Pulsatile Research Articles

Experimental study of parametric vibrations of arc-shaped tubes with pulsating fluid flow

The dynamics of curved tubes with fluid flow fixed on both sides was studied experimentally. Two cases were studied in which the curved tubes differed in curvature. Tests were performed with the flow without pulsation to determine the natural frequencies and with pulsation to determine the interesting dynamic phenomena occurring in the system. Two alternative measurement systems were used to study the motion of the tubes, a contact one based on accelerometers and a non-contact one based on optical technology. Acceleration and displacement time-series were analysed to determine the nature of the motion of the tubes. It was confirmed that the eigenfrequencies of the curved systems are insensitive to flow velocity which is consistent with the extensible centreline hypothesis. The interesting dynamics of tubes with pulsatile flow, the possibility of excitation of simple, combination parametric resonances, including several different combination resonances simultaneously, were identified. The vibrations in the simple resonances were polyharmonic and in the combination resonances quasi-periodic. The motion of the tubes was three-dimensional in nature and its complexity increased with increasing excitation amplitude. It was found that increasing the curvature of the tube reduced the possibility of excitation of parametric vibration.

Choice of hybrid interventions for iliac-femoral arterial lesions

To compare the short-term and long-term outcomes of hybrid interventions after various infrainguinal reconstructions (restoration of blood flow through superficial femoral artery and pulsatile blood flow through deep femoral artery) in patients with iliac-femoral arterial disease. A retrospective analysis included patients after hybrid iliac-femoral interventions between 2014 and 2018. These interventions included stenting of iliac arteries and various open infrainguinal reconstructions. The first group (n=41) consisted of patients who underwent reconstruction of superficial femoral artery, the second group (n=88) - restoration of pulsatile blood flow in deep femoral artery. We analyzed the Rutherford score, perioperative complications, primary patency rates and limb salvage rates after 12 months in both groups. Significant improvement (Rutherford score +3) was achieved in 28 (70%) and 14 (15.9%) patients, respectively (p<0.05). There were no significant between-group differences in the number of postoperative complications. Surgery time was longer in the first group (median 160 and 130 min, respectively, p<0.05). However, intraoperative blood loss was similar. Primary patency rates after 12 months were 82.4% and 95.1%, respectively (p=0.054). Limb salvage rates after 12 months were 94.7% and 100%, respectively (p<0.05). This study highlights the potential advantages of restoring pulsatile blood flow through the deep femoral artery in hybrid interventions. Higher primary patency and limb salvage rates in the second group indicate better long-term outcomes after restoration of blood flow through the deep femoral artery. Further prospective studies are needed to confirm these results and determine the underlying mechanisms of differences.

Computational analysis of patient-specific pulsatile blood flow: The influence of non-Newtonian models on wall shear stress assessment

Blood is a sophisticated biological fluid with components like erythrocytes that give it non-Newtonian behavior. Hemodynamic factors such as velocity magnitude, pressure, and wall shear stress descriptors are the most important factors in the development of atherosclerosis. The wall shear stress descriptors are regulated not only by flow geometry but also by blood rheological properties. In the current study, we carried out a numerical analysis of the non-Newtonian pulsatile blood flow while taking into account a patient-specific geometry and transient boundary conditions. Non-Newtonian blood flow is modeled using the four non-Newtonian models: the power-law model, the Carreau model, the Casson model, and the Quemada model, and compared with the Newtonian model. Streamline analysis vividly illustrates velocity patterns, revealing the presence of recirculation zones near sinus regions. The study suggests the significance of selecting appropriate viscosity models for accurate assessments, particularly in regions with low time-average wall shear stress values, such as those associated with atherosclerotic plaques. The differences in the time-averaged wall shear stress between the four non-Newtonian models were found to be the highest in the Quemada model. The study concluded that the non-Newtonian model is required when the focus is on the low-time-averaged wall shear stress area.

