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ORIGINAL
Effects of vocal nodules on acoustic characteristics of voicein children : an acoustic analysis of voice
Toshihito Aoki1, 2, Takaaki Takeyama1, 2, Yuki Sakamoto1, Aki Shimada1, Eiji Kondo1, Seiichi Nakano1, Junya Fukuda1,
Takahiro Azuma1, Go Sato1, Yoshiaki Kitamura1, Kiyohito Hosokawa3, Jiro Udaka1, 2, and Noriaki Takeda1
Department of Otolaryngology, Tokushima University Graduate School of Biomedical Sciences, Tokushima, Japan, 2Udaka ENT Clinic,
Tokushima, Japan, 3Department of Otolaryngology-Head and Neck Surgery, Osaka University School of Medicine, Osaka, Japan
1

Abstract : Objective : In the present study, an attempt was made to evaluate the acoustic characteristics of voicein pediatric patients with vocal nodules using acoustic analysis of voice. Methods : Thirty-five pediatric patientswith vocal nodules and 32 control children without dysphonia were enrolled in this study. Their voice samples
were analyzed using the Multi-Dimensional Voice Program. Acoustic parameters of voice, such as pitch period
perturbation quotient (PPQ), amplitude perturbation quotient (APQ), and noise-to-harmonic ratio (NHR), were
measured. Results : In phonation at a loudness of over 80 dBA, the PPQ, APQ, and NHR values of the voice significantly increased in children with vocal nodules than in the control children without dysphonia. The sensitivities and specificities of PPQ, APQ, and NHR for prediction of vocal nodules in children were 62.86% and 84.38%,
74.29% and 75.00%, and 31.43% and 93.75%, respectively. Discussion : The present findings suggest that vocal nodules affect vocal fold vibration, resulting in impaired control of pitch and loudness leading to increased noise
components. NHR could be used to evaluate the efficacy of treatment, such as voice rehabilitation, in pediatricpatients with vocal nodules because of its high specificity for prediction of vocal nodules in children. J. Med.
Invest. 68 : 276-279, August, 2021
Keywords : vocal nodules, pediatric patients, dysphonia, acoustic analysis of voice

INTRODUCTION
The prevalence of dysphonia is approximately 6% amongchildren aged eight years (1). Dysphonia develops mainly inchildren aged 7-12 years, predominantly boys, and vocal nodules
are the most common cause of dysphonia in childhood (2). Vocal
abuse and incorrect use of the voice are the main predisposing
factors for vocal nodules (3). Vocal nodules are diagnosed using
video-stroboscopic examinations in adult patients. However, pediatric patients hardly accept the examination because of theirlack of collaboration and patience (4), which prevents regularfollow-up of patients’ laryngeal findings. For the assessmentof voice disorders in children, multi-dimensional assessments,
including perceptual and objective voice evaluations, have been
recommended by the European Laryngological Society (5).
In addition, a minimum protocol for the pediatric voice clinic
recommended measuring acoustic parameters of voice in pediatric patients with dysphonia (4). Recently, the objective andquantitative acoustic analysis of voice has been clinically used
as a complementary assessment method for diagnosis of vocal
nodules in children and for follow-up assessment during voice
rehabilitation (6).
In the present study, an attempt was made to evaluate theacoustic characteristics of voice in pediatric patients with vocal
nodules using acoustic analysis. However, it has been reported
that acoustic parameters of voice vary with different loudnessof phonation in children (7). Therefore, in Experiment 1 of thepresent study, we first examined the effects of predefined or
Received for publication March 15, 2021 ; accepted May 6, 2021.
Address correspondence and reprint requests to Noriaki Takeda,
M.D., Ph.D., Department of Otolaryngology, University of Tokushima
Graduate School of Biomedical Sciences, 3-18-15 Kuramoto, Tokushima
770-8502, Japan and Fax : +81-88-633-7170.

comfortable loudness of phonation on acoustic parameters ofvoice, such as pitch period perturbation quotient (PPQ), amplitude perturbation quotient (APQ) (8), and noise-to-harmonic
ratio (NHR) (9) in children without dysphonia. In Experiment 2,
we compared acoustic parameters of voice in pediatric patientswith vocal nodules to those in control children without dysphonia. Finally, we performed receiver operating characteristic(ROC) analysis to identify the best acoustic parameters of voice
for prediction of vocal nodules in children.

