Effects of ear-canal static pressure on pure-tone thresholds and wideband acoustic immittance

Wideband acoustic immittance (WAI) measures provide information about middle-ear function across the traditional audiometric frequency range from 0.25 to 8.0 kHz. Recent studies have found that WAI is effective in predicting the presence of conductive hearing loss (CHL). It is not known whether WAI can accurately estimate the degree of threshold shift caused by CHL.

The purpose of the present study was to evaluate the relationship between changes in pure-tone threshold and changes in wideband absorbance and acoustic conductance levels induced by positive and negative ear-canal static pressure.

Twenty young adult subjects with normal hearing and a negative history of middle-ear disorders participated in the study.

Experimental pure-tone thresholds at 0.5 and 2.0 kHz were estimated by using a three-interval, three-alternative forced-choice adaptive psychometric procedure under three conditions: ambient ear-canal pressure, +200 daPa static pressure, and -200 daPa static pressure. Wideband absorbance and conductance were obtained in the same subjects by using a Welch Allyn prototype diagnostic middle ear analyzer. Changes in pure-tone threshold from the ambient pressure condition to the static pressure condition were evaluated by using a paired-samples t test and Pearson product-moment correlation.

Wideband middle-ear absorbance and conductance at ambient pressure in this study were consistent with published data in adults with normal hearing. The mean change in threshold at 0.5 and 2.0 kHz with +200 daPa or -200 daPa ear-canal static pressure was similar to the mean change in absorbance and conductance levels in the same conditions. However, there was one statistically significant difference between the shift in pure-tone threshold and the change in conductance level for the +200 daPa pressure condition for 2.0 kHz, with the change in threshold being 1.5 dB greater than the change in conductance level (t = 2.39, p = 0.03). In contrast to the good performance of WAI measures in predicting mean threshold shifts caused by ear-canal pressure, the shifts in WAI were not correlated with threshold shifts. Thus WAI was not well suited to predict individual threshold changes caused by ear-canal static pressure.

For the conditions of this study, results suggest that mean change in absorbance or conductance level caused by ear-canal static pressure of +200 daPa or -200 daPa provides a good estimate of the change in pure-tone threshold in the same conditions. However, individual threshold change was not accurately predicted by the change in absorbance or conductance level.