Journal of Applied Physiology, Vol 68, Issue 3 1186-1194, Copyright © 1990 by American Physiological Society
Unchanged in vivo P50 at high altitude despite decreased erythrocyte age and elevated 2,3-diphosphoglycerate
H. Mairbaurl, W. Schobersberger, O. Oelz, P. Bartsch, K. U. Eckardt and C. Bauer
Institut fur Physiologie, Universitat Innsbruck, Austria.
We measured hematological and erythrocyte O2 transport parameters in whole
blood and density-separated erythrocytes in 11 mountaineers before and
during 5 days of exposure to high altitude (4,559 m). We determined the in
vivo (arterial pHblood and PCO2) and standard (pHblood = 7.4, PCO2 = 40
Torr) O2 tension at 50% O2 saturation of hemoglobin and (P50,vv and P50,st)
and Bohr coefficients (BC) for fixed acid (H+) and CO2 and examined the
contribution of the altered average age of circulating erythrocytes due to
the stimulation of erythropoiesis on whole blood 2,3-diphosphoglycerate
(2,3-DPG) and P50,st. At altitude, whole blood P50,vv remained almost
unchanged, whereas P50,st and 2,3-DPG increased significantly (+4 Torr; 3.5
mumol/g hemoglobin). BCCO2 was elevated significantly at altitude. Serum
erythropoietin increased transiently fourfold, iron utilization increased,
and serum iron decreased by 66%. Reticulocyte counts increased, but other
hematological parameters were unchanged. In density-separated erythrocytes,
P50,st and 2,3-DPG increased with decreasing cell density but were higher
in fractions with comparable reticulocyte counts in cells prepared at
altitude than in those from control studies. Our data show that, despite
the increase in 2,3-DPG and the decrease in average erythrocyte age, the in
vivo hemoglobin-O2 affinity remains unchanged. P50,st values reflect the
elevation of 2,3-DPG, and approximately 50% of the increase in both
parameters can be ascribed to the increase in the number of reticulocytes
and young erythrocytes.
