Acute exposure to high altitude results in a rapid decline in barometric and oxygen partial pressures, which may compromise the body’s ability to maintain cerebral blood flow (CBF) homeostasis, potentially leading to acute mountain sickness or cerebral injury. To investigate cerebrovascular dynamics under hypobaric hypoxic conditions, we developed a noninvasive CBF monitoring device and employed it for real-time CBF measurement. Five healthy volunteers were recruited, and CBF signals were recorded under both low-altitude and acutely induced high-altitude conditions. The root mean square of successive differences (RMSSD) of inter-peak intervals was extracted as an index of CBF variability to evaluate the impact of high-altitude exposure on cerebrovascular dynamics. Results showed that four volunteers who developed high-altitude symptoms exhibited varying degrees of reduced CBF variability, suggesting a decline in cerebral autoregulatory capacity. In contrast, the asymptomatic volunteer showed essentially unchanged CBF variability. These findings provide preliminary evidence for altered CBF regulation during acute high-altitude exposure and suggest inter-individual differences in regulatory capacity.