FIG. 2.

CM absolute thresholds and threshold changes as a result of middle-ear fluid volume. A Across-animal (n = 5 ears) mean CM threshold as a function of frequency; error bars indicate ±1 SD. As the volume of middle-ear fluid was increased from 0.5 mL, the CM thresholds increased. B The data in panel A were further analyzed by computing the MEE-induced change in CM thresholds relative to the baseline with no middle-ear fluid in three frequency ranges: low (0.25–1 kHz), medium (1–3 kHz), and high (3–8 kHz). With 0.5 and 0.75 mL of fluid in the middle ear, there was little change in the CM thresholds. For fluid volumes greater than 1.0 mL, there were substantial increases in CM thresholds in all frequency ranges, indicating a CHL. In the low-frequency range, the maximum change in CM thresholds (18 dB) was reached by 1.0 mL of fluid in the middle-ear space. Large increases in CM thresholds for medium- and high-frequency sounds were observed when 1.0 mL of fluid was present in the middle-ear space, with near maximum threshold increases occurring when volumes of 1.25 mL or more of fluid were present (100 % TM area–fluid contact). Maximum threshold increases for medium- and high-frequency ranges were 30 and 42 dB, respectively. Baseline measurements are not shown as they are not significantly different from 0.5-mL fluid instillation values for CM thresholds.