Measurements of stapes velocity in live human ears

Abstract

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 approximately 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.

Fig. 1

Mean stapes velocity (Vs) magnitude in live (solid line) and cadaveric (dashed line) ears as reported by Huber et al. (2001), Asai et al. (1999), respectively (taken from Chien et al., 2006). The magnitude difference below 1.5 kHz is statistically significant (Huber et al., 2001).

Fig. 2

The change in stapes velocity (ΔVs) in one representative temporal bone when the measurement angle was changed from large to small with respect to the axis of piston-like stapes motion (taken from Chien et al., 2006). All measurements were normalized to an angle of 50°. Top panel: magnitude. Bottom panel: phase. Note that increasing the angle results in a decrease in magnitude of Vs below 2 kHz [modified from Chien et al., 2006].

Fig. 3

(A) Photograph of an intraoperative view of the stapes during Vs measurement (right ear). The stapes head is shown with a naturally reflective spot where Vs measurements were made. (B) Schematic axial view of the measurement setup in live Vs measurements. (C) Schematic axial view of the measurement setup in cadaveric Vs measurements. Note that even though the measurement direction is aimed at the head of stapes, some of our cadaveric Vs measurements were made at the posterior crus, as indicated in the text.

Fig. 4

Normalized Vs measured in 14 live ears (dashed lines), as well as the mean (solid line) and 95% CI around the mean (shaded areas). Top panel: magnitude. Bottom panel: phase.

Fig. 5

The mean and 95% CI of the Vs magnitude measured in 14 live patients in the present study (solid line and shaded areas), compared to the published mean live Vs by Huber et al., 2001 (dot-dashed line).

Fig. 6

Normalized Vs measured at the posterior crus in 13 cadaveric temporal bones (dashed lines), as well as the mean (solid line) and 95% CI around the mean (shaded areas). Top panel: magnitude. Bottom panel: phase.

Fig. 7

Normalized Vs measured at the head of stapes in seven cadaveric temporal bones (dashed lines), as well as the mean (solid line) and 95% CI around the mean (shaded areas). Top panel: magnitude. Bottom panel: phase.

Fig. 8

Change in Vs when measured from head of stapes vs. posterior crus in seven cadaveric temporal bones (dashed lines). The mean change in Vs (solid line) as well as its 95% CI (shaded areas) are also shown. Top panel: magnitude. Bottom panel: phase. Note the Vs measured at the head of stapes is higher than the Vs measured at the posterior crus, but the difference is only statistically significant at higher frequencies.

Fig. 9

The mean and 95% CI of the Vs measured at the head of stapes in seven cadaveric temporal bones (solid black line and shaded areas), compared to the mean live stapes velocity in the present study (dashed line). Top panel: magnitude. Bottom panel: phase. There were no statistically significant differences between the live and cadaveric data (see also Table 1)

Fig. 10

Comparison of Vs measurements in five species (modified from Fig. 8 in Rosowski et al., 1999). The chinchilla data is taken from Ruggero et al. (1990); the cat data is from Guinan and Peake (1967); the gerbil data is from Ravicz et al. (2008) and the guinea pig data is from Manley and Johnstone (1974). Two sets of human Vs measurements are used: the first is from the present study in live human, and the second is from Kringlebotn and Gundersen (1985), labeled “Human cadaveric”] where cadaveric human temporal bones were used. Data from present study include our mean live human Vs (labeled “Human live uncorrected”) as well as a “corrected” live human Vs (labeled “Human live corrected”) where a measurement angle correction is applied to minimize the effect of measurement angle on the measured Vs magnitude (Chien et al., 2006). Measurement in guinea pig and gerbil at frequencies >20 kHz are not shown.