Arterial Shear Stress Research Articles

Abstract 47: Point-of-Care Seeded Blood-Derived Endothelial Cells Rapidly Endothelialize Nitinol Stent in a Pig Model of Personalized Cell Therapy

Intimal hyperplasia after percutaneous intervention is especially problematic in peripheral arteries. In coronary arteries, drug-eluting stents (DES) have greatly reduced intimal hyperplasia; however, DES not only prevent smooth muscle cell proliferation but also inhibit endothelial cell (EC) healing. In an effort to rapidly endothelialize Nitinol vascular stents, we have developed a novel rapid seeding technology (QuickSeeding). 5000 micropores (~32.4 ± 0.4 μm) were laser-drilled circumferentially into Nitinol stent delivery systems to enable ECs to flow across the stent struts and thereby attach to the stent while in its compressed state within 5 min at the point-of-care. To evaluate EC adhesion after stent deployment, ECs were isolated from human umbilical cord blood progenitor cells and QuickSeeded, resulting in a uniform stent surface coverage of 55,000 ± 9,500 cells/cm2 (n=4). QuickSeeded stents were then deployed in tubing and tested in a flow circuit at 15 dynes/cm2, representing arterial flow shear stress. After 48 hr of flow, ECs had spread over the stent surface, demonstrated by PECAM staining of cell junctions. To assess EC function, total nitrite was measured as a marker of NO production and increased from 0.41 ± 0.13 nmol under static conditions to 7.83 ± 1.97 nmol after 24 hr of flow (p<0.05, n=5). These results demonstrate a flow-dependent increase in NO secretion. To test this technology in a large animal model, ECs were grown out from peripheral blood circulating progenitor cells of 4 pigs, fluorescently labeled, and seeded onto 4 stents. The 4 stents were then percutaneously implanted into the carotid arteries of the original 4 pigs. Each pig received an identical uncoated stent in the contralateral artery as control. Fluorescent microscopy and SEM showed that control stents were devoid of ECs but QuickSeeded stents were endothelialized after 2 days. Functionality of ECs adhering to stent struts was confirmed with a metabolic assay after explantation.

Sympathetic nervous system activation, arterial shear rate, and flow-mediated dilation

The aim of this study was to examine the contribution of arterial shear to changes in flow-mediated dilation (FMD) during sympathetic nervous system (SNS) activation in healthy humans. Ten healthy men reported to our laboratory four times. Bilateral FMD, shear rate (SR), and catecholamines were examined before/after 10-min of -35-mmHg lower body negative pressure (LBNP10). On day 1, localized forearm heating (LBNP10+heat) was applied in one limb to abolish the increase in retrograde SR associated with LBNP. Day 2 involved unilateral cuff inflation to 75 mmHg around one limb to exaggerate the LBNP-induced increase retrograde SR (LBNP10+cuff). Tests were repeated on days 3 and 4, using 30-min interventions (i.e., LBNP30+heat and LBNP30+cuff). LBNP10 significantly increased epinephrine levels and retrograde SR and decreased FMD (all P < 0.05). LBNP10+heat prevented the increase in retrograde SR, whereas LBNP10+cuff further increased retrograde SR (P < 0.05). Heating prevented the decrease in percent FMD (FMD%) after LBNP10 (interaction effect, P < 0.05), whereas cuffing did not significantly exaggerate the decrease in FMD% (interaction effect, P > 0.05). Prolongation of the LBNP stimulus for 30-min normalized retrograde SR, catecholamine levels, and FMD (all P > 0.05). Attenuation of retrograde SR during 30 min (LBNP30+heat) was associated with increased FMD% (interaction effects, P < 0.05), whereas increased retrograde SR (LBNP30+cuff) diminished FMD% (interaction effects, P < 0.05). These data suggest that LBNP-induced SNS stimulation decreases FMD, at least in part due to the impact of LBNP on arterial shear stress. Prolonged LBNP stimulation was not associated with changes in SR or FMD%. Our data support a role for changes in SR to the impact of SNS stimulation on FMD.

