Russian Journal of Biomechanics

The aim of this study was to assess the influence of the bicycle ergometer endurance exercise test on the coordination abilities of cross-country skiers and biathletes in the preparatory period of the training process. 12 cross-country skiers and 11 biathletes participated in the study. The coordination test was carried out in the sitting position before and after maximal bicycle ergometer test. Reaction time was registered before endurance exercise test. For the control group, a group of university students ( n = 12) of the same age and with similar anthropometric parameters was recruited. This group did not carry out the maximal cycle ergometer test. We found that time of the first coordination test in athletes was better ( p < 0.001) than in the group of students. The time of the repeated coordination test was reduced in 75% participants of the control group ( p < 0.05), we believe due to the development of the motor action experience. Physical exercise leads to fatigue and reduced the number of athletes who carried out the second coordination test better than the first one. Biathletes completed the maximal bicycle ergometer test with higher physiological values and recovered longer, but carried out the second coordination test faster than cross-country skiers, which was probably due to the specifics of their sport and the training process. We found strong positive correlation between reaction time and time of the first coordination test in athletes. Athletes with higher oxygen consumption during the bicycle ergometer endurance exercise were faster in the coordination test.

The finite-element model describing the change of the stress-strain state of the sclera (the outer shell of an eye) loaded by an impression-type tonometer - the Schiøtz tonometer is presented. The simulation is performed with the software package ANSYS, Inc. The elastic system cornea-sclera is modeled as two thin transversely isotropic adjoint spherical shells with different radii of curvature and biomechanical properties loaded by the internal pressure and two loads with concave bases (footplate and plunger). The effect of the weight of the plunger and the thickness of the cornea on the tonometric pressure readings obtained due to the standard method of data processing for Schiøtz tonometry is studied. The obtained values are compared with the values found from the condition of constant internal volume of the deformed composite shell.

The paper presents the results of experimental studies of the adhesion strength at a static load on the gap of dental cement joints of an individual milled transdental implant with solid tissues of the tooth root. The samples consisted of a composition composed of a conical-shaped structure (similar to a transdental implant made of titanium alloy and zirconium dioxide) inserted into the canal of a natural tooth stump and fixed in it with cement gluing. The experiments were performed on previously removed teeth with a resected root tip in the amount of 78 units. As a result of the study, cements were identified that ensure the highest adhesive strength of the joint “individual transdental implant-dental cement-stump of an extracted tooth” in the specimen. For the root fixation of titanium alloy implants, composite Multilink-N cement is recommended, and for zirconium dioxide implants, Fuji -1 glass ionomer cement is recommended. At the second stage, the effect of artificial surface roughness of the implant on the adhesion properties of the cement joint implant-tooth was investigated. To this end, before conducting experiments on the extrusion of the pins, the samples surfaces were sandblasted with aluminum oxide granules of 50, 150, 250 microns in size. Cements were used for fixation, which showed the highest adhesive characteristics at the previous stage. It turned out that an increase in the roughness size in the range of 50-250 μm improves the adhesion parameters of the cement joint implant - tooth for all tested cements. The presence of implant roughness allows one to withstand a significantly greater load compared to a smooth implant, and an increase in the implant surface roughness value from 50 to 250 μm also significantly (almost 2.5 times) increases the load.

Presently, investigation of relationships between biomechanical processes of regulation of the lumen of peripheral vessels, blood flow dynamics and changes in skin temperature with the aim of imaging of hemodynamic dysfunction is an actual problem of biomedical engineering and diagnostics. Experimental dependences of the velocity and damping of a periodic thermal perturbation in pig skin as a model of human skin have been established in this work. The solution of the heat equation in the case of periodic heating has been used to describe the propagation of thermal perturbation (heat waves) in a human skin model. Assuming proportional changes in the volume blood flow and temperature in the depth of the skin, this will allow restoring the signal of blood flow dynamics based on data of skin surface temperature variation. The latter experimentally justifies the possibility of thermal imaging of the processes of regulation of the vascular lumen of peripheral vessels during the diagnostics and therapy of vascular complications.

The biliary system function is to transport bile into the duodenum for the fat digestion. Metabolic disorders and choledynamics disturbances may cause the cholelithiasis. In Russia, the pathology of the biliary system ranks third in the patients number. The surgical treatment of cholelithiasis is the gallbladder removal (cholecystectomy). However, the percentage of postoperative complications is quite high. One of the reasons is the lack of objective methods: surgeons are not always able to evaluate the surgical intervention consequences. Nevertheless, there are very few works devoted to the numerical simulation of processes associated to a bile flow. There was no complete personalized model that could be used in medical practice to the date. This paper presents a new model of the bile flow in the biliary system. The proposed approach is that the biliary system is considered as a combination of the three parts (the gallbladder, extrahepatic bile ducts, and the major duodenal papilla). The Windkessel model was used to simulate the bile flow in the gallbladder. The bile flow in the extrahepatic bile ducts can be considered as a fluid-structure interaction flow. The bile flow in the major duodenal papilla was considered as a peristaltic transport in a finite-length tapered tube. A complex model of the biliary system allowed us to evaluate choledynamics in the healthy state, pathology, as well as to carry out a numerical assessment of the bile flow after cholecystectomy to predict and prevent complications. The utilization of peristaltic flow modelling in the major duodenal papilla allowed us to determine the quantitative criteria for the occurrence of pathological reflux, which made it possible to ensure its prevention. The model can also be used to analyze surgical interventions in the treatment of cholelithiasis and its complications (stenting, anterior abdominal wall suturing). For example, the mathematical model of the installation of a stent with shape memory reduces the number of complications (soft tissue perforation). The numerical model of the accumulation of particles on the surface of the plastic stent made it possible to predict the replacement period for a particular patient and to improve the quality of his life. The biomechanical analysis of the use of suture materials allowed us to provide a differentiated approach to suture materials and to reduce the number of specific postoperative complications. It is shown that the developed model can be used to create a software to support decision-making when performing cholelithiasis treatment to prevent complications.

A model describing testosterone regulation by distributed input feedback control is considered. It is aimed to hold testosterone concentration above a corresponding level. The distributed feedback control with integral term is proposed. This leads us to analysis of an integro-differential system which describes the connection between the concentration of hormone GnRH, the concentration of the hormone LH and the concentration of testosterone Te. We propose controls in the form of integral operators, i.e. distributed feedback controls, which allows us to hold a suitable testosterone level without loss stability of the biological system.