CAT BRAIN CYTOCHROME-C-OXIDASE REDOX CHANGES INDUCED BY HYPOXIA AFTERBLOOD-FLUOROCARBON EXCHANGE-TRANSFUSION

We used rapid-scanning near-infrared (NIR) spectroscopy (730-960 nm) t o study the effects of graded or acute hypoxia on cerebral cytochrome- e oxidase (cyt aa(3)) redox state in blood-perfluorocarbon-exchanged c ats with somatosensory evoked potential (SEP) monitoring. In graded hy poxia [10 min each at fractional inspiratory O-2 concentration (FIO2) 0.9, 0.8, 0.7, 0.6, and 0.5], cyt aa(3) reduction occurred at FIO2 0.6 when cerebral Oz delivery was < 3.5 ml . 100 g(-1). min(-1). In acute hypoxia (FIO2 0.6 for 10 min), significant cyt aa(3) reduction occurr ed from 5 to 10 min (cerebral O-2 delivery 3.1 +/- 0.3 ml 100 . g(-1). min(-1)) and recovered with reoxygenation (FIO2 1.0). Cyt aa(3) redox changes preceded or coincided with SEP alterations in both hypoxia pr otocols. These results demonstrate that cerebral cyt aa(3) reduction o ccurs with severe reduction of cerebral O-2 delivery, but no significa nt change in cerebral cyt aa(3) redox state occurs with small reductio ns of cerebral O-2 delivery. We conclude that substantial changes in c erebral cyt aa(3) do not occur at physiological levels of O-2 delivery and that current NIR clinical instruments would detect oxygen-depende nt cerebral cyt aa(3) redox changes only when O-2 delivery is extremel y compromised.