Frequency characteristics of arterial catheters – an in vitro study

Abstract

Continuous blood pressure recording carries the most information on the cardiovascular state of a person. Therefore accurate instrumentation is of high importance. Nowadays the most accurate continuous blood pressure measuring method is the intra-arterial catheterization. However, the accuracy of the fluid-filled catheters raises doubts: the elastic wall of the catheter and the transmission tube each has a damping effect that could play a significant role together. Furthermore the intra-arterial part of a cardiac catheter is in a pulsatile flow, which is assumed to affect the pressure transmission within the measuring line. In this paper behavior of two different types of fluid filled catheters (femoral and cardiac) is described. For the in vitro experiments, a pulsatile arterial system model was applied. Simultaneous measurements of the intra-arterial pressure were carried out: directly with use of a pressure transmitter and through the catheter. Thus the accuracy and the frequency response of the catheters could be obtained and a comparison between the two different types could be made. A numerical model – based on the method of impedances – was developed to describe the frequency transmitting ability of the catheters. The numerical results were compared to the measurements. We found that the experimental results of the different catheters show significant similarities; the numerical and experimental results of the femoral catheter were in a good accordance whereas those of the cardiac catheter show discrepancies.