| Summary: | 碩士 === 中原大學 === 醫學工程研究所 === 90 === The aggregation of red cells is formed when the blood flow is low or stopped. This phenomenon is primarily due to those large molecules, such as fibrinogen, in the plasma. The larger aggregation effect for red cells tends to increase higher viscosity of blood. Under such circumference, the blood flow would be hindered. Thus, it could finally lead to the formation of vascular embolism. For these reasons, the characteristics of red cells aggregation are still investigated to date. The laminar flow in a flow field might be found as the blood is flowing in a straight and long tube. The red cells aggregation will be distributed near the center stream of a tube due to that the corresponding location has the lowest shear rate. The phenomenon was validated from larger ultrasonic scattering signals in the centerline in a tube than those near the wall of a tube.
In this study, the blood was circulated in a flowing tube for a certain time and then the driven pump was turn off. The red cells were gradually aggregated and finally formed a rouleau structure. This flow variation was monitored by ultrasonic signals. Results showed that ultrasonic attenuation, sound velocity, and backscattered signals were increased after the stoppage of the blood flow. Experimental results also found that larger variations for attenuation and sound velocity were obtained associated with the decrease of blood hematocrit. However, the relation between hematocrit and backscattering was different. The rate of attenuation coefficient and sound velocity increased corresponding to higher blood flow.
The second study is on the application of ultrasonic backscattering, attenuation, and sound velocity to detect the formation of clot from blood under static and dynamic conditions. Results from both the static and dynamic blood demonstrated that three ultrasonic parameters were increased as the clot was formed. The volume of the clot is larger in the flowing blood than that in the static condition. The increasing variation of viscosity was found corresponding to the higher hematocrit. These results validated that ultrasound could be sensitively used to detect the variation of hemodynamic properties for a blood flow.
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