The effect of shear stress, potassium, adenosine, and acidosis on alpha‐1 adrenergic vasoconstriction of rat soleus feed arteries (1170.14)

Arteries and arterioles constrict less to sympathetic stimulation in contracting compared to resting skeletal muscle (sympatholysis). There is some uncertainty regarding the specific agents causing sympatholysis. We hypothesized that increased levels of arterial wall shear stress, potassium, adenosine, or acidosis contribute to sympatholysis, thereby reducing sympathetic vasoconstriction. Soleus feed arteries (n = 12 per group) were isolated from male Sprague‐Dawley rats and cannulated on two glass micropipettes for in vitro videomicroscopy. We measured the constriction response to the α‐1 agonist phenylephrine (PE; 10‐9 M to 10‐4 M, 0.5 log increments) in the presence of varying levels of shear stress (0 dy/cm2, 25 dy/cm2, and 135 dy/cm2), potassium (5 mM, 7.5 mM, and 10 mM), adenosine (0 μM, 0.8 μM, and 1.6 μM) and acidosis (pH = 7.4, 7.1, 6.8, and 6.5). There was no significant difference in PE induced constriction between levels of shear stress (maximum constriction 67.6 % vs. 68.1 % and 67.6 %), potassium (maximum constriction 63.1 % vs. 56.5 % and 65.0 %), or adenosine (maximum constriction 56.2 % vs. 54.3 % and 54.2 %). However, acidosis reduced constriction to PE (maximum constriction 77.6% vs. 72.0%, 66.6%, and 66.3%). We conclude that acidity, but not shear stress, potassium, or adenosine, is sympatholytic in feed arteries from the predominantly slow twitch soleus muscle.Grant Funding Source: Supported by NSF #DBI‐1062721 and the Seaver Research Council

Assessing the effect of shear stress on Aquaporin 1 expression in vascular endothelial cells in vitro (696.9)

The human saphenous vein (HSV) is commonly used in coronary artery bypass grafts. The patency of the vein graft in an arterial environment is limited, thereby requiring a high percentage of autograft recipients to repeat the bypass surgery within 5 years. The main problem that ensues with HSV grafts is due to the development of intimal hyperplasia (IH) which compromises vessel function. The mechanistic reasons for the development of IH and limited HSV patency are not currently understood. However, it has been proposed that the change from venous to arterial shear stress may be a trigger. Aquaporin 1 (AQP1), a water channel protein, is expressed in the plasma membrane of vascular endothelial cells. It is hypothesized that enhanced AQP1 expression may be an early biomarker for the development of IH. The goal of this study was to assess the effect of shear stress on AQP1 expression in cultured endothelial cells. Primary vascular endothelial cells seeded on a gelatin‐coated Ibidi flow chamber grown in static conditions expressed low levels of AQP1 protein that localized around the nucleus. In contrast, AQP1 was present in vesicles throughout the cytoplasm in increasing abundance in cells subjected to low shear stress (6 dynes/cm²) vs. high shear stress (16 dynes/cm²)(p&lt;0.01). These data show that shear stress alters AQP1 abundance and subcellular distribution in vascular endothelial cells in vitro, thus supporting a role for AQP1 as an environmental sensor in HSV grafts.Grant Funding Source: Supported by the University of Dayton Research Council

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

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.

Characterizaton of the Vessel Geometry, Flow Mechanics and Wall Shear Stress in the Great Arteries of Wildtype Prenatal Mouse

IntroductionAbnormal fluid mechanical environment in the pre-natal cardiovascular system is hypothesized to play a significant role in causing structural heart malformations. It is thus important to improve our understanding of the prenatal cardiovascular fluid mechanical environment at multiple developmental time-points and vascular morphologies. We present such a study on fetal great arteries on the wildtype mouse from embryonic day 14.5 (E14.5) to near-term (E18.5).MethodsUltrasound bio-microscopy (UBM) was used to measure blood velocity of the great arteries. Subsequently, specimens were cryo-embedded and sectioned using episcopic fluorescent image capture (EFIC) to obtain high-resolution 2D serial image stacks, which were used for 3D reconstructions and quantitative measurement of great artery and aortic arch dimensions. EFIC and UBM data were input into subject-specific computational fluid dynamics (CFD) for modeling hemodynamics.ResultsIn normal mouse fetuses between E14.5–18.5, ultrasound imaging showed gradual but statistically significant increase in blood velocity in the aorta, pulmonary trunk (with the ductus arteriosus), and descending aorta. Measurement by EFIC imaging displayed a similar increase in cross sectional area of these vessels. However, CFD modeling showed great artery average wall shear stress and wall shear rate remain relatively constant with age and with vessel size, indicating that hemodynamic shear had a relative constancy over gestational period considered here.ConclusionOur EFIC-UBM-CFD method allowed reasonably detailed characterization of fetal mouse vascular geometry and fluid mechanics. Our results suggest that a homeostatic mechanism for restoring vascular wall shear magnitudes may exist during normal embryonic development. We speculate that this mechanism regulates the growth of the great vessels.

