Thin fluid-filled catheters for more accurate determination of pressures and their time derivatives.

A catheter-transducer system consisting of a thin fluid-filled teflon catheter and a transducer with a low displacement volume is presented. The thin catheter is especially suited for registration of pressure and the time derivatives in small caliber vessels. From theoretical considerations it is concluded that the best way of obtaining a correct damping ratio in the range of 0.6-0.7 in the system is to adjust the diameter of the catheter empirically to the characteristics of the transducer. Residual gas bubbles are a problem in most catheter-transducer systems, but due to the design of the catheter and to a special flushing method, reproducible results are rapidly and easily obtained. The damping ratio of the system is 0.6 and the band width is 35 Hz. In repeated experiments an identical influence of the temperature on the damping ratio could be demonstrated.