Figure 2. Fetal blood gas relationships.

A, the correlation between the umbilical venous and determined by the blood gas analyses was plotted for each of the four groups using a third order polynomial (best fit regression). The low altitude curves overlap for Europeans (□) and Andeans (○). High altitude left-shifts the / curve (P < 0.05), with Andean fetuses (•, continuous line) showing a progressively greater leftward shift with increasing when compared with the Europeans (▪, dashed–dotted line). This results in differences at which the blood is 50% saturated (indicated by the line at 50% on the y axis). The P₅₀ for is equivalent at 400 m (28.4 versus 28.5 for European (dotted line) and Andean (dashed line), respectively). In contrast the blood is half-saturated with oxygen at 25.8 mmHg at 3600 m in Europeans, and 23.4 mmHg at 3600 m in Andean, P < 0.05). The Andean fetuses at 3600 m thus maintain saturation at higher levels for a given when compared with Europeans. (400 m European y=–92.8 + 8.64x– (–0.16x²) + 0.001x³, r²= 0.94, P < 0.0001; 400 m Andean y=–16.4 + 1.09x+ 0.81x²– 0.001x³, r²= 0.97, P < 0.0001; 3600 m European y=–122.4 + 13.33x–0.32x²+ 0.003x³, r²= 0.90, P < 0.0001; 3600 m Andean y=–7.0 – 0.98x+ 0.24x²– 0.004x³, r²= 0.97, P < 0.0001.) B, the maternal curves relating to are also left-shifted at high altitude, but without any apparent difference due to ethnicity at low or high altitude. The line symbols are the same as in A. (400 m European y=–9.6 + 2.94x– 0.81x²– 0.001x³, r²= 0.97, P < 0.0001; 3600 m European y=–122.4 + 13.13x– 0.32x²+ 0.003x³, r²= 0.91, P < 0.0001; 400 m Andean y=–15.7 + 1.02x+ 0.08x²– 0.001x³, r²= 0.97, P < 0.0001; 3600 m Andean y=–1.9 – 1.59x+ 0.27x²– 0.005x³, r²= 0.98, P < 0.0001.) C shows the correlation between maternal and fetal at the two altitude combined. For any given value of maternal , the Andean fetus has a lower than the European fetus. (y= 34.1 + 0.33x, r²= 0.06, P < 0.05 European; y= 30.4 + 0.46x, r²= 0.12, P < 0.005.)