Mechanism of Reduction in Peripheral Arterial Stiffness with Dynamic Exercise

Peripheral arterial stiffness is reduced in the exercised limb after an acute bout of dynamic exercise. The potential mechanisms involved in the reduction of peripheral arterial stiffness are currently unknown, but blood flow and mechanical compressions of the vasculature might be considered as factors. Part A of this study hypothesized that the magnitude of reduction in peripheral stiffness would be proportional to the intensity of exercise and the accompanying increase in blood flow. In part B, we hypothesized that the magnitude of decrease in peripheral arterial stiffness would be related to the magnitude of increase in blood flow elicited by rhythmic exercise or passive compressions and independent of baseline arterial stiffness. Methods: Part A included 20 healthy young participants (10 females, 30 ± 5 yrs). Part B included 19 healthy young participants (10 females, 30 ± 5 yrs). Brachial-radial PWV was measured with tonometers on the brachial and radial arteries of the arm before and at 5-, 15-, and 30-min post-exercise/compressions in both studies. Brachial blood flow was monitored with doppler ultrasound during exercise and passive compressions and beat-by-beat arterial pressure via photoplethysmography. Part A consisted of two 5-min bouts of rhythmic handgrip exercise (2sec contraction/2sec relaxation) at either 30% or 50% of maximal voluntary contraction (MVC) and a set of passive compressions with an automated blood pressure cuff on the forearm inflating/deflating for 5-min at ~200 mmHg (2-sec inflation/2-sec deflation). Part B consisted of two 5-min bouts of rhythmic handgrip exercise at 50% of MVC and two sets of passive compressions. Both exercise and passive compressions were performed with the arm positioned below or above the heart to manipulate blood flow. Results: In Part A, brachial-radial PWV was reduced similarly by handgrip exercise at 30% MVC, 50% MVC, and passive compression. The reduction in peripheral PWV persisted through 30-min for 50% MVC. Thus, exercise intensity did not affect the magnitude of decrease in PWV but affected the duration of the response. The similarity of responses suggests that mechanical compression plays a role in the post-exercise reduction in peripheral PWV. In part B, manipulation of arm position below versus above heart level affected baseline peripheral arterial stiffness but did not affect the magnitude of increase in blood flow with rhythmic handgrip exercise or passive compressions. The decrease in peripheral arterial stiffness after exercise and passive compressions was independent of arm position. The results of this study suggest that compressions of the forearm vasculature, but not the blood flow response, contribute to the initial post-exercise reduction in peripheral PWV. In addition, arm position affects baseline peripheral arterial stiffness, but does not affect the magnitude of reduction in peripheral stiffness after rhythmic handgrip exercise and passive compressions.