Duration Of Shear Stress Research Articles

Shear type and magnitude affect aortic valve endothelial cell morphology, orientation, and differentiation.

Valvular endothelial cells line the outer layer of heart valves and can withstand shear forces caused by blood flow. In contrast to vascular endothelial cells, there is limited amount of research over valvular endothelial cells. For this reason, the exact physiologic behavior of valvular endothelial cells is unclear. Prior studies have concluded that valvular endothelial cells align perpendicularly to the direction of blood flow, while vascular endothelial cells align parallel to blood flow. Other studies have suggested that different ranges of shear stress uniquely impact the behavior of valvular endothelial cells. The goal of this study was to characterize the response of valvular endothelial cell under different types, magnitudes, and durations of shear stress. In this work, the results demonstrated that with increased shear rate and duration of exposure, valvular endothelial cells no longer possessed the traditional cuboidal morphology. Instead through the change in cell circularity and aspect ratio, valvular endothelial cells aligned in an organized manner. In addition, different forms of shear exposure caused the area and circularity of valvular endothelial cells to decrease while inducing mesenchymal transformation validated through αSMA and TGFβ1 expression. This is the first investigation showing that valvular endothelial cells alignment is not as straightforward as once thought (perpendicular to flow). Different types and magnitudes of shear induce different local behaviors. This is also the first demonstration of valvular endothelial cells undergoing EndMT without chemical inducers on a soft surface in vitro. Findings from this study provide insights to understanding the pathophysiology of valvular endothelial cells which can potentially propel future artificial engineered heart valves.

Effect of low wall shear stress on the morphology of endothelial cells and its evaluation indicators

ObjectiveThis study is designed to explore the morphological changes of endothelial cells (ECs) under different levels of shear stress and find the effective evaluation indicators with in vivo and in vitro experiments. MethodsHuman umbilical vein endothelial cells (HUVECs) and Sprague–Dawley rats were used to study the effect of different shear stress which applied by means of parallel plate-flow chamber and abdominal aorta banding model on the morphology of endothelial cells. Then, fluorescence images were acquired by means of a confocal laser-scanning microscope. Finally, Cell morphological indicators were extracted by SRAD-MCW computer image processing algorithm for quantitative analysis. Results1) The morphological changes of HUVECs were observed after exposure to shear stress for 6 h, the HUVECs were elongated and spindle-shaped. And the degree of cell deformability was different while the exposure time was different, then it became stable after 18 h. The HUVECs exposure to high shear stress (HSS) exhibited an ordered cell arrangement, while the HUVECs exposure to low shear stress (LSS) showed a disordered cell arrangement. 2) Traditional cell morphological indicators such as area, perimeter, long axis diameter, short axis diameter and orientation angle were not significantly different between the normal shear stress (NSS) group and the LSS group (P > 0.05), but the intercellular space characteristics such as the junction length per unit area and the triple points per unit area were significantly different (P < 0.05). ConclusionThese results demonstrate that the size and duration of shear stress can affect the morphology and arrangement of endothelial cells. The commonly used evaluation indicators for studying the effect of shear stress on the morphology of endothelial cells, including area, perimeter, long axis diameter, short axis diameter and orientation angle, etc., had no significant statistical significance, while the intercellular space characteristics including the junction length per unit area and the triple points per unit area can be used as effective indicator to study the effect of shear stress on the morphology of endothelial cells.

Hemolysis associated with Impella heart pump positioning: In vitro hemolysis testing and computational fluid dynamics modeling.

Short-term mechanical circulatory support devices provide temporary hemodynamic support in heart failure and are increasingly used to enable recovery or as a bridge to decision. Blood damage with mechanical circulatory support devices is influenced by many factors, including the magnitude and duration of shear stress and obstruction to blood flow. This study aimed to evaluate the effects of the Impella CP® heart pump positioning on hemolysis using in vitro hemolysis testing and computational fluid dynamics modeling. The in vitro hemolysis testing was conducted per the recommended Food and Drug Administration and American Society for Testing and Materials guidelines. The bench hemolysis testing and computational fluid dynamics simulation analysis were performed for both normal operating (outlet unobstructed) and outlet-obstructed condition of Impella CP (mimicking outlet on the aortic valve due to improper positioning). The modified index of hemolysis was 2.78 ± 0.69 at normal operating conditions compared to 18.7 ± 7.8 when the Impella CP outlet was obstructed (p = 0.002). Computational fluid dynamics modeling showed about three times increase in exposure time to regions of high shear stress when the Impella CP outlet was obstructed compared to unobstructed condition, thus supporting the experimental observations. Based on these results, it is recommended to ensure proper placement of Impella CP via regular monitoring using echocardiographic guidance or other methods to minimize the risk of hemolysis associated with an obstructed outflow.

