scholarly journals Increased brachial artery retrograde shear rate at exercise onset is abolished during prolonged cycling: role of thermoregulatory vasodilation

2011 ◽  
Vol 110 (2) ◽  
pp. 389-397 ◽  
Author(s):  
Grant H. Simmons ◽  
Jaume Padilla ◽  
Colin N. Young ◽  
Brett J. Wong ◽  
James A. Lang ◽  
...  
Keyword(s):  
Shear Rate ◽  
Brachial Artery ◽  
Prolonged Exercise ◽  
Vascular Conductance ◽  
Brachial Artery Diameter ◽  
Cutaneous Vasodilation ◽  
Leg Cycling ◽  
Baseline Values ◽  
Retrograde Shear

Acute leg exercise increases brachial artery retrograde shear rate (SR), while chronic exercise improves vasomotor function. These combined observations are perplexing given the proatherogenic impacts of retrograde shear stress on the vascular endothelium and may be the result of brief protocols used to study acute exercise responses. Therefore, we hypothesized that brachial artery retrograde SR increases initially but subsequently decreases in magnitude during prolonged leg cycling. Additionally, we tested the role of cutaneous vasodilation in the elimination of increased retrograde SR during prolonged exercise. Brachial artery diameter and velocity profiles and forearm skin blood flow and temperature were measured at rest and during 50 min of steady-state, semirecumbent leg cycling (120 W) in 14 males. Exercise decreased forearm vascular conductance (FVC) and increased retrograde SR at 5 min (both P < 0.05), but subsequently forearm and cutaneous vascular conductance (CVC) rose while retrograde SR returned toward baseline values. The elimination of increased retrograde SR was related to the increase in FVC ( r2= 0.58; P < 0.05) and CVC ( r2= 0.32; P < 0.05). Moreover, when the forearm was cooled via a water-perfused suit between minutes 30 and 40 to blunt cutaneous vasodilation attending exercise, FVC was reduced and the magnitude of retrograde SR was increased from −49.7 ± 13.6 to −78.4 ± 16.5 s−1( P < 0.05). Importantly, these responses resolved with removal of cooling during the final 10 min of exercise (retrograde SR: −46.9 ± 12.5 s−1). We conclude that increased brachial artery retrograde SR at the onset of leg cycling subsequently returns toward baseline values due in part to thermoregulatory cutaneous vasodilation during prolonged exercise.

Time-course Of Brachial Artery Diameter Responses To Leg Cycling Exercise: Role Of Shear Rate

2011 ◽  
Vol 43 (Suppl 1) ◽  
pp. 746
Author(s):  
Lauro C. Vianna ◽  
Jaume Padilla ◽  
Grant H. Simmons ◽  
Michael J. Davis ◽  
M Harold Laughlin ◽  
...  
Keyword(s):  
Shear Rate ◽  
Brachial Artery ◽  
Time Course ◽  
Brachial Artery Diameter ◽  
Cycling Exercise ◽  
Leg Cycling

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 Effects of posture on shear rates in human brachial and superficial femoral arteries

2008 ◽  
Vol 294 (4) ◽  
pp. H1833-H1839 ◽  
Author(s):  
S. C. Newcomer ◽  
C. L. Sauder ◽  
N. T. Kuipers ◽  
M. H. Laughlin ◽  
C. A. Ray
Keyword(s):  
Shear Rate ◽  
Femoral Artery ◽  
Brachial Artery ◽  
Superficial Femoral Artery ◽  
Upright Posture ◽  
Brachial Artery Diameter ◽  
Shear Rates ◽  
Femoral Arteries ◽  
Lower Shear ◽  
Relative Shear

Shear rate is significantly lower in the superficial femoral compared with the brachial artery in the supine posture. The relative shear rates in these arteries of subjects in the upright posture (seated and/or standing) are unknown. The purpose of this investigation was to test the hypothesis that upright posture (seated and/or standing) would produce greater shear rates in the superficial femoral compared with the brachial artery. To test this hypothesis, Doppler ultrasound was used to measure mean blood velocity (MBV) and diameter in the brachial and superficial femoral arteries of 21 healthy subjects after being in the supine, seated, and standing postures for 10 min. MBV was significantly higher in the brachial compared with the superficial femoral artery during upright postures. Superficial femoral artery diameter was significantly larger than brachial artery diameter. However, posture had no significant effect on either brachial or superficial femoral artery diameter. The calculated shear rate was significantly greater in the brachial (73 ± 5, 91 ± 11, and 97 ± 13 s−1) compared with the superficial femoral (53 ± 4, 39 ± 77, and 44 ± 5 s−1) artery in the supine, seated, and standing postures, respectively. Contrary to our hypothesis, our current findings indicate that mean shear rate is lower in the superficial femoral compared with the brachial artery in the supine, seated, and standing postures. These findings of lower shear rates in the superficial femoral artery may be one mechanism for the higher propensity for atherosclerosis in the arteries of the leg than of the arm.

