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Objectives: The aim of this study was evaluate state cerebrovascular reactivity in condition of hypercapnia- hiperoxia induced cerebrovascular reserve in hypertensive patients.Methods: We used ultasonography of transcranial Doppler`s method in the study of middle cerebral arteries (MCA) from temporal window. We studied the changes of flow velocity (FV) and diameter (D) starting, at the time of hypercapnia (inhalation 2min 4% mixture of carbonic gas (MCG) with air) and hyperoxia (inhalation 2min 100% oxygen), FV in period of recovery (rec) (air-inhalation min) of 77 patients (1group) with essential hypertension of grade II-III and 52 healthy volunteers (2group) without cerebral stroke during of the life history (age 40±12,5 years years) with a new portable device. At the time of vascular evaluation, none of the patients had a history or clinical evidence of peripheral vascular disease, coagulopathy, or any disease predisposing them to vasculitis. All participants of research have given the informed agreement. We used index of flow velocity IFV=(V0-V2)/V0*100, coefficient modification of flow velocity CFV = V2/V0 and new coefficient - normalized to BP auto regulation answer NBPA=(V2-V0)/(V0*(BP2–BP0)) and index of recovery IR=V0/Vrec. V0 and BP0 are starting parameters, V2 and BP2 are during inhalation and Vrec - after inhalation parameters. Statistical analysis: descriptive, M-U-t-test,correlation matrix, multiple regression independent by groups.Results: Patients and healthy volunteers had not distinctions of anthropometrical parameters. Significant difference was found between 1 and 2 groups: IFVCO2=64.5±40.5% and 22.9±24.0% p=0.00; CFVCO2=258.5 and 119.5 U=28.5, Z=3.03 p=0.00; NBPACO2=241 and 137 U=46, Z=2.18 p=0.03; IFVO2=33.7±2.8% and 15.5±2.5% p=0.02; CFVO2=1.34±0.28 and 1.15±0.25% p=0.03; NBPAO2=4.9±2.7 and 10.2±3.8 p=0.00 respectively.Conclusion: Ultasonography transcranial Doppler`s method in the MCA with help new portable device and new coefficient NBPA does possible the quantitative and qualitative description of functional changes of the cerebrovascular reserve. Patients with a hypertension and without cerebral stroke during of the life history have inhibited cerebrovascular reactivity and decrease in adequacy of the answer of arterial blood circulation of a brain in condition of hypercapnia and hiperoxia.