Gediminas Daubaris

Implementation of non-invasive brain physiological monitoring concepts.

The paper presents innovative methods and technology for non-invasive intracranial hemodynamics monitoring based on the measurement of brain parenchyma acoustic properties. The clinical investigation of new technology shows the similarity between the invasively recorded intracranial pressure (ICP) and non-invasively recorded intracranial blood volume (IBV) pulse waves, slow waves and slow trends under intensive care unit (ICU) conditions. Also, the applicability of the non-invasive IBV slow wave monitoring technique for cerebrovascular autoregulation non-invasive long-term monitoring is demonstrated by theoretical and experimental studies.

Clinical study of craniospinal compliance non-invasive monitoring method

BACKGROUND The ability to quantify non-invasively the effect of posture on intracranial physiology by using cine phase-contrast MRI may lead to the development of new diagnostic tests to evaluate such functions as regulation of CBF and ICP, and the effect of pathologies on these functions. METHODS Results similar to MRI technology can be obtained using non-invasive ultrasonic method (Vittamed) for intracranial blood volume pulse wave (IBVPW) measurement and intracraniospinal compliance (ICC) monitoring. FINDINGS IBVPW have been investigated in supine and upright positions of healthy volunteers using Vittamed technology. A group of 13 healthy volunteers (nine females, four males, mean age 25.1 +/- 3.4) was studied. More than 3,000 IBVPW were analysed in order to show the difference of shape and amplitude in supine and upright positions. Averaged shape of ten IBVPW waves was presented in the normalized window with dimensions 1.0 x 1.0. CONCLUSIONS The results show significant difference between averaged IBVPW shapes in upright (highest intracraniospinal compliance) and supine (lower intracraniospinal compliance) body positions. Body posture caused IBVPW subwave P2 and P3 changes deltaP2 = 18% and deltaP3 = 11%. Amplitude of IBVPW in upright body position was significantly higher than in the supine one. The value of IBVPW amplitudes ratio in supine and upright positions was 1.55 +/- 0.61.

Simultaneous measurements of dynamic values using the transit time method

The problem of simultaneous and accurate measurements of two dynamic values, time dependencies of flow velocity and ultrasound velocity in the flow, is analyzed. In order to measure two dynamic values simultaneously a theory of the transit time method has developed, and the theoretical model of a microprocessor-based measuring system has been derived. The ways to improve the accuracy and information of such dual-channel measurement systems have been examined. It is shown that invariance between two channels of a measurement system can be achieved when dynamic, nonlinear, parametric models of these channels are identified in real time during the process of measurement, and when the multipulse irradiation of flow is used. The results of computer simulation of transit time method dynamic errors are represented. A method of minimizing these errors has been proposed. >

Identification problems in high performance microprocessor controlled electromechanical systems design

To increase the adequacy of the dynamic models of sophisticated high-performance elastic electromechanical systems, it is necessary to understand complicated processes involving multimodal and high-frequency vibrations of the systems components, which limit the accuracy of digital control of the system. The identification of such a dynamic state is complicated because it is necessary to use parametric functions as space-time characteristics. The problem is investigated for a microprocessor-controlled magnetic-disk storage device. The results of theoretical amplitude-frequency analysis, computer simulation, and dynamic measurements are used to obtain reliable identification data for system design.<<ETX>>