A STUDY ON HEARING TEST WITH AN ACOUSTIC PROBE IN CONDUCTIVE DEAFNESS

Abstract

The main purpose of this study is to find a way predicting the degree of pathological changes in the conductive system of the middle ear by means of an acoustic probe in hearing examination.Acoustical analysis of hearing loss of air conduction in conductive deafness by means of the test with the acoustic probe is the other purpose of this study.The acoustic probe is attached to a bone conductor.Reference level of hearing test with the acoustic probe is hearing threshold obtained with the acoustic probe applied to the handle of malleus of normal ear.For hearing examination with the acoustic probe, 57 subjects were selected from the patients who showed conductive deafness in audiogram for air and bone conduction test.Following results were obtained:-1) Patients whose ossicular chain was disrupted and connected with granulation tissue showed hearing loss of 10_??_35 db by the hearing test with the acoustic probe. From this finding:the disruption of the ossicular chain could be previously known before middle ear operation was performed.2) In clinical otosclerosis, hearing loss measured with the acoustic probe showed the degree of stapedial fixation. It will be of great value to estimate the degree of stapedial fixation when, we take a choice of operative procedures, such as stapes mobilization or fenestration operation.3) Hearing threshold measured with the acoustic probe applied to the stapes was, on the whole, clinically equal to that applied to the handle of malleus with some exception which showed a deep notch between 1000 and 2000 cps.4) Mobility of the stapes and of the round window membrane was well maintained in many cases on which radical operation had been performed.5) Transmission loss of vibration due to disruption of the ossicular chain (connected with granulation tissue) was comparatively small (0-20db).6) Hearing curves measured with the acoustic probe were divided into two groups, namely high tone loss and low tone loss curve. Cause of difference between two forms of high tone loss and low tone loss curve was attributed to the change of impedance in the conductive system.7) Air conduction loss was divided into two parts by the hearing curve measured with.the acoustic probe. The hearing loss measured with the acoustic probe indicates the loss of transmission in the conductive system, and in cases without perforation of the ear drum the difference between the hearing curve with the acoustic probe and hearing curve of air conduction shows the loss of energy by transmitting the air-vibration to the malleus being caused by the pathological change in the ear drum and or the change of reaction given to the ear drum due to the impedance change in the conductive system.8) Difference between the hearing curve measured with the acoustic probe and the hearing curve of air conduction was larger in the range of low and middle tone than in the range of high tone in many cases without perforation of the ear drum.9) From the results above mentioned that hearing curves measured with the acoustic probe were divided into two groups, namely high tone loss and low tone loss curves. Difference between the hearing curve measured with the acoustic probe and the hearing curve of air conduction was larger in the range of low and middle tone than in the range of high tone in many cases, It is understood that forms of hearing curve of air couduction, viz. low tone loss, flat and high tone loss form, are principally made by the form of hearing curve measured with the acoustic probe, that is the change of impedance in the conductive system.