Significance of Carbon Dioxide Tension in Urine

Abstract

Data from 195 urine samples collected in 43 expts. from 14 normal dogs have been analyzed to establish the range of variability in the CO2 tension in urine and to formulate a hypothesis for the interpretation of this variability. A direct relationship between the PCO2 and the concn. of buffer other than bicarbonate was observed. The CO2 tension was most sensitive to buffer concn. when the urine pH was high, least sensitive when the urine pH was low. At low values for urine pH, CO2 tensions lower in urine than in arterial plasma were regularly noted. An inverse relationship existed between the pCO2 and the urine flow. These relationships were obtained in urine whether collected from renal pelvis or from bladder, and were observed after presumed abolition of H secretion by admn. of inhibitors of carbonic anhydrase. The data conform closely to predictions from the hypothesis that the diffusion equilibrium for CO2 is reached within each nephron, and that subsequent mixture of moieties of disparate pH and buffer concn. in a region in which surface-volume relationships are less favorable to the back diffusion of CO2 produce the observed CO2 tension of bladder urine.