scholarly journals Fluctuation in shear rate, with unaltered mean shear rate, improves brachial artery flow-mediated dilation in healthy, young men

2019 ◽  
Vol 126 (6) ◽  
pp. 1687-1693 ◽  
Author(s):  
Sophie M. Holder ◽  
Ellen A. Dawson ◽  
Áine Brislane ◽  
Jonny Hisdal ◽  
Daniel J. Green ◽  
...  
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Endothelial Function ◽  
Brachial Artery ◽  
Negative Pressure ◽  
Mixed Model ◽  
Linear Mixed Model ◽  
Flow Mediated Dilation ◽  
Conduit Artery ◽  
Artery Flow

Increase in mean shear stress represents an important and potent hemodynamic stimulus to improve conduit artery endothelial function in humans. No previous study has examined whether fluctuations in shear rate patterns, without altering mean shear stress, impacts conduit artery endothelial function. This study examined the hypothesis that 30-min exposure to fluctuations in shear rate patterns, in the presence of unaltered mean shear rate, improves brachial artery flow-mediated dilation. Fifteen healthy men (27.3 ± 5.0 yr) completed the study. Bilateral brachial artery flow-mediated dilation was assessed before and after unilateral exposure to 30 min of intermittent negative pressure (10 s, −40mmHg; 7 s, 0 mmHg) to induce fluctuation in shear rate, while the contralateral arm was exposed to a resting period. Negative pressure significantly increased shear rate, followed by a decrease in shear rate upon pressure release (both P < 0.001). Across the 30-min intervention, mean shear rate was not different compared with baseline ( P = 0.458). A linear mixed model revealed a significant effect of time observed for flow-mediated dilation ( P = 0.029), with exploratory post hoc analysis showing an increase in the intervention arm (∆FMD +2.0%, P = 0.008), but not in the contralateral control arm (∆FMD +0.5%, P = 0.664). However, there was no effect for arm ( P = 0.619) or interaction effect ( P = 0.096). In conclusion, we found that fluctuations in shear patterns, with unaltered mean shear, improves brachial artery flow-mediated dilation. These novel data suggest that fluctuations in shear pattern, even in the absence of altered mean shear, represent a stimulus to acute change in endothelial function in healthy individuals. NEW & NOTEWORTHY Intermittent negative pressure applied to the forearm induced significant fluctuations in antegrade and retrograde shear rate, while mean shear was preserved relative to baseline. Our exploratory study revealed that brachial artery flow-mediated dilation was significantly improved following 30-min exposure to intermittent negative pressure. Fluctuations in blood flow or shear rate, with unaltered mean shear, may have important implications for vascular health; however, further research is required to identify the underlying mechanisms and potential long-term health benefits.

scholarly journals Examining the acute effects of retrograde versus low mean shear rate on flow-mediated dilation

2019 ◽  
Vol 126 (5) ◽  
pp. 1335-1342 ◽  
Author(s):  
Joshua C. Tremblay ◽  
Arman S. Grewal ◽  
Kyra E. Pyke
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Endothelial Function ◽  
Brachial Artery ◽  
Duplex Ultrasound ◽  
Flow Mediated Dilation ◽  
Relative Contribution ◽  
Stress Components ◽  
Retrograde Shear

