Near-infrared monitoring of cerebral oxygen sufficiency: I. Spectra of cytochromecoxidase

Near-infrared (NIR) difference spectra were obtained for oxidized cytochrome c oxidase of isolated mitochondria in vitro and of cerebral tissue in situ observed through scalp and skull. The broad peaks of maximal absorption observed in both were not inconsistent with the customary assignment of an 830 nm peak. However, the ratios of the intensity of the NIR band to that of the visible peak (605 nm), which we found to be identical for in-vitro and in-situ spectra, were consistently and significantly higher than those of the various purified enzyme preparations reported in the literature. In addition the half-band widths of our in-vitro and in-situ preparations were narrower. Haemoglobin spectra in the NIR obtained in clear and in highly light-scattering media showed almost total absence of band distortion in this spectral region, suggesting that the differences observed are not due to scattering effects. Anoxia and the specific oxidase inhibitors, cyanide and carbon monoxide, caused the expected disappearance of the band in both the mitochondria in vitro and the cerebrum in situ. The 830 nm band observed in intact, well-oxygenated animal preparations was therefore identified with the NIR absorption band of oxidized cytochrome c oxidase, notwithstanding the differences with the observations on purified preparations. This points to the possibility of developing instrumentation and techniques for the non-invasive monitoring of the redox state of cytochrome c oxidase as an index to cerebral oxygen sufficiency, i.e. adequate delivery and utilization of oxygen to and by brain tissue.