Evaluation of dynamic performance in liquid-filled catheter systems for measuring invasive blood pressure.

Invasive blood pressure measurement is used in patients with unstable haemodynamics. The demand of the accuracy of these measurements is high. The reliability of the reproduced signal strongly depends on the measurement system's dynamic characteristic-its resonance frequency and damping factor. These characteristics were examined with the frequency response method, which is valuable for second and higher order systems. Most of the pressure measuring systems in use in clinical practice have low damping factor (0.1-0.2), which causes high overshoot in systolic pressure values (up to 13%), since putting all the measuring components in a chain reduces the dynamic properties of a single component and the resonance frequency drops drastically from over 100 Hz to even below 10 Hz. One of the solutions to increase the damping ratio is to insert a damping device R.O.S.E. parallel to the tubing. The resonance frequency remains the same, the damping factor increases to around 0.5. Systems with higher damping factors (0.5-0.7) have lower overshoot (1-2%), therefore the blood pressure measurements are more accurate.