Probe-Tube Microphone Measures in Patients with Open-Mastoid Surgery: Real-Ear-to-Coupler Differences and Real-Ear Unaided Responses

Abstract

Real-ear-to-coupler differences (RECDs) and real-ear unaided responses (REURs) were measured using a probe-tube microphone system in 15 patients who underwent open mastoid surgery. The results show that RECDs are significantly smaller at higher frequencies (1.5, 2.0, 3.0, 4.0 and 6.0 kHz) in mastoid ears. The intrasubject variability of RECDs measures in these patients is on average 2.6 dB larger than for controls. For REURs, mastoid surgery significantly reduced the mean peak resonant frequency without affecting the amplitude and bandwidth. In operated ears, mean resonant frequency is by a factor of 1.4 lower than that for normal ears. Reduced responses (negative gains) at frequencies above the resonance peak occurred in 7 out of the 15 patients. These reduced responses corresponded to the smaller RECD at the middle and high frequencies. The results support the need for individual RECD measures to be made in operated ears instead of using average values from normal subjects. Otherwise, real-ear measures of the aided response should be made for each patient with open-mastoid cavity and the fitting should be done in terms of the target response at the eardrum rather than by defining a target insertion gain.