Arterial endothelial function is acutely and chronically regulated by blood flow-associated shear stress. An acute intervention employing modest forearm cuff occlusion to simultaneously increase retrograde and decrease mean brachial artery shear rate for 30 min evokes transient impairments in flow-mediated dilation (FMD). However, the independent influence of the low mean versus the retrograde shear stress components is unclear. Healthy young adults [ n = 24 (12 women, 12 men); 22 ± 2 yr, body mass index = 25 ± 2 kg/m2 (mean ± SD)] completed three laboratory visits within 1 wk. Visits consisted of 45 min of supine rest followed by a brachial artery FMD test (duplex ultrasound) before and after a 30-min intervention: control (shear rate unchanged), cuff (mean shear rate decreased, retrograde shear rate increased), or arterial compression (mean shear rate decreased, no increase in retrograde shear rate). The mean shear rate on the compression visit was targeted to match that achieved on the cuff visit. Cuff and compression trials decreased mean shear rate to a similar extent (cuff: 43 ± 22 s−1, compression: 43 ± 21 s−1; P = 0.850) compared with control (65 ± 21 s−1; both P < 0.001), with the retrograde component elevated only in the former (cuff: −83 ± 30 s−1, compression: −7 ± 5 s−1; P < 0.001). FMD decreased by 29 ± 30% ( P < 0.001) after the cuff intervention and 32 ± 24% ( P < 0.001) after the compression trial but was unchanged on the control visit (−0.3 ± 18%; P = 0.754). This was not altered by accounting for the shear rate stimulus. An increased retrograde shear stress does not appear to be obligatory for the transient reduction in FMD achieved after a 30-min exposure to low mean shear stress. These findings provide novel mechanistic insight on the regulation of endothelial function in vivo. NEW & NOTEWORTHY Low mean and retrograde shear stress are considered atherogenic; however, their relative contribution to the acute regulation of endothelial function in humans is unclear. Matched reductions in mean shear stress (30 min), with and without increases in retrograde shear stress, elicited equivalent reductions in flow-mediated dilation in men and women. These findings afford novel insight regarding the shear stress components governing the acute (dys)regulation of conduit artery endothelial function in vivo.

Are the dynamic response characteristics of brachial artery flow-mediated dilation sensitive to the magnitude of increase in shear stimulus?

2008 ◽  
Vol 105 (1) ◽  
pp. 282-292 ◽  
Author(s):  
K. E. Pyke ◽  
J. A. Hartnett ◽  
M. E. Tschakovsky
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Dynamic Response ◽  
Phase I ◽  
Brachial Artery ◽  
Flow Mediated Dilation ◽  
Final Phase ◽  
Stimulus Magnitude ◽  
Brachial Artery Diameter ◽  
Response Characteristics

The purpose of this study was to determine the dynamic characteristics of brachial artery dilation in response to step increases in shear stress [flow-mediated dilation (FMD)]. Brachial artery diameter (BAD) and mean blood velocity (MBV) (Doppler ultrasound) were obtained in 15 healthy subjects. Step increases in MBV at two shear stimulus magnitudes were investigated: large (L; maximal MBV attainable), and small (S; MBV at 50% of the large step). Increase in shear rate (estimate of shear stress: MBV/BAD) was 76.8 ± 15.6 s−1 for L and 41.4 ± 8.7 s−1 for S. The peak %FMD was 14.5 ± 3.8% for L and 5.7 ± 2.1% for S ( P < 0.001). Both the L (all subjects) and the S step trials (12 of 15 subjects) elicited a biphasic diameter response with a fast initial phase (phase I) followed by a slower final phase. Relative contribution of phase I to total FMD when two phases occurred was not sensitive to shear rate magnitude ( r2 = 0.003, slope P = 0.775). Parameters quantifying the dynamics of the FMD response [time delay (TD), time constant (τ)] were also not sensitive to shear rate magnitude for both phases (phase I: TD r2 = 0.03, slope P = 0.376, τ r2 = 0.04, slope P = 0.261; final phase: TD r2 = 0.07, slope P = 0.169, τ r2 = 0.07, slope P = 0.996). These data support the existence of two distinct mechanisms, or sets of mechanisms, in the human conduit artery FMD response that are proportionally sensitive to shear stimulus magnitude and whose dynamic response is not sensitive to shear stimulus magnitude.

scholarly journals Endothelial dysfunction following prolonged sitting is mediated by a reduction in shear stress

2016 ◽  
Vol 310 (5) ◽  
pp. H648-H653 ◽  
Author(s):  
Robert M. Restaino ◽  
Lauren K. Walsh ◽  
Takuma Morishima ◽  
Jennifer R. Vranish ◽  
Luis A. Martinez-Lemus ◽  
...  
Keyword(s):  
Shear Stress ◽  
Endothelial Dysfunction ◽  
Endothelial Function ◽  
Internal Control ◽  
Popliteal Artery ◽  
Local Heating ◽  
Underlying Mechanism ◽  
Flow Mediated Dilation ◽  
Prolonged Sitting ◽  
Artery Flow

