voice 1994;8:48-52. |
|3.||Cervera FJ, Vega F, Garcia-Tapia R. Benign lesions of vocal folds. In: Garcia-Tapia R, Cobeta I, editors. Diagnosis and Treatment of Voice Disorders. Madrid, Spain: Garsi; 1996. p. 223-40. |
|4.||Herrington-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. |
|5.||Hammarberg B. Perception and acoustics of voice disorders- A combined approach. In: de Krom G, editor. Proceedings of Voice Data 98, Symposium on Databases in Voice Quality Research and Education. Utrecht, The Netherlands: Utrecht Institute of Linguistics; 1998. p. 1-6. |
|6.||Holmberg EB, Hillman RE, Hammarberg B, Södersten M, Doyle P. Efficacy of a behaviorally based voice therapy protocol for vocal nodules. J Voice 2001;15:395-412. |
|7.||Mathieson L. The Voice and its Disorders. London: Whurr Publishers; 2001. p. 77-107. |
|8.||Kotby MN, Baraka MS, Abou El Ella MY, Khidr AA, Hegazi MA. Aerodynamic analysis of voice disorders. In: Sacristan T, Vicent JJ, Bartual J, Candela FA, Rubio L, editors. Otorhinolaryngol, Head Neck Surg. Proceedings of XIV World Congress of Otorhinolaryngology, Head and Neck Surgery. Vol. II. Amsterdam: Kugler, Ghedini Publication; 1990. |
|9.||Dejonckere PH. Perceptual and laboratory assessment of dysphonia. Otolaryngol Clin North Am 2000;33:731-50. |
|10.||Grillo EU, Perta K, Smith L. Laryngeal resistance distinguished pressed, normal, and breathy voice in vocally untrained females. Logoped Phoniatr Vocol 2009;34:43-8. |
|11.||Hirano M. Objective evaluation of the human voice: Clinical aspects. Folia Phoniatr (Basel) 1989;41:89-144. |
|12.||Smitheran JR, Hixon TJ. A clinical method for estimating laryngeal airway resistance during vowel production. J Speech Hear Disord 1981;46:138-46. |
|13.||Yanagihara. Aerodynamic examination of laryngeal function. Proceeding to the 9 th International Congress. Mexico, 1969. |
|14.||Schutte HK. Aerodynamics of phonation. Acta Otorhinolaryngol Belg 1986;40:344-57. |
|15.||Schutte HK. Integrated aerodynamic measurements. Discussion Report to the Voice Committee. ALP, 1988. |
|16.||Tanaka S, Gould WJ. Vocal efficiency and aerodynamic aspects in voice disorders. Ann Otol Rhinol Laryngol 1985;94:29-33. |
|17.||Van den Berg J. Direct and indirect determination of the mean subglottic pressure; sound level, mean subglottic pressure, mean air flow, subglottic power and efficiency of a male voice for the vowel (a). Folia Phoniatr (Basel) 1956;8:1-24. |
|18.||Sapienza CM, Stathopoulos ET. Respiratory and laryngeal measures of children and women with bilateral vocal fold nodules. J Speech Hear Res 1994;37:1229-43. |
|19.||Isshiki N, Ringel R. Air flow during the production of selected consonants. J Speech Hear Res 1964;50:233-44. |
|20.||Stathopoulos ET, Weismer G. Oral airflow and air pressure during speech production: A comparative study of children, youths and adults. Folia Phoniatr (Basel) 1985;37:152-9. |