The Acute Effects of Passive Vibration on Cardiovascular Function in Individuals With Stroke

Overview

Stroke is the third leading cause of death in the United States. Of those who are affected by stroke, a third becomes permanently disabled. Risk factors for stroke include, but are not limited to, advancing age, physical inactivity, arterial stiffness, and most commonly, high blood pressure. Stroke is a major form of a much boarder problem, cardiovascular disease (CVD). CVD is considered the primary cause of death in the US. Interestingly, increased arterial stiffness of elastic arteries (carotid and aorta) has been shown to be strongly correlated to CVD and stroke. Increased arterial stiffness is considered an independent risk for the development of CVD and stroke. Hence, arterial stiffness has been suggested as a potential therapeutic target for CVD and more specifically stroke. Recently, whole-body vibration (WBV) exercise has been proposed as a new and effective method to improve muscle mass and muscle strength in younger and older individuals. It is known that systemic arterial stiffness decreased 40 min after a single WBV session in healthy men. In our laboratory, we have shown that leg arterial stiffness decreases after a session of WBV. Taken together, this data seems to suggest WBV may be used as a viable way to decrease arterial stiffness. Special populations, such as post-stroke patients, may be unwilling or unable to perform WBV exercise so an inactive form of exercise (vibration) therapy is needed. Passive vibration (PV), allows patients to lie in an inactive, supine position, with their legs placed onto the vibration plate. This exposes the lower limbs to continuous vibration without performing voluntary muscle contraction. PV has been shown to increase skin blood flow on the vibrated extremity through vasodilation in healthy individuals and type 2 diabetics. Previous work in our laboratory has demonstrated that a 10-min session of PV on the legs decreases augmentation index (AIx) , a marker of pressure wave reflection, as well as leg and systemic PWV through decreases in local peripheral resistance in young men. However, the effects of PV on arterial function in post-stroke patients are unknown. It is hypothesized that post-stroke patients will demonstrate a decrease in leg PWV and central AIx. However, greater responses are expected with the lower vibration frequency.

The purpose of this study is to examine the effects of one acute bout of low and high frequency passive vibration on blood pressure, heart rate, arterial stiffness, wave reflection, and autonomic function in post-stroke patients. The specific aim of this study is: -To evaluate the effects of an acute bout of both high (40Hz/low amplitude) and low frequency (25Hz/high amplitude) passive vibration on arterial function and aortic hemodynamics by assessing blood pressures (systolic, diastolic, mean, pulse pressure), arterial stiffness (aortic, systemic, leg), aortic wave reflection (augmentation index), and autonomic function (heart rate variability).