Assessment of Reactive Hyperemia Using Peripheral Arterial Tonometry1

Abstract

Reactive hyperemia (RH) is characterized by temporary increase in blood flow, which occurs in a blood vessel following a brief period of ischemia. Following ischemia there is a shortage of oxygen bioavailability and a build-up of metabolic waste, which must be replenished to restore normal function [1]. An increased blood flow, an increased vessel diameter (cross-sectional area), and increased pulsatility are all characteristic normal physiological responses post ischemia. The vasodilation post ischemia is caused by release of nitric oxide into the blood stream [2]. Over time, the blood flow returns to baseline levels. Endothelial dysfunction (dysfunction of the inner lining of blood vessels), which is commonly associated with reduced nitric oxide levels in the blood stream, is a sign of cardiovascular disease and is a predictor of unsatisfactory clinical results. Peripheral Arterial Tonometry (PAT) signals from patient’s finger have been used in clinical settings to characterize cardiovascular performance, and have shown correlations to central pressures of the heart [3]. The noninvasive nature of PAT makes its applicability attractive as its clinical applications continue to advance. Therefore, PAT has a potential clinical application as a noninvasive metric, which can describe a patient’s endothelial function and overall cardiovascular health by measuring the reactive hyperemia response during a period of induced ischemia. Due to the ability of PAT to measure pulsatility of blood flow through digits, we hypothesize that reactive hyperemia responses can be measured non-invasively by recording PAT signals. Further, we hypothesize that there will be changes in reactive hyperemia responses shown through PAT signals when the length of ischemic time is altered. These results may have important clinical implications in terms of unravelling endothelial dysfunction and vascular elasticity.