In Vivo CO 2 Buffer Curves of Arterial and Mixed Venous Blood 1

Abstract

Summary

Six dogs were hyperventilated to an arterial Pco₂ of less than 15 Torr for 2 hr and then allowed to breathe spontaneously on 100% oxygen. A second group of 6 dogs breathed 10% CO₂-90% O₂ for 6 hr and then returned to breathing 100% oxygen. Arterial and mixed venous blood samples were drawn for determination of pH and Pco₂. From these values plasma bicarbonate concentrations were calculated. CO₂ buffer slopes calculated as ΔHCO^- ₃/ΔpH were determined by comparing bloods drawn before and 10 or 15 min after a step change in Pco₂. In three of the four cases the buffer slope of mixed venous blood was between 8.3 and 14.0 sl with the predicted value, calculated from Hb concentration and assumed values for other parameters, between 11 and 12 sl. Difference between arterial and venous slopes over the range of Pco₂ change utilized in these studies was neither statistically significant nor of a degree to be of practical importance in evaluating acid-base disturbances clinically.