 We designed a protocol which specific aims are 1 to test the effect of local hypoxia on the markers of endothelial damagerepair equilibrium 2 to define whether in elderly patients, local ischemia can be used to mobilize EPC and to increase their proliferation potential compared to EPC isolated in resting conditions. Two groups of healthy volunteers aged 20-30 and 60-70 years from our cohorts will be submitted to forearm transient ischemia as described by Friedrich et al 23. Peripheral blood samples will be obtained before and after 10 min of venous occlusion performed with a cuff pressure midway between systolic and diastolic pressure 24. EPC, CEC and EMP will be enumerated according to the methods described supra and EPC will be tested for proliferating capacity at each time point. The arterial phenotype of conducting arteries will be evaluated, by the acute flow-mediated vasodilatation FMD and endothelium-independent vasodilatation EIV of the brachial artery BA in young and older healthy volunteers using a high-resolution echotracking system. The efficiency of venous occlusion will be evaluated by the release of t-PA by endothelial cells. 