Comprehensive evaluation of cerebral vascular reserve parameters

Aim: The aim of this study was to examine the state of cardiovascular reactivity (CVR) in healthy volunteers (HV) and CVR changes in young patients with essential hypertension by using the developed methods for integrated CVR assessment. Materials and Methods: Transcranial duplex scanning (TCDS) of the middle cerebral arteries (MCA) was performed in HV (n=27) and patients with grade 2 hypertension (n=32) aged 18-38 years by using expert class ultrasound machines in the presence of hyperoxia and hypercapnia according to standard TCDS method. Results: The formulas for mathematical calculations of two CVR phases were developed. For reserve phase based on reaction force, absolute or relative change coefficient (CCabs or CCrel) for blood flow velocity (BFV) were calculated as follows: CCabs.=V2/V0 and CCrel.=(V2-V0)/V0*100%. For reserve phase based on reaction velocity, test change velocity (TCV) of BFV was calculated: TCV=(V2-V0)/Т. For autoregulation phase based on reaction force, BFV recovery index (RI) was calculated: RI=V0/V4. For autoregulation phase based on BFV, recovery rate (RR) was calculated as follows: RR=(V2-V4)/Тr. Autoregulation response normalized by arterial blood pressure (NAR) was calculated as follows: NAR =(V2-V0)/(V0*(SBP2-SBP0), where V was BFV in MCA (cm/c); V2 was BFV after 2 min of inhalation (cm/s); T and Tr were times = 2 (min); SBP was systolic blood pressure (mmHg); and 0, 2, and 4 corresponded to initial values, values after 2 min of inhalation, and values 2 min after inhalation, respectively. Patients had significant decrease in reaction force (CCabs: 0.79±0.16 and 0.91±0.09; р=0.036) and significant slowing down in response velocity (TCV: 8.99±1.61 and 6.24±1.12, р=0.026) and in recovery velocity (RI: 2.59±0.54 and 1.63±0.76; р=0.011) in hyperoxia. No significant BFV abnormalities were found in hypercapnia compared with HV. NAR coefficient in hypertensives was the most effective in hyperoxia and hypercapnia. Differences were illustrated by clinical cases. Conclusions: The study demonstrated valid complex of qualitative CVR indicators. Young patients with arterial hypertension had early signs of abnormal CVR. Developed NAR elucidated bidirectional abnormalities in the adaptive MCA capabilities.