Journal of Applied Physiology, Vol 42, Issue 3 323-326, Copyright © 1977 by American Physiological Society
Can alveolar pCO2 exceed pulmonary end-capillary CO2? Yes
G. H. Gurtner
In 1891 Christian Bohr observed that alveolar PCO2 could exceed arterial
PCO2 when high levels of CO2 were present in the inspired air. He proposed
that CO2 could be secreted by the lung. His hypothesis was dismissed as
being due to experimental error; however, recently the same phenomenon was
rediscovered using modern techniques. A possible explanation for the
phenomenon may involve coupling between diffusion and chemical reaction of
H+, HCO3-, and CO2 in the vicinity of a negatively charged capillary wall,
causing the PCO2 to be higher near the wall that in the bulk phase of
capillary blood. Alveolar PCO2 is related to the PCO2 near the wall rather
than the bulk phase PCO2. The Charged Membrane Hypotheses can explain the
phenomenon of CO2 secretion not by a cellular mechanism, but a physical
chemical disequilibrium within the capillary which is maintained by blood
flow through the capillary.
