Evaluation of dynamic response of catheter-manometer systems for pulmonary arterial pressure

To quantitatively evaluate the waveform distortions observed through a catheter-manometer system, the tolerance range of amplitude errors and that of phase errors are defined as both within +/- 5%, and the frequency bandwidth was calculated where the frequency characteristics of amplitude and those of phase difference satisfy the two tolerance ranges by use of a second-order kinetic equation. The results were expressed by three variables, composed of the natural frequency (fn), damping coefficient (zeta), and highest frequency (fh) corresponding to the frequency bandwidth; a chart was constructed with fn on the x-axis, zeta on the y-axis, and fh as parameter. Also on the chart, the propagation delay times (td's) determined by fn, zeta, and fh were plotted. We measured the frequency characteristics of two 7-Fr Swan-Ganz catheters with lengths of 75 and 110 cm. fn's and zeta's were found to be 13.9 and 10.1 Hz and 0.23 and 0.32, respectively. Referring to this chart, the maximal fh these catheters would be able to reproduce within the tolerance ranges and the propagation td's can be predicted to be 3.2 and 2.4 Hz and 7 and 12 ms, respectively. Suppression of resonance by use of Accudynamic improved the maximal fh's to 3.9 and 2.9 Hz, respectively, but resulted in the increased td's to 14 and 19 ms due to increased zeta.