Brachial artery adaptation to lower limb exercise training: role of shear stress

Abstract

<jats:p>Lower limb exercise increases upper limb conduit artery blood flow and shear stress, and leg exercise training can enhance upper limb vascular function. We therefore examined the contribution of shear stress to changes in vascular function in the nonexercising upper limbs in response to lower limb cycling exercise training. Initially, five male subjects underwent bilateral brachial artery duplex ultrasound to measure blood flow and shear responses to 30-min cycling exercise at 80% of maximal heart rate. Responses in one forearm were significantly ( P &lt; 0.05) attenuated via cuff inflation throughout the exercise bout. An additional 11 subjects participated in an 8-wk cycle training study undertaken at a similar intensity, with unilateral cuff inflation around the forearm during each exercise bout. Bilateral brachial artery flow-mediated dilation responses to a 5-min ischemic stimulus (FMD%), an ischemic handgrip exercise stimulus (iEX), and endothelium-independent NO donor administration [glyceryl trinitrate (GTN)] were measured at 2, 4, and 8 wk. Cycle training increased FMD% in the noncuffed limb at week 2, after which time responses returned toward baseline levels (5.8 ± 4.1, 8.6 ± 3.8, 7.4 ± 3.5, 6.0 ± 2.3 at 0, 2, 4 and 8 wk, respectively; ANOVA: P = 0.04). No changes in FMD% were observed in the cuffed arm. No changes were evident in response to iEX or GTN in either the cuffed or noncuffed arms ( P &gt; 0.05) across the 8-wk intervention period. Our data suggest that lower limb cycle training induces a transient increase in upper limb vascular function in healthy young humans, which is, at least partly, mediated via shear stress.</jats:p>

Time-course of vascular adaptations during 8 weeks of exercise training in subjects with type 2 diabetes and middle-aged controls

“…In agreement with studies of healthy young volunteers (Birk et al 2012;Tinken et al 2008;Tinken et al 2010), two weeks of exercise training in type 2 diabetes and age-matched controls significantly enhanced endothelial function. Whilst continuing exercise training in young healthy controls was associated with return to baseline levels after 6-8 weeks (Birk et al 2012;Tinken et al 2008;Tinken et al 2010), the present study revealed sustained elevation in FMD/GTN-ratios with prolonged training. This suggests that, somewhat in contrast with younger healthy subjects, exercise training leads to improvement in endothelial function that remains elevated in subjects with a priori endothelial dysfunction.…”

“…Although we did not directly compare our results to a young control group, the pre-training values of brachial artery FMD in type 2 diabetes and controls (3.4-3.9%) are lower than typically reported in studies examining healthy young men (Tinken et al 2008;Tinken et al 2010;Birk et al 2012). Regarding the impact of exercise training on endothelial function in type 2 diabetes and controls, we did not find a significant change in brachial artery FMD across the 8-week exercise training.…”

“…In keeping with previous studies in healthy young volunteers, exercise training lead to a rapid functional increase in both groups. Whilst continued exercise training has been associated with normalisation of endothelial function after 6-8 weeks in young healthy subjects (Tinken et al 2008;Tinken et al 2010;Birk et al 2012), we observed preservation of the increase in brachial artery endothelial function after 6-8 weeks in both groups in this study. This suggests the presence of a distinct time-course in vascular adaptations to exercise training in middle-aged type 2 diabetes patients and older subjects, compared with young healthy individuals.…”

“…Studies involving 2-weekly measurements across an 8-week period of large (i.e. cycling/running exercise) (Birk et al 2012;Tinken et al 2008) or small muscle group (i.e. handgrip exercise) (Tinken et al 2010) training in healthy young volunteers have consistently demonstrated that 2 weeks of exercise training is sufficient to significantly enhance vascular function.…”

Impact of 2‐Weeks Continuous Increase in Retrograde Shear Stress on Brachial Artery Vasomotor Function in Young and Older Men

“…Several studies have explored the impact of repeated exposure to elevations in antegrade shear stress via training, heating, or in vitro manipulation of antegrade shear 7, 13, 14, 15, 16, 17. These studies consistently report a dose‐dependent increase in arterial caliber and improvement in endothelial function, possibly through upregulation of endothelial nitric oxide synthase 1, 18.…”