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Physiological Significance of Helical Flow in the Arterial System and its Potential Clinical Applications
Abstract and Figures
Helical flow in the human aorta is possibly a typical example of 'form follows function' in the vascular system. The helical blood flow may provide guaranties for the inner surface of the ascending aortic wall to get smooth and even washing by the blood so that atherosclerotic plaques can hardly form in the area of the ascending aorta. It has been documented that the phenomenon of helical flow of blood is not just localized in the ascending aorta, it also exists in several large arteries and veins as well. Preliminary studies demonstrated the widely existing helical flow might play positive physiological roles in facilitating blood flow transport, suppressing disturbed blood flow, preventing the accumulation of atherogenic low density lipoproteins on the luminal surfaces of arteries, enhancing oxygen transport from the blood to the arterial wall and reducing the adhesion of blood cells on the arterial surface. These roles of helical blood flow may lessen the burden of arteries and protect the arteries from the pathology of atherosclerosis, thrombosis, and intimal hyperplasia. The great development of time-resolved three-dimensional phase contrast MRI (flow-sensitive 4D-MRI) and the advent of dimensionless indices such as helical flow index proposed to characterize helical flow make clinic quantification of the helical flow in the human large arteries possible. Moreover, researchers probed into the possibility to apply the mechanism of helical flow to the design of vascular interventions to reduce thrombus formation and intimal hyperplasia caused by abnormal flow conditions.
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... The high-flow environment of the ascending aorta, characterized by the large blood flow, the high blood pressure and high shear stress, theoretically serves as a protective mechanism against stasis and thrombosis, and contributes to the scarcity of mural thrombi at the proximal ascending aorta. Also, the helical blood flow in the ascending aorta protects the aortic wall from atherosclerosis, thrombus formation, and intimal proliferation [14]. On the other hand, the Valsalva sinuses in the aortic root complex has been reported to alleviate the high sheer stress of the aortic root. ...
Background
Acute coronary syndrome due to coronary artery embolism in the setting of ascending aortic thrombus is an uncommon condition, even rarer when there is no aortic pathology such as aneurysm, severe atherosclerosis, aortic dissection, or thrombophilia (whether inherited or acquired).
Case presentation
We report a case of a 58-year-old male presented with acute chest pain, electrocardiogram showing non-ST-elevation acute coronary syndrome. The computed tomography angiography of coronary artery revealed a mural thrombus in the proximal part of ascending aorta, located above the left coronary artery ostium, without any aortic pathologies. With the exception of hypertension and cigarette smoking, no other risk factors were identified in this patient that may increase the risk of thrombosis. Given the life-threatening risk of interventional therapy and surgery, the patient determinedly opted for anticoagulant and dual antiplatelet therapy. Then he experienced the reoccurrence of chest pain after 6-day treatment, progressed to anterior and inferior ST-segment elevation myocardial infarction. Coronary artery embolism originating from the ascending aortic thrombus was suspected. Considering the hemodynamic instability of the patient, the medical treatment was continued and bridged to warfarin and aspirin after discharge. Follow-up computed tomography angiography at 6 months showed no obstruction in coronary artery and complete resolution of the thrombus. No thromboembolic events occurred henceforward.
Conclusions
Acute coronary syndrome could be a manifestation of secondary coronary embolism due to ascending aortic thrombus. Currently, there is no standardized guideline for the treatment of aortic mural thrombus, individualized treatment is recommended. When surgical therapy is not applicable for the patient, anticoagulation and dual antiplatelet treatment are alternative treatments that may successfully lead to the resolution of the aortic thrombus.
... In both swirling jet cases, high flow rates washed out the local vortices near the pump inlet downstream toward the aortic arch and distributed them along the ascending aorta. While CW swirl combines better with the natural CW helical flow of the aorta formed by the curvature of the aorta [19], a suction impeller that rotates in the CCW direction [32] induces a non-physiological helical flow in the descending aorta, which may also affect blood flow to the branching vessels (to the upper body and renal arteries) [17] and should be further studied. Therefore, if a suction pump is considered, it could be better to have a CW swirling flow to better combine with the natural physiological helical flow. ...
