The benefit of the reverse transfer function in the fitting process of the Vibrant Soundbridge middle ear implant

Reverse transfer function (RTF) measurement of the Vibrant Soundbridge (VSB) middle ear implant (MEI) is an objective method to evaluate the function of the VSB and can be used to adjust the Connexx value required to reach the optimal VSB gain during fitting sessions.

To investigate the sound transfer of the VSB with the RTF in implanted patients and evaluate the role of RTF in the fitting process of the VSB.

This was a prospective study including patients undergoing VSB implantation and RTF recording from March 2007 to October 2010. Three parameters were analyzed. 1) RTF: energy transmitted in dB SPL to ear canal by retrograde vibration of malleus and tympanic membrane. 2) Connexx value: level of amplification in dB delivered by the audioprocessor to the floating mass transducer (FMT). 3) VSB gain: difference in dB HL in free field between aided and unaided conditions.

Ten patients fitted the criteria. RTF measurements revealed a significant inter-patient disparity. We adjusted the Connexx value according to the RTF value to obtain an optimal VSB gain within comfort levels. The VSB gain and RTF with Connexx value were closely correlated together. The mean VSB gain and RTF value converted to dB HL had comparable values.