A study on the development of an ultrasonic system to measure cardiac output

• Main Authors: Huan-Sheng Hung, 洪煥昇
• Other Authors: Shyh-Hau Wang
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/h2s74j

碩士 === 中原大學 === 醫學工程研究所 === 92 === The patients after cardiac surgery often suffer from clinical problems associated with low blood pressure. The conditions of blood circulation for these patients having dangerous diseases relative to circulations should be thoroughly extracted and analyzed. In the past, the cardiac output was frequently measured by using the catheter inserted in a heart, and however, many researchers recently began to investigate the non-invasive approaches for the measurement of cardiac output, such as indicator dilution, Doppler ultrasound, and so forth. Compared to the traditional method based on Doppler ultrasound, this study developed an ultrasonic system to measure the flow by using ultrasonic signals in time-domain. The system was consisted of a 5 MHz ultrasonic pulser/receiver, an analog-to-digital converter, and an interface circuits. A software corresponding to the system was capable of real-time signal analysis and display. The feasibility and stability of the system was evaluated using the experiments on flowing blood in a tube that the range for the hematocrit and the flow is from 25% to 55% and from 62 ml/min to 437 ml/min, respectively. The relationship between hematocrit and flow was also explored. The results obtained from the flow experiments showed that the sensitivity of the measurement system to detect the variation of density was 5.38 corresponding to a correlation coefficient of 0.99 with those obtained from the measurement using the lock-in amplifier (SR844RF, Stanford Research Systems, USA). The experimental results also showed that both the volume and concentration of the indicator is proportional to the area of measurement of the curve. Moreover, the measured flow for higher hematocrits would be smaller than those from lower hematocrits. This is due to that the density of blood cell at high hematocrit is large, resulting in the increase of viscosity and the decrease of flow. This study concluded that this non-invasive ultrasonic measurement system has a high sensitivity to be helpful for the measurement of cardiac output in the clinical diagnosis.