Fig. 1. Study protocol. Endothelial function was established at baseline and was repeated after 20 min of forearm I/R except for controls. Treatment with helium preconditioning was administered directly before forearm I/R (HE-EPC) or 24 h before I/R (He-LPC). Treatment of IPC was administered directly before forearm I/R. Controls = control group without ischemia; He-EPC = helium early preconditioning group; He-LPC = helium late preconditioning group; I/R = ischemia–reperfusion group; IPC = ischemic preconditioning group.