METHODS
Experiment 1
Participants

In Experiment 1, 21 children (11 boys and 10 girls, mean age :7.86 ± 1.56 years) with no vocal symptoms or history of phoniatric disorders were enrolled. The voice quality of all participants
was evaluated as euphonic by otolaryngologists in auditory-perceptual evaluation. This study was approved by the Committee
for Medical Ethics of Tokushima University Hospital. Written
informed consent was obtained from a parent of each child prior
to the experiment.

Recordings
Each child’s voice was recorded while he or she was seated ina quiet room (in a sound-attenuated room with an ambient noiselevel below 30 dB). Recordings were obtained using a microphone(Ultra-Linear Measurement Condenser Microphone ECM8000,
Behringer, Japan) placed on a stand at a distance of 10 cm andat an angle of 45° from the child’s lips to reduce aerodynamic
pop noise, with a sampling rate of 44.1 kHz and 16-bit quantization. Task instructions were given by the examiner prior to
the recording. Three samples of sustained vowel / e / recordingsfor 3 seconds were obtained under the instruction to phonate at

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The Journal of Medical Investigation Vol. 68 August 2021
a loudness of over 80 dBA, confirmed using a sound-level meter(Audio Analyzer PAA3, Phonic, Japan) and at a comfortable
loudness with an instruction of conversational pitch and loudness.
The sound pressure level of the recorded voice was calibrated byrecording of a pure tone of 62 dBA at 1 kHz generated by a soundcalibrator (NC-74, Rion, Tokyo, Japan). Brockmann-Bauser, etal. reported the voice SPL in phonation at a comfortable loudness
ranged from 62.7 to 93.8 dBA in children (10).

Table 1. PPQ, APQ and NHR in phonation at a loudness of comfort-

Experiment 2
Participants

APQ(%)In Experiment 2, 35 pediatric patients with vocal nodules (31boys and 4 girls, mean age : 7.46 ± 1.46 years) and 32 control children with no vocal symptoms or history of phoniatric disorders(24 boys and 8 girls, mean age : 8.53 ± 1.61 years) were enrolled.
Vocal nodules in these pediatric patients were diagnosed byotolaryngologists using video-laryngoscopic examination. Stroboscopic illumination was not applied because all patients could
not sustain the vowels in a relaxed manner during the examination. The voice quality of the control children was evaluated as
euphonic by otolaryngologists in auditory-perceptual evaluation.
There was no sex ratio difference between pediatric patientswith vocal nodules and control children (p = 0.15). This study
was approved by the Committee for Medical Ethics of Tokushima
University Hospital. Written informed consent was obtained
from a parent of each pediatric patient with vocal nodules andcontrol child prior to the experiment.

Recordings
The parameters of the voice recordings were similar to thosein Experiment 1. Three samples of sustained vowel / e / recordings for 3 seconds were obtained for all the participants under
the instruction to phonate at a loudness of over 80 dBA.

able loudness and over 80 dBA in children without dysphonia
Comfortable
phonation>80dBAphonation

p value

1.37 ± 0.58

0.51 ± 0.32

<0.0001Range

0.49-2.75

0.11-1.53

Variance

0.34130.10020.0086

Mean ± SD

3.69 ± 0.99

2.77 ± 1.01

<0.0001Range

2.69-6.99

1.58-6.22

Variance

0.97641.00650.93520.0049Parameters
PPQ(%)