Volumetric arterial wall shear stress calculation based on cine phase contrast MRI

To assess the accuracy and precision of a volumetric wall shear stress (WSS) calculation method applied to cine phase contrast magnetic resonance imaging (PC-MRI) data. Volumetric WSS vectors were calculated in software phantoms. WSS algorithm parameters were optimized and the influence of spatial resolution and segmentation was evaluated. Subsequently, 2D cine PC-MRI data in the carotid and the aorta at varying spatial resolutions were obtained (n = 2) and compared with the simulations. Finally, volumetric WSS was calculated in 3D cine PC-MRI data of the carotid bifurcation and the aorta (n = 6). We found that at least 8 voxels across the diameter are required to obtain a WSS accuracy of 5% and a precision of 20% in software phantoms. Systematic WSS quantification errors up to 40% were found in the case of segmentation errors. The in vivo measurements using 2D cine PC-MRI exhibited WSS increase at increasing spatial resolutions, similar to the results in software phantoms. Volumetric WSS vectors were successfully calculated in three healthy carotid bifurcations and aortas. The effects of resolution and segmentation on the accuracy and precision of the WSS algorithm were quantified. We were able to calculate volumetric WSS in the carotid bifurcation and the aorta.

The use of external mesh reinforcement to reduce intimal hyperplasia and preserve the structure of human saphenous veins

The saphenous vein is the conduit of choice in bypass graft procedures. Haemodynamic factors play a major role in the development of intimal hyperplasia (IH), and subsequent bypass failure. To evaluate the potential protective effect of external reinforcement on such a failure, we developed an ex vivo model for the perfusion of segments of human saphenous veins under arterial shear stress. In veins submitted to pulsatile high pressure (mean pressure at 100 mmHg) for 3 or 7 days, the use of an external macroporous polyester mesh 1) prevented the dilatation of the vessel, 2) decreased the development of IH, 3) reduced the apoptosis of smooth muscle cells, and the subsequent fibrosis of the media layer, 4) prevented the remodelling of extracellular matrix through the up-regulation of matrix metalloproteinases (MMP-2, MMP-9) and plasminogen activator type I. The data show that, in an experimental ex vivo setting, an external scaffold decreases IH and maintains the integrity of veins exposed to arterial pressure, via increase in shear stress and decrease wall tension, that likely contribute to trigger selective molecular and cellular changes.

Association between Ischemic Stroke and Vascular Shear Stress in the Carotid Artery.

Background and PurposeVascular shear stress is essential for maintaining the morphology and function of endothelial cells. We hypothesized that shear stress in the internal carotid artery (ICA) may differ between patients with ischemic stroke and healthy control subjects.MethodsICA shear stress was calculated in 143 controls and 122 patients with ischemic stroke who had a normal ICA or an ICA with <50% stenosis. The stroke group included patients who presented with a first-ever or recurrent ischemic stroke but excluded cardioembolic stroke and uncertain etiologies. Of the 122 patients, 107 (87.7%) and 15 (12.3%) patients were categorized as first-ever and recurrent stroke, respectively.ResultsCarotid diameters were significantly larger, and both peak-systolic and end-diastolic velocities were significantly lower in patients with ischemic stroke than in controls (all p values <0.05). Mean values of peak-systolic and end-diastolic shear stress in both ICAs were significantly lower in patients with ischemic stroke in models that adjusted for age, sex, and vascular risk factors (p for trend <0.05). The ICA shear stress was lowest in patients with recurrent stroke or the subtype of small-vessel occlusion. Higher peak-systolic and end-diastolic shear stresses in both ICAs were independently and negatively associated with ischemic stroke after adjusting for potential confounders (all p values <0.05).ConclusionsICA shear stresses were significantly lower in patients with ischemic stroke than in control subjects. Future studies should attempt to define the causal relationship between carotid arterial shear stress and ischemic stroke.

