Does 24-hour Ambulatory Blood Pressure Monitoring Act as Ischemia Preconditioning and Influence Endothelial Function?

Abstract

Ischemic preconditioning can exert a powerful protection against a subsequent period of ischemia in a variety of organs, via repeated inflation and deflation of a blood pressure cuff. Most often, damages of ischemia reperfusion injury and benefits of preconditioning are evaluated via endothelial function. The ambulatory blood pressure device takes repeated blood pressure measurements and constitutes repeated bouts of ischemia for 24 hours. In practice, measurements of endothelial function and ambulatory (24-hour) blood pressure are often combined. PURPOSE: We determined whether repeated bouts of ischemia accumulated for 24 hours through 24-hour ambulatory blood pressure monitoring influence endothelial function. METHODS: Twenty-two apparently healthy non-medicated middle-aged subjects (41±8 years, 12 males and 10 females) participated in the study. Flow-mediated dilation (FMD; index of endothelium-dependent vasodilation) was measured twice 30 minutes apart at baseline to confirm test-retest reliability. Subsequently, subjects were fitted with an ambulatory (24 hour) blood pressure monitoring device. Blood pressure was measured every 15 minutes during the daytime and 20 minutes at nighttime. Upon returning after 24 hours, FMD was remeasured. Shear rate and reactive hyperemia were also measured simultaneously. RESULTS: The ambulatory blood pressure monitoring device went through an average of 110±13 inflation/deflation cycles, which resulted in 46±6 minutes of cumulative ischemic stimuli. Two measurements of FMD at baseline were not different, showing the measurement stability. Following 24-hours of ambulatory blood pressure monitoring, FMD did not change significantly (6.6±2 vs. 6.8±3%). Similarly, shear rate (4.4±2.6 vs. 5.1±5.9 cm/s) and reactive hyperemia (13.7±12.1 vs. 17.6±21.1 cm/s) were unchanged (all p > 0.05). CONCLUSIONS: Ambulatory blood pressure monitoring and the associated ischemia repeated for 24 hours, did not influence endothelium-dependent vasodilation acting via ischemic preconditioning.