Extracellular pH defense against lactic acid in normoxia and hypoxia before and after a Himalayan expedition |
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Authors: | D Böning N Maassen A Thomas J M Steinacker |
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Institution: | Department of Sports Medicine, University Hospital Benjamin Franklin, Free University Berlin, Clayallee 229, 14195 Berlin, Germany. boening@zedat.fu-berlin.de |
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Abstract: | The extracellular pH defense against the lactic acidosis resulting from exercise can be estimated from the ratios −ΔLa] · ΔpH−1 (where ΔLa] is change in lactic acid concentration and ΔpH is change in pH) and ΔHCO3
−] · ΔpH−1 (where ΔHCO3
−] is change in bicarbonate concentration) in blood plasma. The difference between −ΔLa] · ΔpH−1 and ΔHCO3
−] · ΔpH−1 yields the capacity of available non-bicarbonate buffers (mainly hemoglobin). In turn, ΔHCO3
−] · ΔpH−1 can be separated into a pure bicarbonate buffering (as calculated at constant carbon dioxide tension) and a hyperventilation
effect. These quantities were measured in 12 mountaineers during incremental exercise tests before, and 7–8 days (group 1)
or 11–12 days (group 2) after their return from a Himalayan expedition (2800–7600 m altitude) under conditions of normoxia
and acute hypoxia. In normoxia −ΔLa] · ΔpH−1 amounted to mean (SEM)] 92 (6) mmol · l−1 before altitude, of which 19 (4), 48 (1) and 25 (3) mmol · l−1 were due to hyperventilation, bicarbonate and non-bicarbonate buffering, respectively. After altitude −ΔLa] · ΔpH−1 was increased to 128 (12) mmol · l−1 (P < 0.01) in group 1 and decreased to 72 (5) mmol · l−1 in group 2 (P < 0.05), resulting mainly from apparent large changes of non-bicarbonate buffer capacity, which amounted to 49 (14) mmol · l−1 in group 1 and to 10 (2) mmol · l−1 in group 2. In acute hypoxia the apparent increase in non-bicarbonate buffers of group 1 was even larger 140 (18) mmol · l−1]. Since the hemoglobin mass was only modestly elevated after descent, other factors must play a role. It is proposed here
that the transport of La− and H+ across cell membranes is differently influenced by high-altitude acclimatization.
Accepted: 14 September 2000 |
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Keywords: | Altitude Exercise Buffering Acid-base status |
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