Abstract
Abstract
Life at altitude is characterized by increased erythropoietic activity and hemoglobin concentration ([Hb]). The first aim of the project was to identify the altitudes at which significant increases in hemoglobin mass (Hbmass) and decreases in plasma volume (PV) occur among residents living at different altitudes. The second aim was to evaluate the extent to which Hbmass and PV contribute to changes in [Hb] at moderate altitudes. The study included 133 young men and 148 women from six Andean regions at altitudes ranging from 970 to 2600 m. Hbmass was determined using carbon monoxide rebreathing. PV was calculated using Hbmass, [Hb], and hematocrit. Hbmass increased up to 2600 m by 35.9 ± 11.6 g, while PV decreased by 208 ± 53 mL (both
p
< 0.01). The first significant increase in Hbmass occurred at 2180 m and the first significant decrease in PV occurred at 1730 m. At 2600 m, Hbmass and PV contributed equally to the 1.2 g/dL increase in [Hb], that is, 0.56 and 0.61 g/dL, respectively. The threshold for a decrease in PV in Andeans is ~450 m lower than the threshold for an increase in Hbmass. The contribution of hemoconcentration to the increase in [Hb] at moderate altitudes is equal to the contribution of erythropoiesis.