Mean whole body intracellular pH in unanesthetized dogs: a revised method.

An improved method of calculating the mean whole body intracellular pH (pHi) by means of DMO in unanesthetized dogs is described. The elemination of DMO from the body fluid is assumed to follow a simple exponential decay with a time constant k1. The distribution of DMO into the extracellular and intracellular water is described by an exponential function (1-exp(-k2t)). From experiments in 9 unanesthetized dogs it was found that k1 = 0.008 h-1 and k2 = 1.325 h-1. Mean pHi was 7.08 +/- 0.05 at Pa(c02) = 4.1 kPa (31 mm Hg). The average difference between arterial blood and pHi was 0.35. No statistically different pHi values were found with data from arterial or mixed venous blood. Even after 24 h the method still yields reasonable values for pHi.