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

Abstract

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.

Acid-base status of arterial and femoral-venous blood during and after intense cycle exercise

“…This pattern and the values seen are in line with several former studies [3,4,24,27,33,36,43]. Blood and plasma bicarbonate concentration fell linearly by the lactate concentration, which is in line with data from former studies [4,27,33].…”

“…Possible deviations for venous blood with reduced O 2 -saturation, are addressed in the discussion. Böning and co-workers [3] used a similar approach calculating cCl -C from a relationship proposed by Dell and Winters [6]. Their approach reported identical values of that proposed above when correcting for different water fractions (φ w,C / φ w,P ).…”

“…After a 10 min rest he cycled at a constant power established during the pretests for ≈2 min to exhaustion. Blood samples from the femoral artery and vein were drawn in parallel in 5 ml syringes before the exercise, after 30, 60 and 90 s of exercise, and at 30 s, 1,3,6,10,15,20,30,45, and 60 min after the exhausting bout. The blood samples were handled as described elsewhere [24] to allow measurement of haematocrit (Hct), blood lactate (La) and haemoglobin (Hb) concentrations, blood acidbase parameters (pH, pCO 2 , pO 2 , sO 2 ), concentration of plasma electrolytes (Na + , K + , Cl -, La -, HCO 3 -), and plasma albumin, and proteins.…”

“…In arterial blood the relationship between plasma bicarbonate and lactate concentrations was cHCO 3 , n = 74, r = -0.95) when samples with a pCO 2 > 80 hPa were excluded. The slopes of the two relationships do not differ.…”

“…The process is very fast, taking less than one second for equilibration [19]. However, the extent of this process in relation to high-intensity, anaerobic types of exercise has only been studied in arterialised blood [3], and possible differences between arterial and venous blood is therefore not known.…”