An assessment of the suitability of a Liebau pump in biomedical applications

Impedance pumping and asymmetric pumping are the main mechanisms of the Liebau effect, a type of valveless pumping. The primary objective of this study is to enhance the current understanding of the mechanics and functionality of a Liebau pump. To achieve this, a prototype pump is constructed, incorporating several novel features: a pinch frequency control system to optimize pump performance, a planar actuator developed using soft robotic technology, and a compliant chamber designed to mitigate flow fluctuations and prevent reverse flow, a common feature of this pumping method. Experimental tests conducted with this prototype demonstrate that the Liebau pump holds potential as a viable technology for fluid pumping in biomedical applications, especially when pulsatile flow is essential or when hemolysis needs to be minimized.

Merging inline crystallization and pulsed flow operation to enable enantiospecific solid state photodecarbonylation

Photoelimination of α-chiral ketones in the solid state results in highly regio- and enantiospecific C–C bond formation. By combining inline crystallisation and pulsatile flow, the photochemistry of these slurries can now be run fully continuously.

In vitro study of flow characteristics in abdominal aortic aneurysm

Hemodynamic factors play a key role in the endovascular aneurysm repair of abdominal aortic aneurysm (AAA). This study conducts an in vitro experiment in which a circulating platform for the experiment and modeling of the pulsatility of blood flow in the human body is established and combined with particle image velocimetry The characteristic parameter distribution of intra-tumoral flow under nonsteady conditions is investigated. Results show that counterflow is a crucial factor affecting the distribution of characteristics of nonsteady intra-tumoral flow, and the presence of single-peak pulsatile flow with counterflow causes the effects of counterflow to emerge at the tumor inlet from the near-wall region and then erode gradually to the streamwise flow region. The maximum intra-tumoral shear stress is found to be located at the near-wall region at the tumor inlet and outlet, and the counterflow formed from the attachment of vortices at the near-wall region leads to the drastic change of the intra-tumoral flow state. The results of the present experiment are useful for quantitatively evaluating the key areas of stress distribution in AAA, providing a basis for preventing risks during the implantation of medical devices.

Exploring therapy transport from implantable medical devices using experimentally informed computational methods.

Implantable medical devices that can facilitate therapy transport to localized sites are being developed for a number of diverse applications, including the treatment of diseases such as diabetes and cancer, and tissue regeneration after myocardial infraction. These implants can take the form of an encapsulation device which encases therapy in the form of drugs, proteins, cells, and bioactive agents, in semi-permeable membranes. Such implants have shown some success but the nature of these devices pose a barrier to the diffusion of vital factors, which is further exacerbated upon implantation due to the foreign body response (FBR). The FBR results in the formation of a dense hypo-permeable fibrous capsule around devices and is a leading cause of failure in many implantable technologies. One potential method for overcoming this diffusion barrier and enhancing therapy transport from the device is to incorporate local fluid flow. In this work, we used experimentally informed inputs to characterize the change in the fibrous capsule over time and quantified how this impacts therapy release from a device using computational methods. Insulin was used as a representative therapy as encapsulation devices for Type 1 diabetes are among the most-well characterised. We then explored how local fluid flow may be used to counteract these diffusion barriers, as well as how a more practical pulsatile flow regimen could be implemented to achieve similar results to continuous fluid flow. The generated model is a versatile tool toward informing future device design through its ability to capture the expected decrease in insulin release over time resulting from the FBR and investigate potential methods to overcome these effects.

