Hi Amanda, thank you so much for maintaining your wonderful site – it’s been incredibly useful. I had a query about the diagram on the double Haldane effect on 2007a(14) – I think the umbilical vessels should be above the uterine vessels in relation to the Y axis? (As in I think they carry more CO2). Cheers, Monica
Hi Monica!
Thanks for contributing with such a great question about the Double Haldane Effect and the graph! The confusion with this graph (shamelessly copied from p355 Power and Kam, 1st ed), lies in the y-axis displaying CO2 content. The maternal circulation, from my reading, contains a much higher CO2 content /100ml blood due to the larger capacity of the bicarbonate system (which is responsible for the carriage of 90% of CO2 in the blood). This complicates understanding the Haldane Effect, as the carbamino compounds, which are responsible for 70% of the Haldane effect, are in and of themselves only responsible for a small proportion overall of the CO2 carriage (<10%).
I believe the overall CO2 content of the fetal blood is in fact lower because of the immaturity of the bicarbonate system (which plays a greater role with increasing gestational age, but who knows the age of the fetus for this graph!!). I think the important effect of the double Haldane effect to take on is still that there is a profound change in the affinity of both maternal and fetal Hb for CO2 which results in a large partial pressure gradient facilitating the movement of CO2 from the fetus to maternal circulation. That is why the x-axis indeed shows that fetal pCO2 is higher than maternal pCO2. I hope this clarifies the reason why the graph is actually correct!
I agree with you Amanda. Interestingly, the 3rd edition of Kam has the umbilical artery/veins up the top indicating higher CO2 content and uterine vein/uterine artery down the bottom. I think this is incorrect for the following reasons.
As you said, foetal CO2 content should be lower. Precisely this is the implication of double Haldane effect. That is, greater affinity of O2 make oxygenated foetal Hb have reduced carrying capacity for CO2.
But it is the other way around in the new version of Kam…
Primary Examination SAQs 
Hi Amanda, thank you so much for maintaining your wonderful site – it’s been incredibly useful. I had a query about the diagram on the double Haldane effect on 2007a(14) – I think the umbilical vessels should be above the uterine vessels in relation to the Y axis? (As in I think they carry more CO2). Cheers, Monica
Monica Diczbalis
February 3, 2016 at 8:43 pm
Hi Monica!
Thanks for contributing with such a great question about the Double Haldane Effect and the graph! The confusion with this graph (shamelessly copied from p355 Power and Kam, 1st ed), lies in the y-axis displaying CO2 content. The maternal circulation, from my reading, contains a much higher CO2 content /100ml blood due to the larger capacity of the bicarbonate system (which is responsible for the carriage of 90% of CO2 in the blood). This complicates understanding the Haldane Effect, as the carbamino compounds, which are responsible for 70% of the Haldane effect, are in and of themselves only responsible for a small proportion overall of the CO2 carriage (<10%).
I believe the overall CO2 content of the fetal blood is in fact lower because of the immaturity of the bicarbonate system (which plays a greater role with increasing gestational age, but who knows the age of the fetus for this graph!!). I think the important effect of the double Haldane effect to take on is still that there is a profound change in the affinity of both maternal and fetal Hb for CO2 which results in a large partial pressure gradient facilitating the movement of CO2 from the fetus to maternal circulation. That is why the x-axis indeed shows that fetal pCO2 is higher than maternal pCO2. I hope this clarifies the reason why the graph is actually correct!
A
primarysaqs
February 5, 2016 at 10:25 pm
I agree with you Amanda. Interestingly, the 3rd edition of Kam has the umbilical artery/veins up the top indicating higher CO2 content and uterine vein/uterine artery down the bottom. I think this is incorrect for the following reasons.
As you said, foetal CO2 content should be lower. Precisely this is the implication of double Haldane effect. That is, greater affinity of O2 make oxygenated foetal Hb have reduced carrying capacity for CO2.
But it is the other way around in the new version of Kam…
Rao
December 5, 2017 at 10:41 am