A new approach to assess arterial system function with compliance-pressure loop

High blood pressure has been recognized as a most common risk factor of cardiovascular diseases, which is the leading cause of death. There is a strong correlation of blood pressure(P) and mechanical properties of arteries, as characterized by vascular compliance, peripheral resistance and characteristic impedance. For this reason, an accurate estimation of these parameters is necessary for better interpretation of arterial system function and hypertension.The classic Windkessel model is one of the most popular tools in the clinical setting to describe arterial system function. This model assumes a constant arterial compliance(C) throughout the entire cardiac cycle, although it has been known that compliance is a function of pressure. A recently modified Windkessel, also known as Li model, which incorporates a pressure-dependent nonlinear compliance(C(P)) component has shown that arterial compliance is varying along time, i.e. not a constant value.In this thesis, simultaneously measured aortic pressure and flow data were gathered during normal, hypertension and vasodilator conditions. The accuracy of the nonlinear C(P) model predicted waveforms is first established. This is followed by the use of a new compliance-pressure loop (CPL) approach to evaluate arterial system function under varied vasoactive conditions over a wide range of pressure. Results show CPL can provide a rapid visualization of arterial system function and that reduced compliance due to hypertension and improved compliance due to vasodilator can be readily quantified. This CPL method thus can be further applied to the assessment of severity of hypertension and clinical assessment of drug efficacy.