Abstract 377: Retrograde Shear Stress does not Alter Endothelial Function in Healthy Subjects

2015 ◽  
Vol 35 (suppl_1) ◽  
Author(s):  
Sooraj Shah ◽  
Stuart Katz
Keyword(s):  
Shear Stress ◽  
Endothelial Function ◽  
Healthy Subjects ◽  
Flow Mediated Dilation ◽  
Retrograde Flow ◽  
Experimental Conditions ◽  
Before And After ◽  
Arm Elevation ◽  
The Difference ◽  
Retrograde Shear

Introduction: Endothelial dysfunction is a precursor and plays a significant role in development of atherosclerosis. Retrograde flow and resulting retrograde shear stress has been shown to adversely affect the endothelial function but the results may be flawed due to experimental conditions. Change in the limb position might result in increase in retrograde flow and adversely affect endothelial function. We hypothesized that elevation of arm above the level of the heart will result in increased retrograde flow and reduced endothelial function as measured by flow mediated dilation (FMD). Methods: We enrolled 27 healthy subjects after obtaining informed consent. Endothelial function was measured by FMD in brachial artery before and after arm elevation with elbow support for 30 minutes in fasting state. Flow velocities were recorded and analyzed at baseline, 10 and 20 minutes after arm elevation and at the end of 30 minutes. Results: The mean retrograde flow velocity was 9.9 ± 7.75 cm/sec at baseline, which increased to 15.8 ± 6.56 cm/sec (p=0.0019) after arm elevation. Out of the 27 subjects 21 (78%) subjects had increase in retrograde flow (20% or more). The difference in FMD change between the groups with increased or no change in retrograde flow was statistically non-significant (p=0.4). Conclusion: In conclusion arm elevation for 30 minutes was associated with statistically significant increase in retrograde flow without significant change in endothelial function in normal healthy subjects. The change in endothelial function between subjects who had augmented retrograde shear and those who did not was statistically not significant.

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 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.

Heparan sulphate and hyaluronic acid components of the glycocalyx do not play a role in flow-mediated dilation of the iliac in the anaesthetized pig

2019 ◽  
Vol 97 (8) ◽  
pp. 746-752
Author(s):  
T. Ruane-O’Hora ◽  
D. O’Malley ◽  
M.M. Buckley ◽  
F. Markos
Keyword(s):  
Shear Stress ◽  
Hyaluronic Acid ◽  
Heparan Sulphate ◽  
Flow Mediated Dilation ◽  
Similar Increase ◽  
Shear Stress Sensor ◽  
Before And After ◽  
Student’S T ◽  
Student’S T Test

The shear-stress sensor function of vascular glycocalyx heparan sulphate and hyaluronic acid was investigated in vivo by assessing flow-mediated dilation before and after their removal. Heparinase III exposure (100 mU·mL−1 for 20 min;n = 6) did not significantly affect flow-mediated dilation of the iliac, from 0.42 ± 0.08 mm (mean ± SEM) to 0.34 ± 0.07 mm after (P = 0.12; paired Student’s t test) for a statistically similar increase in shear stress; 18.24 ± 4.2 N·m−2 for the control and 15.8 ± 3.6 N·m−2 for the heparinase III experiment (P = 0.18). Hyaluronidase exposure (0.14–1.4 mg·mL−1 for 20 min; n = 8) also did not significantly reduce flow-mediated dilation of the iliac, which averaged 0.39 ± 0.08 mm before and 0.38 ± 0.09 mm after (P = 0.11) for a statistically similar increase in shear stress; 11.90 ± 3.20 N·m−2 for the control and 9.8 ± 3.33 N·m−2 for the hyaluronidase experiment (P = 0.88). Removal of both heparan sulphate and hyaluronic acid was confirmed using immunohistochemistry. Neither the heparan sulphate nor the hyaluronic acid components of the glycocalyx mediate shear-stress-induced vasodilation in conduit arteries in vivo.

scholarly journals Study of endothelial function in pregnant women with gestational diabetes mellitus by flow mediated dilation of brachial artery

2020 ◽  
Vol 9 (6) ◽  
pp. 2377
Author(s):  
Nidhi Pandey ◽  
Poonam Goel ◽  
Anita Malhotra ◽  
Reeti Mehra ◽  
Navjot Kaur
Keyword(s):  
Gestational Diabetes ◽  
Endothelial Function ◽  
Pregnant Women ◽  
Brachial Artery ◽  
Vascular Function ◽  
Post Partum ◽  
Control Group ◽  
Flow Mediated Dilation ◽  
The Mean ◽  
The Difference

