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

We used rapid-scanning near-infrared (NIR) spectroscopy (730-960 nm) to study the effects of graded or acute hypoxia on cerebral cytochrome-e oxidase (cyt aa(3)) redox state in blood-perfluorocarbon-exchanged cats with somatosensory evoked potential (SEP) monitoring. In graded hypoxia [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 occurred 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 protocols. These results demonstrate that cerebral cyt aa(3) reduction occurs with severe reduction of cerebral O-2 delivery, but no significant change in cerebral cyt aa(3) redox state occurs with small reductions of cerebral O-2 delivery. We conclude that substantial changes in cerebral cyt aa(3) do not occur at physiological levels of O-2 delivery and that current NIR clinical instruments would detect oxygen-dependent cerebral cyt aa(3) redox changes only when O-2 delivery is extremely compromised.