Effects of simulated altitude (normobaric hypoxia) on cardiorespiratory parameters and circulating endothelial precursors in healthy subjects

Background:Circulating Endothelial Precursors (PB-EPCs) are involved in the maintenance of the endothelial compartment being promptly mobilized after injuries of the vascular endothelium, but the effects of a brief normobaric hypoxia on PB-EPCs in healthy subjects are scarcely studied. Methods: Clinical and molecular parameters were investigated in healthy subjects (n=8) in basal conditions (TO)and after 1 h of normobaric hypoxia (TI), with Inspiratory Fraction of Oxygen set at 11.2% simulating 4850 mt of altitude. Blood samples were obtained at TO andTI, as well as 7 days after hypoxia (T2). Results: In all studied subjects we observed a prompt and significanr increase in PB-EPCs, with a return to basal value at T2. The induction of hypoxis was confirmed by Alveolar Oxygen Partial Pressure (PAO2) and Spot Oxygen Saturayion decreases. Heart rate increased, but arterial pressure and respiratory response were unaffected. The change in PB-Epcs percent from TO to T1 was universely related to PAO2 at T1. Rapid (T1) increases in serum levels of hepatppcyte growth factor and erythropoietin, as well as in cellular PB-EPCs-ecpression of Hypoxia Inducible Factor-lalfa were observed. Conclusion: In conclusion, the endothelial compartment seems quite responsive ro standardized brief hypoxia, possibly important for PB-EPCs activation and recruitment.