GLOSSARY

Carbon dioxide transport is the carriage of CO₂ produced in the cells via the blood to the lungs for elimination, occurring in three forms.

Three Forms of Transport

• Bicarbonate (HCO₃⁻): about 70 percent; in the red cell, the enzyme carbonic anhydrase speeds the reaction CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻ thousands of times.
• Carbamino compounds: about 20–23 percent; CO₂ bound to the amine groups of haemoglobin.
• Dissolved in plasma: about 7–10 percent.

Chloride Shift (Hamburger Phenomenon)

Bicarbonate produced in the red cell moves out into the plasma, and chloride (Cl⁻) moves in to maintain electrical balance; the process is reversed in the lungs.

Haldane Effect

Deoxygenated haemoglobin accepts more CO₂ and H⁺, so venous blood has a greater capacity to carry CO₂.

Importance

• Buffer system: bicarbonate is the most important extracellular buffer, maintaining blood pH.
• Henderson–Hasselbalch relationship: blood pH depends on the ratio of HCO₃⁻ to PCO₂.

Relevance to Sport

• Buffering exercise acid: during intense exercise, the H⁺ produced is buffered by bicarbonate, generating extra (non-metabolic) CO₂; this causes the disproportionate rise in ventilation and an RER above 1.
• Sodium bicarbonate supplementation: about 0.3 grams per kilogram of body mass 60–180 minutes before exercise may improve performance in intense 1–7-minute efforts (such as the 800 metres or a 2,000-metre row) by about 1–2 percent; a common side effect is gastrointestinal discomfort.