Late Breaking Abstract - O2 dissociation curve inflection: hemoglobin's built-in Bohr effect trigger

Recent evidence links the O₂ dissociation curve (ODC) inflection point with the first ventilatory threshold (VT1; Burchert et al., 2023). To investigate this relationship, we reanalyzed 12 high-resolution femoral venous blood data pooled from 5 subjects during rest to heavy 6-minute constant work rate exercise (75% Δ VT1 to maximal O₂ consumption, 265 W; Stringer et al., 1994). Using an established biochemical model of the ODC (Dash et al., 2016), we calculated O₂, CO₂, and H⁺ dissociation curves from the levels of O₂, CO₂, 2,3-DPG, hematocrit, hemoglobin (Hb), pH, and temperature. We identified inflection points through numerical differentiation and root-finding. The first 4 samples showed minimal rightward ODC shift. The 4th sample, collected at the ODC inflection point, revealed that the O₂, CO₂, and H⁺ dissociation curves reached their inflections simultaneously. At this moment, the H⁺ curve intersected and surpassed the CO₂ curve. Thus, at the ODC inflection point, O₂ unloading, CO₂ loading, and H⁺ loading of Hb is optimized, with H⁺ loading eventually predominating. For the subsequent samples, Hb continued to bind H⁺ while unloading CO₂, causing the CO₂, and H⁺ curves to diverge, thereby activating the Bohr effect and shifting the ODC to the right. We conclude that the activation of the Bohr effect is an emergent property of the ODC triggered at the inflection point due to intricate interactions of O₂, CO₂ and H⁺ with Hb. <fig><object-id>erj;64/suppl_68/PA1677/F1</object-id><object-id>F1</object-id><object-id>F1</object-id><graphic></graphic></fig>