APPARENT ARTERIAL COMPLIANCE

Recently, there has been renewed interest in estimating total arterial compliance. Because it cannot be measured directly, a lumped model is usually applied to derive compliance from aortic pressure and flow. T he archetypical model, the classical two-element windkessel, assumes 1 ) system linearity and 2) infinite pulse wave velocity. To generalize this model, investigators have added more elements and have incorporat ed nonlinearities. A different approach is taken here. It is assumed t hat the arterial system 1) is linear and 2) has finite pulse wave velo city. In doing so, the windkessel is generalized by describing complia nce as a complex function of frequency that relates input pressure to volume stored. By applying transmission theory, this relationship is s hown to be a function of heart rate, peripheral resistance, and pulse wave reflection. Because this pressure-volume relationship is generall y not equal to total arterial compliance, it is termed apparent compli ance.'' This new concept forms the natural counterpart to the establis hed concept of apparent pulse wave velocity.