Analysis of Variables Influencing Urinary pCO 2 during NaHCO 3 and Water Loading in Normal Man

Abstract

Summary

In the present study the relative influence of several variables, other than distal renal tubular hydrogen ion secretion, on urinary pCO₂, was evaluated. Thirteen studies were conducted in 12 healthy volunteers aged 21-51 years who Received 2 mequiv/kg body weight of NaHCO₃ orally. When urine pH exceeded 7.4, urinary pCO₂, and arterial blood pCO₂, were measured. The maximal difference between urine and arterial blood pCO₂ was 47 ± 2 (SE) mm Hg. In order to obtain data extending over a wide range of urine flow rates, pH, and bicarbonate and phosphorus levels, seven subjects subsequently ingested 20 ml/kg body weight of water. Bivariate Pearson analysis (pre- and post-water-loading data pooled) showed a positive correlation between UpCO₂ and the following variables: UpH (r = 0.77), U_hco3 (r = 0.88), U_HCO3V (r = 0.45), and U_p (r = 0.53) (P < 0.001 for all). A negative correlation was obtained between UpCO₂ and V (r = −0.69, P < 0.001). Multiple regression analysis suggested that U_HCO3 and U_p were the predominant influences on UpCO₂ and that the independent influences of the other variables were small and not statistically significant.