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Objective. To develop a protocol for a normobaric hypoxic test and criteria of resistance assessment — normobaric hypoxia sensitivity in children. Characteristics of children and research methods . 56 healthy children aged from 8 to 12 years underwent a hypoxic test inhaling gas mixture with 10—11% of O 2 through mask to create hypoxemia conditions (SpO 2 = 80%). The authors used a normobaric hypoxic device (certified in the Russian Federation) to produce hypoxic and hyperoxic gas mixtures — ReOxy Cardio (S.A. Aimediq, Luxembourg) with an integrated pulse oximetry sensor (Masimo Rad-5, USA). During hypoxic test they monitored the arterial blood oxygen saturation (SpO 2 ) and heart rate (HR, bpm), and there were automatically recorded the individual minimum values of SpO 2 level (SpO 2 min) and maximum heart rate (HR max). A “hypoxic phase” was terminated in case of decrease in SpO2 to 80% or lower, or breathing with a hypoxic gas mixture during 9 minutes. An additional criterion for termination was an increase in HR by 30% and higher over the initial level. After reaching one of the described criteria, the teenagers began to breathe ambient air and the authors determined the recovery time of SpO 2 to 97%. In addition, the authors calculated the hypoxic index as desaturation/reoxygenation time ratio. Results. The authors developed a protocol for conductance and assessment of hypoxic resistance in children and adolescents. There were determined three types (phenotypes) of response to dosed normobaric hypoxia in adolescents: low, medium and high levels of dosed hypoxic stimulus resistance. Conclusion . The proposed hypoxic test protocol reflects the individual hypoxia tolerance and can be used to individualize hypoxic therapy courses, as well as additional diagnostic tool in assessing the adaptive capabilities and non-specific reactivity in children.

A comprehensive comparative analysis of hemodynamics, microcirculation (the method of laser Doppler flowmetry with occlusal probe and the optical tissue oxymetry), blood circulation neuro-humoral regulation (analysis of heart rate variability - HRV) between almost healthy young people with different levels of subjectively experienced emotional stress is given. Depending on the degree of everyday stress (acute and/or chronic) the character of neuro-autonomic regulation of blood circulation, as well as the state of the microcirculatory blood flow and its regulation are substantially different. Moderate stress is accompanied sympathetic-parasympathetic regulatory mechanisms co-activation with augmented HRV baroreflex regulation circuits that compensate hemodynamic changes and is not accompanied by hypertensive reactions. An increase in the activity of neurogenic and myogenic tone microhemodynamics in the examinees with moderate stress is discovered, which determines a high probability of blood shunting in tested tissue and decrease of relative oxygen extraction. Moderate levels of stress are also associated with increase in a latency of post-occlusive vasoreactive hyperemia, which is considered to be an initial sign of the endothelium-mediated dysfunction of microcirculation.