Chaotic behavior of renal sympathetic nerve activity: effect of baroreceptor denervation and cardiac failure

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Abstract
Nonlinear dynamic analysis was used to examine the chaotic behavior of renal sympathetic nerve activity in conscious rats subjected to either complete baroreceptor denervation (sinoaortic and cardiac baroreceptor denervation) or induction of congestive heart failure (CHF). The peak interval sequence of synchronized renal sympathetic nerve discharge was extracted and used for analysis. In control rats, this yielded a system whose correlation dimension converged to a low value over the embedding dimension range of 10–15 and whose greatest Lyapunov exponent was positive. Complete baroreceptor denervation was associated with a decrease in the correlation dimension of the system (before 2.65 ± 0.27, after 1.64 ± 0.17; P < 0.01) and a reduction in chaotic behavior (greatest Lyapunov exponent: 0.201 ± 0.008 bits/data point before, 0.177 ± 0.004 bits/data point after, P < 0.02). CHF, a state characterized by impaired sinoaortic and cardiac baroreceptor regulation of renal sympathetic nerve activity, was associated with a similar decrease in the correlation dimension (control 3.41 ± 0.23, CHF 2.62 ± 0.26; P < 0.01) and a reduction in chaotic behavior (greatest Lyapunov exponent: 0.205 ± 0.048 bits/data point control, 0.136 ± 0.033 bits/data point CHF, P < 0.02). These results indicate that removal of sinoaortic and cardiac baroreceptor regulation of renal sympathetic nerve activity, occurring either physiologically or pathophysiologically, is associated with a decrease in the correlation dimensions of the system and a reduction in chaotic behavior.