Brain tissue oxygen evaluation by wireless near-infrared spectroscopy

Abstract

Background: Monitoring the partial pressure of oxygen in brain tissue (PbtO(2)) is an important tool for traumatic brain injury (TBI) but is invasive and inconvenient for real time monitoring. Near-infrared spectroscopy (NIRS), which can monitor hemoglobin parameters in the brain tissue, has been used widely as a noninvasive tool for assessing cerebral ischemia and hypoxia. Therefore, it may have the potential as a noninvasive tool for estimating the change of PbtO(2). In this study, a novel wireless NIRS system was designed to monitor hemoglobin parameters of rat brains under different impact strengths and was used to estimate the change of PbtO(2) noninvasively in TBI. Materials and methods: The proposed wireless NIRS system and a PbtO(2) monitoring system were used to monitor the oxygenation of rat brains under different impact strengths. Rats were randomly assigned to four different impact strength groups (sham, 1.6 atm, 2.0 atm, and 2.4 atm; n = 6 per group), and the relationships of concentration changes in oxyhemoglobin (HbO(2)), deoxyhemoglobin (HbR), and total hemoglobin (HbT), and PbtO(2) during and after TBI with different impact strengths were investigated. Triphenyltetrazolium chloride (TTC) staining was also used to evaluate infarction volume. Results: Concentration changes in HbO(2), HbR, and HbT dropped immediately after the impact, increased gradually, and then became stable. Changes in PbtO(2) had a similar tendency with the hemoglobin parameters. There was significant correlation between changes in PbtO(2) and HbO(2) (correlation = 0.76) but not with changes in HbR (correlation = 0.06). In triphenyltetrazolium chloride staining, the infarction volume was highly but negatively associated with oxygen-related parameters like PbtO(2) and HbO(2). Conclusions: Changes in HbO(2) under TBI was highly and positively correlated with changes in PbtO(2). By using the relative changes in HbO(2) as a reference parameter, the proposed