Figure 6.

Selected capillaries Cap4 and Cap5 shown in panel A were analyzed for RBC saturation changes as oxygen levels delivered through the micro-outlet were oscillated in a square wave. The PO₂ level in the chamber was decreased from 16.2% (~123 mmHg) to 0.2% (~1.5 mmHg) for a 120 second hypoxic challenge and back to 16.2%. A six minute video sequence was captured beginning 2 minutes before the hypoxic challenge. The PO₂ distribution profile into the tissue was modelled. Panel B shows 2D contour plot for a micro-outlet PO₂ value of 123 mmHg. Panel C shows the surface (depth=0 cm) PO₂ contour lines superimposed on top of the image showing the micro-outlet and the selected capillaries. The radial change in RBC O₂ saturations at various depths into the tissue (z=0 μm, 10 μm, 30 μm, and 50 μm) were calculated from the modelled PO₂ values using Hill’s equation then plotted against the radial distance from the center of the micro-outlet for a micro-outlet PO₂ values of 123 mmHg (upper set of lines, panel D) and 1.5 mmHg (lower set of lines, panel D). Experimentally calculated SO₂ mean values for Cap4 and Cap5 prior to and during hypoxia were plotted vs. capillary location (upper and lower pair of symbols respectively, panel D).