Measurements of stapes velocity in live human ears

Sound-induced stapes velocity (Vs) was measured intraoperatively in 14 patients undergoing cochlear implantation. All 14 patients had no history of middle-ear pathology, and their ossicular chains appeared normal on intraoperative inspection and palpation. The magnitude of the mean Vs (normalized by simultaneously-measured ear-canal sound pressure) was stiffness-dominated at frequencies below 1 kHz, increased up to ∼4 kHz, and then decreased at higher frequencies. The phase of the mean velocity was +0.2 periods at 0.3 kHz, and gradually became a phase lag at higher frequencies. The mean Vs measured in this study was similar to that of seven ears reported in the only other published study of live human measurements (Huber et al., 2001). We also made measurements of Vs in fresh cadaveric temporal bones using a technique identical to that used in live ears, including similar measurement angles and location. The mean Vs measured in the cadaveric ears under these conditions was similar to the mean Vs measurements in the 14 live ears. This indicates that middle-ear mechanics are similar in live and cadaveric ears. In addition, interspecies comparisons were made between our live human Vs and the Vs reported in different animal studies. There were some clear similarities in Vs across species, as well as differences. The primary interspecies differences were in the magnitude of the Vs as well as in the frequency of transitions in the magnitudes' frequency dependence from rising to flat or falling.