El liderazgo con equilibrio emocional

Investigations of voice using aerodynamic techniques have been reported for more than 30 years. Investigators realized early on that voice production is an aero-mechanical event and that vocal tract aerodynamics reflect the interactions between laryngeal anatomy and complex physiological events. Aerodynamic events do not always have a one-to-one correspondence with vocal tract physiology in a dynamic biological system, but careful control of stimuli and a good knowledge of laryngeal physiology make airflow and air pressure measurements invaluable tools.

Airflow (rate of air movement or velocity) and air pressure (force per unit area of air molecules) in the vo-cal tract are good reflectors of vovo-cal physiology. For example, at a simple level, airflow through the glottis (Vg) is an excellent indicator of whether the vocal folds are open or closed. When the vocal folds are open, there is airflow through the glottis, and when the vocal folds are completely closed, there is zero airflow. With other physiological events held constant, the amount of

Figure 7.Distributions of H1*-A3*, a measure that reflects the reduction of the high-frequency spectrum relative to the low-frequency spectrum, for male (black bars) and female (gray bars) speakers. H1 is the amplitude of the first harmonic and A3 is the amplitude of the strongest harmonic in the F3 peak.

The asterisks indicate that corrections have been applied to H1 and A3, as described in the text. (Adapted with permission from Hanson and Chuang, 1999.)

Voice Disorders in Children 67

airflow can be an excellent indicator of the degree of opening between the vocal folds.

Subglottal air pressure directly reflects changes in the size of the subglottal air cavity. A simplified version of Boyle’s law predicts the relationship in that a particular pressure (P) in a closed volume (V) of air must equal a constant (K), that is, K¼ PV. Subglottal air pressure will increase when the size of the lungs is decreased;

conversely, subglottal pressure will decrease when the size of the lungs is made larger. Changes in subglottal air pressure are mainly regulated through muscular forces controlling the size of the rib cage, with glottal resistance or glottal flow used to help increase or decrease the pressures (the glottis can be viewed as a valve that helps regulate pulmonary flows and pressures).

A small number of classic studies used average air-flow and intraoral air pressure to investigate voice pro-duction in children (Subtelny, Worth, and Sakuda, 1966;

Arkebauer, Hixon, and Hardy, 1967; Van Hattum and Worth, 1967; Beckett, Theolke and Cowan, 1971; Diggs, 1972; Bernthal and Beukelman, 1978; Stathopoulos and Weismer, 1986). Measures of flow and pressure were used to reflect laryngeal and respiratory function. Dur-ing voice production, children produce lower average airflow than adults, and boys tend to produce higher average airflow than girls of the same age. Supraglottal and glottal airway opening most likely account for the di¤erent average airflow values as a function of age and sex. Assuming that pressure is the same across all speakers, a smaller supraglottal or glottal opening yields a higher resistance at the constriction and therefore a restricted or lower flow of air. The findings related to intraoral air pressure have indicated that children pro-duce higher intraoral air pressures than adults, especially because they tend to speak at higher sound pressure levels (SPLs). The higher pressures produced by children versus adults reflect two physiological events. First, children tend to speak at a higher SPL than adults, and second, children’s airways are smaller and less compliant than adults’ (Stathopoulos and Weismer, 1986). Intu-itively, it would appear that the greater peak intraoral air pressure in children should lead to a greater magnitude of oral airflow. It is likely that children’s smaller glottal and supraglottal areas substantially counteract the po-tentially large flows resulting from their high intraoral air pressures.

Children were found to be capable of maintaining the same linguistic contrasts as adults through manipula-tion of physiological events such as lung cavity size and driving pressure, and laryngeal and articulatory config-uration. Other intraoral air pressure distinctions in chil-dren are similar to the overall trends described for adult pressures. Like adults, children produce higher pressures during (1) voiceless compared to voiced consonants, (2) prevocalic compared to postvocalic consonants, (3) stressed compared to unstressed syllables, and (4) stops compared to fricatives.

In the 1970s and 1980s, two important aerodynamic techniques relative to voice production were developed that stimulated new ways of analyzing children’s

aero-dynamic vocal function. The first technique was inverse filtering of the easily accessible oral airflow signal (Rothenberg, 1977). Rothenberg’s procedure allowed derivation of the glottal airflow waveform. The derived volume velocity waveform provides airflow values, per-mitting detailed, quantifiable analysis of vocal fold physiology. The measures made from the derived vol-ume velocity waveform can be related to the speed of opening and closing of the vocal folds, the closed time of the vocal folds, the amplitude of vibration, the overall shape of the vibratory waveform, and the degree of glottal opening during the closed part of the cycle.

The second aerodynamic technique developed was for the estimation of subglottal pressure and laryngeal air-way resistance (Rlaw) through noninvasive procedures (Lofqvist, Carlborg, and Kitzing, 1982; Smitheran and Hixon, 1981). Subglottal air pressure is of primary im-portance, because it is responsible for generating the pressure di¤erential causing vocal fold vibration (the pressure that drives the vocal folds). Subglottal pressure is also important for controlling sound pressure level and for contributing to changes in fundamental frequency—

all factors essential for normal voice production. The estimation of Rlaw o¤ers a more general interpretation of laryngeal dynamics and can be used as a screening measure to quantify values outside normal ranges of vocal function.

