Interaction of blood flow, diffusive transport and cell metabolism in isovolemic anemia.

1) High blood flow can compensate for half-normal hematocrit, leaving the rate at which O2 is offered to the capillaries unchanged. Nevertheless, intracellular PO2 is lower in anemia, indicating impaired diffusive transport. 2) Anemia increases O2 flux per red cell and decreases functional capillary surface area. These changes increase flux density and the extracellular component of resistance to diffusive O2 transport, in accord with current theory (Federspiel and Popel, 1986; Groebe, 1990; Hellums, 1977). 3) Maintenance of diffusive flux in presence of anemia required a larger delta PO2 between Hb and Mb, and higher intracellular O2 conductance brought about by greater Mb-facilitated diffusion. Both compensations depend on lower PmbO2. 4) PmbO2 and creatine charge fall with increasing VO2 and ATP demand. These responses, as well as adaptive changes in redox help maintain VO2 in the presence of a lower O2 drive on electron transport. 5) Greater engagement of reserves of both transport and metabolism limits the range of aerobic performance in anemia. 6) The match between the transcapillary and mitochondrial O2 fluxes depends on interaction of transport and metabolism as a system.