George T. Mencher

Auditory brain stem responses to air- and bone-conducted clicks in the audiological assessment of at-risk infants

Abstract Auditory brain stem responses [ABRs] to air and boneconducted clicks were used to assess the auditory status of 170 atirisk neonates. During the perinatal period, 20.6% [35/170 cases] of the at-risk infants failed ABRs to airconducted clicks at 30 dB nHL in at least one ear. Earspecific results indicated an initial failure rate of 15.0% [51/340 ears]. Approximately two-thirds (32/51 ears] of these initial failures showed purely conductive deficits, whereas the remaining one-third [I9/51 ears] involved suspected sensorineural components. Follow-up audiological evaluations were performed for 87.1% (148 cases] of these atirisk infants at 4 mo and/or 1 yr corrected age. Based on the initial tests and followup assessments, the tentative operating characteristics of ABRs to both air and boneconducted clicks for identification of sensor neural deficits in at-risk neonates were calculated. It was found that the ABR to boneconducted clicks yielded better specificity, predictive value of positive results, and overall efficiency. It is suggested that the ABR to boneconducted stimuli should be viewed as a valuable addition in the assessment of cochlear reserve in infants who fail a newborn auditory screening to airconducted stimuli.

Universal newborn screening: a dream realized or a nightmare in the making?

There is a very strong movement to develop universal newborn hearing screening. This effort is the end product of a long international research effort to determine the most effective means to screen newborns. Now that OAE and ABR together offer a superior mechanism to achieve universal screening, problems related to middle ear effusion, non-high-risk children and adequate resources for all aspects of identification, diagnosis and treatment have come to the fore. Further, what to do in the developing world is also a major problem as audiology embarks on this exciting new frontier. This paper discusses some of the issues, raises some concerns and offers a few small solutions.

Bilateral or unilateral amplification: is there a difference? A brief tutorial.

The literature contains many examples of the terms bilateral and binaural fittings used interchangeably (i.e., Carter, Noe & Wilson, 2001; Chmiel, et al, 1997; Dutt et al, 2002; Dermody & Byrne, 1995). In fact, however, humans are fit with hearing aids on either one ear (a unilateral fitting) or on both ears (a bilateral fitting), and generally, bilateral fittings have an impact on binaural hearing (the integration of two signals arriving from each ear independently). Standardization of this terminology should help to clarify future discussions and is essential to avoid confusion. The choice of when it is better to fit unilateral or bilateral hearing aids has been the subject of research, discussion and controversy for over fifty years (Carhart, 1946; Dirks & Carhart, 1962). It would seem a simple statement of fact and logic, that since humans have two ears, two ears wearing hearing aids would be better than one ear wearing one aid. However, evidence to date has not always been so factual, nor have the results been so logical. Dillon (2001) cites over 100 studies relevant to this topic. In 1999, 68% of hearing aid fittings in the U.S. were bilateral, up by 13% over the previous 10 years (Kochkin, 2000). Further, in 1999, prior to the modernized hearing aid plan, the United Kingdom (10 15%) and Finland (20%) fit fewer bilateral aids than Denmark (50 60%) and Norway (60%), with Sweden at 30% (Joint Nordic-British Project, 2001). Today, however, the number of bilateral fittings in England in some regions is 40% 80%. Why is there such variance? Shouldn’t everyone automatically receive and benefit from bilateral amplification? Unfortunately, the answer to that question is equivocal: some people benefit from two aids, and some do not. Generally speaking, hearing is the sensory system of import for oral communication, providing essential information about the environment that serves to alert and inform. Oft times these two functions interact. Thus, from a purely mechanical point of view, the ideal hearing aid enhances oral communication and permits perfect localization of sound in the environment. Consequently, tests for proper function of a hearing aid should include measures of speech intelligibility, sound quality (clarity, loudness, fullness, brightness, etc.), binaural redundancy (hearing the sound in both ears), noise tolerance and loudness discomfort levels as well as localization (in the vertical, lateral and horizontal planes). Further, consideration should be given to patient attitudes and physical comfort with the aid. The more normal the responses to all of these issues, the more satisfied the user and the more successful the fitting. Patients, as individuals, have unique auditory impairment and a unique set of personal, social, psychological and physical needs and characteristics. This means each fitting, and the results obtained from it, will be different, no matter how consistent the actual fitting process. Further, it should always be understood that any findings or opinions regarding the success or failure of any fitting may be completely independent of the actual benefit derived from the device itself. Measures of unaided versus aided threshold sensitivity are not good predictors of success. Two patients with similar degrees of threshold sensitivity often present with variant degrees of speech recognition in noise (Lyregaard, 1982). Patient attitudes, personality, the impact of the listening environment, perception of handicap and expectations from a hearing aid have all been significantly correlated to overall satisfaction and usefulness. So, even if formal audiometric measures do not show significant benefit from one fitting over another, the patient may feel otherwise (Humes, 1999; Cox & Alexander, 1999; Walden & Demorest, 1984). We know that audiometric measures do not reflect the value of a bilateral fitting. Real Ear Measurements, an excellent mechanism for determining the physical response of the ear itself, also do not adequately address questions of binaural interaction, how sound is perceived, comfort, or any of the myriad of psychological factors that could influence a successful outcome. Finally, current clinical procedures measure speech intelligibility and auditory localization. These excellent measures may not be entirely appropriate when assessing bilateral versus

