Indirect determination of mean whole body and intracellular CO 2 and buffer capacity

Abstract

The DMO method was used to determine mean whole body intracellular pH i in artificially ventilated dogs at different arterial CO 2 tensions. The mean regression lines obtained were pH e = −0.669 log Pa CO 2 + 8.419 and pH i = −0.598 log Pa CO 2 + 7.923. Formulas are derived to convert these regression lines into CO 2 combining curves and buffer curves of the extracellular and the intracellular compartment. For Pa CO 2 = 40 torr the following values for the intracellular space were obtained: pH i = 6.965, HCO − 3 = 9.6 meq/kg H 2O, total CO 2 = 10.9 mM/kg H 2O, buffer capacity = 14.8 slyke/kg H 2O. The corresponding values for the extracellular space were pH e = 7.347, HCO − 3 = 23.2 meq/kg H 2O, total CO 2 = 24.5 mM/kg H 2O and buffer capacity = 26.0 slyke/kg H 2O. Total CO 2 and buffer capacity of the whole body was 8.6 mM/kg tissue and 10.7 slyke/kg tissue at Pa CO 2 = 40 torr. The intracellular space contributed 57% of these values. Position and slope of the calculated CO 2 combining curve agreed well with pertinent data of the literature based on direct tissue analysis, CO 2 elimination experiments or distribution kinetics of radioactive CO 2.