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Computer-Assisted Voice Analysis
Establishing a Pediatric Database
Paolo Campisi, MD, MSc;
Ted L. Tewfik, MD, FRCSC;
John J. Manoukian, MD, FRCSC;
Melvin D. Schloss, MD, FRCSC;
Elaine Pelland-Blais, MOA, SLP(C);
Nader Sadeghi, MD, FRCSC
Arch Otolaryngol Head Neck Surg. 2002;128:156-160.
ABSTRACT
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Objectives To establish and characterize the first pediatric normative database
for the Multi-Dimensional Voice Program, a computerized voice analysis system,
and to compare the normative data with the vocal profiles of patients with
vocal fold nodules.
Design A cross-sectional, observational design was used to establish the normative
database. The comparative study was completed using a case-control design.
Setting University-based outpatient pediatric otolaryngology clinic.
Participants One hundred control subjects (50 boys and 50 girls) aged 4 to 18 years
contributed to the normative database. The voices of 26 patients (19 boys
and 7 girls) with bilateral vocal fold nodules were also analyzed.
Main Outcome Measures Demographic data, including sex, age, height, weight, body mass index,
and cigarette smoke exposure, were obtained. The Multi-Dimensional Voice Program
extracted up to 33 acoustic variables from each voice analysis.
Results The mean (SEM) values of each of the acoustic variables are presented.
At age 12 years, boys experience a dramatic decrease in fundamental frequency
measurements. The voices of patients with vocal fold nodules had significantly
elevated frequency perturbation measurements compared with control subjects
(P<.001).
Conclusions The vocal profile of children is uniform across all girls and prepubescent
boys. Patients with vocal fold nodules demonstrated a consistent acoustic
profile characterized by an elevation in frequency perturbation measurements.
Normal acoustic reference ranges may be used to detect various vocal fold
pathologic abnormalities and to monitor the effects of voice therapy.
INTRODUCTION
ASSESSMENT OF pediatric dysphonia has proven to be problematic for speech
pathologists, pediatricians, and otolaryngologists. Clinical judgments of
vocal quality have been commonly derived from subjective grading systems rather
than from objective measures,1-2
which has resulted in the development of inconsistent descriptive terminology
and severity classifications. Furthermore, standard adult diagnostic modalities
have demonstrated limited usefulness in the assessment of pediatric voice
disorders.3-4 Fiberoptic endoscopy,
for example, is often difficult and rushed in the uncooperative child, and
stroboscopic examination is technically challenging in any young patient.5
Computer-assisted voice analysis represents an important diagnostic
advancement because it provides objective acoustic measurements, and it is
well tolerated by children.6-7
The Multi-Dimensional Voice Program (MDVP), in conjunction with the Computerized
Speech Lab (Kay Elemetrics Corp, Lincoln Park, NJ), is a highly versatile
voice-processing and spectrographic analysis software package ideally suited
for use in the pediatric population.8 It provides
an objective, reproducible, and noninvasive measure of vocal fold function.
The MDVP extracts up to 33 acoustic variables from each voice analysis and
compares them graphically or numerically with a built-in normative database.
The normative data, however, were derived solely from adults. It is apparent
that a pediatric database must be developed if acoustic measures are to be
applied to the identification of pediatric vocal pathologic abnormalities.
The main objective of this study, therefore, was to establish and characterize
the first pediatric normative database for the MDVP. To our knowledge, a pediatric
normative database has not been previously developed for this or any other
computer-assisted voice analysis system. Another objective of this study was
to evaluate the ability of the MDVP to identify vocal pathologic abnormalities.
To achieve the latter objective, the normative data were compared with the
acoustic profiles of patients with vocal fold nodules using a case-control
study design.
PARTICIPANTS AND METHODS
MDVP ANALYSIS
Apparatus
An IBM-compatible personal computer is used to operate MDVP model 4305.
The MDVP is used in combination with Computerized Speech Lab model 4300. The
Computerized Speech Lab consists of a hardware and software system that uses
an MS-DOS–based computer as host. The Computerized Speech Lab includes
signal conditioning capability, 16-bit analog/digital converters, and dual
digital signal processors. The MDVP uses the signal conditioning and analog/digital
hardware to sample speech at 50 kHz for sustained voicing.
