Effect of Mean Pressure Levels on the Dynamic Response Characteristics of the Carotid Sinus Baroceptor Process in Dog

The purpose of this investigation was to delineate the effect of imposed mean pressure levels on the open-loop dynamic response characteristics of the carotid sinus baroceptors in dogs. The experimental design consisted of measuring the intrasinus pressure and the gross baroceptor nerve activity while forcing the isolated sinus with sinusoidal pulse pressures, with peak-to-peak amplitude of 50 mm Hg, superimposed on mean pressures of 75, 125, 175, and 225 mm Hg at frequencies of 0.5, 1, 2, 3, 4, 5, 7, 10, 15 and 20 Hz. With this forcing protocol, we were able to divide the traditional sigmoidal pressurenerve activity relationship into three piecewise linear segments whose input-output (transfer) functions could then be determined by conventional linear system analysis. We found that (a) at each mean pressure level, the transfer function relating nerve activity, N(s), to forcing pressure, P(s), was second order and of the form, N(s)/P(s) = α(1 + ßs + γs
²
), and (b) the coefficients α, Β, and γ were all quadratic functions of the mean pressure level, P Incorporating the equations for each coefficient as a function of mean pressure into the transfer function yielded the nonlinear differential equation, N(t) = kΑ(P) [(P(t) - P) + ß(P) (dp(t)/dt) + γ(P) (d
²
P(t)/dt
²
)], which describes the dynamic response of the carotid sinus baroceptor nerve, N(t), over the entire pressure range, P(t), studied.