We and others have recently reported that prolonged sitting impairs endothelial function in the leg vasculature; however, the mechanism(s) remain unknown. Herein, we tested the hypothesis that a sustained reduction in flow-induced shear stress is the underlying mechanism by which sitting induces leg endothelial dysfunction. Specifically, we examined whether preventing the reduction in shear stress during sitting would abolish the detrimental effects of sitting on popliteal artery endothelial function. In 10 young healthy men, bilateral measurements of popliteal artery flow-mediated dilation were performed before and after a 3-h sitting period during which one foot was submerged in 42°C water (i.e., heated) to increase blood flow and thus shear stress, whereas the contralateral leg remained dry and served as internal control (i.e., nonheated). During sitting, popliteal artery mean shear rate was reduced in the nonheated leg (pre-sit, 42.9 ± 4.5 s−1; and 3-h sit, 23.6 ± 3.3 s−1; P < 0.05) but not in the heated leg (pre-sit, 38.9 ± 3.4 s−1; and 3-h sit, 63.9 ± 16.9 s−1; P > 0.05). Popliteal artery flow-mediated dilation was impaired after 3 h of sitting in the nonheated leg (pre-sit, 7.1 ± 1.4% vs. post-sit, 2.8 ± 0.9%; P < 0.05) but not in the heated leg (pre-sit: 7.3 ± 1.5% vs. post-sit, 10.9 ± 1.8%; P > 0.05). Collectively, these data suggest that preventing the reduction of flow-induced shear stress during prolonged sitting with local heating abolishes the impairment in popliteal artery endothelial function. Thus these findings are consistent with the hypothesis that sitting-induced leg endothelial dysfunction is mediated by a reduction in shear stress.

Preserved flow-mediated dilation in the inactive legs of spinal cord-injured individuals

2004 ◽  
Vol 287 (1) ◽  
pp. H374-H380 ◽  
Author(s):  
Patricia C. E. de Groot ◽  
Fleur Poelkens ◽  
Miriam Kooijman ◽  
Maria T. E. Hopman
Keyword(s):  
Spinal Cord ◽  
Shear Rate ◽  
Endothelial Function ◽  
Femoral Artery ◽  
Brachial Artery ◽  
Rate Ratio ◽  
Arterial Occlusion ◽  
Flow Mediated Dilation ◽  
Dilatory Response ◽  
Spinal Cord Injured

The aim of the study was to assess endothelial function, measured by flow-mediated dilation (FMD), in an inactive extremity (leg) and chronically active extremity (arm) within one subject. Eleven male spinal cord-injured (SCI) individuals and eleven male controls (C) were included. Echo Doppler measurements were performed to measure FMD responses after 10 and 5 min of arterial occlusion of the leg (superficial femoral artery, SFA) and the arm (brachial artery, BA), respectively. A nitroglycerine spray was administered to determine the endothelium independent vasodilatation in the SFA. In the SFA, relative changes in FMD were significantly enhanced in SCI compared with C (SCI: 14.1 ± 1.3%; C: 9.2 ± 2.3%), whereas no differences were found in the BA (SCI: 12.5 ± 2.9%; C: 14.2 ± 3.3%). Because the FMD response is directly proportional to the magnitude of the stimulus, the FMD response was also expressed relative to the shear rate. No differences between the groups were found for the FMD-to-shear rate ratio in the SFA (SCI:0.061 ± 0.023%/s−1; C: 0.049 ± 0.024%/s−1), whereas the FMD-to-shear rate ratio was significantly decreased in the BA of SCI individuals (SCI: 0.037 ± 0.01%/s−1; C: 0.061 ± 0.027%/s−1). The relative dilatory response to nitroglycerine did not differ between the groups. (SCI: 15.6 ± 2.0%; C: 13.4 ± 2.3%). In conclusion, our results indicate that SCI individuals have a preserved endothelial function in the inactive legs and possibly an attenuated endothelial function in the active arms compared with controls.

scholarly journals Brachial Artery Flow-mediated Dilation Following Exercise with Augmented Oscillatory and Retrograde Shear Rate