Hydrologic-hydraulic modeling of sediment transport along the main stem of a watershed: role of tributaries and channel geometry

ABSTRACTCurrent estimations of sediment transport at the watershed scale are limited by the difficulty of accurately simulating the sediment transfer along the main stem. The typical approach to simulating watershed sediment transport involves the adoption of hydrologic sediment routing schemes that do not fully capture the contribution and timing of side tributaries, and the inclusion of a simplified channel geometry that does not include its hydraulic feedback. In this paper, we present the results of a coupled hydrologic-hydraulic model of sediment transport applied to a small watershed of Iowa. The model was developed to simulate both the hydrologic network and non-equilibrium sediment transport that occur during a flood. The model results highlight the importance of including side tributaries in order to capture a realistic duration of shear stress that ultimately affects sediment transport. Comparisons with bank erosion measurements indicate that the presented approach is also promising to estimate sediment sources along the main stem.

Shear Stress Analysis of Synthesis and Nitric Oxide Release from Huvecs Exposed to Supraphysiologic Glucose

The purpose of this study is to analyze the magnitude and duration of shear stress in normal endothelial cell (HUVECs) cultures and those exposed to supraphicological glucose which affected synthesis and release of NO detected by bioassay techniques. The results of this study concluded that large shear stress applied to endothelial cell culture for a long time (± 15 minutes) will increase the synthesis and release of NO. In normal endothelial cell culture a large shear stress exposure in a long time can increase NO synthesis and release very significantly compared to low shear stress (6 dyne/cm2 for 5 minutes). Likewise, endothelial cell culture which was exposed to 22 mM glucose for 7 days, giving a large amount of shear stress for a long time (15 minutes) could increase NO synthesis and release, although it was far compared to normal endothelial cell culture. It can be said that the synthesis and release of NO in endothelial dysfunction can be improved through exposure to large and long-standing shear stress.

Prediction of the level and duration of shear stress exposure that induces subhemolytic damage to erythrocytes.

Current generation mechanical circulatory assist devices are designed to minimize high shears to blood for prolonged durations to avoid hemolysis. However, red blood cells (RBC) demonstrate impaired capacity to deform when exposed to shear stress (SS) well below the "hemolytic threshold". We endeavored to identify how changes in the magnitude and duration of SS exposure alter RBC deformability and subsequently develop a model to predict erythrocyte subhemolytic damage. RBC suspensions were exposed to discrete magnitudes of SS (1-64Pa) for specific durations (1-64s), immediately prior to RBC deformability being measured. Analyses included exploring the maximal RBC deformation (EImax) and SS required for half EImax (SS1/2). A surface-mesh was interpolated onto the raw data to predict impaired RBC deformability. When SS was applied at <16Pa, limited changes were observed. When RBC were exposed to 32Pa, mild impairments in EImax and SS1/2 occurred, although 64Pa caused a dramatic impairment of RBC deformability. A clear relation between SS duration and magnitude was determined, which could predict impaired RBC deformability. The present results provide a model that may be used to predict whether RBC deformability is decreased following exposure to a given level and duration of SS, and may guide design of future generations of mechanical circulatory assist devices.

Interspecies diversity of erythrocyte mechanical stability at various combinations in magnitude and duration of shear stress, and osmolality.

We hypothesized that the results of red blood cell mechanical stability test show interspecies differences. The comparative investigations were performed on blood samples obtained from rats, beagle dogs, pigs and healthy volunteers. Mechanical stress was applied in nine combinations: 30, 60 or 100 Pa shear stress for 100, 200 or 300 seconds. Generally, rat erythrocytes showed the highest capability of resistance. With the applied combinations of mechanical stress pig erythrocytes were the most sensitive. On human erythrocytes 60 Pa for 200 s was the minimum combination to result significant deformability deterioration. By increasing the magnitude and duration of the applied mechanical stress we experienced escalating deformability impairment in all species. 100 Pa shear stress for 300 seconds on human erythrocytes showed the largest deformability impairment. The mechanical stability test results were also dependent on osmolality. At hypoosmolar range (200 mOsmol/kg) the mechanical stress improved EI data mostly in rat and porcine blood. At higher osmolality (500 mOsmol/kg), the test did not show detectable difference, while in 250-300 mOsmol/kg range the differences were well observable. In summary, erythrocytes' capability of resistance against mechanical stress shows interspecies differences depending on the magnitude and duration of the applied stress, and on the osmolality.

