Role of retrograde flow in the shear stimulus associated with exercise blood flow

Effects of Different Eccentric Cycling Intensities on Brachial Artery Endothelial Shear Stress and Blood Flow Patterns

Eccentric exercise has gained attention as a novel exercise modality that increases muscle performance at a lower metabolic demand. However, vascular responses to eccentric cycling (ECC) are unknown, thus gaining knowledge regarding endothelial shear stress (ESS) during ECC may be crucial for its application in patients. The purpose of this study was to explore ECC-induced blood flow patterns and ESS across three different intensities in ECC. Eighteen young, apparently healthy subjects were recruited for two laboratory visits. Maximum oxygen consumption, power output, and blood lactate (BLa) threshold were measured to determine workload intensities. Blood flow patterns in the brachial artery were measured via ultrasound imaging and Doppler on an eccentric ergometer during a 5 min workload steady exercise test at low (BLa of 0-2 mmol/L), moderate (BLa 2-4 mmol/L), and high intensity (BLa levels > 4 mmol/L). There was a significant increase in the antegrade ESS in an intensity-dependent manner (baseline: 44.2 ± 8.97; low: 55.6 ± 15.2; moderate: 56.0 ± 10.5; high: 70.7 ± 14.9, all dynes/cm2, all p values < 0.0002) with the exception between low and moderate and Re (AU) showed turbulent flow at all intensities. Regarding retrograde flow, ESS also increased in an intensity-dependent manner (baseline 9.72 ± 4.38; low: 12.5 ± 3.93; moderate: 15.8 ± 5.45; high: 15.7 ± 6.55, all dynes/cm2, all p values < 0.015) with the exception between high and moderate and Re (AU) showed laminar flow in all intensities. ECC produced exercise-induced blood flow patterns that are intensity-dependent. This suggests that ECC could be beneficial as a modulator of endothelial homeostasis.

The effect of an acute bout of resistance exercise on carotid artery strain and strain rate

Arterial wall mechanics likely play an integral role in arterial responses to acute physiological stress. Therefore, this study aimed to determine the impact of low and moderate intensity double‐leg press exercise on common carotid artery (CCA) wall mechanics using 2D vascular strain imaging. Short‐axis CCA ultrasound images were collected in 15 healthy men (age: 21 ± 3 years; stature: 176.5 ± 6.2 cm; body mass; 80.6 ± 15.3 kg) before, during, and immediately after short‐duration isometric double‐leg press exercise at 30% and 60% of participants' one‐repetition maximum (1RM: 317 ± 72 kg). Images were analyzed for peak circumferential strain (PCS), peak systolic and diastolic strain rate (S‐SR and D‐SR), and arterial diameter. Heart rate (HR), systolic and diastolic blood pressure (SBP and DBP) were simultaneously assessed and arterial stiffness indices were calculated post hoc. A two‐way repeated measures ANOVA revealed that during isometric contraction, PCS and S‐SR decreased significantly (P < 0.01) before increasing significantly above resting levels post exercise (P < 0.05 and P < 0.01, respectively). Conversely, D‐SR was unaltered throughout the protocol (P = 0.25). No significant differences were observed between the 30% and 60% 1RM trials. Multiple regression analysis highlighted that HR, BP, and arterial diameter did not fully explain the total variance in PCS, S‐SR, and D‐SR. Acute double‐leg press exercise is therefore associated with similar transient changes in CCA wall mechanics at low and moderate intensities. CCA wall mechanics likely provide additional insight into localized intrinsic vascular wall properties beyond current measures of arterial stiffness.

Exercise-induced Signals for Vascular Endothelial Adaptations: Implications for Cardiovascular Disease

This article reviews recent advances in our understanding of hemodynamic signals, external/compressive forces, and circulating factors that mediate exercise training-induced vascular adaptations, with particular attention to the roles of these signals in prevention and treatment of endothelial dysfunction and cardiovascular (CV) diseases.

Impact of aging on conduit artery retrograde and oscillatory shear at rest and during exercise: role of nitric oxide

Aging has been recently associated with increased retrograde and oscillatory shear in peripheral conduit arteries, a hemodynamic environment that favors a proatherogenic endothelial cell phenotype. We evaluated whether nitric oxide (NO) bioavailability in resistance vessels contributes to age-related differences in shear rate patterns in upstream conduit arteries at rest and during rhythmic muscle contraction. Younger (n=11, age 26 ± 2 years) and older (n=11, age 61 ± 2 years) healthy subjects received intra-arterial saline (control) and the NO synthase inhibitor N(G)-Monomethyl-L-arginine. Brachial artery diameter and velocities were measured via Doppler ultrasound at rest and during a 5-minute bout of rhythmic forearm exercise. At rest, older subjects exhibited greater brachial artery retrograde and oscillatory shear (-13.2 ± 3.0 s(-1) and 0.11 ± .0.02 arbitrary units, respectively) compared with young subjects (-4.8 ± 2.3 s(-1) and 0.04 ± 0.02 arbitrary units, respectively; both P<0.05). NO synthase inhibition in the forearm circulation of young, but not of older, subjects increased retrograde and oscillatory shear (both P<0.05), such that differences between young and old at rest were abolished (both P>0.05). From rest to steady-state exercise, older subjects decreased retrograde and oscillatory shear (both P<0.05) to the extent that no exercise-related differences were found between groups (both P>0.05). Inhibition of NO synthase in the forearm circulation did not affect retrograde and oscillatory shear during exercise in either group (all P>0.05). These data demonstrate for the first time that reduced NO bioavailability in the resistance vessels contributes, in part, to age-related discrepancies in resting shear patterns, thus identifying a potential mechanism for increased risk of atherosclerotic disease in conduit arteries.

Association between exercise hemodynamics and changes in local vascular function following acute exercise

Skeletal muscle contractions are associated with physical stimuli that act upon muscle vasculature, including increased shear stress and blood pressure. It is unclear if acute dynamic exercise alters local vascular function. The purpose of this study was to examine the role of exercise hemodynamics on the effects of acute exercise on vascular function, as evaluated by brachial artery flow-mediated dilation (FMD). Healthy individuals (n = 14; age, 18–34 years) performed 30 min of handgrip exercise at fast and slow contractions. Blood pressure during exercise was measured using a Vasotrac system (Medwave Inc.), while shear rate during exercise and FMD at rest and after 30 min of recovery from exercise were measured in the brachial artery of the active arm using Doppler ultrasound. Estimated contractile work was correlated with blood pressure (r = 0.61, p < 0.01) and retrograde shear rate (r = –0.78, p < 0.01). As a result, blood pressure was higher (p < 0.05) and oscillatory shear index was lower (p < 0.05) during slow as compared with fast contractions. On average, FMD was unchanged following fast contractions (5.4 ± 3.4%dilation to 6.1 ± 3.8%dilation; p = 0.19), but significantly reduced following slow contractions (6.9 ± 4.2%dilation to 3.6 ± 2.5%dilation; p = 0.01). Within slow contractions, subgroup analysis revealed blood pressure to associate with the change in FMD; such that individuals with mean blood pressure >100 mm Hg (range, 102–139 mm Hg) during exercise had larger decreases in FMD than individuals with lower exercise blood pressure. These results indicate that impaired local vascular function following acute exercise with high contractile activity is associated with blood pressure stimuli in healthy individuals