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Blair D Johnson ◽  
Kieren J Mather ◽  
Sean C Newcomer ◽  
Timothy D Mickleborough ◽  
Janet P Wallace
Keyword(s):  
Shear Rate ◽  
Brachial Artery ◽  
Flow Mediated Dilation ◽  
Artery Flow ◽  
Retrograde Shear

Acute psychological and physical stress transiently enhances brachial artery flow-mediated dilation stimulated by exercise-induced increases in shear stress

2014 ◽  
Vol 39 (8) ◽  
pp. 927-936 ◽  
Author(s):  
Ingrid C. Szijgyarto ◽  
Veronica J. Poitras ◽  
Brendon J. Gurd ◽  
Kyra E. Pyke
Keyword(s):  
Shear Stress ◽  
Shear Rate ◽  
Brachial Artery ◽  
Stress Responses ◽  
Physical Stress ◽  
Flow Mediated Dilation ◽  
Trial Effect ◽  
Condition Effect ◽  
Exercise Induced ◽  
The Impact

Exercise elevates conduit artery shear stress and stimulates flow-mediated dilation (FMD). However, little is known regarding the impact of acute psychological and physical stress on this response. The purpose of this study was to examine the impact of the Trier Social Stress Test (TSST (speech and arithmetic tasks)) and a cold pressor test (CPT) with and without social evaluation (SE) on exercise-induced brachial artery FMD (EX-FMD). A total of 59 healthy male subjects were randomly assigned to 1 of 3 conditions: TSST, CPT, or CPT with SE. During 6 min of handgrip exercise, brachial artery EX-FMD was assessed before and 15 and 35 min poststress with echo and Doppler ultrasound. Shear stress was estimated as shear rate, calculated as brachial artery mean blood velocity/brachial artery diameter. Results are means ± SD. All conditions elicited significant physiological stress responses. Salivary cortisol increased from 4.6 ± 2.4 nmol/L to 10.0 ± 5.0 nmol/L (p < 0.001; condition effect: p = 0.292). Mean arterial pressure increased from 98.6 ± 12.1 mm Hg to 131.9 ± 18.7 mm Hg (p < 0.001; condition effect: p = 0.664). Exercise shear rate did not differ between conditions (p = 0.592), although it was modestly lower poststress (prestress: 72.3 ± 4.5 s−1; 15 min poststress: 70.8 ± 5.4 s−1; 35 min poststress: 70.6 ± 6.1 s−1; trial effect: p = 0.011). EX-FMD increased from prestress to 15 min poststress in all conditions (prestress: 6.2% ± 2.8%; 15 min poststress: 7.9% ± 3.2%; 35 min poststress: 6.6% ± 2.9%; trial effect: p < 0.001; condition effect: p = 0.611). In conclusion, all conditions elicited similar stress responses that transiently enhanced EX-FMD. This response may help to support muscle perfusion during stress.

scholarly journals Assessment of macro and microvascular function in aging males

2020 ◽  
Author(s):  
Matthew C Babcock ◽  
Lyndsey E. DuBose ◽  
Teresa L. Witten ◽  
Ashley Brubaker ◽  
Brian L. Stauffer ◽  
...  
Keyword(s):  
Cardiovascular Disease ◽  
Endothelial Function ◽  
Sensitivity And Specificity ◽  
Brachial Artery ◽  
Healthy Adult ◽  
High Sensitivity ◽  
Flow Mediated Dilation ◽  
Peripheral Artery ◽  
Adult Men ◽  
Artery Flow

Aging is associated with reductions in endothelial function, observations primarily reported using brachial artery ultrasound. There is growing interest in the use of peripheral artery tonometry (PAT) of microvessels in the fingertip to assess endothelial function because it is less technically demanding and has a high sensitivity and specificity for assessing coronary endothelial function. Moreover, similar to brachial artery flow mediated dilation (FMD), PAT predicts cardiovascular disease (CVD) outcomes. However, the relation between PAT and FMD have yet to be examined in the context of aging. To address this question, reactive hyperemic index (RHI) using EndoPAT and flow-mediated dilation (FMD) using brachial artery ultrasound were assessed after five minutes of forearm ischemia in twenty younger (18-40 years old; 29±4 years) and twenty older (60-75 years old; 65±4 years) healthy adult men. Higher values of both FMD and RHI indicate better endothelial function. Endothelial function assessed via brachial artery FMD was lower in older (4.8±2.1%), compared to younger (7.5±1.6%) men (p<0.001). In contrast, the RHI assessed via PAT was greater in older (2.2±0.6), compared to younger (1.8±0.5) men (p=0.014). FMD and RHI were not correlated (r=-0.15; p=0.35). We conclude that PAT may not be an appropriate measure to evaluate age-associated changes in endothelial function.

