Heart valve performance evaluation method considering patient blood personality characteristics

Abstract

The invention relates to a heart valve performance evaluation method considering patient blood personality characteristics, and belongs to the field of heart valve stress analysis, and the method comprises the following steps: S1, building a geometric model of a heart valve, and defining material parameters; importing the geometric model of the heart valve into software, and establishing a finite element mesh model of the heart valve; s2, establishing a non-Newtonian fluid model of the blood, collecting the blood of the patient, fitting the non-Newtonian fluid model according to the blood data of the patient, and calculating the blood viscosity of the patient at the infinite shear rate; s3, setting a boundary condition and a dynamic load of the heart valve; and S4, calculating the stress distribution condition of the heart valve. According to the method, the blood backflow and blood interference conditions generated by a Newtonian fluid blood model can be reduced, the shear thinning characteristic of the blood of the patient is fully considered, blood stress analysis is more accurate, and personalized reference and evaluation schemes are provided for heart valve design of the patient.

Description

Technical Field

[0001] The present invention belongs to the field of heart valve mechanics, and in particular relates to a heart valve performance evaluation method taking into account individual blood characteristics of a patient. Background Art

[0002] With the increase of cardiovascular diseases, replacement of artificial heart valves has become a means of treating cardiovascular diseases. Artificial heart valves need to be evaluated for their mechanical properties.

[0003] Application publication number CN102551919A discloses an artificial heart valve and its performance analysis method based on ANSYS / LS-DYNA. In the method, a finite element model is adopted, boundary conditions and dynamic loads are set, and the stress distribution of the heart valve model is obtained by finite element calculation.

[0004] This prior art solution has the following two defects:

[0005] 1. The differences among individual patients are not taken into consideration. Because the viscosity of blood varies among individual patients, the parameters in the established blood model are also different. The prior art only inputs the conventional data in the blood model into the finite element model calculation, and does not analyze different patients. Therefore, for a specific patient, the final calculated stress distribution is inaccurate.

[0006] 2. The existing technology uses a Newtonian fluid model as a patient's blood model. The blood viscosity in the Newtonian fluid model is affected by factors such as hematocrit, plasma viscosity and deformability, which will cause changes in shear rate. Changes in shear rate will further cause changes in shear stress. Changes in shear stress will cause flow turbulence and increase blood flow energy loss, thereby affecting blood reflux and blood disturbances, making the shear stress inaccurate. Summary of the invention

[0007] The present invention provides a heart valve performance evaluation method that takes into account the individual blood characteristics of patients. While taking into account individual differences among patients, a non-Newtonian fluid is used to establish a blood model, thereby improving the accuracy of heart valve stress analysis after finite element calculation.

[0008] A heart valve performance evaluation method considering the individual characteristics of a patient's blood according to the present invention comprises the following steps:

[0009] S1: Establish a geometric model of the heart valve and define material parameters; import the geometric model of the heart valve into the software and establish a finite element mesh model of the heart valve;

[0010] S2: Establish a non-Newtonian fluid model of blood, collect blood from patients, analyze and obtain blood data of patients, calculate parameters in the non-Newtonian fluid model based on the blood data of patients, calculate the blood viscosity of patients at infinite shear rate based on the non-Newtonian fluid model, and input the blood viscosity at infinite shear rate into the software LS-DYNA;

[0011] S3: In LS-DYNA, set the boundary conditions and dynamic loads of the heart valve;

[0012] S4: The stress distribution of the heart valve is calculated by LS-DYNA numerical simulation.

[0013] Further, step S2 includes the following steps:

[0014] S2.1: Establish Casson model;

[0015] S2.2: For any patient, collect blood from the patient's antecubital vein and store the blood in an anticoagulant;

[0016] S2.3: Within a period of time T after blood collection, measure the blood viscosity at a certain shear rate; record the shear rate and the corresponding blood viscosity; suppose the shear rate is Let the corresponding blood viscosity be μ 1 ;

[0017] S2.4: Measure the hematocrit in the patient's blood, refer to the relationship between blood yield stress and red blood cell percentage, and obtain the yield stress τ of the patient's blood y1 ;

[0018] S2.5: Change the blood flow shear rate in S2.3 to The blood viscosity is μ 1 and the yield stress τ of blood in S2.4 y1 Substitute into the Casson model formula to calculate the Casson viscosity k of the patient at infinite shear rate 1 ;

[0019] S2.6: k 1 Input into LS-DYNA to complete the definition of the patient's non-Newtonian fluid blood.

