Haemoglobinic acid concentration from HbO2 dissociation curves under CO2 effect

Steps:

• Dissociation curves shift right with higher PCO2 due to Bohr effect, increasing H+ from carbonic acid and carbamino compounds.
• Haemoglobinic acid (HbH+) forms via protonation of Hb, highest where curve indicates low O2 affinity and high acidity.
• At fixed pO2, compare points A-D on curves for PCO2= low (left curve) vs high (right curve).
• Select point on high PCO2 curve showing elevated HbH+ via reduced saturation.

Why C is correct:

• C marks the point on the high PCO2 curve where protonation is maximal, per Bohr effect definition linking CO2 to Hb acidification.

Why the others are wrong:

• A: On low PCO2 curve, indicating minimal acidification.
• B: Midpoint on low PCO2 curve, not peak HbH+.
• D: Endpoint on high PCO2 curve, but reflects deoxygenated Hb, not acid concentration.

Final answer: C