Diurnal normobaric moderate hypoxia raises serum erythropoietin concentration but does not stimulate accelerated erythrocyte production

This study was performed to examine the effect of diurnal normobaric hypoxia on hematological parameters. Eleven healthy male volunteers were randomly selected to be in either the hypoxic group (n=6) or the control group (n=5). The hypoxic group was exposed to 8 h of normobaric hypoxia in hypoxic tent systems that elicited a target peripheral O₂ saturation of 81±2% on three consecutive days. The control group spent three consecutive 8-h days in modified tent systems that delivered normoxic air into the tent. Venous blood samples were collected before the exposure (days –5, 0), after each day of the exposure (days 1, 2, 3), and for 3 weeks after the exposure (days 7, 10, 13, 17, 24). Serum erythropoietin concentration significantly increased from 9.1±3.3 U·L⁻¹ to 30.7±8.6 U·L⁻¹ in the hypoxic group. Although there were significant increases in hematocrit (4%), hemoglobin concentration (5%), red blood cell count (4%) on day 7 in the hypoxic group, these observations were likely due to dehydration or biological variation over time. There was no significant change in early erythropoietic markers (reticulocyte counts or serum ferritin concentration), which provided inconclusive evidence of accelerated erythroid differentiation and proliferation. The results suggest that the degree of hypoxia was sufficient to stimulate increased erythropoietin production and release. However, the duration of hypoxic exposure was insufficient to propagate the erythropoietic cascade.