Dynamic characteristics of the middle ear in neonates

Abstract

ObjectiveEarly diagnosis and treatment of hearing disorders in neonates is highly effective for realization of linguistic competence and intellectual development. To objectively and quickly evaluate the dynamic characteristics of the middle ear, a sweep frequency impedance (SFI) meter was developed, which allowed the diagnosis of middle-ear dysfunctions in adults and children. However, this SFI meter was not applicable to neonates since the size of the measurement probe was too large. In the present study, therefore, the SFI meter was improved, i.e., the diameter of the probe was reduced to that of the neonatal external ear canal. By using this newly designed SFI meter, SFI tests were performed in healthy neonates. MethodsA sound of the sweeping sinusoidal frequency between 0.1kHz and 2.0kHz in 0.02-kHz step intervals is presented to the ear canal by an SFI probe while the static pressure of the ear canal is kept constant. During this procedure, the sound pressure level (SPL) is measured. The measurements are performed at 50-daPa intervals of static pressure from 200daPa to −200daPa. ResultsMeasurements were conducted in 10 ears of 9 neonates. The SPL showed two variations at 0.26±0.03kHz and 1.13±0.12kHz. Since the SPL is known to show a variation at frequencies from 1.0kHz to 1.6kHz due to the resonance of the middle ear in adults and children with normal hearing, the second variation is probably related to such resonance in neonates. The measurement of gel models, which mimics the neonatal external ear canal, showed a variation in SPL at around 0.5kHz. This implies that the source of the first variation may possibly be related to the resonance of the external ear canal wall. ConclusionsSFI tests revealed that there were two variations in the SPL curve in neonates, one at 0.26±0.03kHz and the other at 1.13±0.12kHz, the former and the latter being possibly related to the resonance of the external ear canal wall and that of the middle ear, respectively. This result suggests that the dynamic characteristics of the middle ear in neonates are different from those in adults.