Modelling of the dynamic relationship between arterial pressure, renal sympathetic nerve activity and renal bloodflow in conscious rabbits

A linear autoregressive/moving-average model was developed to describe the dynamic relationship between mean arterial pressure (MAP), renal sympatheti c nerve activity (SNA) and renal blood flow (RBF) in conscious rabbits. The RBF and SNA to the same kidney were measured under resting conditions in a group of eight rabbits. Spectral analysis of the data sampled at 0.4Hz sho wed that the low-pass bandwidth of the signal power for RBF was approximate ly 0.05 Hz, An autoregressive/moving-average model with an exogenous input (ARMAX) was then derived (using the iterative Gauss-Newton algorithm provid ed by the MATLAB identification Toolbox), with MAP and SNA as inputs and RB F as output, to model the low-frequency fluctuations. The model step respon ses of RBF to changes in SNA and arterial pressure indicated an overdamped response with a settling time that was usually less than 2s, Calculated res iduals from the model indicated that 79+/-5 % (mean +/- S.D., averaged over eight independent experiments) of the variation in RBF could be accounted for by the variations in arterial pressure and SNA, Two additional single-i nput models for each of the inputs were similarly obtained and showed concl usively that changes in RBF, in the conscious resting rabbit, are a functio n of both SNA and MAP and that the SNA signal has the predominant effect. T hese results indicate a strong reliance on SNA for the dynamic regulation o f RBF, Such information is likely to be important in understanding the dimi nished renal function that occurs in a variety of disease conditions in whi ch overactivity of the sympathetic nervous system occurs.