Correction of Pressure Waveforms Recorded by Fluid-Filled Catheter Recording Systems: A New Method Using a Transfer Equation

BACKGROUND: Pressure measuring systems using fluid-filled catheters can 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 this 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 catheter recording system is considered as an underdamped dynamic system fully 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-tipped catheter (Pref), were used to validate the method. Dynamic response of the catheter used was obtained from a fastflush test. The corrected signal (Ppred) was obtained using omega n, zeta and the following transfer equation: d2Pc/dt2 + 2 omega n zeta dPc/dt + omega n 2Pc = C Ppred (t) After correction of Pc, Ppred was compared, using a linear regression, with Pref taken as reference. RESULTS: Our results showed that Ppred was fitted to Pref with excellent coefficient correlation (0.99). The mean error and the standard error of estimate were respectively -1.16 mmHg and 1.4 mmHg. CONCLUSION: This new method can convert the distorted pressure waveforms transmitted by any fluid-filled catheters into high-fidelity signals. It suppresses the phase delay and the over-estimation of systolic pressure induced by fluid-filled catheters.