Local Effects of Pregnancy on Connexin Proteins That Mediate Ca 2+ -Associated Uterine Endothelial NO Synthesis

Uterine artery adaptations during gestation facilitate increases in uterine blood flow and fetal growth. local expression and distribution of uterine artery connexins play roles in mediating in vivo gestational eNOS activation and NO production. We established an ovine model restricting pregnancy to a single uterine horn and measured uterine blood flow, uterine artery shear stress, connexins 37/43, and P(635)eNOS protein levels in uterine artery and systemic artery (omental and renal) endothelium and connexins in vascular smooth muscle. Uterine blood flow and shear stress were locally (unilaterally) and substantially elevated by gestation. During pregnancy, uterine artery endothelial gap junction proteins connexins 37/43 were locally regulated in the gravid horn and elevated 10.3- and 25.6-fold; uterine artery endothelial P(635)eNOS and total eNOS were elevated 3.3- and 2.9-fold; whereas uterine artery vascular smooth muscle connexins 37/43 were locally elevated 12.5- and 5.9-fold, respectively. Less pronounced changes were observed in systemic vasculature except for significant pregnancy-associated increases in omental artery vascular smooth muscle connexin 43 and omental artery endothelial P(635)eNOS and total eNOS. Gap junction blockade using connexin 43, but not connexin 37-specific Gap peptides, abrogated uterine artery endothelial ATP-induced Ca(2+)-mediated NO production. Thus, uterine artery endothelial connexin 43, but not connexin 37, regulates Ca(2+)-mediated NO production required for the vasodilation to accommodate increases in uterine blood flow and shear stress during healthy pregnancies.

Antiphospholipid Antibodies Increase Von Willebrand Factor-Platelet String Formation From Human Endothelial Cells Under Physiologic Flow Conditions

BackgroundThe antiphospholipid syndrome (APS) is characterized by a predisposition to arterial and venous thromboembolism. The underlying mechanism of thrombosis in APS is uncertain, but is thought to involve a multifactorial activation of various components of the blood and vasculature. The role of von Willebrand factor (VWF), a plasma protein expressed by endothelial cells in response to endothelial cell damage or activation, is not clearly defined in APS. Previous studies have demonstrated that antiphospholipid antibodies increase the release of soluble VWF from human umbilical vein endothelial cells. However, these experiments were performed in static conditions and not in a flow based model. Recent investigations of expressed ultra large VWF (ULVWF) under flow have led to a new model of VWF-platelet strings that remain anchored to endothelial cells and provide a nidus for the formation of thrombi. Consistent with this, increases in VWF and variations in ADAMTS13, the enzyme that modulates ULVWF, have been associated with venous and arterial thrombosis. ObjectivesWe hypothesized that antiphospholipid antibodies would induce VWF-platelet strings on endothelial cells and that this mechanism contributes to APS-associated thrombosis. MethodsHuman umbilical vein endothelial cells were seeded in flow chambers prepared with a collagen substrate. All experiments were performed with cells of passage 5 or under. Confluent cells were incubated in serum-free medium with APS-derived IgG or anti-β2-GPI antibodies vs. control IgG. After incubation, the slides were perfused with lyophilized platelets and washed with Tyrode's buffer prior to image acquisition. Shear stresses were varied from 2-10 dyn/cm2 to assess for shear stress dependent variations in string formation. Pre-determined sites of imaging were set via a standardized method with relief contrast brightfield microscopy. Between 50-100 images were collected per condition. A VWF-platelet string-unit was defined as a 25 µm length of an individual VWF-platelet string. Images were analyzed for the number of VWF-platelet string units per image; quantification of string units was performed blinded to sample vs. control IgG treatment status. Data are shown as means +/- SEM, and significance was determined as p<0.05 by paired t-test. ResultsEndothelial cells treated with human antiphospholipid antibodies demonstrated increased VWF-platelet strings at two different shear stresses, one mimicking venous flow and one mimicking arterial flow. At 2 dyn/cm2, cells incubated for 1 hour with 100 µM of APS patient–derived IgG demonstrated 23.04 +/- 2.139 (SEM) VWF-platelet string units/image vs. 17.64 +/- 1.203 in cells treated with 100 µM control human IgG (p=0.0247). At 10 dyn/cm2, cells incubated for 6 hours with 600 nM of human anti-β2-GPI antibodies demonstrated 1.848 +/- 0.2866 (SEM) VWF-platelet string units/image vs 1.048 +/- 0.2350 in cells treated with 600 nM control human IgG (p=0.0395). ConclusionsAntiphospholipid antibodies, in aggregate (IgG from an APS patient) or specific (anti-β2-GPI), induce the formation of VWF-platelet strings from human endothelial cells. This finding suggests the potential role of VWF-platelet strings in thrombosis associated with APS. The clinical predisposition to arterial and venous thrombi in APS and the observation of increased VWF-platelet strings at arterial and venous shear stresses suggest that modulation of VWF-platelet strings may provide a future therapeutic target. Disclosures:Manco-Johnson:Bayer HealthCare: Membership on an entity's Board of Directors or advisory committees, Research Funding; CSL Behring: Membership on an entity's Board of Directors or advisory committees, Research Funding; Baxter BioScience: Membership on an entity's Board of Directors or advisory committees; Biogen Idec: Membership on an entity's Board of Directors or advisory committees; Novo Nordisk: Membership on an entity's Board of Directors or advisory committees; Eisai: Research Funding. Di Paola:Pfizer: DSMB, DSMB Other; CSL Behring: Consultancy.

