Fig. 7. Model predictions revealing the efficiency of ventilatory and circulatory adjustments. Solid curves show the predicted dependencies of the oxygen consumption rate (100%24 nmol h^-1) upon ambient oxygen tension for the fasting state/food-free conditions (A) and fed state/food-rich conditions (B). Both states differ from each other in the volume-specific oxygen consumption rate (a₀), perfusion rate (_H) and ventilation rate (_M). _H and _M represent normoxic values. Vertical lines mark the critical ambient oxygen tensions (P_O2crit) at which the rates of oxygen consumption decreased to 99% of the maximum. Below P_O2crit, the central tissue cylinder experiences an inadequate supply with oxygen. The overproportional decline in oxygen consumption rate in A and B below 4 kPa and 6 kPa (bold arrows), respectively, indicates the incipient impediment of oxygen provision to the peripheral tissue layer. Horizontal arrows indicate the reductions in P_O2crit by hypothetically doubling either _H or _M. The grey shaded areas reflect the amounts of oxygen transported by the circulatory system; the remaining white areas below the solid curves are those amounts diffusing from the respiratory medium directly into the peripheral tissue layer.