Past studies have suggested that some carbon monoxide (CO) moves from blood haemoglobin to tissue cells and that mitochondrial cytochrome c oxidase oxidizes CO to carbon dioxide (CO
2). However, no study has demonstrated this redistribution and oxidization of CO under physiological conditions. The objective of this study was to trace the redistribution and oxidization of CO in the human body by detecting
13CO
2 production after the inhalation of
13CO. In Experiment 1, we asked a healthy subject to inhale 50 ppm
13CO gas. In Experiment 2, we circulated heparinized human blood in a cardio-pulmonary bypass circuit and supplied 50 ppm
13CO gas to the oxygenator. We sequentially sampled exhaled and output gases and measured the
13CO
2/
12CO
2 ratios. In Experiment 1, the exhaled
13CO
2/
12CO
2 ratio increased significantly between 4 to 31 h of
13CO inhalation. In Experiment 2, the output
13CO
2/
12CO
2 ratio showed no significant increase within 36 h of
13CO input. Experiment 1 demonstrated the oxidization of CO in the human body under physiological conditions. Experiment 2 confirmed that oxidization does not occur in the circulating blood and indicated the redistribution of CO from blood carboxyhaemoglobin to tissue cells.
View full abstract