Percutaneous mechanical circulatory support (MCS) devices are designed for short-term treatment in cases of acute decompensated heart failure as a bridge to transplant or recovery. Some of the known complications of MCS treatments are related to their hemodynamics in the aorta. The current study investigates the effect of MCS on the aortic flow. The study uses combined experimental and numerical methods to delineate complex flow structures. Particle image velocimetry (PIV) is used to capture the vortical and turbulent flow characteristics in a glass model of the human aorta. Computational fluid dynamics (CFD) analyses are used to complete the 3D flow in the aorta. Three specific MCS configurations are examined: a suction pump with a counterclockwise (CCW) rotating impeller, a suction pump with a clockwise (CW) rotating impeller, and a discharge pump with a straight jet. These models were examined under varying flow rates (1–2.5 L/min). The results show that the pump configuration strongly influences the flow in the thoracic aorta. The rotating impeller of the suction pump induces a dominant swirling flow in the aorta. The swirling flow distributes the incoming jet and reduces the turbulent intensity near the aortic valve and in the aorta. In addition, at high flow rates, the local vortices formed near the pump are washed downstream toward the aortic arch. Specifically, an MCS device with a CCW rotating impeller induces a non-physiological CCW helical flow in the descending aorta (which is opposite to the natural helical flow), while CW swirl combines better with the natural helical flow.
... Hartman E M J et al. used four methodologies to allocate low, mid and high WSS in one dataset of human coronary arteries and investigated the predictive power of low WSS for plaque progression [11]. Many researches show that geometric characteristics are not the only factor affecting local hemodynamics, and unstable blood ow and hemorheology are also the decisive factors [12][13][14]. ...
For atherosclerotic diseases, a large number of associated plaque rather than single plaque are found in diseased vessels during clinic diagnosis. For the study of hemodynamic parameters, this paper uses a simplified model to simulate the fluid-structure interaction during a non-Newtonian blood flowing through arteries with different degrees of stenosis caused by atherosclerosis. The influence of the geometry and location of the anterior plaque on the hemodynamic parameters of the posterior plaque have mainly been discussed. The effects of fluid wall shear stress, gradient, normal stress and shear rate on the posterior plaque were studied by changing of the plaque spacing, the stenosis rate, the spatial angle in diseased artery. The simulation results obtained by the ideal model can reveal more complex blood flow characteristics of arterial stenosis. It shows that with the increase of plaque spacing, V, WSS, WNS and SR increased by an average of about 3.2–6.6%. And when δ1 > 60%, the variables V, WSS, WNS, SR, and WSSG increase by more than 37%.These findings are of great significance to the development and prediction of plaque rupture in the diseased vessels.
... An additional future direction to take is to investigate the hemodynamics in terms of helicity. The beneficial role of helical flow in the human cardiovascular system is well known 33 . Several studies have reported that helical flow may suppress flow disturbances that lead to disturbed shear, thus reducing the onset of NH [34][35][36] . ...
Newly created arteriovenous fistulas (AVFs) often fail to mature for dialysis use due to disturbed blood flow at and near the AVF anastomosis. The disturbed flow inhibits the endothelial nitric oxide synthase (NOS3) pathway, thus decreasing the production of nitric oxide, a vasodilator. Previously, our group reported that NOS3 expression levels affect AVF lumen size in a mouse model. In this study, we performed MRI-based computational fluid dynamics simulations to investigate the hemodynamical parameters (velocity, wall shear stress (WSS), and vorticity) in a mouse AVF model at day 7 and day 21 post-AVF creation using three NOS3 strains: overexpression (OE), knockout (KO), and wild-type (WT) control. This study is the first to reveal hemodynamics over time in mouse AVFs, consider spatial heterogeneity along the vein, and reveal the effect of NOS3 on the natural history of mouse AVF hemodynamics. From day 7 to day 21, OE has smoother streamlines and had significantly lower vorticity and WSS than WT and KO, suggesting that WSS was attempting to return to pre-surgery baseline, respectively. Our results conclude that the overexpression of NOS3 leads to desired optimal hemodynamics during AVF remodeling. Future studies can investigate enhancing the NOS3 pathway to improve AVF development.
This article presents a broad overview of the fluid mechanics of the human cardiovascular system. Beginning in the heart, we travel through the main features of our circulation to highlight important functions and diseases where fluid mechanics plays a central role. Of particular focus is the role of computational modelling in uncovering the dynamic flow phenomenon throughout our body, its association with cardiovascular disease mechanisms and progression and its importance in clinical treatment planning. We also emphasize the multiscale nature of the cardiovascular system, and associated challenges. The main aim of this review is to highlight progress and ongoing challenges in our understanding of cardiovascular haemodynamics, as well as the future outlook for translating the current state-of-the-art to widespread clinical application and improved patient outcomes.
