A Proposal for Analysing the Acid-Base Balance at Steady State in Vivo

Abstract

We previously measured the hydrogen ion [H⁺], bicarbonate ion concentration [HCO₃ ^-], and PCO₂, in the arterial blood of elderly patients, and examined the correlation of [H⁺] and [HCO₃ ^-] with PCO₂. We found that the deviations of [H⁺] and [HCO₃ ^-] from their respective regression lines versus PCO₂ were well correlated with each other. When the deviation was close to zero, the deviation of [HCO₃ ^-] was linearly related with that of [H⁺]. This result suggested that the ratio of [HCO)₃ ^-] to [H⁺] on the regression line was constant. Later we found in normal venous plasma that the ratio of [H⁺] to [HCO₃ ^-] was distributed in a narrow range around 1.53 x 10^-6 (Mochizuki, 1995). It has been suggested that the measured [H⁺] value had a Peal-dependent [H⁺]^* and a Peal-independent component Δ[H⁺], and the [H⁺]^* could be approximated by an expression that was proportional to the square root of Peo2 using the Henderson equation (Henderson, 1909). Then, Δ[H⁺] was obtained by subtracting [H⁺]^* from [H⁺]. From the relationship of Δ[H⁺] between arterial and venous blood, we confirmed that the Δ[H⁺] remains unchanged despite a change in Peo, in the lung. Using the slope of the regression line of the V-A difference in Δ[H⁺] plotted-against that in PCO [H⁺]^* could be determined. When the[H⁺]^* was known for an exponential function of PCO₂ the regression line of the V-A difference of Δ[H⁺] lay upon the abscissa, which veri fied that Δ[H⁺] was independent of PCO₂.