Material y métodos.

Sujetos. Se estudiaron 20 niños de 0 a 2 años de edad, con hipoacusia profunda y 20 niños normoyentes. Se registró su llanto con una grabadora digital Sony durante la exploración física rutinaria. Los registros se analizaron en el Laboratorio de Bioacústica del Instituto Nacional de Rehabilitación, utilizando el software Cool Edit 96. El análisis se realizó comparando el grupo de hipoacúsicos con el de normoyentes. Para comparar los resultados entre grupos, se estimaron las medidas de tendencia central y dispersión y se contrastaron mediante análisis de varianza de una vía.

Resultados.

El promedio de la duración del llanto en el grupo de hipoacúsicos fue de 0.5845 ± 0.6150 seg, con un rango de 0.08 a 5.2 seg, en tanto que en el grupo control fue de 0.5387 ± 0.2631, con un rango de 0.06 a 1.75. En el grupo de los hipoacúsicos, se observaron cinco casos con una duración muy prolongada del llanto; en los análisis de varianza de una vía, las diferencias no alcanzaron significado estadístico. En el grupo control no se observaron casos con llanto prolongado. El promedio de los periodos inspiratorios fue de 0.3962 ± 0.2326, con un rango de 0.06 a 1.75, en los hipoacúsicos, y de 0.4083 ± 0.1854, con un rango de 0.21 a 0.96, en los controles. La exploración de datos mediante conglomerados se condujo con el método de Ward. La exploración de las tipologías con los grupos de hipoacúsicos y normoyentes no alcanzó significado estadístico.

En el análisis de contingencia, 57.49% de los llantos de los sordos fueron cortos, 40.72% de duración intermedia y 1.8% muy prolongados. La diferencia del promedio de los llantos pro longados con los de duración intermedia fue de 3.6 s, pero no alcanzó nivel significativo.

En el análisis cualitativo de los llantos se apreciaron cambios consistentes considerados anormales: vibrato, inestabilidad y deficiencia melódicas, consistentes en pérdida de la frecuencia fundamental(F0), pérdida o limitación en la producción de armónicos, llantos explosivos, deslizamientos, bifonación y pérdida de la intensidad del llanto al final del periodo. Aunque estos cambios pueden observarse en los controles, sólo llegan a presentarse de manera esporádica.

Análisis cualitativo de los espectrogramas. En primer término, se procedió a la estandarización del método. Dos observadores calibrados determinaron la presencia de características de variación de la F0 y de los armónicos, y se validó mediante el contraste gráfico con el análisis de Fourier en niños hipoacúsicos y normoyentes, todos ellos pacientes del Instituto Nacional de Rehabilitación.

Conclusiones

Material and methods.

Twenty zero-to two-year old cases were studied; they were deaf children of both sexes; all cases were included in a follow-up program on the Human Communication Department of the National Institute of Perinatology of Mexico and were compared with 20 normal hearing children. We re-corded Brain Stem Evoked Auditory Responses (BEAR) and cry recording using a digital Sony recorder during the physical exploration. We analyzed the frequency (Hz) and duration of the espiratory cries, the duration of inspiration between two cry emissions and the characteristics of the spectrogram.

Quantitative analysis. The usual estimates of means and standard variation were obtained and they were compared with one way analysis of variance. We organized typologies of frequency by means of cluster techniques (Ward method). The distribution of the duration of the periods of crying and silence was explored with a contingency tables.

Qualitative analysis. Two standardized observers visually analyzed all the cries to determine any variation of F0 and of harmonic frequencies. Whenever a variation of F0 was observed, we obtained maximum and minimum frequencies, as well as average duration of each cry emission. The procedure was validated by means of the graphic comparison with a Fouries analysis.

Results.

Mean duration of cries in the deaf group was 0.5845 ± 0.6150 s (range 0.08-5.2 s), while in the group of normal hearing cases was 0.5387 ± 0.2631 (range 0.06-1.75 s). From the deaf group, five cases had very prolonged duration of cries, without statistical significance. The mean duration of the inspiration was 0.3962 ± 0.2326, with a range of 0.06 to 1.75 in the deaf group and of 0.4083 ± 0.1854, with a range of 0.21 at 0.96, in the controls, without difference among groups. There was no correlation between the time of espiratory cry and that of the inspiration. Three cry topologies were organized: one of shorter duration (mean 0.30 s), with 111 spectrograms, an intermediate one (mean 0.73) with 85 spectrograms and one of prolonged duration (mean 4.5 s) with spectrograms of three cases. Three topologies of the inspiratory period were obtained: one of short periods (mean 0.33 s), with 171 spectrograms, one of intermediate duration (mean 0.80 s) with 18 spectrograms and one of prolonged duration (mean 1.60 s) with three cases. There were no statistical differences of tipologies between the deaf groups and normal hearing cases. On the qualitative analysis of cries, we came across several variations which are interpreted as abnormalities: vibratos, poor melodic control, loss of fundamental frequencies, harmonic limited production, plosives, gliding, bi phonation, and a loss of intensity at end of cry emissions. These changes were also observed on the control cases, but only in a very limited number.

Discussion.

Cry spectrogram analysis are non invasive indicators of the neonate's neurophysiologic organization. Although cry duration varies in healthy newborns, the accepted variation for a normal range is 1.1 to 2.8 s, with standard deviations around 0.6 s. Consistent differences have not been demonstrated between risk and control groups. However, abnormal cases such as Down syndrome or severe asphyxia have very short cries, whereas on the Cri du chat syndrome the duration of cries is prolonged. Extended cries imply cardiac and respiratory risks which have been associated with later outcomes as development retardation and sudden death. There are also some questions to solve, such as the regulation and control of cry, starting from breathing mechanisms or from a sensorial afferent, mediated by hearing. The deaf infants are constituted in a study model, considering that the auditory afference is suppressed and the control of the cry is restricted to the breathing environment. In the studied spectrograms, the duration of the cry was within reported normal limits by other authors, inasmuch in the normal hearing control cases as in the deaf, except the dissident cases, but without these reaching statistical significance. Further research of brainstem function is needed for the abnormal cases with prolonged cry periods, since such cries are interpreted as an alteration of the breathing reflexes of Hering-Breuer, which might have a pathological meaning in the sense of the sob's spasm or even more severe risk factors as sleep apnea and even sudden death.

The qualitative analysis in the deaf individuals demonstrated a poor quality and unstable character of melodic control, with a smaller number of harmonics. The deaf cases lost the relationship between the fundamental frequencies and their harmonics, mainly because of the participation of supraglottic structures that modulate pitch and due to the poorness of melodic control, either for monotony or due to the impossibility of returning to a normal pattern, following variations such as vibrato, plosives or noise concentration. In the cases of prolonged cries, starting from the third second, the sound intensity tends to diminish and the harmonics are lost, perhaps due to a decrease of the subglottal pressure of phonation. This finding supports the auditory control of crying related to breathing mechanisms.

Conclusions.

In preliminary terms, by means of the melodic analysis of the spectrograms, differences are demonstrated be-tween the cries of the deaf and of the normal hearing cases. The increase of the complexity of the melody of the cry, or their poverty, are indicative of the neuromuscular function and they may support the evaluation of phonation before language development. The study of the spectrograms of deaf individuals does not constitute an element for the detection or for diagnosis since, to date, estimators of sensibility or of specificity have not been established, but they constitute a support for its integral evaluation, with the possibility of evaluating and of improving therapeutic rehabilitation.