The MDVP extracted up to 33 acoustic voice variables from each voice
analysis. These variables were displayed numerically and graphically and were
classified into 1 of 6 groups: (1) fundamental frequency information; (2)
frequency perturbation; (3) amplitude perturbation; (4) noise and tremor evaluation;
(5) voice break, subharmonic, and voice irregularity; or (6) miscellaneous.
Definitions of the individual variables listed in Table 1 are available from the authors.
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Table 1. Multidimensional Voice Program Acoustic Variables in 94 Patients*
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Technique
A consistent technique was used for each MDVP analysis. Seated in a
quiet room, the subject held a microphone at a fixed distance (8 cm) and at
a 45° off-axis position to reduce aerodynamic noise from the mouth. The
subject was then instructed to vocalize and sustain the vowel a 3 times in a flat tone, at a comfortable pitch and a constant amplitude.
To standardize the input amplitude, the input signal was adjusted to a predetermined
level. This adjustment prevented signal loss and system overloading. Each
subject's third production of a was recorded. A 3-second
voice sample was captured and incorporated into the MDVP using a microphone
(Visi-Pitch; Kay Elemetrics Corp). The voice sample was not trimmed. The MDVP
analysis was then performed, and the acoustic voice variables were displayed.
ESTABLISHING THE NORMATIVE DATABASE
Control Subjects
One hundred control subjects (50 boys and 50 girls) aged 4 to 18 years
contributed to the normative database. Subjects were recruited from a pediatric
otolaryngology outpatient clinic (Montreal Children's Hospital, Montreal,
Quebec). All subjects were healthy and had no history of laryngeal or voice
pathologic abnormalities. Patients with moderate to severe conductive hearing
loss or any degree of sensorineural hearing loss were excluded from the study.
Demographic data, including sex, age, height, weight, body mass index, and
cigarette smoke exposure, were obtained for each subject. The absence of pathologic
abnormalities of the vocal fold was verified in each subject using indirect
mirror laryngoscopy or flexible nasolaryngoscopy. An MDVP analysis was then
performed, as described in the "Technique" subsection. All laryngoscopies
and voice analyses were performed by a single observer (P.C.) to eliminate
interobserver variability.
Statistical Analysis
The normative data were analyzed using a statistical software program
(SPSS/PC+; SPSS Inc, Chicago, Ill). Backward stepwise multiple linear regression
was used to identify statistically significant associations between the acoustic
voice variables and the independent variables of sex, age, height, weight,
and body mass index. A 2-tailed P<.05 was considered
statistically significant. The mean (SEM) of each acoustic variable was calculated.
CASE-CONTROL STUDY
Patients
Twenty-six patients (19 boys and 7 girls) with vocal fold nodules, diagnosed
using flexible nasolaryngoscopy, were recruited into the study. All the patients
had bilateral vocal fold nodules at the junction of the anterior one third
and posterior two thirds of the vocal folds. The presence of hemorrhagic nodules
or other laryngeal pathologic abnormalities resulted in exclusion from the
study. Recruited patients were evaluated by a speech language pathologist
(E.P.-B.) and underwent a perceptual evaluation of the voice. An MDVP analysis
was then performed as described in the "Technique" subsection.
Statistical Analysis
Determination of a statistically significant difference in voice variable
values between the control group and the vocal fold nodule group was achieved
using 1-way analysis of variance. Again, a 2-tailed P<.05
was considered statistically significant.
If a statistically significant difference in a voice variable was detected,
a threshold value was assigned as the upper limit of the 95% confidence interval
(mean + 1.96 x SD) of the control group value. Based on the threshold
value, data for the control and nodule groups were dichotomized, and a 2 x
2 table was constructed. A  2 test was then used to assess
the statistical significance of the distribution of the dichotomized data.
An odds ratio was also calculated to quantify the association between the
presence of vocal fold nodules and a voice variable value greater than the
assigned threshold value.
RESULTS
NORMATIVE DATABASE
Voice samples from 100 control subjects were used to develop the normative
database. Backward stepwise multiple linear regression revealed a statistically
significant association between the fundamental frequency measurements and
the independent variables of age and sex. This association was strongly affected
by the peripubescent changes in the male voice pattern. All other variables
were not affected by age and sex. When boys 12 years and older were excluded
from the analyses, the association between the fundamental frequency measurements
and age and sex was not significant (Figure
1). The independent variables of height, weight, and body mass index
were not associated with any of the acoustic variables.
