Prediction of arterial compliance from pressure and flow waveforms

The goal of this project was to ascertain the feasibility of determining the compliance of an arterial segment from pressure and flow waveform measurements, and to develop a microcomputer based system for collecting and analyzing the data. Vessel area compliance, CA, is defined as dA/dp, where A is the lumenal area and p is the transmural pressure. Direct in vivo measurements of CA require some technique for measuring the instantaneous vessel area; unfortunately, such a technique is not currently available. Thus, indirect techniques have been developed where some measurable quantity can be related to CA through a model formulation. Use of pulse wave velocity to estimate CA is one example of an indirect technique. Other techniques involve the use of a mathematical model which relates pressure, flow and compliance. In the present study, a dynamic technique is used in which the arterial segment of interest is occluded at its distal end and a measurement of the instantaneous flow and pressure is made at its proximal end. Compliance is calculated through the relationship CA = Q/dp/dtL, where Q is the volumetric flow rate, dp/dt is the time rate of change of the pressure, and L is the length of the arterial segment between the proximal end where Q and p are measured, and the occluded distal end. With this approach, the compliance of a particular arterial segment is determined rather than the lumped compliance of an entire limb. To ascertain the feasibility of this technique, an in vitro model system was constructed and tested using thin-walled latex tubing to simulate an arterial segment.(ABSTRACT TRUNCATED AT 250 WORDS)