Development of a flow simulator to study haemodynamic behaviour of naturaland artificial blood vessels under physiologic flow conditions

A new computer-controlled flow simulator has been designed to study the hae modynamic behaviour of natural and artificial blood vessels under physiolog ic flow conditions. The simulator can generate well characterized and fully developed laminar flow properties. It includes a unique perfusion case tha t imposes an axial tension on the vessel segment, and a commercial programm able pump to reproduce pulsatile flow rates. Response to high frequency com mands was greatly attenuated and displayed a frequency dependent phase angl e Thus, for complex pulsating flow rates containing different frequency com ponents, the system response was significantly distinct from the command. T o reproduce physiologic waveforms, the transfer function of the whole syste m was determined for different amplitudes and frequencies of flow rate exci tations. Each input command was compared to the measure flow rate, and the values of the gain and phase angle were evaluated. If the desired flow rate was composed of a sum of n sine wave components, each has a frequency f(j) and an amplitude A(j), a corrected command signal was then reconstructed b y amplifying the attenuated components and advancing those lagged in time. The corrected signal was finally applied as the new command to the pump. Th e results showed an excellent agreement with physiologic waveforms. Example s of different pulsatile flow experiments to investigate the effects of fre quency, pressure, and wall elasticity are presented.