Why the natural frequency and the damping coefficient do not evaluate the dynamic response of clinically used pressure monitoring circuits correctly

Towards the automatic detection and correction of abnormal arterial pressure waveforms

Both over and underdamping of the arterial pressure waveform are frequent during continuous invasive radial pressure monitoring. They may influence systolic blood pressure measurements and the accuracy of cardiac output monitoring with pulse wave analysis techniques. It is therefore recommended to regularly perform fast flush tests to unmask abnormal damping. Smart algorithms have recently been developed for the automatic detection of abnormal damping. In case of overdamping, air bubbles, kinking, and partial obstruction of the arterial catheter should be suspected and eliminated. In the case of underdamping, resonance filters may be necessary to normalize the arterial pressure waveform and ensure accurate hemodynamic measurements.

The 10 Hz dynamic response of a fluid-filled pressure monitoring system is a novel alternative to the fast flush test and indicative of unacceptable systolic pressure overshoot

The standard method for qualitatively evaluating the dynamic response is to see if the gain of the amplitude spectrum curve approaches 1 (input signal = output signal) over the frequency band of the blood pressure waveform. In a previous report, Watanabe reported that Gardner's natural frequency and damping coefficient, which are widely used as evaluation methods, do not reflect the dynamic response of the circuit. Therefore, new parameters for evaluating the dynamic response of pressure monitoring circuits were desired. In this study, arterial pressure catheters with length of 30, 60, 150, and 210 cm were prepared, and a blood pressure wave calibrator, two pressure monitors with analog output and a personal computer were used to analyze blood pressure monitoring circuits. All data collection and analytical processes were performed using step response analysis program. The gain at 10 Hz was close to 1 and the systolic blood pressure difference was small in the short circuits (30 cm, 60 cm), and the gain at 10 Hz was 1.3-1.5 in the 150 cm circuit and over 1.7 in the 210 cm circuit. The difference in systolic blood pressure increased in proportion to the length of the circuit. It could also be inferred that the gain at 10 Hz should be less than 1.2 to meet a clinically acceptable blood pressure difference. In conclusion, the gain at 10 Hz is sufficiently useful as an indicator to determine the correct systolic blood pressure.