Journal of Applied Physiology, Vol 50, Issue 5 1061-1064, Copyright © 1981 by American Physiological Society
Competitive inhibition of carbon monoxide transport: evidence against a carrier
D. Z. Rubin, D. Fujino, C. Mittman and S. M. Lewis
The existence of a saturable carbon monoxide (CO) carrier in the lung
remains controversial. The carrier hypothesis was invoked to explain data
that indicated that pulmonary diffusing capacity for CO (DLCO) decreases
with increasing CO concentration. To test this hypothesis, we measured DLCO
in 14 normal adult subjects at three alveolar CO concentrations (60, 660,
and 2,060 ppm). Each mixture contained a constant amount of labeled C18O
(60 ppm) and a balance of unlabeled C16O. If a saturable carrier exists at
increasing CO concentrations, the unlabeled CO would compete for most of
the sites on the carrier molecule, effectively inhibiting the uptake of the
labeled C18O. C18O diffusing capacities (mean +/- SD) for the three levels
of CO were 34.9 +/- 5.6, 33.0 +/- 6.0, and 34.7 +/- 7.8. There were no
significant differences (P greater than 0.2) among the three levels. In
another group of subjects we repeated the study using a gas mixture
containing 130 ppm C18O. No significant differences were found. As a
result, we find no evidence to support a CO carrier hypothesis.
