CORRECTION OF PRESSURE WAVE-FORMS RECORDED BY FLUID-FILLED CATHETER RECORDING-SYSTEMS - A NEW METHOD USING A TRANSFER EQUATION

Background: Pressure measuring systems using fluid-filled catheters ca n result in the recording of distorted pressure waveforms. It results in phase delay, overestimation of systolic and, to a lesser extent, of diastolic pressure. We designed and evaluated a method to correct thi s pressure waveform distortion using an appropriate transfer equation obtained from the dynamic response of the fluid-filled catheter. This transfer equation is based on the principle that a fluid-filled cathet er recording system is considered as an underdamped dynamic system ful ly characterized by its natural frequency (omega(n)) and damping ratio (zeta). Methods: Pressure waveforms, simultaneously recorded in vitro or in vivo by a fluid-filled catheter (Pc) and a micromanometer-tippe d catheter (Pref), were used to validate the method. Dynamic response of the catheter used was obtained from a fast-flush test. The correcte d signal (Ppred) was obtained using omega(n), zeta and the following t ransfer equation: d(2)P(c)/dt(2)+2 omega(n) zeta dP(c)/dt+omega(n) P-2 (c)=C P-pred (t) After correction of Pc, Ppred was compared, using a l inear regression, with Pref taken as reference. Results: Our results s howed that Ppred was fitted to Pref with excellent coefficient correla tion (0.99). The mean error and the standard error of estimate were re spectively -1.16 mmHg and 1.4 mmHg. Conclusion: This new method can co nvert the distorted pressure waveforms transmitted by any fluid-filled catheters into high-fidelity signals. It suppresses the phase delay a nd the overestimation of systolic pressure induced by fluid-filled cat heters.