In-vivo measurement of cytochrome using NIRS during acute focal cerebral ischaemia and reperfusion in rats.

Objectives: Near-infrared spectroscopy (NIRS) based technology allows in-vivo monitoring of focal tissue cytochrome aa3 (cytochrome-c-oxidase). The aim of this study was to assess early cell alteration during acute focal cerebral ischaemia and reperfusion.
Methods: Focal cerebral ischaemia was induced in 12 rats using an endovascular occlusion technique of the middle cerebral artery (MCA). Occlusion time was 60 minutes followed by reperfusion for another 60 minutes. Monitoring of oxygen saturation (SO2) and oxidized cytochrome complex (oxid. Cytaa3 ) was performed by NIRS via a parietal burr hole before (baseline), during occlusion and reperfusion. Twenty-four hours after MCA occlusion (MCAO) infarction was confirmed by TTC staining.
Results: In all animals SO2 and oxid. Cytaa 3 immediately decreased to zero during occlusion indicating complete ischaemia. According to the results of NIRS measurements during reperfusion animals were subdivided into two groups. All animals of group A demonstrated identical or even higher levels of SO2 and oxid. Cytaa3 compared to baseline. On the contrary, both parameters in group B remained at a distinct lower level compared to baseline (p < 0.05). Average reperfusion/baseline ratios for SO2 and oxid. Cytaa 3 were 0.8 (+/- 0.4) and 0.4 (+/- 0.2), respectively. The results of TTC-staining were distributed to the above mentioned two groups as follows: group A, only lesions in the basal ganglia or little cortical infarction (n = 8); group B, lesions in the basal ganglia and cortical area (n =4).
Conclusions: After 1 hour MCAO a subgroup of animals with associated cortical infarction was identified, whose oxid. Cytaa3 values did not reach baseline values during reperfusion indicating early intracellular disturbance.