Study On Key Technologies In Measuring And Testing Of Thromboelasticity

Complex and impeccable physiological mechanisms of blood coagulation, anti-coagulation and fibrinolysis with the ability of fine regulation and control play important roles in human body. Under physiological conditions, blood circulates in vessels without bleeding nor coagulation to form thrombus. However, once the system or corresponding regulatory mechanism are broken, bleeding or thrombus occur. In the cascade of coagulation reactions, three-dimensional cross linking is formed between fibrin, platelet and blood cells, and finally fibrinolysis occurs in the presence of fibrinolysin. During the coagulation and fibrinolysis stages, blood viscoelasticity changes, which can be monitored by thromboelasticity measuring system and the data could be processed to produce the thromboelastograph. Clinicians can always obtain critical information about different interactions among blood components from the thromboelastograph. In addition, it realizes point of care testing which can assist doctors to fully understand blood coagulation conditions of patients and is useful for rapid diagnosis.So far, theoretical models based on thromboelasticity measurement have not been published. Also, there are no summaries about the influence factors on the measurement accuracy of the thrombelastometry. As to viscoelastic sensing technology, conventional coil inductance angular displacement sensor is hard to be manufactured with high cost and nonlinear characteristics. Moreover, the improvement of resolution is urgently needed. In addition, thromboelasticity measurement has now been focusing on clinical blood coagulation monitoring. To make full use of this technology, more investigations are highly desired. This paper carried out systematic researches on thrombelasticity measurement technology and its applications.In this study, simplified physical model of the thromboelasticity measuring system has been established by the derived theoretical calculation formula as G=(251.22φ)/(2.375-φ), in which G and φ stand for the shear modulus of the blood and the angular displacement of the probe respectively. Next, numerical simulation is carried out based on Ansys Workbench to achieve the mathematical model of actual system which follow the equation G=(255.22φ)/(2.375-φ). The precision of simulation can be ensured. The obtained results show that the resolution of shear modulus G is 1 Pa at the beginning of coagulation and which gradually decreases to 16.53 Pa as G reaches 750 Pa corresponding to the maximum of normal blood. At last, it is degraded to 50.33 Pa when G increases to 1500 Pa. The formula among φ, G and Φ(oscillation angle of the blood) is achieved as φ(G,Φ)=GΦ/(G+255.22) and it implies that φ is proportional to the value of Φ and increases with G value. In order to verify the measuring theory, two-channel thromboelasticity measuring system has been equipped and data processing is employed to construct thromboelastograph with a series of informative parameters.Secondly, the core device of detecting unit called angular displacement sensor is designed based on the principle of differential PCB inductance. Complex derivation is used to establish the equation of this sensor which has been proved by finite element numerical simulation through Ansys Maxwell. Afterward, tests are carried out. The results clearly imply that the sensitivity of the sensor with single coil is improved 1 time after the utilization of differential coils and non-linearity becomes much smaller. All these improvements are derived from the compensation of the errors from external disturbance such as temperature change, vibration and so on The equation of linear regression of calibration is obtained with R2=0.9998. Within the angular range from-6° to 6°, nonlinear error is 0.86%, and the sensitivity is 1559.5 signal/°. The resolution is 0.01°. In the end, the maximum angular range of this sensor can be enlarged to-10°~10°.Thirdly, main characteristics of thrombus formation in vitro environment are analyzed such as thermal field, vibration, shear oscillation and so on through simulation and tests. Results suggest temperature makes great impact on the coagulation and it costs 6 min to reach 36℃ with accurate temperature control ±0.3℃. Oscillation mechanism can provide periodic shear deformation for the sample following the law of sinusoidal accelerated velocity on the first stage, then rest, sinusoidal accelerated velocity on the third stage and rest in the end. The process of motion is shockless and the maximum pressure angle is less than 24°. Vibration of motor affects the measurement insignificantly with the value of 30 sigal, which is less than the resolution of the measuring system. Therefore, more considerations should be taken into account including vibration of external environment.Fourthly, main geometrical errors which influence the accuracy of the thromboelasticity measuring system are studied and the precision is tested through a series of experiments as soon as calibration for the device is carried out. Results indicate the x-axis center error of the sensor has the most significant influence which can lead to an error of 18.34 Pa for G. Tilt error of the cup has the error of 13.34 Pa, and the length error of tungsten wire has the error of 10.05 Pa. To sum up, the general error reaches 29.7 Pa. The calibration curves of both channels are obtained with R2=0.998. The experimental results verify the fine reliability of the device with CV(R)=1.48%,CV(K)=5.33%,CV(α)=1.27%,CV(MA)=1.29%.Lastly, based on the fact that the reaction between the endotoxin is similar to the coagulation of blood, elastograph is used to assay the concentration of endotoxin. Results show there is a linear relationship between logarithms of time reaching the oscillation amplitude of 0.1 and logarithms of endotoxin concentration, the regression equation is obtained with R2 = 0.990. The linear range is from 0.01 to 10 EU·mL-1 and limit of detection is down to 0.002 EU·mL-1. It is observed that the sensitivity of this method is among the highest ones. The detecting time of EG assay can be reduced by up to 55% compared with the electrochemical method and turbidimetric method. Physiological saline and cell culture medium samples spiked with different amount of endotoxin were prepared to confirm its practical utility and satisfactory recoveries are obtained. The relative errors are also rather small with the mean value 5.2%, which promises the accuracy and fine practicality of this method.Through this study, several key technologies on thromboelasticity measuring have been broken through and in vitro thromboelasticity measuring system is realized, which can provide reliable and systematic fundamental theories for the next engineering and industrialization.