The O2-hemoglobin dissociation curves of Figures 1 and 2 are for normal, average blood. However, several factors can displace the dissociation curve in one direction or the other in the manner shown in Figure 3. This figure shows that when the blood becomes slightly acidic, with the pH decreasing from the normal value of 7.4 to 7.2, the O2-hemoglobin dissociation curve shifts, on average, about 15 percent to the right. Conversely, an increase in pH from the normal 7.4 to 7.6 shifts the curve a similar amount to the left.
Fig1. Oxygen-hemoglobin dissociation curve.
Fig2. Effect of blood PO2 on the quantity of oxygen bound with hemoglobin in each 100 milliliters of blood.
Fig3. Shift of the oxygen-hemoglobin dissociation curve to the right caused by an increase in hydrogen ion concentration (decrease in pH). BPG, 2,3-biphosphoglycerate.
In addition to pH changes, several other factors are known to shift the curve. Three of these, all of which shift the curve to the right, are (1) increased CO2 concentration, (2) increased blood temperature, and (3) increased 2,3-biphosphoglycerate (BPG), a metabolically important phosphate compound present in the blood in different concentrations under different metabolic conditions.
