Russian Journal of Biomechanics

Mathematical modeling of the diagnostic procedure of differential tonometry based on loading the eye with a Schiotz tonometer using two or more weights of the plunger, one of the two structural elements of this tonometer, is performed. The model of the eyeball developed earlier by the authors is used, based on the representation of the cornea as a momentless two-dimensional elastic surface and the scleral region as a zero-dimensional elastic element that responds with a change in pressure to a change in the volume of the fluid contained in it. Unlike previous works, in which a theoretical study of differential tonometry was carried out based on a physically linear model of the cornea, the nonlinearity of its elastic behavior is taken into account on the basis of an effective approach that made it possible to describe this nonlinearity by means of a single parameter. It is shown that the dependence of the tonometric pressure on the weight of the plunger remains almost linear, which makes it possible to introduce the pressure difference coefficient γ as the slope of the corresponding straight line. This coefficient increases with both scleral and corneal stiffness and decreases with true pressure. Accounting for nonlinearity leads to increase in the calculated values of γ at sufficiently high both true pressures and stiffnesses of the two components of the eyeball, as well as to an expansion of the pressure range for which these values are large. It is shown that two groups of eyes can be distinguished, in one of which, characterized by high values of the pressure difference coefficient, both components of the corneoscleral coat are very rigid, and in the other, where these values are significantly lower, the stiffness of the eye tissues can be considered normal. At the same time, an intermediate range of γ values remains, for which such definite conclusions cannot be drawn only from the result of differential tonometry. However, the ability to isolate a group of very stiff eyes that are particularly likely to have glaucoma makes this procedure useful in diagnosing this disease.

The aim of this work was is to study of the phase transition during thermal denaturation of DNA by the method of recurrence quantification analysis, which is the most modern and efficient approach for the analysis of complex systems. To achieve the goal, the nonlinear dynamics model of the DNA denaturation is implemented, based on the Peyrard-Bishop-Dauxois approach, which allows determining the state of DNA base pairs at an arbitrary point in time. Next, the dynamics of DNA is simulated at different temperatures, and the evolution of hydrogen bond stretching during DNA heating is studied. To analyze the results obtained, the method of recurrence quantification analysis is used, which make it possible to judge the nature of the processes occurring in the system and are of particular interest in relation to the study of nonlinear DNA dynamics, in particular phase transitions, since on the basis of their analysis it is possible to identify states of repetition and fading (laminarity), the occurrence of extreme events, the presence of hidden periodicity and cyclicity. Using this method of analysis, quantitative measures are calculated in a window shifted along the main diagonal of the recurrent plot (RP). These measures quantify fine-scale RP structures. The calculations reveal the most sensitive measures to the analysis of the process under study, with the help of which the precursors of the phase transition are determined.

Prosthetic alignment plays an important role in the rehabilitation and outcomes of individuals with lower-limb loss. The goal of this work was to systematically review the state-of-the-science related to prosthetic alignment research and to identify the primary outcomes associated with prosthetic alignment as well as considerations for implementing alignment procedures. The review process was conducted papers searching in Scopus, PubMed, and IEEE databases. The PRISMA methodology was used to identify the prevalence of prosthetic alignment procedures from a technical and procedural point of view. Data extracted from papers included population attributes, outcome measures and metrics, alignment procedure characteristics, and the effects of prosthetic alignment on rehabilitation outcomes. The quality of the papers was assessed using thirteen predetermined criteria. Most studies in the sample were rated as low quality based on our formal assessment. The studies found that changes in socket reaction moment, ground reaction force, socket-stump interface pressure, spatiotemporal data, and patient comfort were typically affected by socket and foot angulations and translations. Considerations for alignment research focused on ambulation method, footwear use, accommodation time, and number of trials. The literature provides limited information about the considerations and outcomes of alignment procedures. The evidence is not of high quality and primarily relates to individuals with transtibial amputation.

Diabetes mellitus is a group of chronic metabolic disorders, characterized by an elevated blood sugar level. Due to the rapidly growing number of patients with diabetes mellitus, the complications rates are also increasing dramatically. Currently, non-invasive experimental methods are adopted to evaluate microcirculatory perfusion and reveal early diabetic microangiopathy dysfunction. Since microcirculation function assumes several interrelated processes depending on a large number of parameters, similar clinical manifestation of microcirculation disorder can be caused by various alterations that are often impossible to determine using only experimental data. Mathematical modeling is a promising tool to overcome mentioned above issues and en-hance experimental methods. This paper focuses on the development of mathematical model enabling to predict reperfusion syndrome in diabetic patients. The model of microcirculation can allow estimating other parameters (capillary wall hydraulic conductivity and oncotic pressure) by comparing computed results with capillaroscopic measurements of filtration rate. With the help of presented mathematical model we can propose a possible way for explaining why revascularization can cause aggravation of diabetic foot syndrome.

Approximately 5 million percutaneous coronary interventions are performed worldwide annually. Stent-related complications occur at a fairly low rate. The presented case describes a rare infection-related complex complications of percutaneous coronary interventions. A 46-year-old non-diabetic mail developed a fever of unknown origin after six days from the initial Percutaneous Coronary Intervention and was treated empirically with antibiotic therapy without suspicion on any iatrogenic infection. After two weeks from initial percutaneous coronary interventions a patient complained chest pain and with; stent thrombosis segment elevation myocardial infarction diagnoses were readmitted at our hospital. Early stent thrombosis was diagnosed by coronary angiography followed by second percutaneous coronary interventions. After some hours from the second angioplasty procedure acute stent thrombosis was developed. Coronary angiography revealed multiple extravasations on the site of thrombosis complicated with cardiac tamponade. A patient was urgently transferred to a cardiac operation theater. A Pseudomonas Aeruginosa (multiresistant) - was positive after coronary wall tissue histomorphological examination. The fever manifestation must be considered in the differential diagnosis during one or two weeks after initial percutaneous coronary interventions. Diagnosis is based on positive blood cultures and is helpful to manage treatment strategy