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Carbon dioxide is carried in the blood in 3 major forms
 | Dissolved |
| Combined with H2O in the form of HCO3 (bicarbonate) |
| Combined with haemoglobin (carbamate) |
A concise summary of the CO2 transport system can be found in
RA Klocke, "Carbon Dioxide" Chapter 5.3.2.3, pp 1233-1239 in: THE LUNG: scientific foundations. ed RG Crystal, JB West et al. Raven Press, Ltd., New York ©1991
The CO2 content for a given pressure depends on temperature, acidity of the blood, amount of haemoglobin and the saturation of the haemoglobin. This last dependency is referred to as the Haldane effect). A series of equations that takes all these factors into account can be found in:
AR Douglas, NL Jones & JW Reed, "Calculation of whole blood CO2 content", J.Appl.Physiol.65(1):473-477,1988.
The following applet tests the Java beans used to perform these calculations in the final Javaman model.
Of interest, solubility and pK values used in the Henderson-Hasselbach equation are dependent on temperature and pH. They are calculated in this application.
The intention of this program was to produce some nice CO2 content titration curves as CO2 tension changed.
Sadly the plots came out as straight lines rather than curves. Changing haemoglobin saturation had very little effect on the position of the curve.
The problem was that pH remained constant throughout the plot. This would not occur during titration. As more CO2 dissolved the pH would fall and this would effect the total amount of CO2 carried.
Siggaard-Andersen gave a formula to give Base Excess from CO2 tension, haemoglobin concentration and pH.
Siggaard-Andersen, O. (1966). "Titratable acid or base of body fluids." Ann N Y Acad Sci 133(1): 41-58.
Assuming that Base Excess remains constant during titration this equation can be reversed to derive pH for any given value of pCO2, Base Excess and haemoglobin concentration.
The beans used for these calculations will be found through the Acid-Base page.
You can experiment for yourself by setting base excess to 0 and plotting a curve.
Decrease the haemoglobin saturation and see the curve move up. More CO2 is carried for the same CO2 tension when haemoglobin is reduced. The Haldane-Christensen effect.
The curves produced are all about 10% lower than the figures quoted in the standard text books. The hunt continues for the origin of this systematic variation (error!)