|Abstract: ||在現有的心搏輸出量(Cardiac Output)監測儀器及方法中，除了應用侵入式的方法會有感染的風險外，無法達到連續量測的功能或是需要專業人員的操作才能施行。而現有的市售非侵入式心搏輸出量監測系統大都具有體積龐大、笨重及造價昂貴等缺點，也因為技術及商業機密等緣故不易普及於醫學及學術研究單位。|
因此本研究提出一款可攜式非侵入性心搏輸出量監測系統之設計，主要由混合訊號微處理器(Microprocessor , MCU)控制電壓訊號產生器電路(Function Generator)、電壓控制電流源(Voltage Control Current Source) 輸出50kHz／4mA peak to peak正弦波定電流源。經過儀表放大器(Instrumentation Amplifier)、主動濾波器(Active Filter)及震幅調變解調器(Amplitude Modulation Demodulator)解析訊號後經由微處理器類比數位轉換器(Analog／Digital Convertor)收錄並傳送到電腦搭配MATLAB進行計算及分析。
針對前端類比電路利用NI USB-6255 DAQ儀器及LabVIEW驗證設計及訊號正確性後，接著搭配ATmega328P、AD9833及SD卡模組等數位電路系統。採用生物電阻抗八點量測法實際量測胸腔皮膚阻抗(Chest Skin Impedance , IMP)訊號及第二導程心電圖(Electrocardiogram, ECG)訊號，透過數位電路取樣回傳後利用MATLAB擷取0.7～7Hz皮膚阻抗訊號微分後得到阻抗心動描記術(Impedance Cardiography , ICG)訊號，最後抓取心電圖Q點對齊阻抗心動描記術C、B、X點特徵值後計算出射血前期(Pre-Ejection-Period , PEP)及左心室射血時間(Left Ventricular Ejection Time , LVET)等數據，驗證系統可用性。
本系統除了利用非侵入性量測方法避免感染風險、容易操作的自動量測及監測等優點外，還有體積小、重量輕、成本低急便於攜帶等優點。未來之應用不僅僅只限於大型醫院或加護病房等機構，也可普及於小型醫療機構、戶外急救單位甚至是個人家庭中，實現即時且普及的生理訊號監測。;In the existing Cardiac Output monitoring instruments and methods, in addition to the risk of infection by applying an invasive method, the continuous measurement function cannot be achieved or a professional operation is required. Most of the existing commercially available non-invasive cardiac output monitoring systems have the disadvantages of being bulky, cumbersome and expensive, and are not easily popularized in medical and academic research units due to technical and commercial secrets.
Therefore, this study proposes a portable non-invasive cardiac output monitoring system design, mainly controlled by a mixed signal Microprocessor (MCU) voltage Function Generator circuit, Voltage Control Current Source outputs a 50kHz/4mApeak to peak sine wave constant current source. After the Instrumentation Amplifier, Active Filter and Amplitude Modulation Demodulator analytic signal, it is recorded and transmitted to the computer via a microprocessor Analog/Digital Convertor. Computation and analysis with MATLAB.
For the front-end analog circuit, the NI USB-6255 DAQ instrument and LabVIEW are used to verify the design and signal correctness, and then with the digital system such as ATmega328P, AD9833 and SD card module. The bioelectrical impedance eight-point measurement method is used to actually measure the Chest Skin Impedance (IMP) signal and the second lead Electrocardiogram (ECG) signal. After sampling and returning through the digital circuit, the MATLAB is used to extract 0.7-7 Hz. After the skin impedance signal is differentiated, the Impedance Cardiography (ICG) signal is obtained. Finally, the ECG Q-point alignment Impedance Cardiography C, B, and X point eigenvalues are acquired to calculate the Pre-Ejection Period (PEP). And data such as Left Ventricular Ejection Time (LVET) to verify system availability.
In addition to the advantages of non-invasive measurement methods to avoid infection risk, easy operation and automatic measurement and monitoring, the system has the advantages of small size, light weight, low cost and easy to carry. Future applications are not limited to large hospitals or intensive care units, but also to small medical institutions, outdoor emergency units, and even individual households to achieve immediate and universal physiological signal monitoring.