Affinity of carbon monoxide to hemoglobin increases at low oxygen fractions.
Following systemic inflammation, the lung induces an isoenzyme of heme oxygenase (HO-1), catalyzing carbon monoxide (CO) production through breakdown of heme molecules. However, it is still debated why the paradoxical arterio-venous carboxyhemoglobin (COHb) difference occurs only during critical illness but not in healthy volunteers. To elucidate whether oxygen fractions at (sub-)physiologic ranges alter the affinity of CO to hemoglobin (Hb), we performed an in vitro laboratory experiment, in which we exposed venous blood samples to fixed CO-doses at incrementing oxygen fractions (FiO2). ANOVA demonstrated that the affinity of CO (200 and 400 ppm) to Hb progressively increased with an FiO2 from 0% to 15%, whereas at higher oxygen tensions this effect vanished. This might explain why the arterio-venous COHb difference found in critically ill patients is not reproducible in healthy adults, since the latter ones are characterized by higher venous oxygen saturations.
Westphal
Martin
M
Department of Anaesthesiology and Intensive Care, University of Münster, Münster, Germany.
Weber
Thomas Peter
TP
Meyer
Jörg
J
von Kegler
Stefan
S
Van Aken
Hugo
H
Booke
Michael
M
D000328:Adult; D000704:Analysis of Variance; D002248:Carbon Monoxide / Q000097:blood*; D002263:Carboxyhemoglobin / Q000378:metabolism; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism*; D051547:Heme Oxygenase-1; D006454:Hemoglobins / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins; D008954:Models, Biological; D010100:Oxygen / Q000097:blood*
D006454:Hemoglobins; D008565:Membrane Proteins; D002248:Carbon Monoxide; D002263:Carboxyhemoglobin; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; D010100:Oxygen