Measurement of Cerebral Optical Pathlength 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 changes in cerebral hemoglobin concentrations in neonates to study cerebral oxygenation and hemodynamics. In this study, measurements by time-resolved reflectance spectroscopy (TRS) were performed in a piglet model with various degrees of cerebral oxygenation to estimate the differential pathlength factor (DPF). A portable three-wavelength TRS system (TRS-10, Hamamatsu Photonics K.K.) with a probe attached to the head of a piglet was used. Eleven newborn piglets were anesthetized and respired by a ventilator to induce stepwise hypoxia loading. The DPF showed positive linear relationship with arterial hemoglobin (Hb) oxygen saturation and sagittal sinus venous Hb oxygen saturation at 761 and 795 nm. The DPF at 835 nm also showed very slight positive linear relationship with arterial hemoglobin oxygen saturation. The DPF values obtained in this study should contribute to a better understanding of noninvasive measurements by NIRS in neonates.