[Non-invasive tissue oxygen monitoring by near-infrared spectroscopy]

Biological tissues are relatively transparent to light in near infrared region. Brain oxygen metabolism was non-invasively studied by the simultaneous measurement of hemoglobin (Hb) oxygenation and cytochrome oxidase (Cyt. aa3) redox state in the rat brain using near infrared transmission spectrophotometer. Wavelength pairs at 700-805 nm and 830-805 nm were used for the measurements of Hb oxygenation level and of the redox state of cyt. oxidase in situ. Change in the brain blood volume was also monitored by the absorption change at 805 nm. Our estimation of the oxygenation level of brain Hb revealed that present optical measurement picks up mainly that of venous blood. Sharp reduction of the oxidase occurred at the oxygen concentration below 15% in the inspired gas. But above 30% O2, about 85% of the cyt. oxidase was in the oxidized state which was almost constant up to 100% O2. Applications of our techniques for the studies of brain metabolism in acute hemorrhage and in Ca++-antagonist administration were also presented. This non-invasive optical method for the study of human brain metabolism is concluded to be a promissing technique.