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Disorders of voice may affect up to 5% of children, and instrumental procedures such as acoustics, aerodynamics, or electroglottography (EGG) may complement auditory-perceptual and imaging procedures by providing objective measures that help in determining the nature and severity of laryngeal pathology. The use of these procedures should take into account the developmental features of the larynx and special problems associated with a pediatric population.
An important starting point is the developmental anatomy and physiology of the larynx. This background is essential in understanding children's vocal function as determined by instrumental assessments. The larynx of the infant and young child differs considerably in its anatomy and physiology from the adult larynx (see anatomy of the human larynx). The vocal folds in an infant are about 3–5 mm long, and the composition of the folds is uniform. That is, the infant's vocal folds are not only very short compared with those of the adult, but they lack the lamination seen in the adult folds. The lamination has been central to modern theories of phonation, and its absence in infants and marginal development in young children presents interesting challenges to theories of phonation applied to a pediatric population. An early stage of development of the lamina propria begins between 1 and 4 years, with the appearance of the vocal ligament (intermediate and deep layers of the lamina propria). During this same interval, the length of the vocal fold increases (reaching about 7.5 mm by age 5) and the entire laryngeal framework increases in size. The differentiation of the superficial layer of the lamina propria apparently is not complete until at least the age of 12 years.
Studies on the time of first appearance of sexual dimorphism in laryngeal size are conflicting, ranging from 3 years to no sex differences in laryngeal size observable during early childhood. Sexual dimorphism of vocal fold length has been reported to appear at about age 6–7 years. These reported anatomical differences do not appear to contribute to significant differences in vocal fundamental frequency (f0) between males and females until puberty, at which time laryngeal growth is remarkable, especially in boys. For example, in boys, the anteroposterior dimension of the thyroid cartilage increases threefold, along with increases in vocal fold length.
Acoustic Studies of Children's Voice
Mean f0 has been one of the most thoroughly studied aspects of the pediatric voice. For infants' nondistress utterances, such as cooing and babbling, mean f0 falls in the range of 300–600 Hz and appears to be stable until about 9 months, when it begins to decline until adulthood (Kent and Read, 2002). A relatively sharp decline occurs between the ages of 12 months and 3 years, so that by the age of 3 years, the mean f0 in both males and females is about 250 Hz. Mean f0 is stable or gradually falling between 6 and 11 years, and the value of 250 Hz may be taken as a reasonable estimate of f0 in both boys and girls. Some studies report no significant change in f0 during this developmental period, but Glaze et al. (1988) reported that f0 decreased with increasing age, height, and weight for boys and girls ages 5–11 years, and Ferrand and Bloom (1996) observed a decrease in the mean, maximum, and range of f0 in boys, but not in girls, at about 7–8 years of age.
Sex differences in f0 emerge especially strongly during adolescence. The overall f0 decline from infancy to adulthood is about one octave for girls and two octaves for boys. There is some question as to when the sex difference emerges. Lee et al. (1999) observed that f0 differences between male and female children were statistically significant beginning at about age 12 years, but Glaze et al. (1988) observed differences between boys and girls for the age period 5–11 years. Further, Hacki and Heitmuller (1999) reported a lowering of both the habitual pitch and the entire speaking pitch range between the ages of 7 and 8 years for girls and between the ages of 8 and 9 years for boys. Sex differences emerge strongly with the onset of mutation. Hacki and Heitmuller (1999) concluded that the beginning of the mutation occurs at age 10–11 years. Mean f0 change is pronounced in males between the ages of about 12 and 15 years. For example, Lee et al. (1999) reported a 78% decrease in f0 for males between these ages. No significant change was observed after the age of 15 years, which indicates that the voice change is effectively complete by that age (Hollien, Green, and Massey, 1994; Kent and Vorperian, 1995).
Other acoustic aspects of children's voices have not been extensively studied. In apparently the only large-scale study of its kind, Campisi et al. (2002) provided normative data for children for the parameters of the Multi-Dimensional Voice Program (MDVP). On the majority of parameters (excluding, of course, f0), the mean values for children were fairly consistent with those for adults, which simplifies the clinical application of MDVP. However, this conclusion does not apply to the pubescent period, during which variability in amplitude and fundamental frequency increases in both girls and boys, but markedly so in the latter (Boltezar, Burger, and Zargi, 1997). It should also be noted voice training can affect the degree of aperiodicity in children's voices (Dejonckere et al., 1996) (see acoustic assessment of voice).
