Interpretation of near-infrared spectroscopy signals: a study with a newly developed perfused rat brain model

Abstract

Using a newly developed perfused rat brain model, we examined direct effects of each change in cerebral blood flow (CBF) and oxygen metabolic rate on cerebral hemoglobin oxygenation to interpret near-infrared spectroscopy signals. Changes in CBF and total hemoglobin (tHb) were in parallel, although tHb showed no change when changes in CBF were small (≤10%). Increasing CBF caused an increase in oxygenated hemoglobin (HbO2) and a decrease in deoxygenated hemoglobin (deoxy-Hb). Decreasing CBF was accompanied by a decrease in HbO2, whereas changes in direction of deoxy-Hb were various. Cerebral blood congestion caused increases in HbO2, deoxy-Hb, and tHb. Administration of pentylenetetrazole without increasing the flow rate caused increases in HbO2 and tHb with a decrease in deoxy-Hb. There were no significant differences in venous oxygen saturation before vs. during seizure. These results suggest that, in activation studies with near-infrared spectroscopy, HbO2 is the most sensitive indicator of changes in CBF, and the direction of changes in deoxy-Hb is determined by the degree of changes in venous blood oxygenation and volume.