Pim-1 is up-regulated by shear stress and is involved in shear stress-induced proliferation of rat mesenchymal stem cells

AimsInvestigation of the response of mesenchymal stem cells (MSCs) to vascular mechanical forces is very important in the field of cardiovascular intervention. Ser/Thr-protein kinase Pim-1 is a novel transducer of cell survival and the cell cycle that promotes signals in the hematopoietic cell system. Current studies aim to foster an understanding of Pim-1 expression and regulation in MSCs in response to different durations and strengths of laminar shear stress (SS) and to investigate the role of Pim-1 in SS-induced cell proliferation. Main methodsA parallel-plate flow chamber was used to control the strength and duration of SS. Proliferation was measured with the BrdU cell proliferation assay. The expressions of Pim-1 mRNA and protein were evaluated by reverse transcription-polymerase chain reaction and western blotting, respectively. RNA interference was used to knock down the Pim-1 gene. Key findingsThe results showed that SS up-regulation of Pim-1 mRNA and protein was time-dependent. Pim-1 induction was SS strength-dependent, and the expression level reached a maximum at 30 dynes/cm2. Inhibitors of p38MAPK and ERK attenuated the SS-induced expression of Pim-1. In addition, SS significantly increased BrdU-uptake, which was effectively blocked by the silencing of Pim-1. SignificanceThese results demonstrated that Pim-1 is expressed in MSCs and plays an important role in the SS-induced proliferation of MSCs.

Differential Gene Expression of Integrins Alpha 2 and Beta 8 in Human Mesenchymal Stem Cells Exposed to Fluid Flow

Human bone marrow-derived mesenchymal stem cells (MSCs) have potential applications for tissue engineering because they can differentiate into numerous cell lineages. Mechanical forces and mechanotransduction are important factors influencing cell responses, although such data are limited for MSCs. We investigated the gene expression response of integrin and extracellular matrix (ECM) genes in MSCs exposed to different magnitudes (1, 5, and 10 dyn/cm2) and durations (10 min, 1 h, and 24 h) of fluid flow-induced shear stress. Gene expression was examined using microarray and quantitative real-time RT-PCR analysis. In response to different magnitudes and durations of shear stress, we observed significant differential gene expression for two integrin genes: consistent up-regulation of integrin α2 subunit (ITGA2) [2- to 18-fold] and consistent down-regulation of integrin β8 subunit (ITGB8) [2- to 9-fold]. There was also evidence of ECM gene down-regulation, namely collagen type XI α1 (COL11A1), COL14A1, and COL21A1 (2- to 4-fold for each), and laminin α4 (LAMA4) [2- to 5-fold]. This indicates specific modulation of integrin gene expression in response to shear stress, supporting altered cell–ECM interactions and integrin-mediated mechanotransduction. These findings further our understanding of how mechanical stimuli regulate MSC behavior, which will be important in the development of mechanical conditioning strategies for tissue engineering.

Connexin 43 hemichannel opening associated with Prostaglandin E2 release is adaptively regulated by mechanical stimulation

Osteocytes present in the bone are known to be the major mechanosensory cells. Their involvement in mechanoregulation of bone remodeling is not yet clear. Osteocytes are connected with each other thorough gap junctions formed by Connexin 43 (Cx43). Apart from forming gap junctions; Cx43 in osteocytes is also present in the form of hemichannels. Recently, we have developed a unique antibody that specifically blocks hemichannels and does not have any effect on gap junctions. Cx43 hemichannels present in osteocytes of the bone are mechanosensory in nature as they open when subjected to mechanical stimulation in the form of fluid flow shear stress (FFSS). Opening of Cx43 hemichannels results in the release of molecules like PGE2 that are involved in bone remodeling. Our recent report shows that the opening of Cx43 hemichannels depends on the magnitude and duration of shear stress. When osteocytes are subjected to FFSS followed by a brief incubation and reapplication of FFSS, it led to further increase in opening of Cx43 hemichannels. Application of continuous FFSS for longer periods of time (24 hrs) results in decreased opening of hemichannels. These results show that Cx43 hemichannels are adaptive in response to mechanical stimulation, possibly to regulate the release PGE2 during bone remodeling.

Development of Storm-Water Management Design Criteria to Maintain Geomorphic Stability in Kansas City Metropolitan Area Streams

Fifty-three years of historical precipitation data were applied to the U.S. Environmental Protection Agency Storm Water Management Model (SWMM) to conduct hydrologic and hydraulic simulations, generating continuous stream flow hydrographs in the receiving stream channels. On-site BMP and regional detention criteria were selected to allow postdevelopment replication of predevelopment peak flow frequency exceedance curves and the critical portions of shear stress duration curves. Instream continuous stage data generated by SWMM were used to examine erosion potential through the use of an erosion potential index. Coarse stream bed material were found to be less sensitive to changes in erosion potential due to urbanization, and extended detention ponds designed for flood control and water quality treatment were effective in reducing erosion potential. These controls were less effective in reducing erosion potential of fine loam bed material, indicating reductions of runoff volumes are required to minimize increases in channel erosion. Findings indicate that regional analysis based on local hydrologic and geomorphic characteristics are necessary to identify appropriate storm-water control requirements.

