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.