Clinical Equipment for Measurement of Middle-Ear Muscle Reflexes and Tympanometry

The range of applications of middle-ear muscle reflex measurements is reviewed. Different methods for measuring the relative impedance change, including extratympanic manometry and a method of tympanometry, are discussed in relation to the authors' equipment, which is of four main kinds: the intra-aural reflex indicator, a pressure transducer system for extratympanic manometry, a system for changing and monitoring the air pressure in the ear canal for tympanometry, and a four-channel recorder. The authors have found that intra-aural reflex thresholds are highly similar, whether determined by changes in amplitude or amplitude-phase. Furthermore, extratympanic manometry performed by the authors' method does not show reflex thresholds to be as sensitive as do the other methods. In studies of reflex growth and preliminary measurements of the decay of the stapedial reflex, amplitude-phase method seems superior because of larger responses. The method of tympanometry for measuring ear-drum mobility and the status of the ossicular chain and middle-ear cavity will identify certain pathological conditions of the middle ear. We have found 800 Hz to be the preferred working frequency for this measurement.