Causes of differences in exercise-induced changes of base excess and blood lactate

• Published in: European journal of applied physiology 2007-01, Vol.99 (2), p.163-171
• Main Authors: Böning, Dieter, Klarholz, Carola, Himmelsbach, Bärbel, Hütler, Matthias, Maassen, Norbert
• Format: Article
• Language: English
• Subjects: Acid-Base Equilibrium; Acidosis - blood; Acidosis - metabolism; Acidosis - physiopathology; Adult; Bicarbonates - metabolism; Chlorides - metabolism; Erythrocytes - metabolism; Exercise; Extracellular Fluid - metabolism; Humans; Hydrogen-Ion Concentration; Lactic Acid - blood; Lactic Acid - metabolism; Male; Muscle Fatigue; Muscle, Skeletal - metabolism; Time Factors
• ISSN: 1439-6319; 1439-6327
• DOI: 10.1007/s00421-006-0328-0

It has been concluded from comparisons of base excess (BE) and lactic acid (La) concentration changes in blood during exercise-induced acidosis that more H+ than La- leave the muscle and enter interstitial fluid and blood. To examine this, we performed incremental cycle tests in 13 untrained males and measured acid-base status and [La] in arterialized blood, plasma, and red cells until 21 min after exhaustion. The decrease of actual BE (-deltaABE) was 2.2 +/- 0.5 (SEM) mmol l(-1) larger than the increase of [La]blood at exhaustion, and the difference rose to 4.8 +/- 0.5 mmol l(-1) during the first minutes of recovery. The decrease of standard BE (SBE), a measure of mean BE of interstitial fluid (if) and blood, however, was smaller than the increase of [La] in the corresponding volume (delta[La](if+blood)) during exercise and only slightly larger during recovery. The discrepancy between -deltaABE and delta[La]blood mainly results from the Donnan effect hindering the rise of [La]erythrocyte to equal values like [La]plasma. The changing Donnan effect during acidosis causes that Cl- from the interstitial fluid enter plasma and erythrocytes in exchange for HCO3(-). A corresponding amount of La- remains outside the blood. SBE is not influenced by ion shifts among these compartments and therefore is a rather exact measure of acid movements across tissue cell membranes, but changes have been compared previously to delta[La]blood instead to delta[La](if+blood). When performing correct comparisons and considering Cl-/HCO3(-) exchange between erythrocytes and extracellular fluid, neither the use of deltaABE nor of deltaSBE provides evidence for differences in H+ and La- transport across the tissue cell membranes.