Erschienen in:
01.05.2008 | Original Article
Extracellular pH defense against lactic acid in untrained and trained altitude residents
verfasst von:
D. Böning, J. Rojas, M. Serrato, O. Reyes, L. Coy, M. Mora
Erschienen in:
European Journal of Applied Physiology
|
Ausgabe 2/2008
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Abstract
The assumption that buffering at altitude is deteriorated by bicarbonate (bi) reduction was investigated. Extracellular pH defense against lactic acidosis was estimated from changes (Δ) in lactic acid ([La]), [HCO3
−], pH and PCO2 in plasma, which equilibrates with interstitial fluid. These quantities were measured in earlobe blood during and after incremental bicycle exercise in 10 untrained (UT) and 11 endurance-trained (TR) highlanders (2,600 m). During exercise the capacity of non-bicarbonate buffers (β
nbi = −Δ[La] · ΔpH−1 − Δ[HCO3
−] · ΔpH−1) amounted to 40 ± 2 (SEM) and 28 ± 2 mmol l−1 in UT and TR, respectively (P < 0.01). During recovery β
nbi decreased to 20 (UT) and 16 (TR) mmol l−1 (P < 0.001) corresponding to values expected from hemoglobin, dissolved protein and phosphate concentrations related to extracellular fluid (ecf). This was accompanied by a larger decrease of base excess after than during exercise for a given Δ[La]. β
bi amounted to 37–41 mmol l−1 being lower than at sea level. The large exercise β
nbi was mainly caused by increasing concentrations of buffers due to temporary shrinking of ecf. Tr has lower β
nbi in spite of an increased Hb mass mainly because of an expanded ecf compared to UT. In highlanders β
nbi is higher than in lowlanders because of larger Hb mass and reduced ecf and counteracts the decrease in [HCO3
−]. The amount of bicarbonate is probably reduced by reduction of the ecf at altitude but this is compensated by lower maximal [La] and more effective hyperventilation resulting in attenuated exercise acidosis at exhaustion.