Background: The objective of the study was to assess vascular function in normal pregnant women and women with gestational diabetes and to study its temporal relationship with gestational age at 24-28-week POG and at 36-38-week POG and changes in FMD in postpartum period.Methods: Assessment of vascular function was done at 24-28-week POG, 36-38-week POG and at 6-12-week postpartum by flow mediated dilation of brachial artery in 37 healthy pregnant women and 37 pregnant women with GDM.Results: In GDM group mean FMD at 24-28 weeks of POG, at 36-38 weeks POG was lower as compared to the control group (11.225±6.20,8.464±6.09 versus 14.49±5.21, 10.898±4.12) although the difference in mean FMD in two groups was not statistically significant. It was found that the decrease in FMD at 36-38-week POG as compared to 24-28 weeks POG was statistically significant in both the groups (p<0.001).Conclusions: This study revealed that when endothelial function as assessed by FMD was compared at different period of gestation, the mean decrease in FMD at 36-38-week POG as compared to 24-28-week POG and 6-week post-partum was statistically significant in patients with GDM and as well as the control group, however this trend of change was same in both the groups and was not statistically significant when compared between the two group (GDM versus control). A negative correlation of FMD was found with BMI, and HBA1c, that was stronger in GDM group.

scholarly journals Cardiac baroreflex hysteresis is one of the determinants of the heart period variability asymmetry

2019 ◽  
Vol 317 (4) ◽  
pp. R539-R551 ◽  
Author(s):  
Beatrice De Maria ◽  
Vlasta Bari ◽  
Beatrice Cairo ◽  
Emanuele Vaini ◽  
Raphael Martins de Abreu ◽  
...  
Keyword(s):  
Healthy Subjects ◽  
Age Groups ◽  
Positive Association ◽  
Heart Period ◽  
Experimental Conditions ◽  
Significant Positive Association ◽  
Asymmetric Behavior ◽  
Sequence Method ◽  
The Difference ◽  
Spontaneous Fluctuations

In heart period (HP) variability (HPV) recordings the percentage of negative HP variations tends to be greater than that of positive ones and this pattern is referred to as HPV asymmetry (HPVA). HPVA has been studied in several experimental conditions in healthy and pathological populations, but its origin is unclear. The baroreflex (BR) exhibits an asymmetric behavior as well given that it reacts more importantly to positive than negative arterial pressure (AP) variations. We tested the hypothesis that the BR asymmetry (BRA) is a HPVA determinant over spontaneous fluctuations of HP and systolic AP (SAP). We studied 100 healthy subjects (age from 21 to 70 yr, 54 men) comprising 20 subjects in each age decade. Electrocardiogram and noninvasive AP were recorded for 15 min at rest in supine position (REST) and during active standing (STAND). The HPVA was evaluated via Porta’s index and Guzik’s index, while the BRA was assessed as the difference, and normalized difference, between BR sensitivities computed over positive and negative SAP variations via the sequence method applied to HP and SAP variability. HPVA significantly increased during STAND and decreased progressively with age. BRA was not significantly detected both at REST and during STAND. However, we found a significant positive association between BRA and HPVA markers during STAND persisting even within the age groups. This study supports the use of HPVA indexes as descriptors of BRA and identified a challenge soliciting the BR response like STAND to maximize the association between HPVA and BRA markers.

scholarly journals Effect of Cycloplegia on Keratometric and Biometric Parameters in Keratoconus

2016 ◽  
Vol 2016 ◽  
pp. 1-6
Author(s):  
Nihat Polat ◽  
Abuzer Gunduz
Keyword(s):  
Axial Length ◽  
Healthy Subjects ◽  
Anterior Chamber Depth ◽  
Corneal Curvature ◽  
Corneal Surface ◽  
Biometric Parameters ◽  
Before And After ◽  
The Difference ◽  
Group 2 ◽  
Group 1

Purpose.To obtain information about effect of cycloplegia on keratometry and biometry in keratoconus.Methods.48 keratoconus (Group 1) and 52 healthy subjects (Group 2) were included in the study. We measured the flat meridian of the anterior corneal surface (K1), steep meridian of the anterior corneal surface (K2), lens thickness (LT), anterior chamber depth (ACD), and axial length (AL) using the Lenstar LS 900 before and after cycloplegia.Results.The median K1 in Group 1 was 45.64 D before and 45.42 D after cycloplegia, and the difference was statistically significant (P<0.05). The median K2 in Group 1 was 50.96 D before and 50.17 D after cycloplegia, and the difference was significant (P<0.05). The median K1 and K2 in Group 2 were 42.84 and 44.49 D, respectively, before cycloplegia, and 42.84 and 44.56 D after cycloplegia, and the differences were not statistically significant (allP>0.05). There were significant differences in SE, LT, ACD, and RLP between before and after cycloplegia in either Group 1 (allP<0.05) or Group 2 (allP<0.05). There were not statistically significant differences in AL between before cycloplegia and after cycloplegia in either Group 1 (P=0.533) or group 2 (P=0.529).Conclusions.Flattened corneal curvature and increase in ACD following cycloplegia in keratoconus patients were detected.

