Quantification of cerebral hemoglobin as a function of oxygenation using near-infrared time-resolved spectroscopy in a piglet model of hypoxia

Near-infrared spectroscopy (NIRS) has been used for measurement of cerebral hemoglobin (Hb) concentrations in neonates to study cerebral oxygenation and hemodynamics. We perform measurements by portable three-wavelength NIR time-resolved spectroscopy (TRS) in a piglet hypoxia model with various degrees of oxygenation to estimate the absorption coefficient (mu(a)) and reduced scattering coefficient (mu'(s)) of the head. Measurements of absolute vals ues of mu(a) at three wavelengths enable estimation of Hb concentration and Hb oxygen saturation in the head (SO2). However, there is a problem concerning which background absorption should be used to estimate Hb concentration in the head derived from mu(a) at three wavelengths because it is different from a simple in vitro model. Therefore, we use two different background absorption values with the assumption that background absorption is due only to 85% (by volume) water or that background absorption is equal to absorption of the piglet head with blood exchange transfusion by fluorocarbon (FC), and we compared SO2 measured by TRS with arterial Hb oxygen saturation (SaO(2)) and sagittal sinus venous Hb oxygen saturation (SVO2) measured by a co-oximeter at several inspired fractional O-2(FiO(2))concentrations. We find that SO2 values using the absorption abs of the piglet head with blood exchange transfusion (BET) by FC are not significantly different from SO2 values using the water-only background at FIO2 in the range of 15 to 100%, but that the values using abs of the head with BET by FC are lower than the values using the water-only background at FIO2 in the range of 12 to 4%. The SO2 values calculated from the water-only background are higher than those of SaO(2) at in the range of 10 to 4%. However, SO2 values using the abs of FiO(2) the head with BET by FC are between those of SaO(2) and SVO2 over the whole range of HO2, Therefore, abs of the head with BET by FC is more useful for estimation of the absolute values of oxyHb and deoxyHb of the piglet head. (c) 2005 Society of Photo-Optical Instrumentation Engineers.