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

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.

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.

Occlusion cuff position is an important determinant of the time course and magnitude of human brachial artery flow-mediated dilation

2000 ◽  
Vol 99 (4) ◽  
pp. 261-267 ◽  
Author(s):  
Karen L. BERRY ◽  
R. Andrew P. SKYRME-JONES ◽  
Ian T. MEREDITH
Keyword(s):  
Blood Flow ◽  
Brachial Artery ◽  
Time Course ◽  
Arterial Occlusion ◽  
Flow Mediated Dilation ◽  
Reactive Hyperaemia ◽  
Upper Arm ◽  
Brachial Artery Diameter ◽  
Occlusion Cuff ◽  
Forearm Occlusion

Non-invasive ultrasound techniques to assess flow-mediated vasodilation (FMD) are frequently used to assess arterial endothelial vasodilator function. However, the range of normal values varies considerably, possibly due to differences in methodological factors. We sought to determine the effect of occlusion cuff position on the time course and magnitude of brachial artery blood flow and flow-mediated dilation. Twelve healthy subjects underwent measurements of forearm blood flow using venous occlusion plethysmography (VOP) before and after 5 min of susprasystolic cuff inflation, using two randomly assigned occlusion cuff positions (upper arm and forearm). An additional 16 subjects underwent two brachial ultrasound studies, using the two cuff positions, to assess the extent and time course of changes in brachial artery diameter and blood flow. Maximum increase in blood flow (peak reactive hyperaemia), measured by VOP, occurred immediately upon each cuff deflation, but was greater after upper arm compared with forearm arterial occlusion (33.1±3.1 versus 22.8±2.2 ml/min per forearm tissue, P = 0.001). Maximal brachial artery FMD was significantly greater following upper arm occlusion (9.0±1.2%, mean±S.E.M.) compared with forearm occlusion (5.9±0.7%, P = 0.01). The time course of the change in brachial artery diameter was affected differently in response to each protocol. The time to peak dilation following upper arm occlusion was delayed by 22 s compared with forearm occlusion. Occlusion cuff position is thus a powerful determinant of peak reactive hyperaemia, volume repaid and the extent and time course of brachial artery FMD. Positioning the cuff on the upper arm produces a greater FMD. These results highlight the need for comparisons between FMD studies to be made with care.

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.

scholarly journals Effect of sinusoidal leg cycling exercise period on brachial artery blood flow dynamics in humans

2020 ◽  
Vol 70 (1) ◽  
Author(s):  
Kohei Miura ◽  
Hideaki Kashima ◽  
Anna Oue ◽  
Ayaka Kondo ◽  
Sachiko Watanabe ◽  
...  
Keyword(s):  
Blood Flow ◽  
Brachial Artery ◽  
Flow Dynamics ◽  
Artery Blood Flow ◽  
Cycling Exercise ◽  
Leg Cycling ◽  
Exercise Period ◽  
Blood Flow Dynamics

Contributions of acetylcholine and nitric oxide to forearm blood flow at exercise onset and recovery

1997 ◽  
Vol 273 (5) ◽  
pp. H2388-H2395 ◽  
Author(s):  
J. K. Shoemaker ◽  
J. R. Halliwill ◽  
R. L. Hughson ◽  
M. J. Joyner
Keyword(s):  
Nitric Oxide ◽  
Blood Flow ◽  
Brachial Artery ◽  
Time Course ◽  
Forearm Blood Flow ◽  
Brachial Artery Diameter ◽  
Cholinergic Mechanism ◽  
Pulsed Doppler Ultrasound ◽  
Exercise Onset ◽  
Drug Treatments

The contributions of acetylcholine and/or nitric oxide (NO) to the rapid changes in human forearm blood flow (FBF) at the onset and recovery from mild exercise were studied in eight subjects. Rhythmic handgrip contractions were performed during brachial artery infusions of saline (2 ml/min; control), atropine (0.2 mg over 3 min), to block acetylcholine binding to muscarinic receptors, or atropine + N G-monomethyl-l-arginine (l-NMMA; 4 mg/min for 4 min), to additionally inhibit NO synthase. Brachial artery mean blood velocity (MBV; pulsed Doppler ultrasound) and diameter (echo Doppler) were measured continuously, and FBF was calculated. Atropine reduced acetylcholine-induced increases in FBF by ∼71% ( P < 0.05). FBF at rest was reduced by atropine and further reduced with atropine +l-NMMA. Both drug conditions reduced FBF during exercise by ∼10% compared with control, with no difference between drug treatments. Brachial artery diameter was unchanged from rest by exercise, recovery, and drug treatments. Neither drug treatment altered the rate or magnitude of the increase in FBF above rest. Peak FBF after exercise was reduced by atropine and atropine + l-NMMA. Total FBF during 5 min of recovery was reduced with atropine +l-NMMA compared with control and atropine. The results suggest that 1) acetylcholine and NO mechanisms additively contribute to FBF levels at rest, 2) a cholinergic mechanism adjusts the absolute FBF levels during exercise, 3) neither acetylcholine nor NO is essential to observe the normal time course or magnitude of the exercise response, and 4) NO contributes to the FBF response during recovery from exercise.

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