Diagnosing Conductive Dysfunction in Infants Using Wideband Acoustic Immittance: Validation and Development of Predictive Models

Vibration Measurements of the Gerbil Eardrum Under Quasi-static Pressure Sweeps

Tympanometry provides an objective measurement of the status of the middle ear. During tympanometry, the ear-canal pressure is varied, while the response of the ear to sound pressure is measured. The effects of the pressure on the mechanics of the middle ear are not well understood. This study is a continuation of our previous work in which the vibration response of the gerbil eardrum was measured in vivo under quasi-static pressure steps. In this study, we delivered a continuous pressure sweep to the middle ear and measured the vibration response at four locations for six gerbils. Vibrations were recorded using a single-point laser Doppler vibrometer and glass-coated reflective beads (diameter ~ 40 µm) at the umbo and on the mid-manubrium, posterior pars tensa and anterior pars tensa.The vibration magnitudes were similar to those in the previous step-wise pressurization experiments. Most gerbils showed repeatability within less than 10 dB for consecutive cycles. As described in the previous study, as the frequency was increased at ambient pressure, the vibration magnitude on the manubrium increased slightly to a broad peak (referred to as R1) and then decreased until a small peak appeared (referred to as R2), followed by multiple peaks and troughs as the magnitude decreased further. The low-frequency vibration magnitude (at 1 kHz) decreased monotonically as the pressure became more negative except for a dip (about 500 Pa wide) that occurred between - 700 and - 1800 Pa. The lowest overall magnitude was recorded in the dip at mid-manubrium. The vibration magnitudes also decreased as the middle-ear pressure was made more positive and were larger than those at negative pressures. R1 was only visible at negative and small positive middle-ear pressures, while R2 was visible for both positive and negative pressures. R2 split into multiple branches after the middle-ear pressure became slightly positive. No magnitude dip was visible for positive middle-ear pressures.The low-frequency vibration magnitudes at negative middle-ear pressures on the pars tensa were higher than those on the manubrium. R1 was not visible for large negative middle-ear pressures on the pars tensa. R2 appeared as a multi-peak feature on the pars tensa as well, and a higher-frequency branch on the posterior pars tensa appeared as a trough on the anterior pars tensa. The magnitude dip was not present on the pars tensa. The largest overall magnitude was recorded at the R2 peak on the posterior pars tensa.The results of this study expand on the findings of the step-wise pressurization experiments and provide further insight into the evolution of the vibration response of the eardrum under quasi-static pressures.

Cervical vestibular evoked myogenic potentials in 3-month-old infants: Comparative characteristics and feasibility for infant vestibular screening

Objective

We compared the characteristics of air-conducted sound cervical vestibular evoked myogenic potential (ACS-cVEMP) and bone-conducted vibration cVEMP (BCV-cVEMP) among 3-month-old infants with normal hearing and sensorineural hearing loss (SNHL), and healthy adults to explore the feasibility and optimal strategies for infant vestibular screening.

Methods

29 infants (58 ears) were divided into two groups according to hearing (group I: normal hearing ears; group II: SNHL ears), 20 healthy adults were defined as group III. The results of response rate, P13 and N23 latency, P13-N23 interval, amplitudes, and corrected interaural asymmetry ratio (IAR) were recorded and compared among three groups.

Results

The response rates of ACS-cVEMP in three groups were 88.89, 62.00, 100%, respectively. The P13 and N23 latencies, and P13-N23 interval did not differ significantly between group I and II (p = 0.866, p = 0.190, p = 0.252). A significant difference was found between group I and III (p = 0.016, p < 0.001, p < 0.001). No significant difference was observed in raw or corrected amplitude between group I and II (p = 0.741, p = 0.525), while raw and corrected amplitudes in group III were significantly larger than group I (p < 0.001, p < 0.001). For BCV-cVEMP, the response rates in three groups were 100, 86.36, 100%, respectively, No significant difference existed in the P13 and N23 latency, or P13-N23 interval between group I and II (p = 0.665, p = 0.925, p = 0.806), however, P13 and N23 latencies were significantly longer in group III than group I (p < 0.001, p = 0.018), but not in P13-N23 interval (p = 0.110). There was no significant difference in raw or corrected amplitude between group I and II (p = 0.771, p = 0.155) or in raw amplitude between group I and III (p = 0.093), however, a significant difference existed in corrected amplitude between group I and III (p < 0.001).

Conclusions

Compared with adults, 3-month-old infants with normal hearing presented with equivalent response rates, shorter P13 and N23 latencies, smaller corrected amplitudes, and a wider IAR range for both ACS and BCV-cVEMP. SNHL infants had equivalent response rates of BCV-cVEMP, lower response rates of ACS-cVEMP than normal hearing infants. When responses were present, characteristics of ACS and BCV-cVEMP in SNHL infants were similar with normal hearing infants. ACS combined with BCV-cVEMP are recommended to improve the accuracy of vestibular screening.

Swept-Tone Stimulus-Frequency Otoacoustic Emissions in Human Newborns

Several types of otoacoustic emissions have been characterized in newborns to study the maturational status of the cochlea at birth and to develop effective tests of hearing. The stimulus-frequency otoacoustic emission (SFOAE), a reflection-type emission elicited with a single low-level pure tone, is the least studied of these emissions and has not been comprehensively characterized in human newborns. The SFOAE has been linked to cochlear tuning and is sensitive to disruptions in cochlear gain (i.e., hearing loss) in adult subjects. In this study, we characterize SFOAEs evoked with rapidly sweeping tones in human neonates and consider the implications of our findings for human cochlear maturation. SFOAEs were measured in 29 term newborns within 72 hr of birth using swept tones presented at 2 oct/s across a four-octave frequency range (0.5–8 kHz); 20 normal-hearing young adults served as a control group. The prevalence of SFOAEs in newborns was as high as 90% (depending on how response “presence” was defined). Evidence of probe-tip leakage and abnormal ear-canal energy reflectance was observed in those ears with absent or unmeasurable SFOAEs. Results in the group of newborns with present stimulus-frequency emissions indicate that neonatal swept-tone SFOAEs are adult-like in morphology but have slightly higher amplitude compared with adults and longer SFOAE group delays. The origin of these nonadult-like features is probably mixed, including contributions from both conductive (ear canal and middle ear) and cochlear immaturities.