Advancement in CFD and Responsive AI to Examine Cardiovascular Pulsatile Flow in Arteries: A Review

Advancement in CFD and Responsive AI to Examine Cardiovascular Pulsatile Flow in Arteries: A Review

Influence of Ohmic heating and thermal radiation on chemically reactive pulsatile flow of Casson nanofluid in a vertical porous channel embedded in non-Darcy porous medium

Influence of Ohmic heating and thermal radiation on chemically reactive pulsatile flow of Casson nanofluid in a vertical porous channel embedded in non-Darcy porous medium

Arterial Mechanical Effects of Fluid-Structure Interaction on a Stenosed Carotid Blood Pulsatile Flow under Pressure Conditions of Normal and Hypertension

Arterial Mechanical Effects of Fluid-Structure Interaction on a Stenosed Carotid Blood Pulsatile Flow under Pressure Conditions of Normal and Hypertension

Association Between Kidney Disease Index and Decline in Cognitive Function with Mediation by Arterial Stiffness in Asians with Type 2 Diabetes.

Decline in renal function impairs systemic clearance of amyloid-β which characterizes Alzheimer's disease while albuminuria is associated with blood-brain barrier disruption due to endothelial damage. Arterial stiffness adversely affects the brain with high pulsatile flow damaging cerebral micro-vessels. To examine association between a novel kidney disease index (KDI), which is a composite index of estimated glomerular filtration (eGFR) and urinary albumin-to-creatinine ratio (uACR), and cognitive function with potential mediation by arterial stiffness. This was a longitudinal multi-center study of participants with type 2 diabetes (T2D) aged 45 years and above. We assessed cognitive function with Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). Pulse wave velocity (PWV), an index of arterial stiffness, was measured using applanation tonometry method. KDI was calculated as geometric mean of 1/eGFR and natural logarithmically-transformed (ln)(ACR*100). There were 1,303 participants with mean age 61.3±8.0 years. LnKDI was associated with lower baseline RBANS total score with adjusted coefficient -2.83 (95% CI -4.30 to -1.35; p < 0.001). 590 participants were followed over up to 8.6 years. LnKDI was associated with lower follow-up RBANS score in total, immediate memory, visuo-spatial/construction and attention domains with corresponding adjusted coefficients -2.35 (95% CI -4.50 to -0.20; p = 0.032), -2.93 (95% CI -5.84 to -0.02; p = 0.049), -3.26 (95% CI -6.25 to -0.27; p = 0.033) and -4.88 (95% CI -7.95 to -1.82; p = 0.002). PWV accounted for 19.5% of association between and follow-up RBANS total score. KDI was associated with lower cognitive function globally, and in immediate memory, visuo-spatial/construction and attention domains. Arterial stiffness mediated the association between KDI and cognitive decline in patients with T2D.

Hemodynamic analysis of left ventricular unloading with Impella versus IABP during VA-ECMO

Purpose The utilization of intra-aortic balloon pump (IABP) and Impella has been suggested as means of left ventricular unloading in veno-arterial extracorporeal membrane oxygenation (VA-ECMO) patients. This study aims to assess the local hemodynamic alterations in VA-ECMO patients through simulation analyses. Methods In this study, a 0D-3D multiscale model was developed, wherein resistance conditions were employed to define the flow-pressure relationship. An idealized model was employed for the aorta, and simulations were conducted to contrast the hemodynamics supported by two configurations: VA-ECMO combined with IABP, and VA-ECMO combined with Impella. Results Relative to VA-ECMO alone, the combination treatment had the following differences:(1) Overall mean mass flow rate increased significantly when combined with Impella and did not change significantly when combined with IABP. Blood flow pulsatility was the strongest in ECMO+IABP, and blood flow pulsatility was significantly suppressed in ECMO+Impella. (2) For all arterial inlets, HI was decreased with ECMO+Impella and increased with ECMO+IABP. (3) The flow field did not change much with ECMO+IABP, with better blood flow compliance, whereas the flow field was relatively more chaotic and disorganized with ECMO+Impella. (4) The difference between shear stress values in ECMO+IABP and ECMO alone was small, and ECMO+Impella (P6) had the largest shear stress values. Conclusions Variances in hemodynamic efficacy between VA-ECMO combined with IABP and VA-ECMO combined with Impella may underlie divergent prognoses and complications. The approach to ventricular unloading during ECMO and the degree of support should be meticulously tailored to individual patient conditions, as they represent pivotal factors influencing vascular complications.

