Extracellular pH defense against lactic acid in normoxia and hypoxia before and after a Himalayan expedition

The extracellular pH defense against the lactic acidosis resulting from exe rcise can be estimated from the ratios -Delta [La] . Delta pH(-1) (where De lta [La] is change in lactic acid concentration and Delta pH is change in p H) and Delta [HCO3-] . Delta pH(-1) (where Delta [HCO3-] is change in bicar bonate concentration) in blood plasma. The difference between -Delta [La] . Delta pH(-1) and Delta [HCO3-] . Delta pH(-1) yields the capacity of avail able non-bicarbonate buffers (mainly hemoglobin). In turn, Delta [HCO3-] . Delta pH(-1) can be separated into a pure bicarbonate buffering las calcula ted at constant carbon dioxide tension) and a hyperventilation effect. Thes e quantities were measured in 12 mountaineers during incremental exercise t ests before, and 7-8 days (group 1) or 11-12 days (group 2) after their ret urn from a Himalayan expedition (2800-7600 m altitude) under conditions of normoxia and acute hypoxia. In normoxia -Delta [La] . Delta pH(-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 no n-bicarbonate buffering, respectively. After altitude -Delta [La] . Delta p H(-1) was increased to 128 (12) mmol . l(-1) (P < 0.01) in group 1 and decr eased 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 t o 49 (14) mmol . l(-1) in group I 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 pro posed here that the transport of La- and H+ across cell membranes is differ ently influenced by high-altitude acclimatization.