A new method for the estimation of cerebral oxygen metabolism

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A new method for the estimation of regional cerebral blood flow (rCBF) and oxygen consumption (rCMRO_2) using a stable isotope of oxygen was developed and the validity of the method was estimated.1. The measurement of rCBF(1) The method using trifluoroiodomethane (CF_3I) : The CF_3I resolved in saline was infused to a rat. During infusion, the arterial blood samplings were performed several times, and just after infusion, the brain was extracted and divided into several portions. The concentration of CF_3I both in blood samples and cerebral tissues was measured using gas chromatograph-mass spectrometer equipped with a headspace sampler (GC-MS-HSS). The RCBF was calculated with a modified autoradiographic strategy. However, due to the evaporation of CF_3I during sampling, the calculated values were proved to be incorrect.(2) The method using water-18 (H_2^<18>O) : The saline including 50% water-18 was injected to a rat. Following the injection, the arterial blood was sampled several times, and 30 sec after the injection, the brain was extracted. The concentration of water-18 in blood and tissue samples was measured using GC-MS-HSS, and the RCBF was calculated with a KetySchmit method. The calculated values followed the changes in rCBF induced by hypo- and hyperventilation, and were coincident with the previously reported values.(3) The method using water-18 was applied to rat ischemic models to estimate the validity of this method. The results showed the manifest decreases in RCBF at the site of ischemia, which proved the validity of the method using water-18.2. The measurement of rCMRO_2After the 10 min inhalation of 50% oxygen-18 gas, the rat brain was extracted and the concentration of metabolic water-18 was measured using GC-MS-HSS. However, this method was proved not to be adequate for the measurement of rCMRO_2.