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Metabolic syndrome is associated with hypercholesterolemia, cardiac remodeling, and increased susceptibility to ventricular arrhythmias. Effects of diet-induced hypercholesterolemia on susceptibility to torsades de pointes arrhythmias (TdP) together with potential indicators of arrhythmic risk were investigated in three experimental groups of Carlsson’s rabbit model: (1) young rabbits (YC, young control, age 12–16 weeks), older rabbits (AC, adult control, age 20–24 weeks), and older age-matched cholesterol-fed rabbits (CH, cholesterol, age 20–24 weeks). TdP was induced by α-adrenergic stimulation by methoxamine and IKr block in 83% of YC rabbits, 18% of AC rabbits, and 21% of CH rabbits. High incidence of TdP was associated with high incidence of single (SEB) and multiple ectopic beats (MEB), but the QTc prolongation and short-term variability (STV) were similar in all three groups. In TdP-susceptible rabbits, STV was significantly higher compared with arrhythmia-free rabbits but not with rabbits with other than TdP arrhythmias (SEB, MEB). Amplitude-aware permutation entropy analysis of baseline ECG could identify arrhythmia-resistant animals with high sensitivity and specificity. The data indicate that the TdP susceptibility in methoxamine-sensitized rabbits is affected by the age of rabbits but probably not by hypercholesterolemia. Entropy analysis could potentially stratify the arrhythmic risk and identify the low-risk individuals.

Metabolic syndrome is associated with hypercholesterolemia, cardiac remodeling, and increased susceptibility to ventricular arrhythmias. Effects of diet-induced hypercholesterolemia on susceptibility to torsades de pointes arrhythmias (TdP) together with potential indicators of arrhythmic risk were investigated in three experimental groups of Carlsson’s rabbit model: (1) young rabbits (YC, young control, age 12–16 weeks), older rabbits (AC, adult control, age 20–24 weeks), and older age-matched cholesterol-fed rabbits (CH, cholesterol, age 20–24 weeks). TdP was induced by α-adrenergic stimulation by methoxamine and IKr block in 83% of YC rabbits, 18% of AC rabbits, and 21% of CH rabbits. High incidence of TdP was associated with high incidence of single (SEB) and multiple ectopic beats (MEB), but the QTc prolongation and short-term variability (STV) were similar in all three groups. In TdP-susceptible rabbits, STV was significantly higher compared with arrhythmia-free rabbits but not with rabbits with other than TdP arrhythmias (SEB, MEB). Amplitude-aware permutation entropy analysis of baseline ECG could identify arrhythmia-resistant animals with high sensitivity and specificity. The data indicate that the TdP susceptibility in methoxamine-sensitized rabbits is affected by the age of rabbits but probably not by hypercholesterolemia. Entropy analysis could potentially stratify the arrhythmic risk and identify the low-risk individuals.

Intersticiální buňky Cajalova typu (IC-LC) hrají důležitou roli při fyziologické i patologické funkci močového měchýře. Aautory vyvinutý relativně jednoduchý model sestává z pěti nelineárních obyčejných diferenciálních rovnic (ODE). Jeho přesnost byla ověřena srovnáním s publikovanými experimentálními výsledky. Hlubší analýza tohoto modelu ukázala existenci více stabilních a tzv. skrytých atraktorů, které mohou významně ovlivňovat chování celého měchýře. Jako výhodné se ukázalo využití metody, založené na perpetuálních bodech. V příspěvku je stručně uvedena definice těchto bodů. Ač tato metoda není dosud plně dokázána, dovoluje určit výše uvedené atraktory. Cílem je prokázat aplikaci této metody na uvedeném 5D systému. Toto je demonstrováno na několika příkladech. Cajal-like interstitial cells (IC-LC) play important role in both physiological and pathological function of the bladder. The authors developed relative simple mathematical model consisting of five nonlinear ODEs. The model accuracy was verified using published experimental results. Deeper analysis of this model has shown existence of the multi-stable and hidden attractors which can have important influence on the behavior of the whole bladder. As the most effective way to obtain these attractors seems to be to use the method based on the calculation of the perpetual point. In the contribution is shortly introduced the definition of these points. Although this method is till now not fully proved it allows to calculate some multi-stable or hidden attractors. The goal is to show the application of this method on the more complex 5D system. This is presented on suitably chosen example.

The paper deals with the dynamical analysis of the system of first-order ODE’s describing the isometric stimulation of the muscle fibre. This system is considered to be a non-autonomous one having the periodical excitation. For the analysis of dynamical behaviour the system the multiple scale method (MSM) is employed. The main goal of this contribution is to show the application of MSM to the non-autonomous dynamical system using the first order approximation of the solution. The existence of the degenerated Hopf’s bifurcation of the gained solution is presented.