Acute head-down tilt decreases the postexercise resting threshold for forearm cutaneous vasodilation

2000 ◽  
Vol 89 (6) ◽  
pp. 2306-2311 ◽  
Author(s):  
Glen P. Kenny ◽  
Dwayne N. Jackson ◽  
Francis D. Reardon
Keyword(s):  
Treatment Protocol ◽  
Whole Body ◽  
Treatment Protocols ◽  
Pretreatment Condition ◽  
Exercise Treatment ◽  
Cutaneous Vasodilation ◽  
Head Up Tilt ◽  
Baseline Values ◽  
Sequential Measurements

The purpose of this study was to evaluate the role of baroreceptor control on the postexercise threshold for forearm cutaneous vasodilation. On four separate days, six subjects (1 woman) were randomly exposed to 65° head-up tilt and to 15° head-down tilt during a No-Exercise and Exercise treatment protocol. Under each condition, a whole body water-perfused suit was used to regulate mean skin temperature (T̄sk) in the following sequence: 1) cooling until the threshold for vasoconstriction was evident; 2) heating (∼7.0°C/h) until vasodilation occurred; and 3) cooling until esophageal temperature (Tes) and T̄sk returned to baseline values. The Exercise treatment consisted of 15 min of cycling exercise at 70% maximal O2 uptake, followed by 15 min of recovery in the head-up tilt position. The No-Exercise treatment consisted of 30 min resting in the head-up tilt position. After the treatment protocols, subjects were returned to their pretreatment condition, then cooled and warmed again consecutively. The calculated Tes threshold for cutaneous vasodilation increased 0.24°C postexercise during head-up tilt ( P < 0.05), whereas no difference was measured during head-down tilt. In contrast, sequential measurements without exercise demonstrate a time-dependent decrease for head-up tilt (0.17°C) and no difference for head-down tilt. Pretreatment thresholds were significantly lower during head-down tilt compared with head-up tilt. We have shown that manipulating postexercise venous pooling by means of head-down tilt, in an effort to reverse its impact on baroreceptor unloading, resulted in a relative lowering of the resting postexercise elevation in the Tesfor forearm cutaneous vasodilation.

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

Thermoregulatory Vasodilation During Prolonged Cycling Abolishes Increases In Brachial Artery Retrograde Shear Rate At Exercise Onset

2010 ◽  
Vol 42 ◽  
pp. 39
Author(s):  
Grant H. Simmons ◽  
Jaume Padilla ◽  
Colin N. Young ◽  
Brett J. Wong ◽  
James A. Lang ◽  
...  
Keyword(s):  
Shear Rate ◽  
Brachial Artery ◽  
Exercise Onset ◽  
Retrograde Shear

Low flow-mediated constriction occurs in the radial but not the brachial artery in healthy pregnant and nonpregnant women

2010 ◽  
Vol 108 (5) ◽  
pp. 1097-1105 ◽  
Author(s):  
Tracey L. Weissgerber ◽  
Gregory A. L. Davies ◽  
Michael E. Tschakovsky
Keyword(s):  
Shear Rate ◽  
Pregnant Women ◽  
Radial Artery ◽  
Brachial Artery ◽  
Vascular Function ◽  
Low Flow ◽  
Flow Mediated Dilation ◽  
Brachial Artery Diameter ◽  
Function Test ◽  
Positive Correlations

Radial artery diameter decreases when a wrist cuff is inflated to stop blood flow to distal tissue. This phenomenon, referred to as low flow-mediated vasoconstriction (L-FMC), was proposed as a vascular function test. Recommendations that L-FMC be measured concurrently with flow-mediated dilation (FMD) were based on radial artery data. However, cardiovascular disease prediction studies traditionally measure brachial artery FMD. Therefore, studies should determine whether L-FMC occurs in the brachial artery. The hypothesis that reduced shear causes L-FMC has not been tested. Brachial and radial artery L-FMC and FMD were assessed in active nonpregnant ( n = 17), inactive nonpregnant ( n = 10), active pregnant ( n = 15, 34.1 ± 1.2 wk gestation), and inactive pregnant ( n = 8, 34.2 ± 2.2 wk gestation) women. Radial artery diameter decreased significantly during occlusion in all groups (nonpregnant, −4.4 ± 4.2%; pregnant, −6.4 ± 3.2%). Brachial artery diameter did not change in active and inactive nonpregnant, and inactive pregnant women; however, the small decrease in active pregnant women was significant. Occlusion decreased shear rate in both arteries, yet L-FMC only occurred in the radial artery. Radial artery L-FMC was not correlated with the reduction in shear rate. L-FMC occurs in the radial but not the brachial artery and is not related to changes in shear rate. Positive correlations between L-FMC (negative values) and FMD (positive values) suggest that radial artery FMD may be reduced among women who experience greater L-FMC. Studies should clarify the underlying stimulus and mechanisms regulating L-FMC, and test the hypothesis that endothelial dysfunction is manifested as enhanced brachial artery L-FMC, but attenuated radial artery L-FMC.

