Ultrasound Assessment of Cerebral Blood Flow Changes Upon Rapid Exposure to Hypoxic High-Altitude Environment.

Objectives: To investigate cerebral blood flow (CBF) regulation and cerebrovascular reactivity (CVR) in response to rapid high-altitude exposure and identify hemodynamic characteristics of CVR impairment.

Methods: Transcranial color-coded duplex sonography (TCCD) and breath-holding tests were used to assess CBF in rapid high-altitude entrants (n = 64, 26 ± 6 years) and long-term residents (n = 66, 25 ± 4 years). The breath-holding test can alter CBF through the dilation of intracranial small vessels, and the breath-holding index (BHI) can be utilized to quantify the changes in CBF associated with vasodilation. With reference to prior research, participants were stratified into normal and impaired CVR groups based on a BHI threshold of <0.69. CBF parameters (PSV [peak systolic flow velocity], MV [mean flow velocity], EDV [end diastolic flow velocity], PI [pulsatility index], RI [resistance index]) were measured at rest and during breath-holding before and after ascent.

Results: No resting CBF differences were observed between CVR-normal and impaired groups (P > .05). Post-ascent breath-holding revealed significant CBF alterations in the impaired group, including decreased EDV and MV and increased PI and RI (P < .05). The normal group showed elevated PSV (P < .05), while the impaired group exhibited higher vascular resistance and lower EDV compared to long-term residents (P < .05).

Conclusion: Increased cerebrovascular resistance and reduced EDV are the primary hemodynamic characteristics of high-altitude CVR impairment. Individual variations in hypoxia sensitivity likely play a significant role in cerebrovascular adaptations to high-altitude exposure, highlighting the importance of CBF regulation in preventing high-altitude-related cerebral injury.