[0020] In this solution, the Casson model of non-Newtonian fluid is used to describe the mechanical properties of blood, which reduces blood reflux and blood disturbance and makes shear stress accurate. In addition, blood sampling and testing are performed according to different patients, and the data in the established model is more accurate, which can form corresponding heart valve stress maps according to different patients.

[0021] Furthermore, in step S2.3, when measuring the blood viscosity of the patient at a certain shear rate, the shear rate is less than 10 2 .

[0022] If the shear rate is too high, the blood will become closer to a Newtonian fluid, affecting the results.

[0023] Furthermore, in step S2.3, within 1 hour after blood collection, the blood viscosity at a certain shear rate is measured.

[0024] Avoid changes in blood viscosity over time.

[0025] Furthermore, in step S2.1, the Casson model is improved and the improved Casson model is adopted. The formula of the improved Casson model is:

[0026]

[0027] Where k is the Casson viscosity at infinite shear rate; τ y is the patient's blood yield stress, which is related to the patient's red blood cell percentage; is the blood flow shear rate; μ is the patient's fluid viscosity.

[0028] The Casson model was improved by multiplying the patient's blood yield stress by a coefficient of 2 to make the blood viscosity more in line with actual conditions.

[0029] Furthermore, in step S2.2, the patient's blood is stored in a vacuum bottle containing ethylenediaminetetraacetic acid anticoagulant.

[0030] A simple blood preservation method can be implemented relatively easily.

[0031] Beneficial effects:

[0032] 1. This scheme uses the Casson model to simulate blood. The Casson model is a non-Newtonian fluid model, which reduces the blood reflux and blood disturbance caused by Newtonian fluid. Compared with Newtonian fluid, the stress finally calculated by this scheme is more accurate.

[0033] 2. For each patient, this program collects blood and obtains the viscosity of the blood at a certain shear rate to calculate the parameters in the Casson model, so that each patient has his or her corresponding heart valve stress map. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is a schematic diagram of the finite element mesh model of the heart valve;

[0035] Figure 2It is a comparison chart of blood viscosity at different shear rates;

[0036] Figure 3 It is a graph comparing the percentage of red blood cells and the yield stress of blood;

[0037] Figure 4 It is the stress distribution diagram of the heart valve under non-Newtonian fluid;

[0038] Figure 5 This is the stress distribution diagram of the heart valve under Newtonian fluid. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] A method for evaluating heart valve performance taking into account individual characteristics of a patient's blood comprises the following steps:

[0041] S1: Establish a geometric model of the heart valve and define material parameters; import the geometric model of the heart valve into the software and establish a finite element mesh model of the heart valve.

[0042] This step S1 is identical to the content recorded in CN102551919A mentioned in the background technology, so it will not be described in detail.

[0043] In this embodiment, PRO / E is used to perform geometric modeling of the heart valve, and the modeling is imported into ANSYS in the IGES format. ANSYS meshes the geometric modeling of the heart valve to generate a finite element model for dynamic mechanical analysis. Figure 1 This is the finite element mesh model of the heart valve after being imported into ANSYS.

[0044] In ANSYS, set the parameters of the heart valve. In this embodiment, the heart valve is regarded as bovine pericardium material, which is approximately a linear elastic material. The parameters of the heart valve are set as follows: Poisson's ratio is 0.49, elastic modulus is 5.4 MPa, density is 1.0×10 9 ton / mm 3 The above material parameters are defined in LS-DYNA.

[0045] S2: Collect the patient's blood and obtain blood parameters, establish a non-Newtonian fluid model of the blood, and use the patient's blood parameters to calculate the parameters in the non-Newtonian fluid model of the blood.

