Pitfalls in Comparison of Exercise-Induced Changes of Base Excess and Lactate Concentrations in Blood

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It has been concluded from comparisons of base excess (BE) and lactate (La) concentration changes in blood during exercise-induced non-respiratory acidosis that much more H+ than La- leave the muscle and enter interstitial fluid and blood. PURPOSE: To check this hypothesis. METHODS: Incremental cycle tests to exhaustion were performed with 13 untrained (UT) and 21 endurance-trained (TR) young males. Acid base status in arterialized blood and [La] in arterialized blood, plasma and red cells were measured until 21 min after exercise. RESULTS: Actual BE decrease (-?ABE) was 2.2 + 0.5(SEM) mmol.l-1 larger than [La]blood increase at exhaustion (P< 0.01) and rose to 4.8 + 0.5 mmol.l-1 during the first minutes of recovery in the UT (P< 0.05 for the additional increase). The decrease of standard BE (SBE), a measure of extracellular BE including the erythrocytes, however, was smaller than the estimated increase of [La] in the corresponding volume (0.14 [La]ery + 0.86 [La]plasma) during exercise and approximately equal during recovery. In the TR the changes in - ΔBE - Δ [La] from exercise to recovery were slightly reduced. The discrepance between -Δ ABE and Δ [La]blood is mainly caused by the Donnan effect hindering the rise of [La]ery to equal values like in plasma. It can be calculated that instead Cl- enter firstly the plasma and then the erythrocytes in exchange for HCO3- corresponding to inflow of HCl into the blood while La- partly remain in the interstitial fluid. SBE is not influenced by ion shifts among compartments but changes have been compared to Δ [La]blood instead of extracellular Δ La] in a former investigation. CONCLUSION: Our results thus disprove the hypothesis of large differences in H+ and La- transport across the muscle cell membrane which was based on neglection of the Donnan effect and erroneous comparisons.