Developmental changes in multifrequency tympanograms.

The normal maturational course of tympanometric shape, static aural acoustic admittance and ear canal wall characteristics were investigated in healthy infants, who were followed at various time intervals in the first 4 months of life. Susceptance and conductance tympanograms were recorded from both ears of each subject at four probe frequencies or more. 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 an increase in admittance magnitude with increasing age at frequencies above 226 Hz. Admittance phase angle increased with age at all frequencies, indicating a growing contribution of compliant elements in the first 4 months of life. The course of development of input admittance at the tympanic membrane differed among individual infants. Otoscopic findings indicated that external ear canal differences cannot completely account for tympanometric differences between young infants and adults.