[0046] The specific steps include:

[0047] S2.1: The improved Casson model is used to establish the hemodynamic model; the formula of the improved Casson model is:

[0048]

[0049] Where k is the Casson viscosity at infinite shear rate; τ y is the patient's blood yield stress, which is related to the patient's red blood cell percentage; is the blood flow shear rate; μ is the patient's blood fluid viscosity.

[0050] S2.2: For any patient, collect blood from the antecubital vein and store the blood in a vacuum bottle containing ethylenediaminetetraacetic acid (EDTA) anticoagulant;

[0051] S2.3: Within 1 hour after blood collection, measure blood viscosity under certain shear rate conditions.

[0052] See Figure 2 Because the greater the shear rate, the closer the blood viscosity is to Newtonian fluid, so in order to ensure that the blood viscosity conforms to the characteristics of non-Newtonian fluid, the shear rate should be less than 10 2 , assuming the patient's blood flow shear rate is At this shear rate, the patient's blood viscosity was measured to be μ 1 .

[0053] S2.4: Continue to measure the hematocrit of the patient's blood, and refer to the relationship diagram between blood yield stress and red blood cell percentage to obtain the yield stress τ of the patient's blood. y1 .

[0054] Among them, see Figure 3 , the relationship diagram between blood yield stress and red blood cell percentage is an existing relationship diagram.

[0055] S2.5: Change the blood flow shear rate in S2.3 to The blood viscosity is μ 1 and the yield stress τ of blood in S2.4 y1 Substituting into formula (1), the Casson viscosity k of the patient at infinite shear rate is calculated: 1 .

[0056] S2.6: k 1 Input into LS-DYNA to complete the definition of the patient's non-Newtonian fluid blood.

[0057] S3: In LS-DYNA, set boundary conditions and dynamic loads.

[0058] This step S3 is the same as the step mentioned in CN102551919A in the background technology, so it will not be described in detail.

[0059] Setting of valve boundary conditions: The sutured edge between the bioprosthesis and the valve frame is fully constrained. There is no constraint on the free edge of the valve.

[0060] The boundary conditions of the finite element model were defined as follows: the freedom of the points at the lower boundary of the bioprosthesis (the sutured edge of the bioprosthesis and the valve frame) was restricted, and the points at the upper boundary (the free edge of the valve) could move freely.

[0061] When the valve is subjected to dynamic load analysis, the SHELL 163 thin shell element is used. This element is a 4-node space thin shell element and adopts the fully integrated Belytschko-Tsay thin film element algorithm.

[0062] Valve fluid-structure coupling analysis:

[0063] The dimensionless Reynolds number is used to determine the flow state of the fluid. The Reynolds number is defined as:

[0064]

[0065] Where ρ is the fluid density (kg / m), u is the velocity (m / s), D is the inner diameter of the tube (mm), and μ is the fluid viscosity (mm 2 / s), during the entire calculation process, the maximum Reynolds number is about 600.

[0066] The calculation of the fluid part is based on the three-dimensional, unsteady, incompressible Navier-Stokes equations:

[0067]

[0068] Where u is the velocity (m / s); p is the pressure (pa); and ρ is the fluid density (kg / m 3 ), μ is the fluid viscosity (mm 2 / s), t is time (s);

[0069] Equivalent stress of fluid:

[0070]

[0071] Where u(x,t) is the fluid flow velocity of the spatial particle x at time t; ρ is the fluid density; p(x,t) is the pressure of the spatial particle x at time t; μ is the fluid viscosity; and E is the unit matrix.

