Refining Measurements of Power Absorbance in Newborns: Probe Fit and Intrasubject Variability

Abstract

Because unresolved debris in the ear canal or middle ear of newborns may produce high false positive rates on hearing screening tests, it has been suggested that an outer/middle ear measure can be included at the time of hearing screening. A potential measure is power absorbance (absorbance), which indicates the proportion of power in a broadband acoustic stimulus that is absorbed through the outer/middle ear. Although absorbance is sensitive to outer/middle dysfunction at birth, there is large variability that limits its accuracy. Acoustic leaks caused by poor probe fitting further exacerbate this issue. The objectives of this work were to: (1) develop criteria to indicate whether a change in absorbance occurs in association with probe fit; (2) describe the variability in absorbance due to poor fitting; and (3) evaluate test-retest variability with probe reinsertions, excluding poor fits.Design: An observational cross-sectional design was used to evaluate changes in absorbance due to probe fit and probe reinsertion. Repeated measurements were recorded in 50 newborns (98 ears) who passed TEOAE screenings and were <48 hours of age. One absorbance measurement was chosen as the baseline that served as a best-fit reference in each ear. Changes in absorbance, called absorbance probe-fit Δ, were calculated relative to the baseline in each ear. Correlations were assessed between the absorbance probe-fit Δ and low-frequency absorbance, impedance magnitude, impedance phase, and equivalent volume, to determine which measures predicted poor fits. Criteria were derived from the strongest of these correlations and their performance was analyzed. Next, measurements with poor/leaky fits were identified, and the changes in absorbance that they introduced were analyzed. Excluding the poor fits, test-retest differences in absorbance, called reinsertion Δ, were determined. Variability was assessed using the SDs associated with absorbance, absorbance probe-fit Δ, and reinsertion Δ. Results:Based on the analysis of 12 moderate-strong correlations, the following criteria were adopted to identify measurements with poor fits:(1) impedance phase-based criterion (500 to 1000 Hz) > −0.11 cycles and (2) absorbance-based criterion (250 to 1000 Hz) > 0.58. Poor-fit measurements introduced statistically significant increases in absorbance up to 0.1 for 1000 to 6000 Hz, and up to 0.4 for frequencies <1000 Hz. Reinsertion Δ were ≤0.02, and were significant for 500 to 5000 Hz. The SDs of absorbance probe-fit Δ were greatest and similar to overall absorbance SD in the low frequencies. Separately, the SDs of reinsertion Δ were also greatest and similar to low-frequency absorbance SD. Conclusions:Poor probe fits introduced the greatest inflation in absorbance for frequencies < 500 Hz, and a smaller but significant inflation for higher frequencies, consistent with controlled experiments on acoustic leaks in adults. Importantly, inflation of absorbance in diagnostically sensitive 1000 to 2000 Hz may impact its clinical performance. Test-retest with pr...

Use of Wideband Acoustic Immittance in Neonates and Infants

“…To illustrate the use of normative WBA area, a subset of the data that were previously described by AlMakadma and Prieve 38 were used for the construction of normative WBA area plots. The 10th and 90th percentile values were computed using 532 WBA repeated measurements from 84 newborn ears with normal hearing, indicated by transient-evoked OAE (TEOAE) hearing screening tests.…”

“…55 In newborns, loose probe fitting has been associated with large artificial increase in absorbance at frequencies < 1,000 Hz, and smaller but significant increases at frequencies between 1,000 and 6,000 Hz. 38 Such artificial increases may negatively impact clinical assessment of sound conduction; for example, a measurement with poor fitting maybe erroneously classified as normal due to artificially increased absorbance into the normal range, whereas in fact the sound conduction in the outer/middle ear may be abnormal.…”

“…Another approach is to use criteria based on absorbance, and other WAI measures, in the low frequencies where leak-related changes are most obvious. Recent work by AlMakadma and Prieve 38 showed that changes in absorbance in association with loose probe fitting were best predicted by low-frequency absorbance and low-frequency impedance phase. They recommended that leak-related inflation in absorbance can be determined whenever absorbance average in the 250- to 1,000-Hz frequency interval is greater than 0.58 and impedance phase average in the 500- to 1,000-Hz interval is greater than −0.11 cycles.…”

“…Two absorbance and corresponding impedance phase measurements (brown-colored solid lines) fall within the green-outlined boxes are examples of well-fitted probe tips, and the three measurements (shown in different degrees of blue-colored solid lines) that fall within the red-outlined boxes are examples of affected measurements due to poor/leaky probe fits. It should be noted that the criteria suggested by AlMakadma and Prieve 38 have been tested for ears with normal outer- and middle-ear sound conduction, and that efforts to validate the use of these criteria in ears with abnormal sound conduction are underway.…”

“…High test–retest variation in low-frequency absorbance when acoustic leaks are present has been reported. 32 38…”