It is recognized that a mild-moderate hearing impairment in young infants prior to 6 months of age can cause speech and language deficits. Unfortunately, middle ear dysfunction in this age group, which can result in a mild-moderate conductive hearing loss, is not uncommon. Currently used screening tests are inadequate in measuring middle ear function, especially in the detection of a mild conductive hearing loss. Conventional (226 Hz) tympanometry gives unreliable results in infants below the age of 7 months. The literature has shown some promise in the use of a higher frequency probe tone (such as 1000 Hz) in tympanometry when assessing neonates. Although 1,000 Hz tympanometric data for newborn babies are presently available, there have not been any reports in the literature, which describe the characteristics of the tympanograms of 3- week-old babies. Undoubtedly, postnatal maturational changes of the middle ear will result in changes in tympanometric findings. However, there are yet no reports, of a sizeable subjects number (N> 100) investigating the tympanometric findings of newborn babies with age. The present study aimed to describe the characteristics of the conventional (226Hz) tympanometry and 1 kHz tympanometry of newborns and 3- week-old infants, in relation to the developmental changes in their middle ears.
Transient evoked otoacoustic emission (TEOAE) and tympanometry (226 Hz and 1 kHz) testing were performed, using a Madsen Capella OAE / middle ear analyzer on 151 (69 male, 82 female) healthy full-term neonates (mean age of 1.57 days, SD = 0.95 days) and repeated on 118 (55 male, 63 female) 3-week-old babies (mean age of 22.46 days, SD = 1.21 days). The TEOAE outcomes (pass / fail) were compared against the tympanometric findings. The TEOAE and tympanometric test results obtained from the two age groups were compared.
The results showed a significantly increased proportion of TEOAE pass outcomes [94.1% (at 3 weeks) versus 69.92%(at birth)] and a higher proportion of 226 Hz single-peaked [67% (at 3 weeks) versus 47%(at birth)] relative to double-peaked tympanograms. In addition, 1 kHz tympanometry performed on newborns and the 3-week-babies with a TEOAE pass demonstrated a predominance of Type 1 (single distinct peak), and more Type 1 and Type 2 (mild rise but mostly down sloping) tympanograms taken together (up to 91%). In contrast, Type 3 (flat or sloping down) tympanograms were predominant (up to 71.43%) in babies who failed the TEOAE test.
A rough estimate of the performance of the 1 kHz tympanometric test using TEOAE as a surrogate - gold standard revealed relatively high specificity (82.0%) but a low sensitivity (39.5%) of the test for newborn babies. However, its performance improved to 90.1 % (specificity) and 75.0% (sensitivity) in 3-week-old babies.
The tympanometric changes in the intervening 3 weeks were accompanied by statistically significant changes in some tympanometric parameters. For instance, a significant group effect for admittance at + 200 daPa (Y200) (mmho) and peak compensated static admittance (Ypc) (mmho) was found, with the 3-week-old babies showing higher Y200 and Ypc than newborns. A significant group effect for ear canal pressure (Pec) (daPa) was also observed, with newborns having greater ear canal pressure than the 3-week-old babies. Overall, there was no significant gender effect and group x gender interaction (birth versus 3 weeks) for Y200, Ypc and ear canal pressure.
Based on the range of differential 1000 Hz tympanometric morphology, it may be concluded that the 1000 Hz tympanometry would be a suitable test for many measuring the middle ear function of newborn and especially 3-week-old babies. Furthermore, the maturation of the auditory system of the neonates has resulted in significantly different tympanometric results between the two subject groups.