Neonatal asphyxia, definitive markers and hearing loss.

A study of 56 severely asphyxiated infants (8 hearing impaired and 46 normally hearing) was designed to identify specific markers associated with asphyxia which could be related to hearing loss. Sixteen variables, including such items as: one- and five-minute Apgar scores, muscle tone, use of a ventilator, prolonged stay in the NICU, hypoxic-ischemic encephalopathy (HIE), other organ damage, and intra-uterine growth retardation (IUGR) were considered. Results suggested four factors related to asphyxia which are often found in the presence of hearing loss, but none of these was considered a definitive marker or predictor of such a disability. A combination of HIE, seizures, associated organ damage and IUGR should be considered a strong marker for the probability of a sensorineural hearing loss.

Challenge of Epidemiological Research in the Developing World: Overview: Reto a la investigacion epidemiológies en el mundo en desarrollo: Una revision

Listing the eight most important aspects of epidemiological research relevant to hearing loss, this paper reviews some of the difficulties encountered in trying to do such research in the developing world. Various research formats are discussed. This paper concludes with a review of what has been reported in the worlds literature about the incidence and prevalence of sensorineural hearing loss in children. The average finding from 34 nations is 1.368 hearing impaired per 1,000. Sumario Este reporte revisa algunas de las dificultades encon-tradas al intentar la realización de estudios epidemiológicos en el mundo en desarrollo, presentando, además, un listado de los ocho aspectos más impor-tantes de la investigación epidemiológica, relevantes para la sordera. El artiAculo concluye con una revisión de lo que ha sido reportado en la literature mundial sobre la incidencia y prevalencia de los trastornos sen-sorineurales en niños. El hallazgo promedio de alteraciones auditivas en 34 naciones es de 1.368/1000.

Prevalence of Sensorineural Hearing Loss in Children in Costa Rica: Prevalencia de la hipoacusia infantil en Costa Rica

