Examination of Normal and Pathologic Middle Ears by Acoustic Time-Domain Reflectometry.

摘要

The technique of time-domain reflectometry (TDR), commonly used to locate and identify distant impedance mismatches on electrical transmission lines, was utilized in an attempt to accomplish the time-domain equivalent of acoustic impedance measurements on normal and a variety of pathologic middle ears. An acoustic transmission line and transceiver were used to deliver acoustic impulses to the middle ear through the external auditory canal and display the reflected acoustic signals on a CRO. No recognizable difference between the reflectograms of otosclerotic and normal ears was seen, and the reflections from ears with ossicular discontinuity were inconsistently different from those of normal ears. Perforated ears and ears containing fluid, however, did provide characteristic reflectograms. Several simple physical models of the external auditory canal and middle ear were tested with the acoustic reflectometer and found to provide responses similar to those from real ears. Transient responses of simple electrical analogs of normal and fluid-filled ears were generated on a computer, and waveforms similar to those seen in the corresponding acoustic reflectograms were obtained. Present short-comings and potential strengths of acoustic TDR are discussed, and several means of improving its precision are suggested. (Author)