Estimating input original waveform from catheter-manometer system output waveform--an experimental study with...

The present study was performed to investigate the precision of and problems in arithmetic operations for synthesis/estimation of the input waveform from the output waveform of a pulmonary artery catheter (PAC) manometer system, by imposing arterial pressure waveform as an input pressure waveform. When a PAC manometer system is regarded as a second-order system, the input waveform can be synthesized/estimated from the output waveform by determining the natural frequency (fn), and damping coefficient (ζ) of the said system. The precision of synthesis/estimation diminished with the decreasing fn of the PAC manometer system. An attempt was thus made to explore the cause of the reduction in precision of estimation due to decreases in fn by constructing a second-order system equivalent circuit and a differentiation arithmetic circuit on the circuit simulator. The results demonstrated that correct synthesis/estimation of input waveform were attainable only when the set of fn and ζ for the arithmetic circuit coincided with that of the PAC manometer system. Decreases in fn correspond to such instances where the PAC manometer system can no longer be regarded as a second-order system, thus nullifying the measured fn and ζ. This accounts for the reduction in precision.