Investigation of Two-Way Fluid-Structure Interaction of Blood Flow at Different Temperature using CFD

At this work, fluid-structure interaction was used to biomechanical challenges relating to blood flow in artery bifurcation to investigate potential solutions. The purpose of this study was to evaluate the influence that artery geometry has under constant flow, pulsatile flow, and varied blood temperatures. In this study, the flow of blood through the artery was simulated using a non-Newtonian fluid model, and the finite element technique was utilized to analyse the data. For the purpose of analysing the differences between pulsatile flow and steady flow, a user-defined function, or UDF, was developed as part of the suggested input velocity model. In order to accurately estimate the pressure distribution, velocity flow, wall shear stress, and wall deformation, a simulation called ANSYS 17.2 is used to model the fluid-structure interaction that occurs when blood flow is superimposed on an arterial wall. According to the findings, the pressure amplitude steadily increases in the artery zone for high temperatures, demonstrating that the projected pressure is 15% greater than it was when the temperature was low. This is in contrast to the low temperature, for which the predicted pressure was 15% lower. In addition, the area close to the apex has the highest levels of shear stress, which then drop down precipitously farther along the wall until they reach an almost constant level. In general, the location of maximum total deformation is shown at peak systole for the artery when the temperature is high. This is the location where the pressure is high, particularly at the artery bifurcation, and where there is a maximum wall deformation of 0.447 mm. In addition, this is the location where the maximum total deformation occurs. These findings are of great use in the design of arterial bifurcation as well as the assessment of recurrent mechanical loads, both of which contribute to the prediction of life.

Influence of Fluid Rheology on Blood Flow Haemodynamics in Patient-Specific Arterial Networks of Varied Complexity – In-Silico Studies

Abstract Results obtained with computational fluid dynamics (CFD) rely on assumptions made during a pre-processing stage, including a mathematical description of a fluid rheology. Up to this date there is no clear answer to several aspects, mainly related to the question of whether and under what conditions blood can be simplified to a Newtonian fluid during CFD analyses. Different research groups present contradictory results, leaving the question unanswered. Therefore, the objective of this research was to perform steady-state and pulsatile blood flow simulations using eight different rheological models in geometries of varying complexity. A qualitative comparison of shear- and viscosity-related parameters showed no meaningful discrepancies, but a quantitative analysis revealed significant differences, especially in the magnitudes of wall shear stress (WSS) and its gradient (WSSG). We suggest that for the large arteries blood should be modelled as a non-Newtonian fluid, whereas for the cerebral vasculature the assumption of blood as a simple Newtonian fluid can be treated as a valid simplification.

A Rare Case of Symmetrical Peripheral Gangrene in Central Venoarterial Extracorporeal Membrane Oxygenator in a Pediatric Patient, an Unusual Complication of Extracorporeal Membrane Oxygenation

Symmetrical peripheral gangrene is an unusual complication of extracorporeal membrane oxygenation (ECMO) which can arise due to low cardiac output state, high inotropic support, inadequate anticoagulation, disseminated intravascular coagulation, and sepsis. In symmetrical peripheral gangrene, there is no evidence of large vessel occlusion or vasculitis. It can be due to the absence of pulsatile flow in the peripheral arteries that result in stasis and microthrombi formation which causes occlusion of small arterioles. A 10-month-old male child who underwent anomalous left coronary artery from pulmonary artery repair and required central venoarterial ECMO support post-surgery due to severe myocardial dysfunction developed symmetrical peripheral ischemia with gangrenous changes in the right-hand fingers while on extracorporeal membrane oxygenation (ECMO). The limb ischemic changes improved to normal after the child convalesced from heart failure. We describe these changes and the management here.