Free Thiol Groups In Von Willebrand Factor (VWF) Are Required For Its Proper Function Under Physiological Flow Conditions

BackgroundThe multimeric plasma glycoprotein von Willebrand factor (VWF) is exceptionally rich in cysteine, and its structure is largely determined by inter- and intramolecular disulfide bonding. Additionally, VWF was shown to contain unpaired cysteine residues potentially affecting protein function. The significance of free thiols on the surface of plasmatic VWF has been confirmed previously with respect to platelet binding under pathologically high shear stress. Furthermore their potential involvement in functional VWF self-association occurring at elevated shear stress has been suggested. AimsObjective of the present study was to investigate whether free thiol groups of plasma VWF contribute to the physiological VWF function under high physiological arterial shear stress conditions. Furthermore, we aimed to elucidate possible underlying mechanisms involved in this regulation. MethodsFree and accessible thiol groups of plasma-derived VWF were blocked with N-ethylmaleimide (NEM). Derivatization was followed by detailed structural and functional examination including multimer analysis (MMA) and Fourier transform infrared spectroscopy (FTIR). Functional differences between the NEM-derivatized sample and the control sample were detected using an in vitro flow chamber system with respect to VWF-mediated platelet adhesion to collagen. Interactions with collagen type III and platelet glycoprotein (GP)Ib receptor were investigated using surface plasmon resonance (SPR). Identification of accessible cysteine residues was accomplished using biotin-linked maleimide (MPB) followed by analysis of multimer and domain incorporation as well as mass spectrometry. ResultsBlocking free thiol groups provoked substantial loss of VWF activity with respect to platelet recruitment to collagen type III under flow. The lowered platelet adhesion to collagen type III was shown to be a combined effect of inhibition of (i) the initial VWF binding to collagen type III as well as (ii) VWF-platelet GPIb interaction. Free thiol groups were accessible for derivatization solely on the surface of coiled multimers. Domain incorporation studies revealed a high level of derivatization in VWF N- and C-terminus. This was in accordance with the mass spectrometric analysis, where 19 MPB-derivatized peptides, predominantly located at the N- and C-terminus, could be identified. ConclusionBlocking free thiol groups in VWF significantly impaired mediation of platelet adhesion under physiological shear stress conditions. This result suggests an essential functional role of free thiol groups in VWF regarding binding to subendothelial matrix as well as platelet recruitment. Disclosures:Solecka:Octapharma AG: Employment. Fuchs:Octapharma AG: Employment. Kannicht:Octapharma AG: Employment.