[0072] The solid part satisfies the elastic mechanics formula, ignoring gravity:

[0073]

[0074] Where σ is the stress tensor and ρ is the fluid density (kg / m 3 ),u i is the displacement, t is the time (s);

[0075] Boundary constraints: u f (x,t)=u s (x -1 (x,t),t)

[0076] σ f (x,t)·n=σ s (x -1 (x,t),t)·n

[0077] Where: x -1 (x, t) is the inverse mapping of x(x, t), which means that the spatial particle x is mapped to the physical coordinate X at time t; n is the normal vector of the fluid-solid interface. f (x, t) represents the fluid velocity of the spatial particle x at time t; u s Expressed as solid velocity; σ f (x, t) represents the fluid stress tensor at coordinate x at time t; σ s represents the solid stress tensor;

[0078] S4: The stress distribution of the heart valve is calculated through numerical simulation using LS-DYNA.

[0079] See Figure 4 , Figure 4 This is an image of heart valve stress for non-Newtonian fluid. Figure 5 is the stress image of the heart valve for a Newtonian fluid. Figure 4 and Figure 5 It can be seen that the non-Newtonian fluid has a significant effect in the low-speed reflux area of ​​the inferior vena cava, reducing blood reflux and blood disturbance, making the reflected shear stress more accurate.

[0080] Based on the above ideal embodiments of the present invention, the relevant staff can make various changes and modifications without departing from the technical concept of the present invention through the above description. The technical scope of the present invention is not limited to the contents of the specification, and its technical scope must be determined according to the scope of the claims.

Claims

1. A method for evaluating heart valve performance taking into account individual characteristics of a patient's blood, characterized in that: The following steps are involved: S1: Establish a geometric model of the heart valve and define material parameters; import the geometric model of the heart valve into the software and establish a finite element mesh model of the heart valve; S2: Establish a non-Newtonian fluid model of blood, collect blood from patients, analyze and obtain blood data of patients, calculate parameters in the non-Newtonian fluid model based on the blood data of patients, calculate the blood viscosity of patients at infinite shear rate based on the non-Newtonian fluid model, and input the blood viscosity at infinite shear rate into the software LS-DYNA; S3: In LS-DYNA, set the boundary conditions and dynamic loads of the heart valve; S4: The stress distribution of the heart valve is calculated by LS-DYNA numerical simulation.

2. A heart valve performance evaluation method considering the individual characteristics of a patient's blood according to claim 1, characterized in that: Step S2 includes the following steps: S2.1: Establish Casson model; S2.2: For any patient, collect blood from the patient's antecubital vein and store the blood in an anticoagulant; S2.3: Within a period of time T after blood collection, measure the blood viscosity at a certain shear rate; record the shear rate and the corresponding blood viscosity; suppose the shear rate is Assume the corresponding blood viscosity is μ1; S2.4: Measure the hematocrit in the patient's blood, refer to the relationship between blood yield stress and red blood cell percentage, and obtain the yield stress τ of the patient's blood y1 ; S2.5: Change the blood flow shear rate in S2.3 to The blood viscosity is μ1 and the yield stress τ of the blood in S2.4 y1 Substitute it into the Casson model formula to calculate the Casson viscosity k1 of the patient at infinite shear rate; S2.6: Input k1 into LS-DYNA to complete the definition of the patient's non-Newtonian fluid blood.

3. A heart valve performance evaluation method considering the individual characteristics of a patient's blood according to claim 2, characterized in that: In step S2.3, when measuring the blood viscosity of the patient at a certain shear rate, the shear rate is less than 10 2 .

4. A heart valve performance evaluation method considering the individual characteristics of a patient's blood according to claim 3, characterized in that: In step S2.3, within 1 hour after blood collection, the blood viscosity at a certain shear rate is measured.

5. A heart valve performance evaluation method considering the individual characteristics of a patient's blood according to claim 3, characterized in that: In step S2.1, the Casson model is improved and the improved Casson model is adopted. The formula of the improved Casson model is: Where k is the Casson viscosity at infinite shear rate; τ y is the patient's blood yield stress, which is related to the patient's red blood cell percentage; is the blood flow shear rate; μ is the patient's fluid viscosity.

6. A heart valve performance evaluation method considering the individual characteristics of a patient's blood according to claim 3, characterized in that: In step S2.2, the patient's blood is stored in a vacuum bottle containing ethylenediaminetetraacetic acid anticoagulant.

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