Effects of analog filtering on brain stem auditory-evoked potentials in dogs

Effects of analog filter frequency on brain stem auditory-evoked potentials (BAEP) were investigated in 7 non-sedated dogs. The BAEP were recorded successively at various low-pass (LP) and high-pass (HP) filter frequency settings. The analog filters had a rolloff of 6 dB/octave. Decrease of LP filter frequency from 30 khz to 100 Hz caused prolongation of the peak latency and reduction of the peak-to-peak (from a positive peak to the following trough) and absolute (from a positive peak to the baseline) amplitudes for aU peaks, except the peak latency for P5 and the absolute amplitude for P4. Changes in these variables were statistically significant (P < 0.05) at different cutoff frequencies specific for the individual peaks. The inter-peak latency between P1 and P4, and P4/P1 peak to-peak amplitude ratio were not changed significantly. At the lowest LP filter frequency of 100 Hz, positive peaks (fast waves) seemed to be superimposed on a slow positive wave (slow wave). In contrast, increase of HP filter frequency from 0.53 to 160 Hz did not result in significant changes for any peaks, except for reduction in the absolute amplitude of P4. The various effects of LP filter frequency and negligible effects of Hp filter frequency on individual peaks may be attributable to their frequency composition and/or elimination of the slow wave at higher HP filter frequency settings. On the basis of our results, LP filter setting of 3 kHz and HP filter setting of less than or equal to 53 Hz are recommended for recording of BAEP in dogs. These settings sufficiently attenuate unwanted high-frequency artifacts, are adequate for recording of fast and slow waves, and have only slight effects on configurations, peak latencies, and amplitudes.