2007, Piran, Slovenia

Altitude Physiology
Figure 1. Mean change in Hb after 3 apneas during ascent through descent (read from left).
200
180
160
140
120
100
80
60
40
change in [Hb] g/L
6
5
4
3
2
1
0
1230m 3840m 5100m 3840m 1230m
altitude
(97%) (83%) (78%) (85%) (98%)
Hemoglobin (g/L)
Apnea Time (s)
1230m 3840m 5100m 3840m 1230m
altitude
Figure 2. Mean pre-apneic Hb and apneic time during ascent through descent (read
from left). Baseline SaO2 values are provided in brackets.
DISCUSSION
The attenuated Hb increase with ascent suggests that hypoxia during altitude
acclimatization causes splenic contraction to occur already during eupneic periods and
thus eliminates apnea-induced increases in Hb. After acclimatization and upon
descent, a polycythemia-associated increase in pre-apnea Hb was noted, and Hb
increases caused by apnea were comparatively larger than those observed during
ascent. This suggests that, after acclimatization, a) the level of tonic splenic
contraction during eupnea was reduced, or b) there was a greater storage of
erythrocytes in the spleen resulting from altitude-related polycythemia, or both. A
study on mice suggested that 2/5 of the erythrocyte increase observed during long
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