NHR

Mean ± SD

Mean ± SD

0.14 ± 0.04

0.12 ± 0.01

Range

0.10-0.24

0.10-0.16

Variance

0.00130.0002<0.0001

Experiment 2
The mean values of APQ, PPQ, and NHR in the pediatricpatients with vocal nodules were significantly larger than thoseof the control children without dysphonia (PPQ in Fig. 1, p < 0.01,
APQ in Fig. 2, p < 0.01, HNR in Fig. 3, p < 0.05). The abilities of
PPQ, APQ, and NHR to predict vocal nodules were assessedusing ROC analysis. The optimum cut-off value of PPQ was
0.774 for prediction of vocal nodules in dysphonic children with asensitivity of 62.86% and a specificity of 84.38%. The optimum
cut-off value of APQ was 2.902 with a sensitivity of 74.29% anda specificity of 75.00%. The optimum cut-off value of NHR was
0.142 with a sensitivity of 31.43% and a specificity of 93.75%(Table 2).

Acoustic analysis
All recordings were analyzed using the Multi-Dimensional
Voice Program (MDVP, Kay Pentax, USA) (11) in both experiments. A second mid-vowel portion of each sample without theonset and offset of phonation was prepared for analysis. The
acoustic parameters of PPQ, APQ, and NHR were measured inthree samples from each child, and the avalage value was used
for statistical analyses.

Statistical analysis
The F test and paired t-test were used in Experiment 1, andChi-square for independence test, Student’s t-test and ROC
analysis were used in Experiment 2 for statistical analysis using
Statcel version 4 (OMS Publishing Inc., Saitama, Japan) andstatistical software EZR (12). p < 0.05 was considered statisticalsignificant. The optimum cut-off values were defined using thepoints closest to (0, 1) on the ROC curve.

Figure 1. PPQ in pediatric patients with vocal nodules and control

children without dysphonia. PPQ (pitch period perturbation quotient).
*p < 0.01.

RESULTS

Experiment 1
The variances of PPQ and NHR, but not APQ, in phonation ata loudness of over 80 dBA were significantly lower than those inphonation at a comfortable loudness in children without dysphonia (p < 0.01) (Table 1). The mean values of PPQ, APQ, and NHRin phonation at a loudness of over 80 dBA were significantly
lower than those in phonation at a comfortable loudness in children without dysphonia (p < 0.01) (Table 1).
Figure 2. APQ in pediatric patients with vocal nodules and control
children without dysphonia. APQ (amplitude perturbation quotient).
*p < 0.01.

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278

Figure 3. NHR in pediatric patients with vocal nodules andcontrol children without dysphonia. NHR (noise-to-harmonic ratio).
*p < 0.05.

Table 2. Cut-off value, sensitivity and specificity of PPQ, APQ and

NHR

Parameters

Cut-off

Sensitivity(%)

Specificity
(%)

PPQ

0.774

62.86

84.38

APQ

2.902

74.29

75.00

NHR

0.142

31.43

93.75

DISCUSSION
Although phonation at a comfortable loudness was used inacoustic analysis of voice in children according to the recent
guideline (4), it was reported that acoustic parameters of voice
varied with different loudness of phonation in children (7). In
adults, acoustic parameters of voice are reliably measured inphonation at a loudness of over 80 dBA (13). In Experiment 1,
the variances of PPQ and NHR, but not APQ, in phonation ata loudness of over 80 dBA were smaller than those in phonation
at a comfortable loudness in children without dysphonia. Thesefindings suggest that phonation at a predefined loudness of over
80 dBA increases the reliability of acoustic parameter measurements of voice in pediatric patients without dysphonia. The
values of PPQ, APQ, and NHR in phonation at a loudness of over
80 dBA were smaller than those in phonation at a comfortable
loudness in children without dysphonia. Brockmann-Bauser
et al. also reported that the values of jitter (similar to PPQ)
and shimmer (similar to APQ) decreased in phonation at thepredefined loudness of over 80 dBA in children (10). Because
subglottal pressure and medial compression of the vocal folds
increased during loud phonation, the present findings suggestthat the vibratory pattern of the vocal folds became stable in phonation at a loudness of over 80 dBA, resulting in decreased PPQ,
APQ, and NHR values. Therefore, we decided to use phonation
at a loudness of over 80 dBA in acoustic analysis of voice in pediatric patients with vocal nodules in Experiment 2.
In Experiment 2, we performed acoustic analysis of voice inphonation at a loudness of over 80 dBA using MDVP, and foundthat PPQ, APQ, and NHR values increased in children withvocal nodules than in the control children without dysphonia.
Vocal nodules are mediolaterally symmetrical submucosal lesions at the anterior midsection of the vocal folds, and develop
due to overuse of the voice, repeated vocal abuse over time, andvocal strain (14). Because PPQ and APQ are indices of frequency
and amplitude perturbation of voice, respectively, these findings