Measures made using the Smitheran and Hixon (1981) technique include the following:

1. Average oral air flow: Measured during the open vowel /A/ at midpoint to obtain an estimate of laryn-geal airflow.

2. Intraoral air pressure: Measured peak pressure dur-ing the voiceless [p] to obtain an estimate of sub-glottal pressure.

3. Estimated laryngeal airway resistance: Calculated by dividing the estimated subglottal pressure by esti-mated laryngeal airflow. This calculation is based on analogy with Olm’s law, R¼ V=I, where R ¼ resistance, V¼ voltage, and I ¼ current. In the speech system, R¼ laryngeal airway resistance, V ¼ subglottal pressure (P), and I¼ laryngeal airflow (V).

Thus, R¼ P=V.

Measures made using the derived glottal airflow waveform important to vocal fold physiology include the following (Holmberg, Hillman, and Perkell, 1988):

1. Airflow open quotient: This measure is comparable to the original open quotient defined by Timcke, von Leden, and Moore (1958). The open time of the vocal folds (defined as the interval of time between the instant of opening and the instant of closing of the vocal cords) is divided by the period of the glottal cycle. Opening and closing instants on the airflow waveform are taken at a point equal to 20% of alter-nating airflow (OQ-20%).

2. Speed quotient: The speed quotient is determined as the time it takes for the vocal folds to open divided by the time it takes for the vocal folds to close. Opening

and closing instants on the waveform are taken at a point equal to 20% of alternating air flow. The mea-sure reflects how fast the vocal folds are opening and closing and the asymmetry of the opening and closing phases.

3. Maximum flow declination rate: The measure is obtained during the closing portion of the vocal fold cycle and reflects the fastest rate of airflow shut-o¤.

Di¤erentiating the airflow waveform and then identi-fying the greatest negative peak on di¤erentiated waveform locates the fastest declination. The flow measure corresponds to how fast the vocal folds are closing.

4. Alternating glottal airflow: This measure is calculated by taking the glottal airflow maximum minus mini-mum. This measure reflects the amplitude of vibra-tion and can reflect the glottal area during vibratory cycle.

5. Minimum flow: This measure is calculated by sub-tracting minimum flow from zero. It is indicative of airflow leak due to glottal opening during the closed part of the cycle.

Additional measures important to vocal fold physiol-ogy include the following:

6. Fundamental frequency: This measure is obtained from the inverse-filtered waveform by means of a peak-picking program. It is the lowest vibrating fre-quency of the vocal folds and corresponds perceptu-ally to pitch.

7. Sound pressure level: This measure is obtained at the midpoint of the vowel from a microphone signal and corresponds physically to vocal intensity and percep-tually to loudness.

Voice production arises from a multidimensional system of anatomical, physiological, and neurological components and from the complex coordination of these biological systems. Many of the measures listed above have been used to derive vocal physiology. Stathopoulos and Sapienza (1997) empirically explored applying ob-jective voice measures to children’s productions and dis-cussed the data relative to developmental anatomical data (Stathopoulos, 2000). From these cross-sectional data as a function of children’s ages, a clearer picture of child vocal physiology has emerged. Because the ana-tomical structure in children is constantly growing and changing, children continually alter their movements to make their voices sound ‘‘normal.’’ Figures 1 through 7 show cross-sectional vocal aerodynamic data obtained in children ages 4–14 years. One of the striking features that emerge from the aerodynamic data is the change in function at 14 years of age for boys. After that age, boys and men functionally group together, while women and children seem to have more in common aerodynamically and physiologically. The data are discussed in relation to their physiological implications.

Estimated subglottal pressure: Children produce higher subglottal pressures than adults, and all speakers produce higher pressures when they produce higher

SPLs (Fig. 1). Anatomical di¤erences in the upper and lower airway will a¤ect the aerodynamic output of the vocal tract. The increased airway resistance in children could substantially increase tracheal pressures (Muller and Brown, 1980).

Airflow open quotient (OQ-20%): Open quotient has traditionally been very closely correlated with SPL. In adults, it is widely believed that as SPL increases, the open quotient decreases. That is, the vocal folds remain closed for a longer proportion of the vibratory cycle as vocal intensity increases. As seen in Figures 2A and 2B, which show data from a wide age span and both sexes, only adults and older teenagers produce lower open quotients for higher SPLs. It is notable that the younger children and women produce higher OQ-20%, indicating that the vocal folds are open for a longer proportion of the cycle than in men and older boys, regardless of vocal intensity.

Maximum flow declination rate (MFDR): Children and adults regulate their airflow shut-o¤ through a combination of laryngeal and respiratory strategies.

Their MFDRs range from about 250 cc/s/s for com-fortable levels of SPL to about 1200 cc/s/s for quite high SPLs. In children and adults, MFDR increases as SPL increases (Fig. 3). Increasing MFDR as SPL increases a¤ects the acoustic waveform by emphasizing the high-frequency components of the acoustic source spectra (Titze, 1988).

