“…T 1 versus pO 2 peaks at SO 2 = 100%, and has a negative and linear relationship above that point [11,13,42]. A decrease in T 1 with maternal air breathing makes sense for only fully saturated maternal arterial blood, but many blood compartments in the placenta are less than fully saturated even during maternal hyperoxia [43]. A spatial average between compartments where T 1 increased alongside SO 2 , and those where T 1 decreased with increased pO2 beyondm SO2=100%, could explain why we did not observe a change in T 1 with hyperoxia in the placenta.…”