Design and Implementation of Non-Invasive Cardiac Output Monitoring System

Hemodynamic monitoring can reflect cardiac function and blood perfusion, and is an indispensable monitoring method in clinical practice. Invasive hemodynamic monitoring methods represented by thermodilution method are limited in their clinical application scope because they require vascular cannulation. Noninvasive hemodynamic monitoring has attracted extensive attention from medical companies and clinicians at home and abroad in recent years due to its advantages such as safety, noninvasiveness, continuous monitoring, simple operation and low cost. This paper designs a noninvasive hemodynamic monitoring system based on the cardiac impedance method, including hardware, algorithm, software design and performance parameter evaluation. Among them, the hardware part mainly includes differential high-frequency constant current source stimulation circuit, cardiac impedance signal acquisition and ECG signal acquisition circuit. Signal processing includes filtering, cardiac impedance signal calibration, ECG signal and cardiac impedance signal feature point recognition. According to the collected cardiac impedance and ECG signals, the hemodynamic parameters such as heart rate (HR), stroke volume (SV), cardiac output (CO), stroke index (SI), cardiac index (CI) and cardiac contraction index (ICON) are calculated based on the Nyboer thoracic cylinder model. After testing, the key technical indicators of the system hardware are better than the relevant medical device standards. The system was used to collect cardiac impedance and ECG signal data from 40 volunteers. The calculated HR, SV, and CO, three important hemodynamic indicators, were compared with the ICONCore non-invasive cardiac output monitor of OSYPKA Medical in Germany. The Pearson correlation coefficients were 0.992 (P<0.001), 0.948 (P<0.001), and 0.933 (P<0.001), respectively, verifying that the designed system has high accuracy and reliability.