Clinical studies based on coronary computed tomography angiography (CCTA) images suggest that the presence of Ramus Intermedius (RI) in the left coronary artery (LCA) may aggravate the atherosclerotic depositions in the furcation region. In this study, computational fluid dynamics simulations are performed in patient-specific coronary models consisting of bifurcating LCA and two models having trifurcating LCA. Three-dimensional patient-specific coronary models are constructed from CCTA images obtained from NEIGRIHMS Shillong, India. Results indicate that the flow redistribution happens in the left coronary branch due to the presence of RI and the flow to LAD is reduced significantly. Recirculation and flow separation regions are observed in the proximal parts of the left anterior descending artery (LAD) and left circumflex artery (LCX) for trifurcation geometries. The qualitative and quantitative analysis of wall shear stress-based descriptors suggests that the presence of the intermediate branch may affect the atherosusceptibility of the proximal region of LAD. The study indicates that the presence of RI may act as a contributing factor for plaque development and progression in the furcation region and proximal parts of LAD.
The carotid artery sinus is often the site of vascular diseases such as atherosclerosis, which may induce cerebral stroke. Individual differences in the carotid artery can lead to different possibilities for atherosclerosis, and the different hemodynamics of the carotid artery with stenosis can help to reveal the occurrence of atherosclerosis. In this work, the hemodynamics in the patient-specific carotid bifurcation are studied by using the modified Herschel–Bulkley model. Calculations show that the helical flow is presented in the healthy carotid sinus and disappears in the stenosed carotid sinus. The disappearance of helical flow in the carotid artery enhances the risk of atherosclerosis. The atherosclerotic lesion is more prone to occur in the distal portion of the carotid sinus than in the proximal portion where the oscillatory shear index (OSI) is also high. The presence of stenosis makes the atherosclerotic lesion develop toward the proximal portion. The disappearance of helical flow in the carotid artery is an important risk signal for the occurrence of atherosclerosis.
The cross-limb (CL) technique is a commonly used endovascular treatment for addressing unfavorable anatomical features in patients with abdominal aortic aneurysm (AAA). The configuration of CL stent-graft plays a critical role in determining the postoperative hemodynamic properties and physiological behaviors, which ultimately impact the efficacy and safety of endovascular AAA treatment. This study aims to investigate the relationship between hemodynamics and CL stent-graft configuration from a hemodynamic perspective.
Five distinct geometric models of cross-limb (CL) stent-graft configurations were constructed by optimizing the real clinical computed tomography angiography (CTA) data. These models varied in main body lengths and cross angles and were used to perform numerical simulations to analyze various hemodynamic parameters. Flow pattern, distribution of wall shear stress (WSS)-related parameters, localized normalized helicity (LNH), pressure drop, and the displacement force of all models were examined in this paper.
In patient-specific cases, helical flow and WSS increase with the main body. However, it also generated secondary flow in localized areas, leading to increased oscillation in the WSS direction. Notably, increasing the stent graft’s main body length or decreasing the cross angle reduced the displacement force exerted on the stent-graft. Reducing the cross angle did not significantly alter the hemodynamic characteristics.
In the clinical practice of CL deployment, it is crucial to carefully consider the stent-graft configuration and the patient specific to achieve optimal postoperative outcomes. This study provides valuable insights for guiding stent selection and treatment planning in patients with abdominal aortic aneurysm undergoing CL techniques, from a hemodynamic perspective.
Atherosclerosis, the leading cause of death in the developed world and
nearly the leading cause in the developing world, is associated with systemic
risk factors including hypertension, smoking, hyperlipidemia, and diabetes
mellitus, among others. Nonetheless, atherosclerosis remains a geometrically
focal disease, preferentially affecting the outer edges of vessel bifurcations.
In these predisposed areas, hemodynamic shear stress, the frictional force
acting on the endothelial cell surface as a result of blood flow, is weaker
than in protected regions. Studies have identified hemodynamic shear stress
as an important determinant of endothelial function and phenotype. Arterial-level
shear stress (>15 dyne/cm2) induces endothelial quiescence and
an atheroprotective gene expression profile, while low shear stress (<4
dyne/cm2), which is prevalent at atherosclerosis-prone sites, stimulates
an atherogenic phenotype. The functional regulation of the endothelium by
local hemodynamic shear stress provides a model for understanding the focal
propensity of atherosclerosis in the setting of systemic factors and may help
guide future therapeutic strategies.
