Table II. Calculated gas-exchange characteristics at the microscale.
The critical gas concentrations are the minimal and maximal intracellular O2 and CO2 concentrations, respectively. Values are expressed in terms of partial pressure by using Henry’s law. The macroscale model was computed with the measured apparent diffusivities from Table I. CO2 (a) and CO2 (b) represent microscale simulations of CO2 diffusion without and with HCO3− transport in the cytoplasm, respectively (Supplemental Text S8). The values reported for the microscale model are the average simulated values for eight different tissue geometries ± sd.
| Scale | Variable | O2 | CO2 (a) | CO2 (b) |
| Microscale (1.28 × 1.28 × 1.28 mm3) | Critical concentration (kPa) | 6.0 ± 0.19 | 8.421 ± 0.008 | 8.419 ± 0.007 |
| Local concentration gradient (kPa mm−1) | ||||
| Cell | 0.97 ± 0.19 | 0.039 ± 0.009 | 0.0368 ± 0.008 | |
| Intercellular space | 5.08 × 10−5 | 4.72 × 10−5 | 4.48 × 10−5 | |
| Maximal local concentration gradient (kPa mm−1) | 19.9 ± 7.3 | 0.78 ± 0.29 | 0.73 ± 0.26 | |
| Cellular conductance (m s−1) | (3.45 ± 1.13) × 10−6 | (7.98 ± 2.53) × 10−5 | (7.84 ± 2.37) × 10−5 | |
| Macroscale | Critical concentration (kPa) | 6.696 | 8.399 | |
| Local concentration gradient (kPa mm−1) | 1.93 × 10−2 | 5.6 × 10−3 | ||