Erythrocyte flux in capillary networks during maturation: implications for oxygen delivery

Erythrocyte (RBC) flow variables were measured with videomicroscopy in hamster cremaster muscle capillary networks. Capillary networks consist of subgroups, termed modules, with architectural characteristics that are invariant with maturation [B. R. Berg and I. H. Sarelius. Am. J. Physiol, 268 (Heart Circ. Physiol. 37): H1215-H1222, 1995]. RBC flux in modules decreased from 82.0 +/- 4.3 (SE) cells/s at 51 days of age to 59.5 +/- 7.5 and 27.5 +/- 2.8 cells/s at 65 and 79 days of age, respectively. Mean cell velocity at 51 days (385 +/- 10 microns/s) was higher than at 65 or 79 days (285 +/- 15 and 241 +/- 12 microns/s, respectively). Cell content (number of cells per unit length) decreased later, between 65 and 79 days (from 0.21 +/- 0.01 and 0.23 +/- 0.02 cells/micron at 51 and 65 days, respectively, to 0.12 +/- 0.01 cells/micron at 79 days). These temporal differences in the decrease in cell velocity and cell content suggest different regulatory mechanisms. The capacity of capillary networks to deliver oxygen was modeled by using the calculated mean PO2 at the capillary wall to indicate the capacity to delivery oxygen. During maturation, the mean capillary wall PO2 remained unchanged (15.5 +/- 1.2 and 11.4 +/- 2.7 Torr in maximal dilation and 24.5 +/- 1.4 and 22.8 +/- 2.4 Torr at rest at 51 and 79 days, respectively). Thus, despite changes in RBC flow variables with maturation, the capacity for networks to deliver oxygen remains constant.