Xian Chen

INFLUENCE OF MODELING METHODS FOR CARTILAGE LAYER ON SIMULATION OF PERIACETABULAR OSTEOTOMY USING FINITE ELEMENT CONTACT ANALYSIS

Finite element (FE) analysis has been used in the simulation of periacetabular osteotomy (PAO) to predict the improvement of contact pressure concentration in dysplastic hip joint. Since the cartil...

Computer simulation of nerve conduction study of a sural nerve to evaluate human peripheral nervous system

Nerve conduction study is a test to examine the function of electric signal transmission at the trunk of a peripheral nerve, which is an effective method for the diagnosis of diabetes to quantify the peripheral numbness and to evaluate the stage of this complication. In a routine test, the feature to measure in the electric potential waveform observed in this test is limited to the velocity and the amplitude of the peaks. To make the measurement more precise, the production process of the electric potential waveform should be observed carefully. In this study, nerve conduction study of a sural nerve, which is the most popular for the patients with diabetes, was simulated in a computer using general cable equation and neuroanatomical data. As a result, the approximate electric potential waveform was reproduced, whereas the conduction velocity of the peaks was not completely conformed to the physiological data.

A 3D COUPLED MATHEMATICAL MODEL FOR THE GROWTH OF AVASCULAR SOLID TUMOR

We develop a coupled mathematical model of avascular tumor growth based on porous media mechanics. This comprises of the migration of tumor cells (TCs), the degradation of extracellular matrix (ECM), the transport of matrix-degrading enzymes (MDEs), the seepage of tissue fluid and the supplement and consumption of oxygen. The simulation that a solid tumor grows in the micro-environment composed of the pre-existing capillaries and the surrounding tissues, and the specific property of varying porosity with the growth of TCs in a tumor micro-environment are taken into account. We propose functional coefficients for fluid seepage and oxygen diffusion, and incorporate the convection–diffusion of oxygen and the convection of MDEs. From this modified model the main findings include: first, a solid tumor originating in the inlet region undergoes necrosis in the outlet region because of a low supply of oxygen, while a solid tumor originating in the outlet region undergoes necrosis at the primary site because of overconsumption of oxygen; second, tumors further from capillaries grow faster than tumors close to adjacent capillaries; third, the pre-existing capillaries cause some impact to the transport of those chemical factors involved in tumor growth, and further affect tumor migration and necrosis.

Modeling Complex Current Waves of a Sural Nerve after Electric Stimulation in case of a Thin Myelin Sheath

A nerve conduction test checks whether the function of a nerve to conduct action potentials is normal or not by measuring compound action potential on the skin. In some neuropathies, a decrease in the thickness of the myelin sheath is observed. This is considered to be a cause of any delay or decay of the conduction of compound action potentials. However degenerated nerves include those with missing nerve fibers, which also decreases the velocity and amplitude of the potential. To investigate the effect of myelin sheath exfoliation, the compound action current was defined as modeling the source of compound action potentials, which are constructed as a complex of axonal currents of each nerve fiber inside a nerve. As a result, the thickness of the nerve fiber contributed to slowing the velocity of the current wave; however, the amplitude of the wave did not always decrease.