The effect of THAM and sodium bicarbonate on the oxygen dissociation curve and pH difference across the red cell.

Abstract

Extract: This report presents the difference (Δ [H+)], and ratio (Δ pH), of the hydrogen ion activity between the inside and outside of the red cell for THAM-buffered and NaHCO3-buffered ACD blood of man. Figure 2 shows that there was a significant difference in Δ pH and Δ [H+] between bloods buffered with THAM or sodium bicarbonate, this difference being due to the fact that normal Δ pH was reduced in THAM-buffered blood to a Δ pHof 0.072 (see table I). The oxygen dissociation curves were constructed at a variety of whole blood pHs for THAM-buffered and sodium bicarbonate-buffered ACD blood. As predicted from the measured difference in Δ pH, the oxygen dissociation curves were different for these two bloods. Table II presents the appropriate constants for the general equation log pO2 = k1 + k2 (7.4-pH) + k3 log (s/100−s). With the use of a computer program and Calcomp plot routine, the log (s/100−s)/log pO2 plot for THAM-buffered (fig. 3) and sodium bicarbonate-buffered ACD blood (fig. 4), together with their 95% confidence limits, were constructed. Speculation: Comparison of Δ pH measurements with oxygen dissociation curves should help in distinguishing between direct effect of acids and bases upon the oxygen affinity of hemoglobin and their indirect effect on oxygen affinity through an alteration in Δ pH across the red cell membrane. Secondly, the use of THAM to increase the oxygen affinity of whole blood may be of help to those studying fetal physiology and interested in determining whether fetal oxygen consumption is limited by an increased oxygen affinity in fetal blood.