Wideband absorbance measures in neonates and young infants

Abstract

Evaluation of middle ear status in young infants is a challenge in both screening and diagnostic contexts due to a lack of valid and objective tools of middle ear assessment (Kei & Zhao, 2012). The standard tools used to determine the middle ear status in older children are neither efficient nor accurate in evaluating young infants. Wideband absorbance (WBA) is recommended as a tool for middle ear assessment in young infants due to its time efficiency, reliability, objectivity and ability to provide clinical information over a range of frequencies. Despite its clinical application in the assessment of middle ear function in older children, investigation into the use of WBA with young infants has been inadequate. Development of normative data and evaluation of WBA in this population have been limited. The limitation of using the distortion product otoacoustic emissions (DPOAE) test as a reference standard for evaluation of middle ear status has been acknowledged. Hence, further consideration must be afforded to evaluation of WBA using more robust reference standards in young infants. Despite the high prevalence of conductive hearing loss in Australian Aboriginal children, limited research has occurred into the investigation of middle ear function in the neonatal period. Hence the present study explored the development of normative data and evaluation of test performance of WBA, developmental and pathologic effects in middle ear function and the feasibility of using WBA as an adjunct tool in newborn hearing screening (NHS) programs in an Australian context. The present research study aimed to: (1) determine the prevalence of middle ear dysfunction and conductive hearing loss in neonates referred through a NHS program in Australia (2) establish normative WBA measures in healthy neonates with normal middle ear function (3) compare test performance of WBA against nine reference standards (4) compare WBA between Australian Aboriginal and Caucasian neonates and (5) compare WBA in healthy newborns and infants aged 1, 2, 4 and 6 months. A chart review of 234 infants referred from a NHS program in North Queensland was conducted. Further, 204 neonates were tested using automated auditory brainstem response (AABR), high frequency tympanometry (HFT), acoustic stapedial reflex (ASR), transient evoked otoacoustic emissions (TEOAE), DPOAE and WBA. The neonates were tested prior to their discharge from the hospital. In addition, a total of 36, 30, 33 and 30 infants were seen at 1, 2, 4, and 6 months of age, respectively. These infants were tested using HFT, DPOAE and WBA. The results revealed that conductive hearing loss was common among infants referred through NHS. Australian Aboriginal infants had significantly higher rates of middle ear pathology and conductive hearing loss at birth and showed poor resolution of middle ear pathology over time compared to non-Aboriginal infants. Use of a test of middle ear function (eg. WBA) as an adjunct to the screening tool to facilitate management and prioritisation of infants for further testing was recommended (Chapter Two). Normative ambient pressure WBA data were established for 66 neonates who passed a test battery of AABR, HFT, ASR, TEOAE and DPOAE tests. There was a significant difference in WBA across frequencies from 250 to 8000 Hz (Chapter Three). Test performance of WBA was compared across four single tests and five test battery reference standards in 192 neonates. The test performance of WBA against the test battery reference standards was better than that against single test reference standards (Chapter Four). Despite equal pass rates as determined by a test battery of HFT and DPOAE, the WBA of Aboriginal neonates who passed the test battery was significantly lower suggesting that Aboriginal neonates had more significant outer/middle ear conditions than Caucasian neonates. WBA appeared to be more sensitive to middle ear status than test battery comprising HFT and DPOAE (Chapter Five). In a cross sectional study of infants, developmental effects were evident during the first six months of life, with WBA reducing with age. Although data from the study could be used as reference standard for detecting middle ear disorders, further development of age-specific normative WBA was recommended (Chapter Six). Overall, the present research study demonstrated WBA to be a feasible tool for evaluation of middle ear function in neonates and young infants (Chapters Three, Four, Five). In conclusion, this thesis has evaluated WBA in neonates and young infants and has enhanced the minimal literature available concerning normative data, test performance, developmental changes and application in targeted groups such as Australian Aboriginal infants where the prevalence of otitis media is very high. The normative data developed in the study may be used as a reference for objective evaluation of the sound conduction pathways (outer and middle ear) in neonates and young infants. Ultimately, this thesis contributes to the application of WBA as a clinical tool in the assessment of middle ear function during screening or diagnostic assessment of neonates and young infants.