Lactate increases oxygen unloading of preconditioned blood from male elite breath-hold divers

Physical performance can be improved in aerobic athletes and breath-hold divers (BHD) by limb exposure to repetitive ischemia: remote ischemic conditioning (RIC). RIC protects against cardiac ischemia, and its blood-borne transferable substrate could be lactate. Accordingly, lactate added to whale blood increases oxygen unloading and adult seals possess higher cardiac lactate dehydrogenase activity (LDHa) than terrestrial mammals. Because BHD and adult diving mammals share adaptations to hypoxia, including lactate metabolization during apnea, we hypothesized that BHD compared to BMI/VO₂max-matched aerobic controls have higher LDHa and lactate added to blood from BHD unloads oxygen more efficiently. Six BHD and six matched aerobic controls underwent RIC: three cycles of 5-min inflation and 4-min deflation of a blood pressure cuff on the dominant arm, maximum apnea after three submaximal apneas (BHD only), and a VO₂max-test. Blood-samples were collected from the nondominant radial artery and the vena basilica of the dominant arm at rest, before termination of the three interventions, and for LDHa. Blood gases were compared to samples added lactate or placebo suspension. BHD had ⁓30% higher cardiac/erythrocyte LDHa compared to controls (p < 0.05). Lactate added to arterial blood from BHD after RIC increased oxygen unloading (p < 0.05). PaO₂ decreased ⁓66% during apnea (375+/-49 s; p < 0.001; BHD only). We conclude that 1 (erythrocyte- and cardiac-LDHa is higher in BHD compared to matched controls, and 2) lactate facilitates oxygen-unloading in blood from BHD after RIC, similar to diving mammals.