Synchrony analysis between blood pressure and sympathetic nerve signal inhibited by atrial receptor stimulation in Wistar rats.

Recently attempts have been made to analyse blood pressure (BP) and renal sympathetic nerve activity (RSNA) to determine how patterns contained within them might reflect control by the autonomic nervous system. To date, these studies have primarily used coherence analysis of BP and RSNA in the frequency domain. However, this analysis is unable to assess the non-linear properties of the underlying cardiovascular control system. In this study we employed not only coherence analysis but also cross-entropy analysis using balloon inflation ('balloon-on') to assess the influence of right atrial receptors on the relationship between BP and RSNA under two conditions in anaesthetised Wistar rats. Balloon-on stimulation alone inhibited RSNA by 28 +/- 4% in eight rats without changing BP. This effect on integrated nerve activity was not present when atrial stimulation was applied during stimulation of a site in the paraventricular nucleus (PVN) of the hypothalamus which increased RSNA by 158.7 +/- 58% and increased BP by 17.1 +/- 2.3 mmHg. However, the cross-entropy measurement was significantly decreased (P < 0.05) during balloon-on stimulation in both the conditions revealing that there is greater synchrony between the oscillating signals contained within the BP and RSNA time series. Thus during the enhanced RSNA elicited by stimulation of the PVN, the inhibitory influence of atrial receptors, although apparently blocked, was still effective in that it resulted in the energy of the RSNA spectrum becoming more evenly distributed over a range of frequencies. The data show that cross-entropy calculations are able to characterize the non-linearities of underlying cardiovascular control.