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.
Department of Anaesthesiology and Intensive Care, University of Münster, Münster, Germany.
Martin
M
Westphal
Thomas Peter
TP
Weber
Jörg
J
Meyer
Stefan
S
von Kegler
Hugo
H
Van Aken
Michael
M
Booke
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