Cardiopulmonary Bypass Settings for the Prevention of Early Hypotension During CABG.

Vasoplegic syndrome is a form of vasodilatory shock that can occur before, during or after cardiopulmonary bypass (CPB). We introduce a strategy to reduce the incidence of early hypotension phenomena during Coronary Artery Bypass Graft (CABG) procedures. In this prospective cohort study, 100 patients underwent elective CABG with two perioperative CPB settings. The study group (50 patients) was managed with retrograde autologous priming (RAP), 3-minute stepwise for the institution of CPB, and pulsatile flow (PP). The control group (50 patients) was managed without RAP, with the rapid initiation of CPB, and non-pulsatile (NP) flow. The primary endpoints were MAP (mmHg), number of hypotensive phenomena (MAP < 50 mmHg for > 30 sec), the venous return volume on CPB (ml), the cardiac index (L/min/m2), hemoglobin (g/dL), indexed oxygen delivery (DO2i, ml/min/m2), the systemic vascular resistance index (SVRI, dynes s m2/cm5), number of 1-ml boluses of a vasoactive substance (norepinephrine), the positive fluid balance (ml), and the number of red blood cell units for transfusion. During CPB, the mean values in the study and control groups were as follows: MAP, 68± 7 vs 56 ± 7 (p-value, 0.0019); hypotensive phenomena, 3 ± 1 vs 8 ±2 (p-value, 0.019); venous return volume, 840±79 vs 1129 ±123 (p-value, 0.0017); cardiac index, 2.4 ± 0.4 vs 2.7 ±0.2 (p-value, 0.0023); hemoglobin, 9.13 ± 0.29 vs 7.8± 0.23 (p-value, 0.0001); DO2i, 301± 12 vs 276±23 (p-value, 0.0011); SVRI, 1879 ±280 vs 2210 ±140 (p-value, 0.0017); norepinephrine, 1±2 vs 8 ±3 (p-value, 0.0023); positive fluid balance, 750 ±212 vs 1450 ±220 (p-value, 0.005); and total number of red blood cell units for transfusion, 16 ±4.2 vs 27 ± 5.3 (p-value, 0.008). In this prospective cohort study, during CPB, the study group showed a better preservation of MAP, SVRI, and DO2i, and a reduction of vasoconstrictor use in a CPB setting with the RAP technique, 3-minute stepwise for the initiation of CPB and pulsatile pump flow, compared to the control group. Further studies are needed to validate this perioperative approach to CPB.

Aortic Characteristic Impedance and Suspected Mild Cognitive Impairment in a Community-Based Healthy Population.

Aging of the proximal aorta can lead to increased pressure and flow pulsatility in the cerebral microcirculation, which may cause cognitive impairment. This study investigated the association between aortic characteristic impedance (Zc), an indicator of regional stiffness of the proximal aorta, and suspected mild cognitive impairment (MCI), compared with carotid-femoral pulse wave velocity (CFPWV). A total of 1461 healthy community residents (46.4% men; age range, 35-96 years [mean±SD, 59.9±11.8 years]) without a history of cardiovascular events or stroke were included in the study. Zc was estimated using applanation tonometry and echocardiography. Cognitive function was assessed using the Mini-Mental State Examination. Education-adjusted cut points were used to define suspected MCI. Subjects with suspected MCI (n=493 [33.7%]) had significantly higher Zc and CFPWV than those without. In multivariable analysis, both Zc and CFPWV were inversely associated with Mini-Mental State Examination score. Zc (odds ratio per 1 SD, 1.22 [95% CI, 1.09-1.37] and CFPWV (odds ratio per 1 SD, 1.18 [95% CI, 1.01-1.38]) was also significantly associated with suspected MCI, after adjusting for age, sex, education level, mean arterial pressure, hypertension, diabetes, low-density lipoprotein cholesterol, and smoking status. In joint analysis, Zc was significantly associated with suspected MCI, but CFPWV was not. In the age subgroups of <50 years and 50 to 70 years, only Zc was significantly associated with suspected MCI. This study found that Zc was significantly associated with Mini-Mental State Examination score and suspected MCI, especially in younger and middle-aged adults. These findings suggest that Zc may be a useful biomarker for identifying individuals at risk for MCI.