Preserved flow‐mediated dilation but delayed time‐to‐peak diameter in individuals with metabolic syndrome

Inconsistent evidences of the metabolic syndrome (MetS) impact on vascular reactivity raise questions on flow-mediated dilation (FMD) discriminatory power for disturbances induced by this clustering of risk factors. Previous reports, however, suggest that covariates such as the follow-up of the artery diameter changes, the arterial size and shear stress affect FMD responses and consequently its discriminatory power for distinctive clinical profiles. To determine the impact of MetS on traditional, arterial size- and shear-rate-adjusted FMD, the follow-up-derived time-to-peak diameter (TP), as well as their power for discriminating subjects with this clustering of risk factors from a sample of healthy individuals. Twenty-one MetS and ten healthy subjects underwent an assessment of endothelial function via FMD. Traditional and allometrically scaled FMD did not differ between groups (P>0·05) as well as the approach in which the covariate was the peak diameter shear rate. In the existence of MetS, TP was longer (67·7 ± 16·4 s versus healthy 42·1 ± 16·3 s, P = 0·001). ROC curve analysis indicated that TP (AUC = 0·871 [95% CI, 0·718-1·000]) had greater power of discrimination for MetS than FMD approaches. In addition, TP presented a moderate and significant association with sE-selectin (r = 0·458, P = 0·048). Time-to-peak diameter (TP) rather than FMD distinguished MetS from a healthy profile. Therefore, at least in subjects with MetS, TP may provide insights into the impact of this clustering of risk factors on the vascular phenotype.

Chronic skeletal unloading of the rat femur: Mechanisms and functional consequences of vascular remodeling

Chronic skeletal unloading diminishes hindlimb bone blood flow. The purpose of the present investigation was to determine 1) whether 7 and 14days of skeletal unloading alter femoral bone and marrow blood flow and vascular resistance during reloading, and 2) whether putative changes in bone perfusion are associated with a gross structural remodeling of the principal nutrient artery (PNA) of the femur. Six-month old male Sprague–Dawley rats were assigned to 7-d or 14-d hindlimb unloading (HU) or weight-bearing control groups. Bone perfusion was measured following 10min of standing (reloading) following the unloading treatment. Histomorphometry was used to determine PNA media wall thickness and maximal diameter. Bone blood flow, arterial pressure and PNA structural characteristics were used to calculate arterial shear stress and circumferential wall stress. During reloading, femoral perfusion was lower in the distal metaphyseal region of 7-d HU rats, and in the proximal and distal metaphyses, diaphysis and diaphyseal marrow of 14-d HU animals relative to that in control rats. Vascular resistance was also higher in all regions of the femur in 14-d HU rats during reloading relative to control animals. Intraluminal diameter of PNAs from 14-d HU rats (138±5μm) was smaller than that of control PNAs (162±6μm), and medial wall thickness was thinner in PNAs from 14-d HU (14.3±0.6μm) versus that of control (18.0±0.8μm) rats. Decreases in both shear stress and circumferential stress occurred in the PNA with HU that later returned to control levels with the reductions in PNA maximal diameter and wall thickness, respectively. The results demonstrate that chronic skeletal unloading attenuates the ability to increase blood flow and nutrient delivery to bone and marrow with immediate acute reloading due, in part, to a remodeling of the bone resistance vasculature.

In Vitro Method for Real-Time, Direct Observation of Cell–Vascular Graft Interactions under Simulated Blood Flow

In the development of engineered vascular grafts, assessing the material's interactive properties with peripheral blood cells and its capacity to endothelialize are important for predicting in vivo graft behavior. Current in vitro techniques used for characterizing cell adhesion at the surface of engineered scaffolds under flow only facilitate a terminal quantification of cell/surface interactions. Here, we present the design of an innovative flow chamber for real-time analysis of blood-biomaterial interactions under controllable hemodynamic conditions. Decellularized human umbilical veins (dHUV) were used as model vascular allografts to characterize platelet, leukocyte, and endothelial cell (EC) adhesion dynamics. Confluent EC monolayers adhered to the lumenal surface of the grafting material were flow conditioned to resist arterial shear stress levels (up to 24 dynes/cm(2)) over a 48 h period, and shown to maintain viability over the 1 week assessment period. The basement membrane was imaged while whole blood/neutrophil suspensions were perfused across the HUV surface to quantify cell accumulation. This novel method facilitates live visualization of dynamic events, including cell adhesion, migration, and morphological adaptation at the blood-graft interface on opaque materials, and it can be used for preliminary assessment of clinically relevant biomaterials before implantation.