suggest that vocal nodules on bilateral vocal folds affect the control of pitch and intensity of the voice. It was reported that thevalue of PPQ of the voice was affected by the width of the vocal
nodules in pediatric patients (15) and that vocal polyp, a unilateral vocal mass lesion, had greater effect on vocal vibration to
induce higher elevations of jitter and shimmer (similar to PPQ
and APQ, respectively) than bilateral vocal nodules (16). Taken
together with the present findings, it is suggested that vocal nodules, as a mass lesion on bilateral vocal folds, affect the vibrationof vocal folds, resulting in impaired control of pitch and loudnessof the voice. Gramuglia et al. also reported that children withvocal nodules showed elevations in PPQ and APQ of voice (17).
The elevation in the value of NHR of the voice in children withvocal nodules in the present study is consistent with previous reports (17, 18). Because NHR is an index of the noise component,
the findings suggest that vocal nodules on bilateral vocal folds
produce a noise component, an essential element of dysphonia. It
has been reported that the value of HNR (a semantic inverse of
NHR) of voice is affected by the mediolateral width of the vocal
nodules in children (15). Therefore, the increased NHR in thepresent study suggests that glottal insufficiency due to protruded vocal nodules exacerbates noise components in voice signals.
Although the video-stroboscopic examination is considered thebest modality for diagnosing and assessing vocal nodules, it isdifficult for pediatric patients to cooperate with an uncomfortable examination (4). Therefore, there ia an essential need forquick, non-invasive, and well-tolerated methods, such as computer-assisted voice analysis, for pediatric patients. In general,the clinical evaluation of voice disorders consists of diagnosis andmonitoring steps. It would be ideal for both steps to be examinedusing a non-invasive modality. For this purpose, the degree ofsensitivity of the examination is crucial for the diagnosis. In thepresent study, sensitivites and specificities of the three acoustic
parameters were evaluated to predict vocal nodules in children.
Among the three vocal parameters, sensitivity was highest in
APQ. However, its value of 74.28% is too low for screening anddiagnosing the presence of vocal nodules in children. Therefore,
acoustic analysis seemed not to be suitable for the diagnosis ofpediatric voice disorders. That is, an invasive method of video-stroboscopy / laryngoscopy is still necessary for diagnosis. Because the highest specificity of 93.75% in NHR demonstrates its
ability to designate an individual who does not have the disease,
it is suggested that NHR can monitor the efficacy of treatment,such as voice rehabilitation, in pediatric patients with dysphonia. Moreover, it was reported that jitter (similar to PPQ), shimmer (similar to APQ), and NHR improved after voice therapy inchildren with vocal nodules (19, 20). Therefore, regular follow-up
using NHR combined with PPQ and APQ could be acceptable formonitoring pediatric patients with vocal fold nodules if an occasional video-stroboscopy / laryngoscopy is performed.

CONCLUSION
Because the variances of PPQ and NHR, but not APQ inphonation at a loudness of over 80 dBA were smaller than thosein phonation at a comfortable loudness in children, we usedphonation at a predefined loudness of over 80 dBA in acoustic
analysis of voice using MDVP in pediatric patients with vocal
nodules. Of the three acoustic parameters, NHR could be used toevaluate the efficacy of voice rehabilitation in pediatric patientswith vocal nodules because of its high specificity for prediction of
vocal nodules in children.

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CONFLICT OF INTEREST
The authors declare no conflicts of interest in this study.

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