In clinical practice, the prediction of changes in blood pressure during hemocatharsis therapy depends on invasive monitoring, the physician's experience, or blood pressure measurement when patients ask for it. It is extremely difficult to predict blood pressure variation in patients under general anesthesia or with disturbance of consciousness. Therefore, the prediction of blood pressure variation during hemocatharsis therapy is an important issue. To address this issue, we invented a new noninvasive continuous blood flow monitor using arteriolar blood flow measurement by laser Doppler flowmetry. Then we examined and determined some extremely important phenomena, including the relationship between rapid blood pressure change and arteriolar blood flow, and failures of the cerebral blood flow autoregulatory mechanism, through measurements in clinical practice of hemodialysis, specific hemocatharsis therapy, and drug monitoring. The results suggest that blood pressure variation during hemocatharsis therapy is highly predictable by arteriolar blood flow measurement. Therefore, this new method for arteriolar blood flow measurement might be widely useful for patients under anesthesia, anesthesia monitoring in neonatal infants and animals (no conversation ability), as well as for hemocatharsis therapy.