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Introduction
Arterial stiffness is a consequence of a variety of factors, including changes in the composition of the arterial wall matrix [1, 2] and properties of the vascular smooth muscle [3, 4–5]. Chronic changes in arterial wall stiffening usually occur via changes in structural characteristics of the arterial wall while acute changes in arterial wall stiffening usually occur via changes in vascular smooth muscle contractility. The gold standard method for evaluating arterial stiffness in vivo is through the measurement of pulse wave velocity (PWV), which indicates the speed at which arterial pressure waves propagate through the vasculature [6, 7].
The change in PWV velocity observed in response to a reactive hyperemia stimulus is referred to as flow-mediated slowing (FMS). FMS has emerged as an alternative method for evaluating endothelial function which has traditionally relied on measuring the vasodilation of a conduit artery (flow-mediated dilation) following an increase in shear stress induced by a reactive hyperemia stimulus [8, 9]. Proponents of the FMS approach argue that a decrease in PWV during reactive hyperemia is flow-dependent and serves as an indicator of endothelial function. However, the relationship between the increase in blood flow and the decrease in PWV deserves further exploration.
The magnitude of blood-flow increase with reactive hyperemia can be altered by manipulating limb position below or above heart level. Both Jasperse et al. [10] and Bartlett et al. [11] observed a greater magnitude of reactive hyperemia when the arm was positioned below heart level compared to when it was positioned above heart level. We took advantage of this approach to explore the mechanism of action for the reduction in peripheral arterial stiffness following reactive hyperemia. The purpose of this study was to examine the changes in PWV following reactive hyperemia-induced increases in conduit artery blood flow. We did not intend to evaluate FMS as a measure of endothelial function, rather to study the relationship between increases in blood flow and changes in PWV. We hypothesized that a larger magnitude of reactive hyperemia would result in a greater reduction in peripheral arterial stiffness.
Methods
Participants
Fourteen healthy young adults volunteered for this study. Participants were excluded for smoking, presence of cardiovascular, metabolic, and pulmonary diseases. Other exclusion criteria include hypertension or hypotension, diabetes, obesity (body mass...