L.P. Safonova - Ph.D.(Eng.), Associate Professor, Department «Medical and technical information technology» (BMT-2), Bauman Moscow State Technical University
T.O. Pika - Assistant, Department «Medical and technical information technology» (BMT-2), Bauman Moscow State Technical University
A.I. Dyachenko - Dr.Sc.(Eng.), Head of laboratory, A.M. Prokhorov Institute of General Physics of RAS (Moscow); Leading Research Scientist, SSC-Institute of Biomedical Problems of RAS; Professor, Bauman Moscow State Technical University

In this work an individual reaction of each examined person, а volunteer subject, was investigated during breathing under the negative inspiratory pressure. The validity of the breathing stress load was also investigated using parameters of the local cerebral circulation and blood oxygen saturation and tissue saturation measured by a tissue oximeter. The level of tissue oxygen saturation and dynamics of additionally calculated parameters such as a local cerebral blood volume (CBV) and a tissue oxygenation index (TOI) were used to estimate a type of the individual reaction and the adequacy of breathing stress load. Phase analysis of the tissue oximetry signals was performed on the base of Hilbert transform and distribution histograms of the momentary phase difference of the pairwise grouped signals: oxy-, deoxy- and total hemoglobin concentrations and tissue oxygen saturation. As it was revealed during experimental data analysis, there were four dynamic types of the oximetry signals that characterize individual reaction and the adequacy of breathing stress load. Several criteria were imposed: a criterion based on phase dynamics of tissue oximetry signals pairwise analysed; a critical low value of tissue oxygen saturation, a criterion based on directions of changes of CBV and TOI values due to breathing under the negative inspiratory pressue. Decrease of CBV, decrease of TOI and significant reduction of tissue oxygen saturation may indicate that applied breathing stress load is not adequate to current reserve capacities of a subject. Such changes of the mentioned above parameters reflect the balance between the tissue metabolic demands and the oxygen delivery. Pairwise phase analysis of the tissue oximetry signals demonstrated that relative dynamics of the total hemoglobin concentration and the deoxyhemoglobin concentration was the most informative. In-phase dynamics was revealed for the group of volunteers who had adequate breathing stress load, and conversely anti-phase dynamics was observed in case of non-adequate stressing for another group of volunteers. The received research results might be useful for developing of a noninvasive method of multivariable monitoring of cerebral blood circulation and prevention of hypoxic conditions with the help of the tissue oximeter. Such method is required by the modern clinical practice, in surgery, anesthesiology, neonatology, neurology, functional diagnostics, sport and space medicine.