Magnetic resonance imaging (MRI) has become an important tool for the clinical evaluation of patients with cardiovascular disease. Since its introduction in the late 1980s, 2-dimensional phase contrast MRI (2D PC-MRI) has become a routine part of standard-of-care cardiac MRI for the assessment of regional blood flow in the heart and great vessels. More recently, time-resolved PC-MRI with velocity encoding along all three flow directions and three-dimensional (3D) anatomic coverage (also termed '4D flow MRI') has been developed and applied for the evaluation of cardiovascular hemodynamics in multiple regions of the human body. 4D flow MRI allows for the comprehensive evaluation of complex blood flow patterns by 3D blood flow visualization and flexible retrospective quantification of flow parameters. Recent technical developments, including the utilization of advanced parallel imaging techniques such as k-t GRAPPA, have resulted in reasonable overall scan times, e.g., 8-12 minutes for 4D flow MRI of the aorta and 10-20 minutes for whole heart coverage. As a result, the application of 4D flow MRI in a clinical setting has become more feasible, as documented by an increased number of recent reports on the utility of the technique for the assessment of cardiac and vascular hemodynamics in patient studies. A number of studies have demonstrated the potential of 4D flow MRI to provide an improved assessment of hemodynamics which might aid in the diagnosis and therapeutic management of cardiovascular diseases. The purpose of this review is to describe the methods used for 4D flow MRI acquisition, post-processing and data analysis. In addition, the article provides an overview of the clinical applications of 4D flow MRI and includes a review of applications in the heart, thoracic aorta and hepatic system.
In this study, magnetic resonance imaging techniques have been used to
examine the geometry of arterial curvature and branching in casts and in
vivo, and to measure the distribution of axial velocity in the
associated flow. It is found, contrary to a widely held view, that the
geometry is commonly non-planar. Moreover, relatively small values of
the parameters which render the geometry non-planar appear significantly
to affect the velocity distribution. The findings suggest that
non-planarity is an important factor influencing arterial flows,
including wall shear. The implications are not restricted to vascular
biology, pathology and surgery, but may extend to the design of general
piping systems.
Four-dimensional magnetic resonance MR velocity mapping was developed to study normal now patterns in the thoracic aorta using time-resolved cardiac gated three-directional velocity data. Sixteen normal subjects were studied, one young group (average age 31 years) and one group with elderly people (average age 72 years). Blood flowed in a right-handed helix from the ascending aorta to the aortic arch, A straight flow pattern or a left-handed helix was seen in the descending aorta. Blood now was never parabolic. Blood flowed forward in early systole, retrograde in mid-to-end systole, and forward again in diastole in all subjects as a basic pattern. Continuous retrograde now over a long distance was not seen, but blood entered a retrograde now column at various levels, In young people blood passed from the aortic valve to the mid-descending aorta in less than one heartbeat, In people in their sixties It took two heartbeats and in people older than 78 years, it took three heartbeats. The maximum systolic forward velocities were higher in young subjects than in elderly while the retrograde velocities were lower. (C) 1999 Wiley-Liss, Inc.
Objective: The ideal prosthetic graft to use for lower extremity bypass in patients with no vein conduit is yet to become available. Spiral laminar flow graft (SLFG) was designed to reduce turbulent flow at the distal anastomosis, hence reducing neointimal hyperplasia to improve graft patency. We examined our data for this type of graft and compared it to the Propaten graft by W.L. Gore (PG), which is another polytetrafluoroethylene (ePTFE) graft. Method: Single-center data were retrospectively reviewed for patients undergoing infrainguinal bypass using prosthetic grafts between January 2010 and January 2012. Kaplan-Meier analyses were performed to estimate primary and secondary patency rates for patients undergoing femoral to popliteal artery bypass (above and below the knee) as well as femoral to tibial artery bypass. The same was done for patients undergoing infrainguinal bypass using PG during the same time period. Results: 20 infrainguinal bypasses were performed using SLFG and 39 using PG were identified. A majority of the SLFG cases (14, 70%) were femoral to popliteal bypass (above and below the knee) and 6 cases (30%) were femoral to tibial artery bypass. Similar percentages were seen in the PG group. Statistically, the 6-, 12-, 18-, and 24-month primary and secondary patency rates for both grafts were the same regardless of the distal target artery. The primary patency for the popliteal artery (above and below knee) target group were 94%, 61%, 61%, and 54% for the PG group, and 79%, 50%, 50%, and 50% for the SLFG group, respectively. The secondary patency rates were 94%, 66%, 66%, and 66% for the PG group and 86%, 57%, 57%, and 57% for the SLFG group, respectively. The 6-, 12-, and 18-month primary patency rates for the tibial artery bypass groups were 51%, 36%, and 37% for the PG group and 50%, 33%, and 17% for the SLFG group, respectively. The secondary patency rates were 54%, 34%, and 34% for the PG group and 60%, 40%, and 20% for the SLFG group, respectively. Conclusion: The design of the SLFG to mimic physiologic flow at the distal anastomosis is an interesting concept, but it has not translated into clinical benefit in comparison to another ePTFE graft in our series. Further research and modifications are needed to achieve the ideal graft for infrainguinal arterial bypass.
