Factors affecting whole blood O2 transfer kinetics: implications for theta(O2)

Half times (t0.5) of O2 uptake (on) and release (off) were measured on thin layers of whole blood (WB). Increasing film thickness (L = 1-6 microns) increased t0.5(on) from 10 to 20 ms and t0.5(off) from 20 to 45 ms. At all L, for changes in saturation (S) 0----1, t0.5(off) was about twofold greater than t0.5(on). Doubling initial onloading PO2 gradient decreased t0.5(on) 36%; t0.5(off) was unchanged. A 10-Torr change in WB O2 affinity (P50) had no significant effect on t0.5. Specific O2 conductance [theta(O2), ml O2.(min.Torr.ml WB)-1] was also computed as a function of S from these data. A bell-shaped theta(O2) vs. S relationship was always obtained; maximum values of theta(O2) reached 25. Measured values for theta(O2) at any S were highly sensitive to choice of experimental conditions, i.e., L, affinity, flux direction, initial PO2 gradient, and initial level of S. We show experimentally and theoretically that no unique relationship exists for theta(O2) as a function of S for erythrocytes in WB.