Aerodynamic Studies of Children's Voice
There are only limited data describing developmental patterns in voice aerodynamics. Table 1 shows normative data for flow, pressure, and laryngeal airway resistance from three sources (Netsell et al., 1994; Keilman and Bader, 1995; Zajac, 1995, 1998). All of the data were collected during the production of /pi/ syllable trains, following the procedure first described by Smitheran and Hixon (1981). Flow appears to increase with age, ranging from 75–79 mL/s in children aged 3–5 years to 127–188 mL/s in adults. Pressure decreases slightly with age, ranging from 8.4 cm H2O in children ages 3–5 years to 5.3–6.0 cm H2O in adults. Laryngeal airway pressure decreases with age, ranging from 111–119 cm H2O/L/s in children aged 3–6 years to 34–43 cm H2O/L/s in adults. This decrease in laryngeal airway pressure occurs as a function of the rate of flow increase exceeding the rate of pressure decrease across the age range.
Table 1 : Aerodynamic normative data from three sources: N (Netsell et al., 1994), K (Keilman & Bader, 1995), and Z (Zajac, 1995, 1998). All data were collected using the methodology described by Smitheran and Hixon (1981). Values shown are means, with standard deviations in parentheses
| Reference |
Age (yr) |
Sex |
N |
Flow (mL/s) |
Pressure (cm H2O) |
LAR (cm H2O/L/s) |
| N |
3–5 |
F |
10 |
79 (16) |
8.4 (1.3) |
111 (26) |
| N |
3–5 |
M |
10 |
75 (20) |
8.4 (1.4) |
119 (20) |
| K |
4–7 |
F&M |
|
|
7.46 (2.26) |
|
| N |
6–9 |
F |
10 |
86 (19) |
7.4 (1.5) |
89 (25) |
| N |
6–9 |
M |
9 |
101 (42) |
8.3 (2.0) |
97 (39) |
| Z |
7–11 |
F&M |
10 |
123 (30) |
11.4 (2.3) |
95.3 (24.4) |
| K |
8–12 |
F&M |
|
|
6.81 (2.29) |
|
| N |
9–12 |
F |
10 |
121 (21) |
7.1 (1.2) |
59 (7) |
| N |
9–12 |
M |
10 |
115 (42) |
7.9 (1.3) |
77 (23) |
| K |
13–15 |
F&M |
|
|
5.97 (2.07) |
|
| K |
4–15 |
F&M |
100 |
50–150 |
|
87.82 (62.95) |
| N |
Adult |
F |
10 |
127 (29) |
5.3 (1.2) |
43 (10) |
| N |
Adult |
M |
10 |
188 (51) |
6.0 (1.4) |
34 (9) |
| F = female, M = male, N = number of participants, LAR = laryngeal airway resistance. |
Netsell et al. (1994) explained the developmental changes in flow, pressure, and laryngeal airway pressure as secondary to an increasing airway size and decreasing dependence on expiratory muscle forces alone for speech breathing with age. No consistent differences in aerodynamic parameters were observed between female and male children. High standard deviations reflect considerable variation between children of similar ages (see aerodynamic assessment of voice).
Electroglottographic Studies of Children's Voice
Although EGG data on children's voice are not abundant, one study provides normative data on a sample of 164 children, 79 girls and 85 boys, ages 3–16 years (Cheyne, Nuss, and Hillman, 1999). Cheyne et al. reported no significant effect of age on the EGG measures of jitter, open quotient, closing quotient, and opening quotient. The means and standard deviations (in parentheses) for these measures were as follows: jitter—0.76% (0.61), open quotient—54.8% (3.3), closing quotient—14.1% (3.8), and opening quotient—31.1% (4.1). These values are reasonably similar to values reported for adults, although caution should be observed because of differences in procedures across studies (Takahashi and Koike, 1975) (see electroglottographic assessment of voice).
One of the most striking features of the instrumental studies of children's voice is that, except for f0 and the aerodynamic measures, the values obtained from instrumental procedures change relatively little from childhood to adulthood. This stability is remarkable in view of the major changes that are observed in laryngeal anatomy and physiology. Apparently, children are able to maintain normal voice quality in the face of considerable alteration in the apparatus of voice production. With the mutation, however, stability is challenged, and the suitability of published normative data is open to question. The maintenance of rather stable values across a substantial period of childhood (from about 5 to 12 years) for many acoustic and EGG parameters holds a distinct advantage for clinical application. It is also clear that instrumental procedures can be used successfully with children as young as 3 years of age. Therefore, these procedures may play a valuable role in the objective assessment of voice in children.
See also voice disorders in children.
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