The complex model of the lower part of the urinary tract is introduced. It consists of the detrusor smooth muscle cell model and the detailed 1D model of the urethra flow. The nerve control is taken into account. In future this model will allow to simulate the influence of different drugs and mechanical obstructions in the bladder neck and urethra. A general muscle model involving the calcium dynamics in the smooth muscle cell and the growth and remodelling theory will be shortly introduced. For the modelling calcium dynamics the approach of Koenigsberger published in Biophysical Journal (Koenigsberger, M., Sauser, R., Seppey, D., Beny, J.-L., Meister, J.-J., Calcium dynamics and vosomotion in arteries subject to isometric, isobaric and isotonic conditions, Biophysical Journal 95 (2008) 2 728–2 738.) was adopted. The model includes the ATP consumption calculation according to Hai et al. (Hai, C. M., Murphy, R. A., Adenosine 5’-triphosphate consumption by smooth muscle as predicted by the coupled four-state crossbridge model, Biophysical Journal 61(2) (1992) 530–541.). The main part is devoted to the development of a simple bladder model and the detrusor contraction during voiding together with the detailed model of the urethra flow.

Muscle fibre contraction is a complex thermomechanical process. The change in muscle fibre length (isotonic contraction) and tension (isometric contraction) may be regarded as muscle fibre growth (change in length) and remodelling (change in stiffness). In this study a general mathematical model based on the growth and remodelling theory and the theory of irreversible thermodynamics is proposed. The isometric contraction of muscle fibre is treated as an isothermal process. The relevance of chemical agents diffusion is also discussed.

The theory of growth and remodeling is applied to the 1D continuum. This can be mentioned e.g. as a model of the muscle fibre or piezo-electric stack. Hyperelastic material described by free energy potential suggested by Fung is used whereas the change of stiffness is taken into account. Corresponding equations define the dynamical system with two degrees of freedom. Its stability and the properties of bifurcations are studied using multiple-scale method. There are shown the conditions under which the degenerated Hopf’s bifurcation is occuring.

Contribution contains the short description of the general theory of growth and remodeling based on Di’Carlo’s approach. This theory is applied to the one dimensional continuum using the quadratic form of the free energy function. Two different forms of loading are dealt – isometric and isotonic one. For both cases the corresponding equations describe the dynamical system. Its properties are analyzed using the methods of nonlinear dynamics. It’s shown the influence of the constant growth and remodeling parameters on the stability of the equilibrium point

Background: The aortic and pulmonary allograft heart valves (AHV) are used in the cardiac surgery for replacing the impaired semilunar valves. They are harvested from donor hearts and cryostored in tissue banks. The expiration period was set to 5 years arbitrarily. We hypothesized that their mechanical and structural properties do not reasonably deteriorate after this period. Methods: A total of 64 human AHV (31 aortic and 33 pulmonary) of different length of cryopreservation (fresh, 0-5, 5-10, over 10 years) were sampled to different tissue strips (artery, leaflet, ventriculo-arterial junction, arterial ring) and tested by tensile test with loading velocity 10 mm/min until tissue rupture. Neighbouring regions of tissue were processed histologically and evaluated for elastin and collagen area fraction. The results were evaluated statistically. Results: In aortic AHV, the physical deformation response of wall samples to stress did not changed significantly neither during the process of cryopreservation nor during the first 10 years of storage. In pulmonary AHV, the ultimate strain dropped after 5 years of cryopreservation indicating that pulmonary artery was significantly less deformable at the time of rupture. On the other hand, the ultimate stress was equal during the first 10 years of...

Mitral allograft has never been as widely used as the aortic one for the treatment of infective endocarditis in clinical practice. Results of mitral valve replacements with mitral allograft were poor. Development of better techniques of mitral valve repair and improving quality of valve prostheses led surgeons to abandon use of mitral allografts in mitral position. On the other hand that technique could be helpful for treatment of tricuspid valve pathology, mainly of infectious endocarditis. We were evaluating the possibility of inserting a cryopreserved mitral allograft into the tricuspid position in a sheep experimental model. Within the framework of this experimental project the mechanical properties of the cryopreserved mitral allograft were tested. A novel methodology of graft tissue mechanical properties testing was developed. It reflexes the surgical technique of mitral allograft transplantation as it investigates whole functional unit composed of mitral annulus, leaflet, chordae tendinaea, and papillary muscle together. A five-parameter Maxwell model was applied to characterize the viscoelastic behavior of sheep mitral valves. A control group of 39 fresh mitral specimens and a test group of 13 cryopreserved mitral allografts processed according to the tissue bank standards were tested. The testing...

Introduction: Scoliosis influences the optimal posture and locomotion of the human body. Lumbar and thoraco-lumbar scoliosis has possibly an even greater impact due to the close relation with the pelvic region, a major determinant of gait. The effect of moderate idiopathic scoliosis on the gait cycle of young adults is of major interesting. Discussion-Hypothesis and aims: Young adults (20-40 years old) with MIS (lumbar and thoraco-lumbar primary curves) present kinematic modifications regarding the convex (ipsilateral extremity) or concave (controlateral extremity) side of the body as well as variations compared to non-scoliosis individuals during the gait cycle. Aim of this study was to indentify these variations on the physical quantities exerted from the major joints of the lower extremities as well as the center of gravity too and examine their significance in adult patients with MIS. Materials and methods: A cohort of twenty young adult patients (group A, 12 females- 8 males, mean age 39,7 years) having MIS with mean Cobb's angle 29o (24o to 34o ) and a control group (B) of fifteen (8 females, 7 males) of healthy individuals were submitted in clinical examination and 3-D gait analysis. Direct linear transformation (DLT) was used for analysis of linear displacement on the three axes (x, y and z) as well...