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. Author manuscript; available in PMC: 2013 Jul 29.
Published in final edited form as: Respir Physiol Neurobiol. 2010 Feb 10;170(3):215–225. doi: 10.1016/j.resp.2010.02.001

Fig. 2.

Fig. 2

Changes in maternal and fetal [HbCO] during and after a 24 h exposure to 68 ppm CO and a 4 h exposure to 300 ppm CO. If the maternal value of 10% HbCO were obtained at equilibrium (point A), the fetal [HbCO] would be equal to about 11%. If the sample was taken at point B during the washout phase, the fetal [HbCO] would be about 14%. However, if the blood sample was taken during the uptake phase (point C), the fetal [HbCO] would be 2%. Not only is it impossible to predict fetal [HbCO] on the basis of a single maternal blood sample, but the length of time necessary to reduce the fetal [HbCO] depends on whether the concentration has already peaked or is still rising. In the case of lung diffusing testing, which could require up to about 3 min of 3000 ppm CO inhalation, the maternal [HbCO] may increase to 5%, but the fetal HbCO would hardly increase. This is typified by the enhanced “Detail” on the right panel in figure. Figures reproduced from Longo (1977).