Why the natural frequency and the damping coefficient do not evaluate the dynamic response of clinically used pressure m
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ORIGINAL ARTICLE
Why the natural frequency and the damping coefficient do not evaluate the dynamic response of clinically used pressure monitoring circuits correctly Hiroaki Watanabe1 · Shin‑ichi Yagi2 Received: 26 December 2019 / Accepted: 13 August 2020 © Japanese Society of Anesthesiologists 2020
Abstract Purpose The dynamic response of pressure monitoring circuits must be evaluated to obtain true invasive blood pressure values. Since Gardner’s recommendations in 1981, the natural frequency and the damping coefficient have become standard parameters for anesthesiologists. In 2006, we published a new dynamic response evaluation method (step response analysis) that can plot frequency spectrum curves instantly in clinical situations. We also described the possibility of the defect of the standard parameters. However, the natural frequency and the damping coefficient are considered the gold standard and are even included in a major anesthesiology textbook. Therefore, we attempted to clarify the issues of these parameters with easy-to-understand pressure waves and basic numerical formulae. Methods A blood pressure wave calibrator, a single two-channel pressure amplifier, and personal computer were used to analyze blood pressure monitoring circuits. All data collection and analytical processes were performed using our step response analysis program. Results We compared two different circuits with almost the same natural frequency and damping coefficients. However, their amplitude spectrum curves and input/output pressure values were significantly different. Conclusions The natural frequency and the damping coefficient are inadequate for the dynamic response evaluation. These parameters are primarily obtained from the phase spectrum curve and not from the amplitude spectrum curve. We strongly recommend an evaluation using the amplitude spectrum curve with our step response analysis method. It is crucial to maintain an amplitude gain of 1 (input amplitude = output amplitude) in the pressure wave frequency range of 0–20 Hz. Keywords Dynamic response · Natural frequency · Damping coefficient · Monitoring catheter calibration · Blood pressure monitors
Introduction In clinical situations, almost all pressure waves through pressure monitoring circuits are distorted due to the resonance effect and usually show high systolic pressure values. To evaluate the dynamic response of monitoring circuits, drawing an amplitude spectrum curve has been the standard * Hiroaki Watanabe [email protected] 1
Department of Anesthesiology, School of Medicine, Sapporo Medical University, South‑1, West‑16, Chuo‑ku, Sapporo 060‑8543, Japan
School of Information Science, Ultrasonic Engineering in Medicine, Meisei University, Tokyo, Japan
2
evaluation method. Actually, the frequency components of a blood pressure waveform range from 0 to 20 Hz [1] and generally all blood pressure monitoring amplifiers used clinically have a filter that cuts signals over 20 Hz. To obtain the true pressure values, a pressure monitoring circuit
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