Background: Modern cochlear implants have integrated recording systems for\r\nmeasuring electrically evoked compound action potentials of the auditory nerve. The\r\ncharacterization of such recording systems is important for establishing a reliable\r\nbasis for the interpretation of signals acquired in vivo. In this study we investigated\r\nthe characteristics of the recording system integrated into the MED-EL PULSARCI100\r\ncochlear implant, especially its linearity and resolution, in order to develop a\r\nmathematical model describing the recording system.\r\nMethods: In-vitro setup: The cochlear implant, including all attached electrodes, was\r\nfixed in a tank of physiologic saline solution. Sinusoidal signals of the same\r\nfrequency but with different amplitudes were delivered via a signal generator for\r\nmeasuring and recording on a single electrode.\r\nComputer simulations: A basic mathematical model including the main elements of\r\nthe recording system, i.e. amplification and digitalization stage, was developed. For\r\nthis, digital output for sinusoidal input signals of different amplitudes were calculated\r\nusing in-vitro recordings as reference.\r\nResults: Using an averaging of 100 measurements the recording system behaved\r\nlinearly down to approximately -60 dB of the input signal range. Using the same\r\nmethod, a system resolution of 10 �µV was determined for sinusoidal signals. The\r\nsimulation results were in very good agreement with the results obtained from invitro\r\nexperiments.\r\nConclusions: The recording system implemented in the MED-EL PULSARCI100\r\ncochlear implant for measuring the evoked compound action potential of the\r\nauditory nerve operates reliably. The developed mathematical model provides a\r\ngood approximation of the recording system.
Loading....