Frequency Response Testing in Catheter‐Transducer Systems

In order to obtain a faithful reproduction of the arterial pressure waveform, the dynamic response characteristics of a pressure-monitoring system must possess amplitude and phase linearity, and adequate bandwidth. Numerous tests have been devised to evaluate dynamic-response characteristics of pressure-monitoring systems. It was the purpose of this study to investigate the validity of the more popular tests through computer simulations and models. Two typical pressure-monitoring systems, each consisting of a 7-F thermodilution catheter, either a 12-in. or 48-in. monitoring/administration line and pressure transducer, were simulated as electrical circuits containing resistors, capacitors and inductors. The circuit models were then subjected to “impulse,” “step,” “pop,” “flush,” “stopcock” and “snap” tests to determine each test's ability to provide useful information. Results of the simulations indicated that 3 of the 13 simulations were able to correctly determine the proper resonant frequency and effective damping. Impulse and step tests were shown to be reliable only if the signal could be applied at the catheter tip. The only in situ test able to provide useful information was the “snap test” as described in this paper. Computer simulations also demonstrated that an impulse, or perturbation, located within the transducer could not provide correct information in terms of the proper transfer characteristics of the monitoring system. This may not be a suitable method to use in automated or self-correcting monitoring systems.