Development of an in vitro setup for flow studies in a stented carotid artery bifurcation.

To investigate flow conditions in a double-layered carotid artery stent, a bench-top in vitro flow setup including a bifurcation phantom was designed and fabricated. The geometry of the tissue-mimicking phantom was based on healthy individuals. Two identical phantoms were created using 3D-printing techniques and molding with PVA-gel. In one of them, a clinically available CGuard double-layer stent was inserted. Measurements were performed using both continuous and pulsatile flow conditions. Blood flow studies were performed using echoPIV: a novel ultrasound-based technique combined with particle image velocimetry. A maximum deviation of 3% was visible between desired and measured flow patterns. The echoPIV measurements showed promising results on visualization and quantification of blood flow in and downstream the stent. Further research could demonstrate the effects of a double-layered stent on blood flow patterns in a carotid bifurcation in detail.

Effect of Vascular Lumen Reduction on the Performance and Energy Consumption of an Innovative Implantable LVAD

This paper presents the results of a study on the effect of vascular lumen reduction on the performance of an innovative implantable LVAD (left ventricular assist device). It details the pressures in the individual cardiac chambers as a function of device frequency. In addition, mass flow rates and energy consumption of the device are examined, varying with lumen reduction and operating frequency. While the lumen reduction of the vessels has little effect on energy consumption, the mass flow rates vary considerably, i.e., above 140 cyc/min, the mass flow rate increment is no longer achieved for specified initial conditions. There are also differences regarding the pressures in the heart; namely, it was found that the pressure plots look similar in all cases, leading to the conclusion that the reduction of the vessel lumen does not affect their shape, but does affect the maximum values of the left ventricular and aortic pressures. Importantly, the innovative device in the form of an intra-cardiac balloon assembly for circulatory support is based on a pulsatile flow strategy and is synchronized with the ECG signal. Other advantages of the proposed solution include a minimally invasive method of implantation, which is important for patients with end-stage heart failure. The design of the device is portable and the device itself is battery-powered, allowing for shorter hospitalization times and faster recovery, even in patients with end-stage heart failure associated with mitral regurgitation and pulmonary hypertension.

A revised gap-averaged Floquet analysis of Faraday waves in Hele-Shaw cells

Existing theoretical analyses of Faraday waves in Hele-Shaw cells rely on the Darcy approximation and assume a parabolic flow profile in the narrow direction. However, Darcy's model is known to be inaccurate when convective or unsteady inertial effects are important. In this work, we propose a gap-averaged Floquet theory accounting for inertial effects induced by the unsteady terms in the Navier–Stokes equations, a scenario that corresponds to a pulsatile flow where the fluid motion reduces to a two-dimensional oscillating Poiseuille flow, similarly to the Womersley flow in arteries. When gap-averaging the linearised Navier–Stokes equation, this results in a modified damping coefficient, which is a function of the ratio between the Stokes boundary layer thickness and the cell's gap, and whose complex value depends on the frequency of the wave response specific to each unstable parametric region. We first revisit the standard case of horizontally infinite rectangular Hele-Shaw cells by also accounting for a dynamic contact angle model. A comparison with existing experiments shows the predictive improvement brought by the present theory and points out how the standard gap-averaged model often underestimates the Faraday threshold. The analysis is then extended to the less conventional case of thin annuli. A series of dedicated experiments for this configuration highlights how Darcy's thin-gap approximation overlooks a frequency detuning that is essential to correctly predict the locations of the Faraday tongues in the frequency–amplitude parameter plane. These findings are well rationalised and captured by the present model.