Fig. 4.

Imaging of oxygen saturation changes during modulation of FiCO₂ in the mouse (C57BL/6) neocortex through a thinned-skull cranial window. Microvascular oxygen saturation was mapped using visible light spectroscopic OCT and displayed on a false-color scale during (A) 0% FiCO₂, (B) 5% FiCO₂. A large increase in oxygen saturation was observed in veins, while the sO₂ in arteries remained unchanged. The reduced oxygen extraction is a consequence of arterial and arteriolar dilation and subsequently, increased CBF during hypercapnia. Note the heterogeneity of oxygen extraction, as evidenced by regionally varying venous sO₂ values both before and after hypercapnia (white and gray arrows). An artery and vein are labeled as “a” and “v” respectively.