Alternating glottal airflow: Fourteen-year-old boys and men produce higher alternating glottal airflows than younger children and women during vowel production for the high SPLs (Fig. 4). We can interpret the flow data to indicate that older boys and men produce higher alternating glottal airflows because of their larger laryn-geal structures and greater glottal areas. Additionally, men and boys increase their amplitude of vibration dur-ing the high SPLs more than women and children do.

Greater SPLs result in greater lateral excursion of the vibrating vocal folds; hence the higher alternating glottal airflows for adults. Younger children also increase their

Figure 1. Estimated subglottal pressure as a function of age and sound pressure level.

Voice Disorders in Children 69

amplitude of vibration when they increase their SPL, and we would assume an increase in the alternating flow values. The interpretation is somewhat complicated by the fact that younger children and women have a shorter vocal fold length and smaller area (Flanagan, 1958), thereby limiting airflow through the glottis.

Fundamental frequency: As expected, older boys and men produce lower fundamental frequencies than women and younger children. An interesting result pre-dicted by Titze’s (1988) modeling data is that the 4- and 6-year-olds produce unusually high f0 values when they increase their SPL to high levels (Fig. 5). Changes in fundamental frequency are more easily e¤ected by increasing tracheal pressure when the vocal fold is char-acterized by a smaller e¤ective vibrating mass, as in young children ages 4–6 years.

Laryngeal airway resistance: Children produce voice with higher Rlaw than 14-year-olds and adults, and all speakers increase their Rlaw when increasing their SPL (Fig. 6). Since Rlaw is calculated by dividing subglottal

Figure 2. A, Airflow open quotient as a function of age and sex.

B, Airflow open quotient as a function of age and sound pres-sure level.

Figure 3. Maximum flow declination rate (MFDR) as a func-tion of age, sex, and sound pressure level.

Figure 4.A, Alternating glottal airflow as a function of age and sex. B, Alternating glottal airflow as a function of age and sound pressure level.

pressure by laryngeal airflow, the high Rlaw for high SPL is largely due to higher values of subglottal pres-sure, since the average glottal airflow is the same across age groups. A basic assumption needs to be discussed here, and that is, that glottal airflow will increase when subglottal air pressure increases if laryngeal configura-tion/resistance is held constant. The fact that subglottal pressure increases for high SPLs but flow does not in-crease clearly indicates that Rlaw must be increasing.

Physiologically, the shape and configuration of the laryngeal airway must be decreasing in size to maintain the constant airflow in the setting of increasing sub-glottal pressures. In sum, children and adults alike continually modify their glottal airway to control the important variables of subglottal pressure and SPL.

The cross-sectional aerodynamic data, and in partic-ular the flow data, make a compelling argument that the primary factor a¤ecting children’s vocal physiology is the size of their laryngeal structure. A general scan of the cross-sectional data discussed here shows a change in

vocal function at age 14 in boys. It is not merely coinci-dental that at 14 years, male larynges continue to in-crease in size to approximate the size of adult male larynges, whereas larynges in teenage girls plateau and approximate the size of adult female larynges (Fig. 7).

Regardless of whether it is size or other anatomical fac-tors a¤ecting vocal function, it is clear that use of an adult male model for depicting normal vocal function is inappropriate for children. Age- and sex-appropriate aerodynamic, acoustic, and physiological models of normal voice need to be referred to for the diagnosis and remediation of voice disorders.

See also instrumental assessment of children’s voice.

—Elaine T. Stathopoulos

References

Arkebauer, H. J., Hixon, T. J., and Hardy, J. C. (1967). Peak intraoral air pressure during speech. Journal of Speech and Hearing Research, 10, 196–208.

Beckett, R. L., Theolke, W. M., and Cowan, L. A. (1971).

Normative study of airflow in children. British Journal of Disorders in Communication, 6, 13–17.

Bernthal, J. E., and Beukelman, D. R. (1978). Intraoral air pressure during the production of /p/ and /b/ by children, youths, and adults. Journal of Speech and Hearing Research, 21, 361–371.

Diggs, C. C. (1972). Intraoral air pressure for selected English consonants: A normative study of children. Unpublished master’s thesis, Purdue University, Lafayette, Indiana.

Flanagan, J. L. (1958). Some properties of the glottal sound source. Journal of Speech and Hearing Disorders, 1, 99–

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Holmberg, E. B., Hillman, R. B., and Perkell, J. (1988). Glot-tal airflow and transglotGlot-tal air pressure measurements for male and female speakers in soft, normal, and loud voice.

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Lofqvist, A., Carlborg, B., and Kitzing, P. (1982). Initial vali-dation of an indirect measure of subglottal pressure Figure 5.Fundamental frequency as a function of age, sex, and

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Figure 6. Laryngeal airway resistance as a function of age and sound pressure level.

Figure 7. Length of vocal fold as a function of age and sex.

Voice Disorders in Children 71

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