Endothelial function of young healthy males following whole body resistance training

2005 ◽  
Vol 98 (6) ◽  
pp. 2185-2190 ◽  
Author(s):  
M. Rakobowchuk ◽  
C. L. McGowan ◽  
P. C. de Groot ◽  
J. W. Hartman ◽  
S. M. Phillips ◽  
...  
Keyword(s):  
Blood Flow ◽  
Shear Rate ◽  
Resistance Training ◽  
Endothelial Function ◽  
Resistance Exercise ◽  
Brachial Artery ◽  
Whole Body ◽  
Flow Mediated Dilation ◽  
Body Resistance ◽  
Time Point

Given the increasing emphasis on performance of resistance exercise as an essential component of health, we evaluated, using a prospective longitudinal design, the potential for resistance training to affect arterial endothelial function. Twenty-eight men (23 ± 3.9 yr old; mean ± SE) engaged in 12 wk of whole body resistance training five times per week using a repeating split-body 3-day cycle. Brachial endothelial function was measured using occlusion cuff-induced flow-mediated dilation. After occlusion of the forearm for 4.5 min, brachial artery dilation and postocclusion blood flow was measured continuously for 15 and 70 s, respectively. Peak and 10-s postocclusion blood flow, shear rate, and brachial artery flow-mediated dilation (relative and normalized to shear rate) were measured pretraining (Pre), at 6 wk of training (Mid), and at 13 wk of training (Post). Results indicated an increase of mean brachial artery diameter by Mid and Post vs. Pre. Peak and 10-s postocclusion blood flow increased by Mid and remained elevated at Post; however, shear rates were not different at any time point. Relative and normalized flow-mediated dilation was also not different at any time point. This study is the first to show that peripheral arterial remodeling does occur with resistance training in healthy young men. In addition, the increase in postocclusion blood flow may indicate improved resistance vessel function. However, unlike studies involving endurance training, flow-mediated dilation did not increase with resistance training. Thus arterial adaptations with high-pressure loads, such as those experienced during resistance exercise, may be quite different compared with endurance training.

scholarly journals UBC-Nepal expedition: upper and lower limb conduit artery shear stress and flow-mediated dilation on ascent to 5,050 m in lowlanders and Sherpa

2018 ◽  
Vol 315 (6) ◽  
pp. H1532-H1543 ◽  
Author(s):  
Joshua C. Tremblay ◽  
Ryan L. Hoiland ◽  
Howard H. Carter ◽  
Connor A. Howe ◽  
Mike Stembridge ◽  
...  
Keyword(s):  
Shear Stress ◽  
Endothelial Function ◽  
High Altitude ◽  
Blood Viscosity ◽  
Lower Limb ◽  
Adaptation To Hypoxia ◽  
Flow Mediated Dilation ◽  
Conduit Artery ◽  
Arterial Blood ◽  
Retrograde Shear

