Partial spectral analysis of cardiac-related sympathetic nerve discharge

We have studied the relationship between pulse synchronous baroreceptor inp ut (represented by the arterial pulse, AP) and the cardiac-related rhythm i n sympathetic nerve discharge (SND) of urethan-anesthetized cats by using p artial autospectral and partial coherence analysis. Partial autospectral an alysis was used to mathematically remove the portion of SND that can be dir ectly attributed to the AP, while partial coherence analysis was used to re moved the portion of the relationship between the discharges of sympathetic nerve pairs that can be attributed to linear AP-SND relationships that are common to the nerves. The ordinary autospectrum of SND (AS(SND)) and coher ence functions relating the discharges of nerve pairs (Coh(SND-SND)) contai ned a peak at the frequency of the heart beat. When the predominant mode of coordination between AP and SND was a phase walk, partialization of the au tospectra of SND with AP (AS(SND/AP)) left considerable power in the cardia c-related band. In contrast, when the predominant mode of coordination betw een AP and SND was phase-locking, there was virtually no cardiac-related ac tivity remaining in AS(SND/AP). Partialization of Coh(SND-SND) with AP redu ced the peak coherence within the cardiac-related band in both modes of coo rdination but to a much greater extent during phase-locking. After barorece ptor denervation, CohSND-SND at the cardiac frequency remained significant, although a clear peak above background coherence was no longer apparent. T hese results are consistent with a model in which the central circuits cont rolling different sympathetic nerves share baroreceptor inputs and in addit ion are physically interconnected. The baroreceptor-sympathetic relationshi p contains both linear and nonlinear components, the former reflected by ph ase-locking and the latter by phase walk. The residual power in AS(SND/AP) during phase walk can be attributed to the nonlinear relationship, and the residual peak in partialized nerve-to-nerve coherence (Coh(SND-SND/AP)) ari ses largely from nonlinearities that are common to the two nerves. During b oth phase walk and phase-locking, in addition to common nonlinear AP-SND re lationships, coupling of the central circuits generating the nerve activiti es may contribute to Coh(SND-SND/AP) because significant Coh(SND-SND) was s till observed following baroreceptor denervation.