Influence of different preamplifier bandpass cutoff frequencies on the basic pattern of sympathetic nerve discharge.

Autospectral analysis reveals that most of the power in sympathetic nerve discharge (SND) is contained between 1 and 10 Hz in anesthetized animals. The synchronized discharge bursts of the fibers comprising sympathetic nerves are usually recorded after capacity-coupled preamplification with a bandpass of 1-1000 Hz. However, cardiac- and respiratory-related movement artifacts can adversely affect the signal when this wide bandpass (1-1000 Hz) is used. To eliminate the influence of movement artifacts on the basic pattern of SND, we have routed the output of a preamplifier (bandpass 30-1000 Hz) through a frequency analyzer which measures the frequency of spike discharges exceeding a threshold voltage. After the impulses are rectified and integrated a smooth envelope of the synchronized sympathetic nerve discharge bursts is produced. The following observations have been made: 1) The autospectra of SND constructed after either wide-band preamplification or 30-1000 Hz using the frequency analyzer are similar and 2) Narrow-band preamplification (30-1000 Hz) eliminates movement-related artifacts which adversely influence the sympathetic nerve signal. These results indicate that the basic pattern of SND can be faithfully recorded after narrow-band preamplification which eliminates potential movement-related artifacts.