This paper describes a computational and experimental investigation of flow in a prototype model geometry of a fully occluded 45 deg distal end-to-side anastomosis. Previous investigations have considered a similar configuration where the centerlines of the bypass and host vessels lie within a plane, thereby producing a plane of symmetry within the flow. We have extended these investigations by deforming the bypass vessel out of the plane of symmetry, thereby breaking the symmetry of the flow and producing a nonplanar geometry. Experimental data were obtained using magnetic resonance imaging of flow within perspex models and computational data were obtained from simulations using a high-order spectral/hp element method. We found that the nonplanar three-dimensional flow notably alters the distribution of wall shear stress at the bed of the anastomosis, reducing the peak wall shear stress peak by approximately 10 percent when compared with the planar model. Furthermore, an increase in the absolute flux of velocity into the occluded region, proximal to the anastomosis, of 80 percent was observed in the nonplanar geometry when compared with the planar geometry.
• Five types of 4-mm diameter arterial prostheses (three Dacron, one expanded Teflon, one preserved umbilical vein) were studied in the dog to assess graft thrombogenicity. Separate experiments involving six hours of controlled blood flow, one-week carotid implantation, and aortocoronary implantation were performed. In general, graft thrombogenicity derived from controlled flow study was more predictive of a graft's long-term implantation success than were one-week implantation results. In order of increasing thrombogenicity, we ranked grafts studied as follows: noncrimped Dacron, expanded Teflon, crimped Dacron, umbilical vein. Results of 19 experimental left coronary artery implantations using Dacron or Teflon prostheses are reported that indicate grafts with low measured thrombogenicity are most likely to succeed in this site. Data presented in this report suggest there is reason to evaluate noncrimped, kinkresistant, porous Dacron grafts for use both in the left coronary artery and below the knee when there is compelling clinical indication and no autogenous vessels are available.
(Arch Surg 114:687-691, 1979)
We thank Hope and colleagues for their interesting and pertinent letter on our recent study in patients with bicuspid aortic valve (BAV), in which the relationship between bicuspid aortic valve morphology, the resulting flow patterns, and the aortopathy phenotype was examined.1 To confirm their initial comment, indeed, the ascending aortic flow displacement parameter was not normalized to the individual vessel diameter. We agree with Hope et al that flow displacement should ideally be normalized by the lumen diameter to account for interindividual differences in aortic geometry. Nonetheless, aortic diameters in the aorta size control group and the BAV patient groups in our study cohort were similar (4.1 versus 4.0 cm, respectively). Thus, the process of normalization did not affect the …
Aortic 3D blood flow was analyzed to investigate altered ascending aorta (AAo) hemodynamics in bicuspid aortic valve (BAV) patients and its association with differences in cusp fusion patterns (right-left, RL versus right-noncoronary, RN) and expression of aortopathy.
4D flow MRI measured in vivo 3D blood flow in the aorta of 75 subjects: BAV patients with aortic dilatation stratified by leaflet fusion pattern (n=15 RL-BAV, mid AAo diameter=39.9±4.4mm; n=15 RN-BAV, 39.6±7.2mm); aorta size controls with tricuspid aortic valves (n=30, 41.1±4.4mm); healthy volunteers (n=15, 24.9±3.0mm). Aortopathy type (0-3), systolic flow angle, flow displacement, and regional wall shear stress (WSS) were determined for all subjects. Eccentric outflow jet patterns in BAV patients resulted in elevated regional WSS (p<0.0125) at the right-anterior walls for RL-BAV and right-posterior walls for RN-BAV compared to aorta size controls. Dilatation of the aortic root only (type 1) or involving the entire AAo and arch (type 3) was found in the majority of RN-BAV patients (87%) but was mostly absent for RL-BAV (87% type 2). Differences in aortopathy type between RL-BAV and RN-BAV were associated with altered flow displacement in the proximal and mid AAo for type 1 (42-81% decrease versus type 2) and distal AAo for type 3 (33-39% increase versus type 2).
The presence and type of BAV fusion was associated with changes in regional WSS distribution, systolic flow eccentricity, and expression of BAV aortopathy. Hemodynamic markers suggest a physiologic mechanism by which valve morphology phenotype can influence phenotypes of BAV aortopathy.