Oxygen equilibrium curve of fetal blood is a major determinant of tissue oxygen tension Grad thus of oxygen supply to fetal tissue. Despite the great clinical importance of this area, oxygen binding properties of fetal blood currently are known only at one point on the curve, i.e. the affinity at half saturation, P50 and also direct measurement of carbon monoxide´s effect on oxygen binding are not known for fetal blood.
The goal of this study was to synthesize the results of these measurements into clinically useful practical equations describing oxygen transport in the presence and absence of carbon monoxide in normal fetal blood.
Oxygen equilibrium curves of fetal blood samples were measured by means of thin blood film dual wave length spectrophotometer and electrode oximetry using sorest wave lengths of 430-453 nm under standard condition.
All measurements was made on blood whose isohemoglobin profile has been established by isoelectric focusing.
Obtained results are summarized as follows.
1. HbF content of cord blood was 66. 2±1. 35% of total Hb.
2. The oxygen equilibrium curves of fetal blood were shifted to the left with increasing CO saturation of Hb. P50 of normal fetal blood and of blood saturated by 11. 7, 19. 0, 31. 8,and 45. 7%
carbon monoxide were 23.83±0.47, 20.16±0.28, 19.34±0.83, 15.88±0. 73, and 12.11±0.28 mmHg, respectively.
3. The relationship between log P50 and (COHb, %) of the fetal blood was log Pro=1. 382-0. 006 [COHb, %).
The correlation coefficient(r = -0. 95) was statistically significant. The P50 of fetal blood in the presence or absence of carbon monoxide can be obtained by the following equation. P50(mmHg)=antilog[1.382-0.006[COHb, %]]
4. Hill´s constant(n) and K values of normal fetal blood were 2.55 and 3.2 x 10 -?
An inc. ease in the K values and a decrease in the Hill´s constant (n) were associated with the increased saturation of carbon monoxide in the fetal blood. Hill´s relationship (log (S,/1-S) vs. log Poe) in the presence [COHb, %) and absence of carbon monoxide exhibited linear and correlation coefficient (r>0.99). were statistically significant
5. The relationships between Hill´s constant (n) or log K and log (COHb, %] can be expressed as following equation.
n=2.693-0.65 log [COHb, %) log K = 1. 48 log [COHb, ,]-1.48
Both of correlation coefficient, -0. 99 and 0. 99, were statistically significant.
6. Oxygen equilibrium curve of fetal blood saturated partially with carbon monoxide can be obtained from the following formulas.
PO²=[SO2/K (1-SO2))¹?n n.=2.693-0.65 log [COHb, %] . K=antilog[1.48 log [COHb, %)-4.18)
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