The Air-Bone Gap as a Criterion for Identification of Hearing Losses

Abstract

Research reports (6, '7, 9, 10, 11, 13) indicate that there is a greater incidence of hearing loss in the cleft palate population than in the normal population. These losses are primarily of the conductive type and they are most usually bilateral. It has been hypothesized that the losses orig— inate with infection and/or obstruction in the Eustachian tube and may subsequently involve the rest of the middle ear structures. Although the increased incidence of hearing loss has been recognized, there seems to be little agreement regarding the general extent of such losses. This lack of agreement most likely reflects the use by various investigators of different criteria and different testing techniques. Most studies concerning hearing loss in the cleft palate population have dealt only with the degree of air conduction loss relative to audi-ometric zero1 and not relative to bone conduction thresholds (4, 13). Few studies have considered the total air-bone gap. Miller (10) states that a bone conduction test was performed whenever the air conduction loss was greater than 25 dB but no results were reported. Halfond and Ballenger (6) reported that some of their cleft palate subjects demonstrated very slight air conduction losses. Significant differences were obtained , however, between air and bone conduction test results which suggested middle-ear pathologies in a group which had previously been defined as being " without hearing losses ". The primary purpose of the present project was to design a method for assessing the actual air-bone gap and to evaluate the usefulness of such a technique. Conventional audiometers, calibrated in terms of 1951 ASA standards, test bone conduction to a limit of ~10 dB. Such a level would appear to be sufficient to test bone conduction responses adequately. In Mr. Sweitzer, formerly clinical audiologist in the Department of Otolaryngology and Maxillofacial Surgery, University Hospitals, Iowa City, Iowa, is now associate audiologist in the