Normative Sweep Frequency Impedance Measures in Healthy Neonates

Abstract

Background: Diagnosing middle ear disorders in neonates is a challenging task for both audiologists and otolaryngologists. Although high-frequency (1000 Hz) tympanometry and acoustic stapedial reflex tests are useful in diagnosing middle ear problems in this age group, they do not provide information about the dynamics of the middle ear in terms of its resonance frequency (RF) and mobility. The sweep frequency impedance (SFI) test can provide this information, which may assist in the diagnosis of middle ear dysfunction in neonates. Purpose: This study aimed to investigate the feasibility of testing neonates using the SFI technique, establish normative SFI data for RF and mobility of the middle ear in terms of changes in sound pressure level (ΔSPL in dB), and describe the dynamics of the middle ear in healthy Australian neonates. Study Sample: A prospective sample of 100 neonates (58 males, 42 females) with a mean gestational age of 39.3 wk (SD = 1.3 wk; range = 38–42 wk), who passed all three tests, namely, automated auditory brainstem response, transient evoked otoacoustic emissions, and 1000 Hz tympanometry, were included in this study. Data Collection and Analysis: A SFI research prototype was used to collect the data. First, the SPL in the ear canal was measured as a probe-tone frequency was swept from 100–2000 Hz with the ear canal static pressure held constant at 200 daPa. Then, this measurement was repeated with the static pressure reduced in 50 daPa steps to –200 daPa. Additional measurement was also performed at the static pressure, where the peak of the 1000 Hz tympanogram occurred. A graph showing the variation of SPL against frequency at all static pressures was plotted. From this graph, the RF and ΔSPL at tympanometric peak pressure (TPP) were determined. Descriptive statistics and an analysis of variance (ANOVA) were applied to the RF and ΔSPL data with gender and ear as independent variables. Results: The results showed two resonance regions of the outer/middle ear with the high RF (mean = 1236 Hz; 90% range: 830–1518 Hz) being approximately equal to four times that of the low RF (mean = 287 Hz; 90% range = 209–420 Hz). The low RF was more easily identifiable than the high RF. The ΔSPL at the low RF (mean = 8.2 dB; 90% range = 3.4–13 dB) was greater than that at the high RF (mean = 5.0 dB; 90% range = 1.5–8.1 dB). There were no significant differences or interactions between genders and ears. Conclusion: The study showed that the SFI is a feasible test of middle ear function in neonates. The SFI results revealed two regions of resonance with the lower resonance (287 Hz) possibly related to the movements of the outer ear canal wall and higher resonance (1236 Hz) related to the resonance of the middle ear. The normative data developed in this study will be useful in evaluating outer and middle ear function in neonates.