Retrograde shear rate in formerly preeclamptic and healthy women before and after exercise training: relationship with endothelial function

2014 ◽  
Vol 307 (3) ◽  
pp. H418-H425 ◽  
Author(s):  
Ralph R. Scholten ◽  
Marc E. A. Spaanderman ◽  
Daniel J. Green ◽  
Maria T. E. Hopman ◽  
Dick H. J. Thijssen
Keyword(s):  
Shear Rate ◽  
Exercise Training ◽  
Endothelial Function ◽  
Brachial Artery ◽  
Low Frequency ◽  
Power Spectral Analysis ◽  
Aerobic Exercise Training ◽  
Before And After ◽  
The Impact ◽  
Retrograde Shear

Blood flow patterns in conduit arteries characterized by high levels of retrograde shear stress can be detrimental for vascular health. In this study we examined whether retrograde shear rate and endothelial function are related in healthy and formerly preeclamptic (PE) women and whether this relationship is altered by exercise training. Formerly PE women (32 ± 4 yr, n = 20) and controls (32 ± 4 yr, n = 20), all 6–12 mo postpartum, performed 12-wk aerobic exercise training. We measured brachial artery shear rate (SR) and endothelial function by flow-mediated dilation (FMD, echo-Doppler). We additionally performed power spectral analysis of heart rate variability and calculated low-frequency/high-frequency (LF/HF) ratio. Antegrade SR was not different between groups, while retrograde SR was significantly higher and FMD% lower in PE women compared with controls (both P < 0.05). Retrograde shear correlated strongly with FMD% in PE women and controls ( P < 0.05). LF/HF ratio inversely correlated with brachial artery retrograde SR and FMD% (both P < 0.05) in PE women and controls. Exercise training reduced retrograde shear, improved FMD%, and reduced LF/HF ratios similarly in both groups (all P < 0.05). Training-induced changes in retrograde SR correlated with changes in FMD% and LF/HF ratio. A higher brachial artery retrograde SR relates to lower brachial artery endothelial function, in both controls and formerly PE women. Exercise training improves retrograde SR, while the magnitude of this change correlated strongly with improvements in FMD and reductions in LF/HF ratio. Therefore, the impact of PE and exercise training on endothelial health may, at least partly, be related to retrograde shear rate.

scholarly journals The BB-Paraoxonase Genotype Is Associated with Impaired Brachial Reactivity after Acute Hypertriglyceridemia in Healthy Subjects

2001 ◽  
Vol 86 (3) ◽  
pp. 1078-1082 ◽  
Author(s):  
Giuseppe Paolisso ◽  
Daniela Manzella ◽  
Maria Rosaria Tagliamonte ◽  
Michelangela Barbieri ◽  
Raffaele Marfella ◽  
...  
Keyword(s):  
Brachial Artery ◽  
Healthy Subjects ◽  
Vascular Reactivity ◽  
The Other ◽  
Gender Ratio ◽  
Brachial Artery Diameter ◽  
Plasma Triglycerides ◽  
Before And After ◽  
Basal Plasma ◽  
Baseline Values

The possible relationship between paraoxonase (PON) gene polymorphism and brachial reactivity in healthy adult subjects in the presence of acute hypertriglyceridemia (HT), as a prooxidant factor, was investigated. In 101 healthy subjects the response to flow- induced vasodilatation was measured before and after Intralipid infusion. In the same subjects the A/B PON polymorphism was detected. The frequency was 0.545 for AA genotype, 0.356 for the AB genotype, and 0.099 for the BB genotype. At baseline all genotype groups had a similar increase in brachial artery diameter and flow. After Intralipid infusion, subjects sharing the BB genotype had a significant decrease vs. baseline values in changes in brachial artery diameter (P for trend &lt; 0.001 vs. the other genotypes), but not in flow. In a subgroup of 55 subjects distributed among the 3 PON genotypes the same study protocol was repeated by buccal nitroglycerine administration to study the endothelium-independent vasodilatation. Again, subjects with the BB genotype had the worse vasodilation (P for trend &lt; 0.001). Furthermore, subjects sharing the BB genotype had the lowest endothelium-independent and -dependent changes in diameter (P for trend &lt; 0.001 vs. the other genotypes) independently of gender ratio, basal plasma triglycerides concentrations, and changes in plasma triglycerides concentrations. In conclusion, our study demonstrates that transient HT decreases vascular reactivity more in subjects with the PON BB genotype than in those with the other PON genotypes.

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.

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