NONLINEAR-ANALYSIS OF RENAL AUTOREGULATION UNDER BROAD-BAND FORCING CONDITIONS

Linear analysis of renal blood flow fluctuations, induced experimental ly in rats by broad-band (pseudorandom) arterial blood pressure forcin g at various power levels, has been unable to explain fully the dynami cs of renal autoregulation at low frequencies (1). This observation ha s suggested the possibility of nonlinear mechanisms subserving renal a utoregulation at frequencies below 0.2 Hz. This paper presents results of 3rd-order Volterra-Wiener analysis that appear to explain adequate ly the nonlinearities in the pressure-flow relation below 0.2 Hz in ra ts. The contribution of the 3rd-order kernel in describing the dynamic pressure-flow relation is found to be important. Furthermore, the dep endence of 1st-order kernel waveforms on the power level of broadband pressure forcing indicates the presence of nonlinear feedback (of sigm oid type) based on previously reported analysis of a class of nonlinea r feedback systems (11).