Longitudinal typanometry and pneumatic otoscopy in healthy newborn infants

Tympanometry provides an objective and quantitative assessment of middle ear status. The sensitivity of this diagnostic tool in infants under seven months of age is uncertain, primarily because of anatomical and physiological differences between the external and middle ears of neonates and those of older children and adults. The definition of normal tympanograms in infants will be determined by the course of normal developmental changes. Little is known about maturational changes in tympanograms, particularly at frequencies above 226 Hz. Before the sensitivity of tympanometry in neonates can be established, more data are needed about the characteristics of normal tympanograms in the first few months of life. The present investigation was carried out to examine the normal maturational course of tympanometric shape, static aural acoustic admittance, and ear canal wall characteristics in individual infants. Subjects were twenty-three healthy, full-term infants, who were followed at various time intervals in the first four months of life. Attrition was high: Ten subjects were still enrolled at four months of age. Susceptance and conductance tympanograms were recorded from both ears of each subject at four probe frequencies. In addition, quantitative pneumatic otoscopy was performed utilizing air pressure changes of the same magnitude as those typically used in tympanometry. Results for the group were in an increase in admittance magnitude with increasing age at frequencies above 226 Hz. Admittance phase angle increased with increasing age at all frequencies, indicating a growing contribution of compliant elements in the first four months of life. By four months of age, mean admittance magnitude did not yet reach adult values, but mean admittance phase was similar to values obtained from adults. There were individual differences in the course of development. By four months of age, all but one subject\u27s ears had adult-like phase angle values. In contrast, admittance magnitude values of some subjects showed no signs of maturation by this age. The course of development of input admittance at the tympanic membrane differed for individual infants. The data were most homogeneous across age at 226 Hz, indicating this may be the frequency of choice for diagnosing middle ear pathology in this age group. Otoscopic examination revealed no distention of the ear canal walls after two months of age in response to air pressure pulses similar to those used in tympanometry. Multiple tympanometric peaks were seen at low probe frequencies in ears with immobile ear canal walls and the proportion of multiple tympanometric peaks decreased steadily with age. Findings indicate that external ear canal differences can not completely account for tympanometric differences between young infants and adults. Recommendations abut the clinical use of tympanometry in infants are included and explanations for the data are linked to existing anatomical and physiological data