True arterial system compliance estimated from apparent arterial compliance

A new method has been developed to estimate total arterial compliance from measured input pressure and flow. In contrast to other methods, this method does not rely on fitting the elements of a lumped model to measured data. Instead, it relies on measured input impedance and peripheral resistance to calculate the relationship of arterial blood volume to input pressure. Gen erally, this transfer function is st complex function of frequency and is c alled the apparent arterial compliance. At very low frequencies, the confou nding effect of pulse wave reflection disappears, and apparent compliance b ecomes total arterial compliance. This study reveals that frequency compone nts of pressure and flow below heart rate an generally necessary to obtain a valid estimate of compliance. Thus, the ubiquitous practice of estimating total arterial compliance from a single cardiac cycle is suspect under mos t circumstances, since a single cardiac cycle does not contain these freque ncies. (C) 2000 Biomedical Engineering Society. [S0090-6964(00)00103-X].