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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
(PO2crit) at which the rates of oxygen
consumption decreased to 99% of the maximum. Below
PO2crit, 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
PO2crit 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.
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