Abstract
Using a near infrared (NIR) spectrophotometry, brain oxygen metabolism was noninvasively studied by simultaneous measurement of oxygenated homoglobin (Hb), reduced Hb, and total Hb content in rat and human brain in situ. The computer-controlled spectrometer was built whereby NIR light from three lacer diodes (wavelengths 780, 805, and 830nm) could be illuminated on the head through a fiber-optic bundle. The transmitted or reflected light was guided into a photomultiplier tube operating in photon counting mode through another fiber bundle. The change of oxygenated and total Hb content was monitored using the following equations of -3ΔA805+3ΔA830 and 1.6ΔA780-5.8ΔA805+4.2ΔA830 respectively (ΔA780, ΔA805, ΔA830 were absorption change at wavelength 780, 805 and 830nm). With anesthetized and artificially ventilated rats, about 90% of brain Hb was in oxygenated state at 95% O2+5% CO2 in the inspired gas and 50% at 7% O22+5% CO2, which correlated well with oxygen satulation of the jugular vein blood. Brain oxygenation was continuously monitored in the cardiopulmonary bypass (CPB) patients in reflectance mode. The blood volume tended to increase during later phase of CPB but mostly returned to pre-CPB level when patient's hemodynamics became stable after CPB discontinued. During CPB the Hb oxygenation level was kept roughly constant at mean perfusion pressure over 60mmHg, whereas below 40mmHg the decrease in oxygenated Hb was observed. NIR spectrophotometry provides valuable informations for the proper management of CPB patients.