Longitudinal heterogeneity of arterial remodeling and endothelial shear stress in human coronary artery plaques and their effects on the natural history of atherosclerosis

Purpose: Expansive remodeling (ER) and low endothelial shear stress (ESS) critically determine the natural history of atherosclerosis, but they have only been investigated in a cross-sectional arterial axis. In this study, we assessed the longitudinal variation of remodeling and ESS along the length of individual plaques in human coronary arteries and their relation to subsequent plaque growth. Methods: We performed 3D coronary reconstruction by angiography/IVUS at baseline and at 6-10 months follow-up as part of the PREDICTION Study. In discrete baseline plaques (max thickness >0.5 mm, length 9 to 30 mm), we assessed arterial remodeling and ESS (using computational fluid dynamics) in 3mm-long segments. Plaque growth was evaluated in the same locations at follow-up. Results: In 313 arteries from 220 patients, 371 plaques (average length 16.6±0.4 mm) were identified. Of these plaques, 237 (63.9%) had evidence of remodeling while the remaining 134 (36.1%) showed no remodeling. The vast majority of remodeled plaques (93.2%) displayed heterogeneous remodeling patterns along their length: 52 plaques (23.5%) exhibited two remodeling patterns, 14 (6.3%) exhibited three remodeling patterns and 155 plaques (70.1%) showed a combination of one remodeling pattern in some areas of the plaque with absence of remodeling elsewhere (p<0.001). Of plaques with homogeneous remodeling, 18.8% had Excessive ER, 6.2% Compensatory ER, 12.5% Inadequate ER and 62.5% Constrictive remodeling (p<0.05). Similarly, 75.7% of all plaques demonstrated heterogeneous ESS profiles along their length: 20 plaques (7.1%) exhibited both low and high ESS, 79 (28.1%) both low and moderate ESS, 67 (23.8%) both moderate and high ESS; and 115 plaques (40.9%) showed all three ESS patterns (p<0.001). Of plaques with homogeneous ESS, 40% had low ESS, 20% moderate ESS and 40% high ESS. Segments with Excessive ER were associated with low ESS while constrictively remodeled segments with high ESS (p<0.001). Plaque growth at follow-up was primarily evident in segments with baseline low ESS (OR 1.4, 95% CI 1.1-1.7, p<0.05). Conclusions: Arterial remodeling and ESS patterns are not homogeneously distributed along the length of individual coronary plaques, but show significant longitudinal heterogeneity. Since Excessive ER is related to low ESS and subsequent plaque growth, the detailed characterization of remodeling and ESS profiles along the longitudinal aspect of lesions may enhance early identification of highest-risk plaques.

Blood pressure regulation VIII: resistance vessel tone and implications for a pro-atherogenic conduit artery endothelial cell phenotype

Dysfunction of the endothelium is proposed as the primary initiator of atherosclerotic peripheral artery disease, which occurs mainly in medium- to large-sized conduit arteries of the lower extremities (e.g., iliac, femoral, popliteal arteries). In this review article, we propose the novel concept that conduit artery endothelial cell phenotype is determined, in part, by microvascular tone in skeletal muscle resistance arteries through both changes in arterial blood pressure as well as upstream conduit artery shear stress patterns. First, we summarize the literature supporting the involvement of sympathetic nerve activity (SNA) and nitric oxide (NO) in the modulation of microvascular tone and arterial blood pressure. We then focus on the role of elevated blood pressure and shear stress profiles in modulating conduit artery endothelial cell phenotype. Last, we discuss findings from classic and emerging studies indicating that increased vascular resistance, as it occurs in the context of increased SNA and/or reduced NO bioavailability, is associated with greater oscillatory shear stress (e.g., increased retrograde shear) in upstream conduit arteries. The ideas put forth in this review set the stage for a new paradigm concerning the mechanistic link between increased microvascular tone and development of conduit artery endothelial dysfunction and thus increased risk for peripheral artery disease. Indeed, a vast amount of evidence supports the notion that excessive blood pressure and oscillatory shear stress are potent pro-atherogenic signals to the endothelium.