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Figure 1. Fundamental frequency in all boys,
all girls, and boys younger than 12 years. Values are expressed as mean ±
1.96 x SEM.
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The mean value of each of the acoustic variables is presented in Table 1. The corresponding SEM is also
presented to provide an estimate of the variability in the population at large.
To eliminate the effect of peripubescent voice changes on the fundamental
frequency measurements, the summary data in Table 1 do not include data from boys 12 years and older.
CASE-CONTROL STUDY
Twenty-six patients (19 boys and 7 girls) with vocal fold nodules were
recruited into the case-control study. Three boys older than 12 years were
excluded. The voice profiles of the remaining 23 patients were compared with
the normative database that included all girls and boys younger than 12 years.
The demographic data for the 2 groups were similar (Table 2). Consistently, patients with vocal fold nodules had statistically
significant elevations in their frequency perturbation measurements (absolute
jitter, jitter percentage, relative average perturbation, pitch period perturbation
quotient [PPQ], and smoothed PPQ) (P<.001 for
all) (Figure 2). The significant
increase in frequency perturbation measurements corroborates the findings
of the perceptual voice evaluation performed by the speech language pathologist.
The perceptual evaluation revealed anomalies in the control of pitch rather
than in the control of intensity.
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Table 2. Demographic Characteristics of the Control and Vocal Fold
Nodule Groups
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Figure 2. Frequency perturbation measurements
in the control and vocal fold nodule groups. Asterisk indicates P<.001; Jitt, jitter; RAP, relative average perturbation; PPQ, pitch
period perturbation quotient; and sPPQ, smoothed PPQ. Values are expressed
as mean ± 1.96 x SEM.
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When the control (n = 94) and vocal fold nodule (n = 23) group data
were dichotomized relative to the defined normative threshold values (mean
+ 1.96 x SD), a significant distribution of the data was observed for
each of the frequency perturbation measurements (P<.001
by 2 test). The calculated odds ratios suggest a high risk
of having vocal fold nodules with a variable value greater than the assigned
threshold value. The calculated odds ratios range from 28.4 to 41.6, and the
95% confidence intervals do not approach unity (Table 3).
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Table 3. Two-by-Two Tables Generated by Dichotomizing Data for Frequency
Perturbation Measurements in Individuals With and Without Vocal Fold Nodules*
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COMMENT
The functional assessment of pathologic voices is commonly achieved
using perceptual and equipment-based clinical tools.1
Perceptual analyses such as the Wilson Voice Profile System and the GRBAS
(grade, roughness, breathy, asthenic, strained) scale are based on the subjective
interpretation of the individual speech language pathologist.1-2
The lack of consistency and standardization in the basic methods of perceptual
assessment continues to be a major clinical problem. Instrumental diagnostic
modalities such as video stroboscopy, electroglottography, and phonetography
are indispensable components of a modern voice laboratory.1
These equipment-based tools, however, require costly and specialized instrumentation,
an experienced operator, cooperative patients, and interpretation of complicated
graphs and mathematical formulas.
The assessment of pediatric dysphonia presents unique challenges to
the voice scientist. First, it is difficult for children to cooperate with
lengthy, uncomfortable examinations. Fiberoptic endoscopy, for example, is
often rushed in the uncooperative child. Second, pediatric normative data
are unavailable. Therefore, the question arises as to whether a given voice
measurement is normal or pathologic and, if pathologic, how severe. Computer-assisted
voice analysis, such as the MDVP, represents a clinically important contribution
to the assessment of pediatric dysphonia. This system provides objective and
reproducible results. Assessments are noninvasive, completed in a short time,
and well tolerated by patients as young as 4 years. However, the development
and characterization of a normative pediatric database is a prerequisite to
the application of this technology to the assessment of pediatric voice pathologic
abnormalities.
The main objective of this study was to establish and characterize the
first pediatric normative database for the MDVP. Multiple linear regression
was used to assess the association between the derived acoustic variables
and the independent variables of age, sex, height, weight, and body mass index.
