Relationship between urine acidification and intracellular pH in respiratory acidosis

The renal net acid excretion (NAE), the blood pH (pHe), the total body intracellular pH (pHi) and the urinary pH (pHu) were calculated in 10 patients with chronic obstructive lung disease and hypercapnia and in 5 normocapnic subjects. The mean value of NAE was significantly higher in hypercapnic subjects than in normocapnic ones. pHe was significantly lower in hypercapnic than in normocapnic subjects. The differences of pHi and pHu between normo and hypercapnic subjects were not significant. NAE is significantly correlated with PaCO2, pHe, pHu and pHi in all the subjects considered together. H+-secretion probably depends on the H+-availability and pHi of tubular cells, but from our results it is not possible to confirm this relationship, because the method used for pHi is fundamentally a measure of muscle-pHi.