There is very limited information available about hearing loss in children in Latin America and in Central America in particular. Costa Rica is a peaceful, well-organized country with an excellent health care system and a very good infrastructure of roads, programs, and services. It served as the site for a four-phase study to determine the incidence and prevalence rate for sensorineural hearing loss in children in that region of the world. The four phases involved (1) screening over 12,500 children in the public schools, (2) examining those enrolled at programs for the hearing impaired, (3) searching the community for children not in schools or special programs, and (4) an extensive questionnaire designed to obtain basic demographic data about hearing-impaired children in the country. Included were questions about age of identification, etiology, and hearing aid use. Results of phases 1 and 2 are reported here. Using a 1.368 per 1,000 live birth average (a figure reported for 36 nations), the projected number of hearing-impaired children in Costa Rica should be about 1,068. After concluding the first two phases of the study, it was determined that the actual number of hearing-impaired children in Costa Rica is between 1,174 and 1,274. That is a ratio oi between 1.50 and 1.63 hearing impaired per 1,000 live births, well within the ranges reported elsewhere. Since this is the first national study of a Latin American country, that information is significant suggesting that the general prevalence of hearing loss in that part of the world is the same as in the developed nations of Europe and North America. Existe información muy limitada en Latinoamérica, particularmente en Centro América, sobre la hipoacusia en niños. Costa Rica es un país pacífico, bien organizado, con un sistema de salud excelente y una buena infraestructura de carreteras, de programas y de servicios. Este fue el marco para un estudio de cuatro fases para determinar la incidencia y prevalencia de la hipoacusia sensorineural en niños de esa región del mundo. Las cuatro fases fueron (1) identification por tamizaje en alrededor de 12,500 niños en escuelas públicas, (2) evaluation de aquellos que assistían a un programa para hipoacúsicos, (3) búsqueda dentro de la comunidad de niños que no assistían a escuelas o a programas especiales, y (4) apliacación de un cuestionario extensivo para obtener datos demográficos básicos de los niños hipoacúsicos del país. Se incluyeron preguntas sobre la edad de identificatión, la etiología y el uso de auxiliares auditivos. Aquí se reportan los resultados de las fases 1 y 2. Utilizando el promedio de 1.368 por 1000 nacidos vivos (promedio reportado en 36 países), se esperaría que existieran 1,068 niños sordos en Costa Rica. Una vez concluidas las primeras dos fases del estudio, se determineó que el número actual de sordos en Costa Rica está entre 1, 172 y 1,274. Esto representa una proporción de 1.50 a 1.63 por cada 1000 nacidos vivos, información dentro del rango de otros reportes. Al ser este el primer estudio nacional de un país Latinoamericano esta informatión es significativa y sugiere que la prevalencia general de hipoacusia en esta parte del mundo es igual a la encontrada en las naciones desarrolladas de Europa y Norte América.

Maturation of behavioral response

The level of maturation of the auditory system markedly affects the results of all forms of infant hearing screening. The same test repeated in two weeks may yield significantly different results. The paper reviews some of the maturational changes which occur, considers male/female differences, and offers some normative developmental information about the preterm infant.

Intensive care nursery noise and its influence on newborn hearing screening

Numerous studies have recently reported the possible damaging effects noise exposure may have on premature infants. While noise levels appear to be within established damage risk criteria for an adult, there is little evidence to support the assumption that intensity levels and duration are similar for an infant population. It was the purpose of this study to measure sound pressure levels within an intensive care nursery and a series of isolettes and to report the behavioral pass/fail screening status of infants who were confined to those settings immediately after birth. It is suggested from the results of our study that due to the stimulus parameter used in behavioral testing, noise exposure is not an influencing factor in infant hearing screening.

Auditory Pathologies in Infancy

Auditory pathologies are generally grouped into two categories, hearing loss and central auditory dysfunction. Tennyson was certainly correct, however, in pointing out that the only language of the infant is the cry. Therefore, central auditory deficits involving auditory discrimination (ability to differentiate contrasting vowels and consonants), auditory association (ability to relate meaning to sound), auditory closure (ability to fill in missing sounds), auditory memory (ability to recall an auditory sequence), auditory localization (spatial orientation), and auditory figure—ground perception (the ability to isolate related sounds from their background) do not really appear as problems until the infant has become the toddler and language, mobility, personality, and potty training become the bane of mother’s existence. Therefore, the focus of this chapter is on pathologies resulting in hearing loss. That is not to say that central auditory dysfunction does not occur, or is any less important a topic for discussion. It does say, however, that our diagnostic procedures (binaural fusion, filtered speech, alternating speech, and competing messages) require a far more sophisticated approach than can be utilized with the infant. Perhaps even more important, although it is nice to know the locus of a lesion, that knowledge will have little effect on the treatment the child and the family would receive during those early months of life, regardless of the type of auditory pathology present.