ABSTRACT
Objective To make the stent expand uniformly along the axial, an improved kriging optimization algorithm is applied for to the optimal design of stent-balloon system to find the optimal length of the balloon. Methods Based on finite element method results, kriging surrogate model combining with Latin hypercube sampling (LHS) approach and expected improvement (EI) function was employed for the optimization of balloon length to reduce stent dog-boning effect during its dilation. Results The kriging surrogate model could approximately establish the relationship between stent dog-boning rate and balloon length and so to replace the expensive reanalysis of stent dilation. Sample points from LHS could perfectly represent the vector space. EI function could be used to effectively find out the global optimal solution with high probability. The optimal length of balloon could make the stent expand uniformly. Conclusions This adaptive optimization method based on kriging surrogate model can optimize the design of stent–balloon system effectively.
ABSTRACT
Objective To compare the effects of continuous veno-venous hemofiltration (CVVH) and intermittent hemofiltration (IHF) on the hemodynamics and clinical outcomes of patients with type 1 cardiorenal syndrome. Methods From May 2008 to June 2011, 34 patients diagnosed with type 1 cardiorenal syndrome were admitted to our hospital and received CVVHQ9 cases) or IHF (15 cases). The general data, acute hemodynamic changes before and after hemofiltration and clinical outcomes at 28 days after hemofiltration were evaluated. Results There were no significant differences in the heart rates, diastolic blood pressure between the two groups before and after hemofiltration (P>0.05). The systolic pressure was similar between the two groups before hemofiltration (P>0.05), but that in the IHF group was significantly lower than that in the CVVH group after hemofiltration (P0.05), but the minimal mean pressure in IHF group was significantly lower than that in the CVVH group (P0.05). Multivariate analysis suggested that APACHE II was the main influence factor of 28-day mortality of patients, and APACHE II and net ultrafiltration were the main influence factor of the minimal mean pressure. Conclusion Compared with IHF, CVVH fails to greatly reduce the mortality of patients with type 1 cardiorenal syndrome. The severity of the disease is the main influence factor for the hemodynamic changes and the 28-day mortality of patients with type 1 cardiorenal syndrome.
ABSTRACT
Objective To evaluate the fatigue life of coronary stent under the effect of blood flow and thus optimize the stent design.MethodsA simplified model of the stent, blood, plaque and artery was established using Pro/Engineering, and the periodic blood flow impact on the vascular stent was simulated by finite element method via ANSYS. The result on hemodynamics from such stent was then used to evaluate its fatigue life. The geometric parameters of the stent were chosen as design variables for optimization. By using Latin Hypercubic sampling and ANSYS program, responses of the sample points could be obtained and the Kriging surrogate model was then constructed to optimize the fatigue life of the coronary stent.Results Goodman’s method showed that the optimized stent was safe. The cumulative damage method indicated that the largest damage occurred at the second cross-section of the bridge struts. The fatigue life of the optimized stent could be enhanced by 30.55%. Conclusions The finite element method can be used to evaluate the fatigue life of the coronary stent, and the optimization of stent by establishing Kriging model can effectively enhance the fatigue life of the stent.