Early Enhanced External Counter Pulsation Improves Neurological Recovery After the Return of Spontaneous Circulation in a Mongrel Dog Cardiac Arrest Model*

The aim of this study was to investigate whether early enhanced external counter pulsation therapy after cardiopulmonary resuscitation improved neurological outcome in a mongrel dog cardiac arrest model. Randomized, animal study. Assisted circulation laboratory. Twenty-four healthy male adult dogs (12-14 kg). After minutes of untreated ventricular fibrillation followed by 2 minutes of cardiopulmonary resuscitation, the dogs were randomized to receive 4 hours of enhanced external counter pulsation therapy, to receive 4 hours of hypertension with over 140 mm Hg or to be a control. Blood pressure and left ventricular ejection fraction were recorded. Cerebral flow was assessed using magnetic resonance imaging. Arterial blood gases and endothelium-derived vasoactive substances were assessed before cardiac arrest and 4 hours after the return of spontaneous circulation. Neurological outcome was assessed by the neurologic deficit score and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling staining. Enhanced external counter pulsation significantly improved the left ventricular ejection fraction and increased common carotid artery blood flow and shear stress. Enhanced external counter pulsation increased both relative cerebral blood volume (RCBV, p = 0.043) and relative cerebral blood flow (RCBF, p = 0.012) in animals 4 hours after return of spontaneous circulation. Enhanced external counter pulsation therapy promoted the production of nitric oxide and tissue plasminogen activator and decreased the release of endothelin-1 (p = 0.013) after return of spontaneous circulation. Treatment with norepinephrine in the high mean artery pressure also increased common carotid artery blood flow and shear stress. However, no effects on the left ventricular ejection fraction, the production of nitric oxide and tissue plasminogen activator, or the release of endothelin-1 were found. The neurologic deficit scores of the animals were significantly lower at 24, 48, 72, and 96 hours in the enhanced external counter pulsation group, as well as at 24, 72, and 96 hours compared with animals in the control group after return of spontaneous circulation. Fewer apoptotic neurons were observed in the animals in the enhanced external counter pulsation group compared with the animals in the control and hypertension groups. These data indicated that the treatment of early enhanced external counter pulsation improved neurological outcome by both increasing cerebral blood flow and improving the recovery of microcirculation after return of spontaneous circulation. The treatment of early enhanced external counter pulsation can be a good option for protecting the brain after return of spontaneous circulation.

VEGF-bound stent: arterial shear stress augments the differentiation

VEGF-bound stent: arterial shear stress augments the differentiation

Shear rate specific blood viscosity and shear stress of carotid artery duplex ultrasonography in patients with lacunar infarction

BackgroundThis study describes a new method for determining site-specific vascular shear stress using dynamic measures of shear rate and blood viscosity (BV) in the carotid arteries, and examines characteristics of carotid arterial shear stress among patients with lacunar infarction.MethodsVascular shear stress measurements were conducted in 37 patients (17 lacunar infarction patients and 20 control subjects) using duplex ultrasonography. Vessel wall diameters and velocities were measured in each arterial segment at peak-systolic (PS) and end-diastolic (ED) phases, for calculation of PS/ED shear rates. PS/ED shear stresses [dyne/cm2] were determined with PS/ED shear rates and shear-rate dependent BV values. For comparison, both values of hematocrit-derived BV and BV measurements at 300 s-1 were used for calculation of shear stress.ResultsAll cardiovascular disease (CVD) risk factors including BV values were similar between the two groups. In both common carotid arteries, PS and ED shear stresses were significantly lower in the patients with lacunar infarction than in controls in multivariate models that included age, sex, and other major CVD risk factors. PS and ED shear stresses using the shear rate specific BV were 4.5% lower and 7.3% higher than those using the two other BVs, respectively.ConclusionLacunar infarction was associated with reduced carotid arterial shear stress. The use of estimated BV for calculating carotid arterial shear stress provides more accurate assessment of the hemodynamic contribution of shear stress than previous models that have arbitrarily assigned a constant value to this dynamic flow property.