BEAT-TO-BEAT DETERMINATION OF PERIPHERAL RESISTANCE AND ARTERIAL COMPLIANCE DURING +GZ CENTRIFUGATION

This study focused on the problem of describing changes in total perip heral resistance (TPR) and systemic arterial compliance (SAC) under ti me-varying +Gz acceleration stress. Nonsteady-state measures of periph eral resistance can only be derived when arterial compliance is taken into account. We have developed a successful analytical model to track simultaneous changes in peripheral resistance and systemic arterial c ompliance during non-stationary periods of increased gravitational loa d on a beat-to-beat basis, Using a 2-element windkessel model, aortic flow into an input node was defined as equal to the sum of a capacitat ive (Cao) and ct resistive (Rarterial) flow leaving the node such that : Iao = Caod(Pao - Ppleural)/dt + (Pao - Pra)/Rarterial We made the as sumption that Cao and Rarterial were constant over ct cardiac cycle, a nd divided the pressure and flow signals for each beat of a record int o two different intervals, integrating this equation over each, giving two equations in two unknowns. Cao and Rarterial were then obtained f rom the matrix solutions. To test the model, we used recordings from c hronically instrumented baboons subjected to a 10 s rapid onset +Gz (h ead-to-foot) stress. Beat-to-beat calculations of peripheral resistanc e and systemic arterial compliance from our model were compared to val ues obtained from a previously reported 3-element windkessel model.