Figure 4. Correlations among fetal variables.

A, the mean flow velocity of the blood travelling through the umbilical vein is inversely related to the diameter of the vein velocity (r²= 0.45, P < 0.0001 all subjects). (400 m Europeans (dotted line) y= 18.6 – 9.69x, r²= 0.26, P < 0.0005; 3600 m Europeans (dashed–dotted line) y= 18.4 – 12.91x, r²= 0.30, P < 0.0005; 400 m Andean (dashed line) y= 18.41 – 9.58x, r²= 0.28, P < 0.0002; 3600 m Andean (continuous line) y= 18.26 – 10.96x, r²= 0.22, P < 0.005.) The slope of the relationship is similar between altitudes (centre inset left, P= 0.40) and did not differ between ancestry groups (P= 0.56). B, fetal fractional O₂ extraction is increased when umbilical venous O₂ delivery is reduced (r²= 0.35, P < 0.0001, all subjects). Fetuses receiving less O₂ through the umbilical vein increase their umbilical venous to arterial oxygen extraction. (400 m Europeans (dotted line) y= 83.3–0.62x, r²= 0.21, P < 0.005; 3600 m Europeans (dashed–dotted line) y= 93.22 – 0.84x, r²= 0.33, P < 0.005; 400 m Andean (dashed line) y= 78.31 – 0.50x, r²= 0.20, P < 0.01; 3600 m Andean (continuous line) y= 80.0 – 0.62x, r²= 0.28, P < 0.0005). The slope of the relationship is similar between altitudes (centre inset right, P= 0.81) and did not differ between ancestry groups (P= 0.61).