Enhancing the differentiation of walking and standing via the ratio of plantar pressures.

Differentiation of standing and walking based on plantar pressures is helpful in developing strategies to reduce health risks in the workplace. In order to improve the differentiation ability, the paper proposes a new metric for posture differentiation, that is, the pressure ratio on the two anatomical plantar regions. The plantar pressures were collected from 30 persons during walking and standing. After verifying the normal distribution of the pressure ratio by the Monte Carlo method, two-way repeated-measures ANOVA was conducted for the pressure ratios. The advantage of the pressure ratio over two conventional pressure metrics (the average pressure and the peak pressure) is demonstrated by its much larger size effect. Furthermore, the pressure ratio permits to establish value ranges corresponding to walking and standing, which are less influenced by specific person factors, thus facilitating the design of a standardized posture recognition system. The underlying mechanism underlying the pressure ratio is discussed from the aspect of biomechanics of movement.

Finite element analysis of left ventricle during cardiac cycles in viscoelasticity.

To investigate the effect of myocardial viscoeslasticity on heart function, this paper presents a finite element model based on a hyper-viscoelastic model for the passive myocardium and Hill's three-element model for the active contraction. The hyper-viscoelastic model considers the myocardium microstructure, while the active model is phenomenologically based on the combination of Hill's equation for the steady tetanized contraction and the specific time-length-force property of the myocardial muscle. To validate the finite element model, the end-diastole strains and the end-systole strain predicted by the model are compared with the experimental values in the literature. It is found that the proposed model not only can estimate well the pumping function of the heart, but also predicts the transverse shear strains. The finite element model is also applied to analyze the influence of viscoelasticity on the residual stresses in the myocardium.

Viscoelastic modeling of the contact interaction between a tactile sensor and an atrial tissue.

Modeling and parameter identification of soft tissue are essential in establishing an accurate contact model for tool-tissue interaction, which can be used in the development of high-fidelity surgical instruments. This paper discusses the interaction between a tissue and a tactile sensor in minimally invasive surgery, the focus being a novel technique for robotic-assisted mitral valve repair, in which tactile sensors are used to distinguish between different kinds of tissue by their relative softness. A discrete viscoelastic model is selected to represent the tissue behavior. To populate the model of the tissue with actual data, a set of tissue-testing experiments is designed and implemented on the atrial tissue of a swine heart by analyzing its dynamic response. By means of a genetic algorithm, data of the complex compliance are extracted and used to find the coefficients of the model. Further, a viscoelastic contact model is developed to model the interaction between the tissue and the tactile sensor with annular shape. Finally, the relation among the indentation displacement, the ratio of the radii, and the applied force is established parametrically.