Stanislav Otáhal

Simulation of cerebrospinal fluid transport

The pulsatile nature of the CSF movement is a result of the cardiac-related pulsations in blood volume in cranial region. According to Monro-Kellie Doctrine, the net inflow of arterial blood during systole is compensated by an equal outflow of venous blood and by caudal displacement of the CSF. Knowledge of the distribution of physical properties (compliance, resistance) along the craniospinal system is crucial for understanding of the CSF hydrodynamics. The synthesis of both invasively and non-invasively obtained data is needed. The aim of our project was to develop a lumped-parameter compartment model of the craniospinal system and, in relation to the cardiac-related blood-volume pulsations, to describe its basic hydrodynamic properties. The model consists of six compartments representing major parts of the craniospinal system. Each compartment has its own set of physical properties which describe its behavior. The pressure transmission from head arteries to the brain compartment serves as a source of pulsations. The simulation tightly mimics pressure waves of the CSF and thus the flow characteristics and magnitudes. The fitted compliance of the spinal compartment in our model was two orders higher (9x10^-^1^0m^3/Pa) then the cranial compartment (5.2x10^-^1^2m^3/Pa): only in this adjustment pulsations were present. It makes 99.5% of compliance related to the spinal canal and 0.5% to the intracranial structures. Our fitting showed that this model might be used in medical education as well as in medical practice.

Identification of viscoelastic parameters of skin with a scar in vivo, influence of soft tissue technique on changes of skin parameters.

The goal of the experiment was to develop an identification method capable of objective detection of changes of viscoelastic properties of skin with a scar remaining after a modified radical mastectomy. We compared the intact skin and the skin with a scar, a scar before and after physiotherapy. We used two methods. The first one is based on measurements of the local dynamic deformation response of the skin and the second one is the matrix identification of static deformation that identifies properties of the whole tested region of the explored tissues. We identified the skin stretchability, shiftability against deeper layers and deeply analysed both the methods. In some patients, we found statistically proven difference. In all these cases the measurement methods have detected changes of the observed tissue condition. We found both methods to be potentially applicable after further improvements as a diagnostic tool, which can contribute to the improvement of postoperative care of patients.

Examination of the Microrheology of Intervertebral Disc by Nanoindentation

Micro- and Nanoindentation technique has become a standard method for material testing of mechanical properties recently. Especially, indentation method with Oliver and Pharr theory for an analysis of isotropic elastic materials is very strait forward and become a part of every indenter’s software. Some multidirectional indentation analyses have been successfully applied on bone tissues such as cortical osteons and trabecular lamellae to identify their local elastic orthotropic or transverse isotropic properties. Present nanoindenters make possible an acquisition of creep and relaxation data, for that a model of creep or relaxation function can be found in the literature and the viscoelastic material parameters are derived.

Nanoindentation of porcine bone lamellae

Representative volume element (RVE) is widely used in the modelling of a bone. Single bone lamella creating the trabeculae in trabecular bone or the interstitial and osteonal lamellae within cortical bone is suggested to be the proper RVE. Once the lamella’s material constants are determined, the stiffness or compliance matrix is given in case of elastic material, the RVEs can be mathematically assembled in macroscopic anisotropic model (Mares 2006). Nanoindentation with in situ scanning of topography allows the placement of indents in a single lamella of few microns width (Hengsberger et al. 2002). Analysis of indentation of isotropic elastic material by Oliver and Pharr theory is a standard method of indenter software for determination of the hardness and the elastic modulus of samples. Swadener and Pharr (2001) have proposed the technique and solution of an indentation problem of an anisotropic material. We used fabric tensor theory (Zysset and Curnier 1995) to build up the calibration stiffness tensors in order to solve the Swadener and Pharr problem backwards: know the directional indentation moduli and derive the anisotropic stiffness tensor. We validated the procedure on mineralised turkey leg tendons with well-oriented collagen fibres in longitudinal direction (Lukes et al. 2009). This composition is mostly considered to be the bone lamella architecture.

Interconnecting measured data of in vivo kinematics and spinal functional unit in vitro

Presently, the biomechanics community is closely focused on scientific research of a phenomenon called the low back pain. The sphere of interest has turned to the whole spinal mechanism in order to develop a satisfactory solution for many people suffering from low back pain. This work concerns the possibility of interconnecting measured data of in vivo kinematics and spinal functional unit in vitro with a closer analysis of behaviour of the instantaneous axis of rotation (IAR; Holub et al. 2008). It was empirically found out that there is a very close relation between the IAR’s location and degenerative changes or the IAR and the consequences of phenomenon called whiplash (Grip et al. 2008). Irregularity of the IAR’s position has been associated with pain in a majority of cases.

Skull Base Surgery and Venous problems

The cerebral venous system is as important as its arterial system. The authors have been studying cerebral venous problem for a long time. In the prezent study, the authors have researched venous complications and problem correlated to biomechanical and hemodynamical studies. The histobiomechanical characteristics of bridging veins and cerebral sinuses were studies with the tests system MTS 858.2 Mini Bionix (unique testing system in Europe). The bridging veins have a very low stronghold on longitudinal traction. Sinuses, on the other hand, are very rigid. This might influence blood outflow from the brain in normal physiology and any pathological situation, including head trauma. The authors developed a special program for modeling the cardiovascular system and the cerebral venous system. In this study, they illustrate the problem of bridging veins and the venous sinuses. From biomechanical and physiological view-point, they propose a venous classification of the cardiovascular system has the potential to change after application of treatment. The authors report on clinical problem and aspects (destruction of bridging veins during trauma, carotid-cavernous fistulas, and venous neurological deficits).