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.

Does habitual endurance exercise protect endothelial function against acute exposure to oscillatory shear stress?

2019 ◽  
Author(s):  
A. S. Grewal ◽  
J. C. Tremblay ◽  
N. Preobrazenski ◽  
B. J. Gurd
Keyword(s):  
Physical Activity ◽  
Shear Stress ◽  
Endothelial Function ◽  
Endurance Exercise ◽  
Lower Limb ◽  
Rest Period ◽  
Oscillatory Shear ◽  
Acute Exposure ◽  
Before And After ◽  
Oscillatory Shear Stress

Introduction: Acute exposure to increases in oscillatory shear stress (increased retrograde shear stress and decreased mean shear stress) reduces flow-mediated dilation (FMD). This impairment may be mediated via increased oxidative stress. Habitual endurance exercise training results in increased antioxidant protection. However, it is currently unknown whether these adaptations protect against oscillatory shear stress-induced impairments in FMD. Purpose and Hypothesis: The purpose of this study is to determine whether lower limb endurance-trained athletes have protection against oscillatory shear stress-induced impairments in FMD compared to sedentary individuals. It is hypothesized that athletes will have a preserved FMD after an acute oscillatory shear stress intervention, compared to their sedentary counterparts. Methods: Healthy, young adult volunteers (18-29 years old) will be screened for physical activity (PA) through a physical activity recall questionnaire. 12 sedentary individuals (<3h of structured PA/week) and 12 lower limb endurance athletes will be recruited to participate.  All participants will complete a VO2 peak test to objectively measure cardiorespiratory fitness. Participants will visit the laboratory twice in the same week for vascular testing. Both 90-minute visits will begin with 45 minutes of supine rest, followed by a brachial artery FMD test before and after 30 minutes of either imposed oscillatory shear stress (forearm cuff inflated to 70 mmHg) or a 30 min rest period (control).  Significance: This will be the first study to investigate whether endurance-trained athletes are resistant to oscillatory shear-stress induced impairments in endothelial function. This will provide insight into mechanism contributing to the vasoprotective effects of habitual endurance exercise.

scholarly journals Acute exposure to nocturnal train noise induces endothelial dysfunction and pro-thromboinflammatory changes of the plasma proteome in healthy subjects

2019 ◽  
Vol 114 (6) ◽  
Author(s):  
Johannes Herzog ◽  
Frank P. Schmidt ◽  
Omar Hahad ◽  
Seyed Hamidreza Mahmoudpour ◽  
Alina K. Mangold ◽  
...  
Keyword(s):  
Endothelial Dysfunction ◽  
Endothelial Function ◽  
Vascular Function ◽  
Healthy Subjects ◽  
Noise Exposure ◽  
Subclinical Atherosclerosis ◽  
Flow Mediated Dilation ◽  
Protein Levels ◽  
Randomized Crossover Study ◽  
Study Center

Abstract Nocturnal train noise exposure has been associated with hypertension and myocardial infarction. It remains unclear whether acute nighttime train exposure may induce subclinical atherosclerosis, such as endothelial dysfunction and other functional and/or biochemical changes. Thus, we aimed to expose healthy subjects to nocturnal train noise and to assess endothelial function, changes in plasma protein levels and clinical parameters. In a randomized crossover study, we exposed 70 healthy volunteers to either background or two different simulated train noise scenarios in their homes during three nights. After each night, participants visited the study center for measurement of vascular function and assessment of other biomedical and biochemical parameters. The three nighttime noise scenarios were exposure to either background noise (control), 30 or 60 train noise events (Noise30 or Noise60), with average sound pressure levels of 33, 52 and 54 dB(A), respectively. Flow-mediated dilation (FMD) of the brachial artery was 11.23 ± 4.68% for control, compared to 8.71 ± 3.83% for Noise30 and 8.47 ± 3.73% for Noise60 (p < 0.001 vs. control). Sleep quality was impaired after both Noise30 and Noise60 nights (p < 0.001 vs. control). Targeted proteomic analysis showed substantial changes of plasma proteins after the Noise60 night, mainly centered on redox, pro-thrombotic and proinflammatory pathways. Exposure to simulated nocturnal train noise impaired endothelial function. The proteomic changes point toward a proinflammatory and pro-thrombotic phenotype in response to nocturnal train noise and provide a molecular basis to explain the increased cardiovascular risk observed in epidemiological noise studies.

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