Figure 5. Fetal adaptive range. Geometric and line symbols are the same as in prior figures.

A, fetal oxygen consumption per kg fetal weight increases as oxygen delivery is increased (r²= 0.50, P < 0.0001, all subjects). Fetuses receiving more O₂ through the umbilical vein have greater O₂ consumption relative to their weight (400 m Europeans y= 6.3 + 0.41x, r²= 0.491, P < 0.0001; 3600 m Europeans y= 6.1 + 0.46x, r²= 0.45, P < 0.0001; 400 m Andean y= 6.2 + 0.42x, r²= 0.56, P < 0.0001; 3600 m Andean y= 7.9 + 0.33x, r²= 0.35, P < 0.0001.) The slope of the relationship is similar between altitudes (centre inset left, P= 0.59) and did not differ between ancestry groups (P= 0.50). B, fetal oxygen extraction is correlated with umbilical arterial , such that those fetuses with the greatest O₂ extraction have the lowest arterial (r²= 0.64, P < 0.0001 all subjects). (400 m Europeans y= 34.6 – 0.29x, r²= 0.71, P < 0.0001; 3600 m Europeans y= 42.3 – 0.38x, r²= 0.69, P < 0.0001; 400 m Andean y= 29.6 + 0.20x, r²= 0.31, P < 0.0005; 3600 m Andean y= 32.0 – 0.26x, r²= 0.75, P < 0.0001.) The slope of the relationship is virtually identical between altitudes (centre inset right, P= 0.98), and did not differ between ancestry groups (P= 0.26).