T.O. Pika, L.P. Safonova

In critical condition medicine, in surgery and anesthesiology, in neurology, on-line control and precaution of the brain hypoxic conditions are the most important problems. Tissue oximetry is one of the promising methods of the cerebral hypoxia monitoring/ The method provides estimation of the oxygen delivery parameters which are results of activity of the hemodynamic and respiratory systems. Tissue oximetry also allows to determine the local tissue oxigenation level and the cerebral perfusion parameters, the main biological chromophores' concentrations including water content in the tissue. Concentrations of oxy- and deoxyhemoglobin are the most important variables that characterize tissue oxygen delivery and utilization levels. These concentrations are used to calculate several parameters of the local cerebral circulation of blood such as cerebral blood flow and cerebral blood volume. The control of water and cyto-chrome oxidase concentrations demands application of the additional light sources of the needed wavelengh in the technical solution of the oximeter. The last parameter is the important indicator of the cellular oxygen utilization. In this preliminary research the possibilities of a tissue oximeter based on multidistance phase modulation approach have been investigated. Estimation of such system parameters as the heart rate and the breathing rate was experimentally demonstrated. The same initial measurements permit calculation of the arterial blood oxygen saturation. The received results allow to make a conclusion about the possible replacement of the pulse oximeter functions by the tissue oximeter operation. Based on reference findings, the cerebral blood volume and its dynamics were estimated during functional activity of the subjects. The received values correspond to the values of the normal physiological diapason. A big number of the tissue oximetry calculated parameters demands finding of their optimal representation for the support of decision-making that is important in critical condition monitoring. In this work a combination of oxy-, deoxyhemoglobin and tissue saturation has been analyzed. The found way of presentation permits simultaneous monitoring of the cerebral blood volume and the tissue oxygen saturation in the local investigated tissue volume. In medicine of critical conditions it is necessary to solve several optimization problems: to find the optimal sets of the controled life-important parameters and the optimal ways of their representation.