Interrelations of laser doppler flowmetry and brain tissue oxygen pressureduring ischemia and reperfusion induced by an experimental mass lesion

The objective of this study was to assess interrelations between bilateral changes of cortical laser doppler flowmetry and intraparenchymal, subcortic al partial tissue oxygen tension in the course of an experimental trauma. T en animals served as a sham group, 8 Sprague-Dawley rats received an unilat eral, focal parietal mass lesion. The bilateral course of cortical blood fl ow measured by laser doppler flowmetry (LDF) was correlated with subcortica l, intraparenchymal partial tissue oxygen tension [p(ti)O-2]. In the sham-o perated group, laser doppler mean flow values drifted between 9.0% and 9.5% and showed no significant changes over time neither between the hemisphere s nor within each hemisphere. Absolute mean p(ti)O-2 in sham-operated anima ls was 32.4 mm Hg in the left and 30.5 mm Hg in the right hemisphere. In th e trauma group, mean laser doppler flow values during maximum brain compres sion decreased ipsilateral to 20.3% and contralateral to 34.4% of the basel ine values. P(ti)O-2 decreased ipsilateral from 25.9 to 6.6 mmHg (25.4%) an d contralateral from 22.6 to 9.8 mm Hg (43.6%). After balloon deflation, co rtical LDF was restored much faster compared to p(ti)Oz, but did not reach baseline values [ipsilateral 61.6% (p < 0.05); contralateral 75.8% of basel ine values]. The p(ti)O-2 values reached 25.2 mm Hg (97%) ipsilateral and 2 3.7 mm Hg (105%) contralateral. A temporary phase of reactive hyperemia occ urred sporadically shortly after decompression. Both parameters showed a si gnificant but rather weak correlation (r = 0.56; p < 0.001). Based upon the se findings, we conclude that intraparenchymal, subcortical p(ti)O-2 measur ements supplemented on-line cortical CBF monitoring and score out discontin uous alternative measurement techniques in detecting hemodynamically releva nt events. The small spatial resolution of LDF and p(ti)Oz probes, however, which in the small animal model may be of negligible influence, does raise the question whether the values obtained represent the microcirculatory si tuation of the human brain.