A DUAL-INPUT NONLINEAR-SYSTEM ANALYSIS OF AUTONOMIC MODULATION OF HEART-RATE

Linear analyses of fluctuations in heart rate and other hemodynamic va riables have been used to elucidate cardiovascular regulatory mechanis ms. The role of nonlinear contributions to fluctuations in hemodynamic variables has not been fully explored, This paper presents a nonlinea r system analysis of the effect of fluctuations in instantaneous lung volume (ILV) and arterial blood pressure (ABP) on heart rate (HR) fluc tuations, To successfully employ a nonlinear analysis based on the Lag uerre expansion technique (LET), we introduce an efficient procedure f or broadening the spectral content of the ILV and ABP inputs to the mo del by adding white noise, Results from computer simulations demonstra te the effectiveness of broadening the spectral band of input signals to obtain consistent and stable kernel estimates with the use of the L ET, Without broadening the band of the ILV and ABP inputs, the LET did not provide stable kernel estimates, Moreover, we extend the LET to t he case of multiple inputs in order to accommodate the analysis of the combined effect of ILV and ABP effect on heart rate, Analyzes of data based on the second-order Volterra-Wiener model reveal an important c ontribution of the second-order kernels to the description of the effe ct of lung volume and arterial blood pressure on heart rate, Furthermo re, physiological effects of the autonomic blocking agents propranolol and atropine on changes in the first- and second-order kernels are al so discussed.