The study of conduit artery endothelial adaptation to hypoxia has been restricted to the brachial artery, and comparisons with highlanders have been confounded by differences in altitude exposure, exercise, and unknown levels of blood viscosity. To address these gaps, we tested the hypothesis that lowlanders, but not Sherpa, would demonstrate decreased mean shear stress and increased retrograde shear stress and subsequently reduced flow-mediated dilation (FMD) in the upper and lower limb conduit arteries on ascent to 5,050 m. Healthy lowlanders (means ± SD, n = 22, 28 ± 6 yr) and Sherpa ( n = 12, 34 ± 11 yr) ascended over 10 days, with measurements taken on nontrekking days at 1,400 m (baseline), 3,440 m ( day 4), 4,371 m ( day 7), and 5,050 m ( day 10). Arterial blood gases, blood viscosity, shear stress, and FMD [duplex ultrasound of the brachial and superficial femoral arteries (BA and SFA, respectively)] were acquired at each time point. Ascent decreased mean and increased retrograde shear stress in the upper and lower limb of lowlanders and Sherpa. Although BA FMD decreased in lowlanders from 7.1 ± 3.9% to 3.8 ± 2.8% at 5,050 versus 1,400 m ( P < 0.001), SFA FMD was preserved. In Sherpa, neither BA nor SFA FMD were changed upon ascent to 5,050 m. In lowlanders, the ascent-related exercise may favorably influence endothelial function in the active limb (SFA); selective impairment in FMD in the BA in lowlanders is likely mediated via the low mean or high oscillatory baseline shear stress. In contrast, Sherpa presented protected endothelial function, suggesting a potential vascular aspect of high-altitude acclimatization/adaptation. NEW & NOTEWORTHY Upper and lower limb arterial shear stress and flow-mediated dilation (FMD) were assessed on matched ascent from 1,400 to 5,050 m in lowlanders and Sherpa. A shear stress pattern associated with vascular dysfunction/risk manifested in both limbs of lowlanders and Sherpa. FMD was impaired only in the upper limb of lowlanders. The findings indicate a limb-specific impact of high-altitude trekking on FMD and a vascular basis to acclimatization wherein endothelial function is protected in Sherpa on ascent

scholarly journals Vascular Endothelial Function in Midlife/Older Adults Classified According to 2017 American College of Cardiology/American Heart Association Blood Pressure Guidelines

2020 ◽  
Vol 9 (17) ◽  
Author(s):  
Daniel H. Craighead ◽  
Kaitlin A. Freeberg ◽  
Douglas R. Seals
Keyword(s):  
Reactive Oxygen Species ◽  
Older Adults ◽  
Endothelial Function ◽  
Brachial Artery ◽  
American Heart Association ◽  
American Heart ◽  
Heart Association ◽  
Flow Mediated Dilation ◽  
Oxygen Species ◽  
Artery Flow

Background Impaired endothelial function is thought to contribute to the increased cardiovascular risk associated with above‐normal blood pressure (BP). However, the association between endothelial function and BP classified by 2017 American College of Cardiology/American Heart Association guidelines is unknown. Our objective was to determine if endothelial function decreases in midlife/older adults across the 2017 American College of Cardiology/American Heart Association guidelines BP classifications and identify associated mechanisms of action. Methods and Results A retrospective analysis of endothelial function (brachial artery flow‐mediated dilation) from 988 midlife/older adults (aged 50+ years) stratified by BP status (normal BP; elevated BP; stage 1 hypertension; stage 2 hypertension) was performed. Endothelium‐independent dilation (sublingual nitroglycerin), reactive oxygen species–mediated suppression of endothelial function (∆brachial artery flow‐mediated dilation with vitamin C infusion), and endothelial cell and plasma markers of oxidative stress and inflammation were assessed in subgroups. Compared with normal BP (n=411), brachial artery flow‐mediated dilation was 12% ( P =0.04), 15% ( P <0.01) and 20% ( P <0.01) lower with elevated BP (n=173), stage 1 hypertension (n=248) and stage 2 hypertension (n=156), respectively, whereas endothelium‐independent dilation did not differ ( P =0.14). Vitamin C infusion increased brachial artery flow‐mediated dilation in those with above‐normal BP ( P ≤0.02) but not normal BP ( P =0.11). Endothelial cell p47 phox ( P <0.01), a marker of superoxide/reactive oxygen species–generating nicotinamide adenine dinucleotide phosphate oxidase, and circulating interleukin‐6 concentrations ( P =0.01) were higher in individuals with above‐normal BP. Conclusions Vascular endothelial function is progressively impaired with increasing BP in otherwise healthy adults classified by 2017 American College of Cardiology/American Heart Association guidelines. Impaired endothelial function with above‐normal BP is mediated by excessive reactive oxygen species signaling associated with increased endothelial expression of nicotinamide adenine dinucleotide phosphate oxidase and circulating interleukin‐6.

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