Intra-arterial pressure wave parameters modeled using electrical analogs

An Electrical Model was developed to help identify parameters obtained from dynamic pressure data on the in vitro rat aortic artery. The data was obtained using a Multifunction Pressure Generator (MPG) and recording MPG Input Pressure (Pi) and Intraarterial Pressure (Po). Transfer functions of the form Po/Pi = (A1S+Ao)/(B2S2 + B1S+Bo) were obtained and it is necessary to link A1, Ao, B2, B1 and Bo to the Biological Parameters of Inertance (M), Vascular Resistance (R) and Compliance (C). Using the Electrical Analogs to P, M, R and C which are Voltage (V), Inductance (L), Resistance (Re), and Capacitance (Ce), an Electrical Model was built. The Electrical Model has the form Vo/Vi = (Re1S + 1/Ce)/[LS2 + (Re1 + Re2)S + 1/Ce]. Since Ao = Bo = 1 from our experimental data we multiplied the denominator and numerator by Ce to obtain Vo/Vi = (CeRe1S + 1)/[CeLS2 + Ce(Re1 + Re2)S + 1]. We then transformed our Electrical Model to its Pressure Equivalent and obtained Po/Pi = (CR2S + 1)/[CMS2 + C(R1 + R2)S + 1]. Since R2 is less than R1 + R2 we theorize that total R is composed of two viscoelastic or resistive elements R1 and R2. Using measured values of compliance it should be possible to obtain reasonable values for R1, R2 and Inertance.