Two types of stapedectomy, wire-fat graft and teflon piston, were studied in cats by measurement of cochlear microphonics at the round window in order to determine how the operating characteristics of the transducer might be affected by structural alterations. The wire-fat graft produced a loss of sensitivity that increases progressively with frequency. The teflon piston operation produced a flat loss of sensitivity which was greater for low tones and less for high tones than seen with the wire-fat graft. Neither operation caused any reduction in dynamic range. Evidence indicates that all of the changes produced are mechanical rather than degenerative or metabolic. In other words, a high tone conduction type hearing loss without loudness distortion is characteristic of the wire-fat graft operation. A flat conduction type hearing loss is characteristic of the teflon piston operation. The processes of injury, healing and inflammation may, of course, introduce additional changes.
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