Sudden blood flow restoration to an ischemic vessel paradoxically damages endothelial cells. Ischemic preconditioning, caused by repeated bouts of brief ischemia using local or remote cuff inflation before reperfusion, attenuates endothelial dysfunction following an ischemia-reperfusion injury in young adults but does not consistently protect endothelial function in older adults prone to ischemic events. Intermittent exposure to systemic hypoxemia, induced via brief bouts of breathing low levels of oxygen, attenuates endothelial dysfunction following an ischemia-reperfusion injury in young adults. The aim of this study was to determine whether systemic hypoxic preconditioning protects against ischemia-reperfusion injury in older adults. Twelve adults (five women, 57 ± 9 yr) participated in this randomized crossover trial. Endothelium-dependent vasodilation was assessed by brachial artery flow-mediated dilation using a semiautomated diagnostic ultrasound system before and after a 20-min blood flow occlusion that was preceded by either intermittent hypoxia, consisting of three 4-min hypoxic cycles at an oxygen saturation of 80% interspersed with 4-min room air cycles, or intermittent normoxia, consisting of three 4-min normoxic cycles separated by 4-min room air cycles. When preceded by intermittent normoxia, ischemia-reperfusion injury reduced flow-mediated dilation by 4.1 ± 2.6% (6.5 ± 1.7 to 2.4 ± 1.7%). In contrast, flow-mediated dilation was reduced by 2.0 ± 1.5% when ischemia-reperfusion injury was preceded by intermittent hypoxia (5.6 ± 1.7 to 3.6 ± 2.3%). In conclusion, hypoxic preconditioning significantly attenuated the reduction in brachial artery flow-mediated dilation induced by an ischemia-reperfusion injury in older adults at greater risk for ischemic events.
Keywords: aging; flow-mediated dilation; intermittent hypoxia; ischemia-reperfusion injury.