In vivo and in vitro CO₂ blood buffer curves

¹ Department of Physiology, University of Kansas Medical Center, Kansas City, Kansas

In vivo CO₂ blood buffer curves determined on blood drawn from dogs breathing 100% O₂, 15% CO₂ in O₂, and 25–30% CO₂ in O₂ have a distinctly lower slope than in vitro curves obtained by equilibrating blood from the same animal with 5, 15, and 30% CO₂ in O₂. The lower slope of the in vivo curve is due to the greater volume of distribution of bicarbonate in vivo. With hyperventilation of 10–15 min duration the in vivo curve is regularly depressed so that its slope is essentially the same as the in vitro curve. This depression is probably due to an increase in blood lactic acid. The increase in total bicarbonate in the extracellular fluid, resulting from an increase in CO₂ tension, is more than can be accounted for by the increase in blood. This suggests that some source of buffer, other than blood, is available to the interstitial fluid.

Note:
(With the Technical Assistance of Patricia Elledge and Rita Herman)

Submitted on October 28, 1964