Vascular Adaptation to Exercise in Humans: Role of Hemodynamic Stimuli

Abstract

On the 400 th anniversary of Harvey's Lumleian lectures, this review focusses on the impact of physical exercise on "hemodynamic" forces associated with the movement of blood through arteries in humans and the functional and structural adaptations that result from repeated episodic exposure to such stimuli. The late 20 th century discovery that endothelial cells modify arterial tone via paracrine transduction, provoked studies exploring the direct mechanical effects of blood flow and pressure on vascular function and adaptation in vivo. In this review, we address the impact of distinct hemodynamic signals that occur in response to exercise, the inter-relationships between these signals, the nature of the adaptive responses that manifest under different physiological conditions and the implications for human health.Exercise modifies blood flow, luminal shear stress, arterial pressure and tangential wall stress, all of which can transduce changes in arterial function, diameter and wall thickness.There are important clinical implications of the adaptation that occurs as a consequence of repeated hemodynamic stimulation associated with exercise training in humans, including impacts on atherosclerotic risk in conduit arteries, the control of blood pressure in resistance vessels, oxygen delivery and diffusion, and microvascular health. Exercise training studies have demonstrated that direct hemodynamic impacts on the health of the artery wall contribute substantially to the well-established decrease in cardiovascular risk attributed to physical activity.

Effects of Exercise on Vascular Function, Structure, and Health in Humans

“…Another prominent possibility is that exercise has direct, or "primary," mechanical effects on the arteries by virtue of repetitive exposure to increases in blood pressure, blood flow, and arterial shear stress that occur during each exercise bout ( Fig. 1) (Green et al 2017). Exercise induces adaptations in the vessel wall that are antiatherogenic Joyner and Green 2009), including effects on endothelial and smooth muscle cell function, along with structural remodeling of the arteries.…”

“…One approach was to induce maximal limb dilation using prolonged cuff occlusion or a combination of ischemia and exercise. Given that such stimuli induce peak reactive hyperemic blood flow responses (Folkow 1978;Naylor et al 2005), increases with training infer remodeling Green et al 2017;adapted, with permission. ) of the resistance vessels.…”

“…4) (Green et al 2002b;Thijssen et al 2011a). The literature relating changes in hemodynamic stimuli and arterial adaptation was recently summarized in Physiological Review (Green et al 2017). In brief, it is clear that exercise is a stimulus that modifies transmural pressure, cyclic circumferential strain on the artery wall, along with endothelial shear stress (Fig.…”

“…These studies all adopted the use of a cuff on one limb to unilaterally decrease shear stress responses to handgrip exercise, leg exercise, forearm heating and leg heating. In all cases, an increase in shear stress was necessary for adaptations in arterial function and/or structure to be expressed (see Green et al 2017 for further details). Note the pattern of change in function that is typically superseded by changes in structure, particularly in response to handgrip and leg exercise training.…”

“…Whereas some of the exercise impact may be ascribed to changes in traditional CV risk factors, it is now clear that repeated hemodynamic stimulation as a result of episodic bouts of exercise, and consequent changes in blood pressure, tangential wall stress, and shear stress contribute to arterial adaptation (Green et al 2017). However, there are a number of important physiological questions that remain unanswered requiring future animal and human studies of the impacts of exercise training.…”