In general, we found that girls of all ages and boys younger than 12 years
had the same vocal profiles. However, age and sex were significantly associated
with fundamental frequency measurements when boys aged 12 years and older
were included in the statistical analyses. Fundamental frequency measurements
in boys sharply decreased and approached adult values beginning at age 12
years. No association was detected between the acoustic variables and the
independent variables of height, weight, and body mass index. Our findings
are consistent with previously published study results.9-10
Sussman and Sapienza9 examined the developmental
and sex trends in fundamental frequency in 17 boys and 14 girls aged 6.1 to
9.2 years. They found that the fundamental frequency for vowel production
of boys and girls (aged <12 years) was not significantly different but
were markedly different from men. Harries and colleagues10
reported abrupt changes in male speaking and singing fundamental frequencies
during puberty between Tanner stages G3 and G4, corresponding to an average
age of 13 years.
Vocal fold nodules are a common cause of pediatric dysphonia. In fact,
38% to 78% of children evaluated for chronic hoarseness have vocal fold nodules.11 Nodules are the result of voice misuse or abuse,
and they occur at the junction of the anterior and middle third of the vocal
folds, often bilaterally. Nodules result from injury to the superficial layer
of the lamina propria and the basement membrane zone caused by extensive vibration
that destroys the tissue.12-13
An aberrant healing response occurs with excessive deposition of collagen
type IV and fibronectin.
The normative acoustic data were compared with the vocal profiles of
patients with vocal fold nodules using a retrospective, case-control study
design. Patients with vocal fold nodules demonstrated a consistent acoustic
profile characterized by markedly elevated frequency perturbation measurements.
This finding was exemplified by abnormal jitter values. Jitter is defined as the cycle-to-cycle variation of frequency.14 In other words, it is a measure of unintended frequency
unsteadiness during prolonged phonation. This abnormality was corroborated
by the perceptual analysis, which demonstrated an inability of these patients
to control pitch. Furthermore, several of our patients who were treated with
voice therapy demonstrated normalization of their frequency perturbation measurements
as the size of their nodules decreased.
Abnormally elevated frequency perturbation measurements in children
with vocal fold nodules have been reported in the literature.7, 15-16
In a small series of 10 patients, aged 6 to 8 years, Kane and Wellen15 demonstrated a correlation between perceptual severity
ratings and elevated PPQ measurements. In 1997, Boltezar and colleagues16 failed to reveal an elevation in PPQ in 11 adolescents
(aged 10-17 years) with vocal fold nodules compared with a control group (jitter
and relative average perturbation were not measured). However, PPQ measurements
were abnormally elevated compared with adult values published in the literature.
To evaluate the ability of the MDVP to detect vocal pathologic abnormalities,
the frequency perturbation measurement data were dichotomized in controls
and patients according to an assigned threshold value. The calculated odds
ratios strongly suggest that an elevated frequency perturbation measurement
is highly associated with the presence of vocal fold nodules. Indeed, the
strong statistical association suggests that the MDVP may be useful in detecting
early, subclinical pathologic abnormalities and in monitoring treatment. The
role of the MDVP in detecting other vocal pathologic abnormalities, such as
respiratory papillomatosis, polypoid degeneration, and congenital sulcus vocalis,
needs to be further investigated.
In conclusion, the MDVP is an objective, noninvasive diagnostic tool
that complements existing functional voice analysis modalities. It represents
an important advancement in the assessment of pediatric dysphonia. The normative
database may be used to reliably assess the voices of girls and prepubescent
boys. However, boys older than 12 years should be compared with age-matched
controls.
AUTHOR INFORMATION
Accepted for publication September 10, 2001.
Presented in part at the 2000 Annual Meeting of The American Academy
of Pediatrics, Section on Otolaryngology and Bronchoesophagology, Chicago,
Ill, October 29, 2000.
We thank the Gustav Levinschi Foundation, Montreal, Quebec, for donation
of the Voice and Speech Laboratory.
Corresponding author and reprints: Ted L. Tewfik, MD, FRCSC, Director
of Otolaryngology, The Montreal Children's Hospital, 2300 Tupper St, Suite
B240, Montreal, Quebec, Canada H3H 1P3.
From the Departments of Otolaryngology (Drs Campisi, Tewfik, Manoukian,
Schloss, and Sadeghi) and Speech-Language Pathology (Ms Pelland-Blais), The
Montreal Children's Hospital, McGill University Health Centre, Montreal, Quebec.
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