Figure 2: Kinetic study of the effect of hyperoxia, radiation, or double-hit combination on blood oxygenation Separate cohorts of mice (n=5-15 / group) were exposed to 100% O2 for 8 hours only (O2), 0.25 Gy total body ionizing gamma irradiation (IR) only, or a double-hit combination of both challenges (O2+IR) followed by intermittent normoxia (21% pO2) for repeated cycles 3 times a week for 4 weeks. Mice were sacrificed at weeks 1, 2, and 4 weeks (acute) and 8, 12,,16, and 20 weeks (chronic). Arterial blood oxygenation was determined prior to sacrifice 8, 12, 16, and 20 weeks. Data is represented as mean ± SEM. Letter a indicates p< 0.05 for all challenges vs. untreated at each respective time point. Letter b indicates p< 0.05 for O2+IR vs. O2 at each respective time point. Letter c indicates p< 0.05 for O2+IR vs IR at each respective time point.