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Articles in PresS, published online ahead of print October 3, 2002
Am J Physiol Regu Physiol, 10.1152/ajpregu.00002.2002
Submitted on January 7, 2002
Accepted on September 21, 2002
1 Department of Chemistry and Physics, Asbury College, Wilmore, KY, USA; Department of Physiology, University of Kentucky College of Medicine, Lexington, KY, USA
2 Department of Physiology, University of Kentucky College of Medicine, Lexington, KY, USA; Center for Biomedical Engineering, University of Kentucky, Lexington, KY, USA; Department of Biology, Asbury College, Wilmore, KY, USA
3 Department of Physiology, University of Kentucky College of Medicine, Lexington, KY, USA
4 Center for Biomedical Engineering, University of Kentucky, Lexington, KY, USA
* To whom correspondence should be addressed. E-mail: deburgess{at}asbury.edu.
The object of this study is to explore the functional association between renal sympathetic nerve activity, or nerve traffic (NT), and arterial blood pressure (BP)in the very low frequency range (i.e., < 0:1 Hz). Rats were instrumented for chronic recordings of NT and BP (n = 6). In addition we used data from a group of rats instrumented for BP alone (n = 17). Data were collected at 10kHz for 2-5 hours and subsequently compressed to a 500Hz signal. Wavelet transforms were calculated from data epochs up to one hour in length. From these wavelet transforms, we obtained probability distributions for fuctuation amplitudes over a range of time scales. Secondly, we computed the cross-wavelet power spectrum between NT and BP in order to detect the ccurrence in time of large-amplitude-transient events that may be important in the regulation of BP by the sympathetic nervous system. Finally, we computed a time sequence of cross-correlations between NT and BP from overlapping data segments in order to follow the correlation between NT and BP in time. Our wavelet analysis revealed that NT and BP fuctuations both follow similar self-similar scaling relationships. In other words, both NT and BP fluctuations exhibit a certain type of power law behavior. The presence of scaling points to underlying dynamics occurring over a wide range of scales. This scaling behavior is related to large amplitude events which contribute to the very low frequency variability of NT and BP. During many of these transient events, there is a strong correlation between NT and BP. These strong correlations and the uniformity in scaling give evidence for a functional connection between these two signals at frequencies where we had found no connection using spectral coherence.
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