Effects of fluid shear stress on apoptosis of cultured human umbilical vein endothelial cells induced by LPS

The objective of our research was to reveal the effects of shear stress on the apoptosis of cultured human umbilical vein endothelial cells (HUVECs) induced by lipopolysaccharide (LPS). A parallel-plate flow chamber was used to control the strength and duration of shear stress (SS), and apoptosis was measured by immunocytochemistry and radio-immunoassay. Some important conclusions were drawn. In the stationary state, apoptosis of HUVECs could be induced by LPS (50 microg/ml). An SS of 15 dyn/cm(2) could inhibit the apoptosis induced by LPS. However, an SS of 4 dyn/cm(2) had less effect on the same process. At the same time, the experiment demonstrated that the increase in IL-6 secretion by LPS can be inhibited by two different levels of shear stress. Moreover, the inhibition effect was more obvious under high level stress than under low level. We also found that the effect of shear stress on IL-8 was less effective than on IL-6. This research provides data for understanding the mechanism of the contribution of hemodynamic forces to atherosclerosis.

Streamlined shape of endothelial cells

Flow induced shape change is important for spatial interpretation of vascular response and for understanding of mechanotransduction in a single cell. We investigated the possible shapes of endothelial cell (EC) in a mathematical model and compared these with experimental results. The linearized analytic solution from the sinusoidal wavy wall and Stokes flow was applied with the constraint of EC volume. The three dimensional structure of the human umbilical vein endothelial cell was visualized in static culture or after various durations of shear stress (20 dyne/cm2 for 5, 10, 20, 40, 60, 120min). The shape ratio (width: length: height) of model agreed with that of the experimental result, which represented the drag force minimizing shape of stream-lining. EC would be streamlined in order to accommodate to the shear flow environmented by active reconstruction of cytoskeletons and membranes through a drag force the sensing mechanism.

The influence of temperature on red cell deformability

This study was undertaken to examine the influence of temperature on physical properties of red cell membranes. Red cells adhering to cover slips were subjected to fluid shear stress in a rotating disc apparatus for 1 min or for 10 min at temperatures ranging from 2 degrees to 50 degress C. They were fixed while subject to shear stress by addition of glutaraldehyde and then processed for examination and photography by reflected-light microscopy. Cell dimensions were obtained with a computerized planimeter. At shear stresses under 2 dynes/sq cm, cells changed shape from biconcave discs to tear drops, the dimensions of which were influenced very little by temperature or duration of shear stress. Above 2 dynes/sq cm, filamentous processes or “tethers” developed at attachment points of cells to cover slips. Tether length and the percentage of cells possessing tethers increased markedly with increasing temperature and duration of shear stress. At approximately 48 degrees C, a dramatic change occurred over a narrow temperature range such that cells were markedly elongated and irregularly deformed by a shear stress of 1 dyne/sq cm or less. These observations demonstrate that elongation of human red cells subjected to fluid shear stress in a rotating disc system is markedly influenced by temperature as well as by magnitude and duration of shear stress. They also indicate that significant increases in red cell membrane fluidity occur between 2 degrees and 24 degrees-37 degrees C and again between 48 degrees and 50 degrees C.

The Influence of Temperature on Red Cell Deformability

This study was undertaken to examine the influence of temperature on physical properties of red cell membranes. Red cells adhering to cover slips were subjected to fluid shear stress in a rotating disc apparatus for 1 min or for 10 min at temperatures ranging from 2 degrees to 50 degress C. They were fixed while subject to shear stress by addition of glutaraldehyde and then processed for examination and photography by reflected-light microscopy. Cell dimensions were obtained with a computerized planimeter. At shear stresses under 2 dynes/sq cm, cells changed shape from biconcave discs to tear drops, the dimensions of which were influenced very little by temperature or duration of shear stress. Above 2 dynes/sq cm, filamentous processes or "tethers" developed at attachment points of cells to cover slips. Tether length and the percentage of cells possessing tethers increased markedly with increasing temperature and duration of shear stress. At approximately 48 degrees C, a dramatic change occurred over a narrow temperature range such that cells were markedly elongated and irregularly deformed by a shear stress of 1 dyne/sq cm or less. These observations demonstrate that elongation of human red cells subjected to fluid shear stress in a rotating disc system is markedly influenced by temperature as well as by magnitude and duration of shear stress. They also indicate that significant increases in red cell membrane fluidity occur between 2 degrees and 24 degrees-37 degrees C and again between 48 degrees and 50 degrees C.