Pulsatile Model Research Articles

Novel Expansible Aortic Annuloplasty Ring Exhibits Similar Characteristics as the Dacron Ring-an In Vitro Evaluation.

An increasing body of research indicates that annular stability plays a key role for a successful aortic valve repair. The aim of this study was to evaluate and compare a novel open aortic annuloplasty ring (the A-ring) with the Dacron ring. Both rings were compared with native aortic roots in vitro. Eighteen aortic roots were included in the study and randomized into three groups: the native, Dacron, and A-ring group. The roots were evaluated in an in vitro physiologic pulsatile model simulating the left side of the heart. Aortic annulus diameters were significantly reduced both in the Dacron ring group (p = 0.003) and the A-ring group (p = 0.020) when compared with the native group. Both the Dacron ring and A-ring effectively downsized the aortic annulus diameter. The A-ring also displayed an ability to maintain aortic root distensibility during the cardiac cycle equally to the Dacron ring.

Baroreflex control model for cardiovascular system subjected to postural changes under normal and orthostatic conditions

Baroreflex dysfunction is one of the common causes associated with the cardiovascular system. The buffering capability and baroreflex gain influences large variation in blood pressure for short term control. For regulating the blood pressure, an integrated analytical model for baroreflex control along with the cardiovascular system is presented to study the complex interactions between autonomic nervous system and cardiovascular system. In the proposed model, the autonomic nervous system utilizes sympathetic and parasympathetic nerve activities. This comprises a heart modeled by Mulier’s approach, systemic vasculature, baroreceptor sensor using stress-strain based Voigt model and Hodgkin-Huxley based autonomic nervous control. This model can handle the distribution of total blood volume changes under the influence of gravity upon postural changes by means of short term baroreflex control. The simulation is carried out for the integrated model along with (i) non pulsatile and (ii) pulsatile model of heart. The proposed model is validated for supine to standing position under influence of gravity. To show the efficiency of the proposed model, the simulation is carried out further for (i) postural changes like supine to standing and standing to supine under normal condition and (ii) Orthostatic hypotension and hypertension conditions. Also the robustness of the proposed pulsatile model is tested by introducing disturbance signal in mean arterial pressure under various postural changes.

Effect of Pulsatility on the Transport of Thrombin in an Idealized Cerebral Aneurysm Geometry

Computational models of cerebral aneurysm thrombosis are designed for use in research and clinical applications. A steady flow assumption is applied in many of these models. To explore the accuracy of this assumption a pulsatile-flow thrombin-transport computational fluid dynamics (CFD) model, which uses a symmetrical idealized aneurysm geometry, was developed. First, a steady-flow computational model was developed and validated using data from an in vitro experiment, based on particle image velocimetry (PIV). The experimental data revealed an asymmetric flow pattern in the aneurysm. The validated computational model was subsequently altered to incorporate pulsatility, by applying a data-derived flow function at the inlet boundary. For both the steady and pulsatile computational models, a scalar function simulating thrombin generation was applied at the aneurysm wall. To determine the influence of pulsatility on thrombin transport, the outputs of the steady model were compared to the outputs of the pulsatile model. The comparison revealed that in the pulsatile case, an average of 10.2% less thrombin accumulates within the aneurysm than the steady case for any given time, due to periodic losses of a significant amount of thrombin-concentrated blood from the aneurysm into the parent vessel’s bloodstream. These findings demonstrate that pulsatility may change clotting outcomes in cerebral aneurysms.

A quasi-equilibrium reduced model of pancreatic insulin secretion.

Much attention has been devoted in the last few decades to mathematical models of insulin secretion, in order to better understand the regulation of glycemia and its derangements. The glucose-insulin homeostatic mechanism is so complex and gives rise to such diverse behavior following perturbations that different models had been published, which reproduced the results of single experiments. More recently, a unifying model of pancreatic insulin secretion was proposed, which is able to account, with a single value of the (meta)parameters, for the wide array of clinically observed behavior. This model explicitly represented the pulsatile nature of the many pancreatic hormone-secreting firing units: the price to pay for its flexibility and performance is the very high dimensionality (hundreds of thousand equations) of the corresponding dynamical system. Clearly, it would be desirable to reduce this model to a much simpler form while retaining its power to reproduce heterogeneous phenomena. The present work reviews the qualitative behavior of this pancreas pulsatile model and offers some insight into its reduction in equilibrium and quasi-equilibrium conditions, also considering single-shot (non-repeated) glucose jumps from an approximately resting condition (such as would occur in standard Intra-Venous bolus dosing of glucose during diabetes diagnostic maneuvers). The resulting quasi-steady-state model can be further endowed with additional lower-order dynamics to also approximate transient behavior. Although a more accurate reduction of the original pulsatile model is left to further investigation, numerical results confirm the biomedical applicability of the formulation already obtained.

Ultrasound-Guided Percutaneous Arterial Puncture and Closure Device Training in a Pulsatile Model

The current study assesses the feasibility of in vitro practice of percutaneous puncture techniques in a pulsatile flow-model. Prospective, controlled, randomized study. The percutaneous access to endovascular aortic repair is considered safe, but success rates may be dependent on surgeon experience with the technique. Fourteen vascular surgery trainees and consultants were enrolled and randomized to a study or control group with both groups receiving instructions by a tutor on how to perform ultrasound guided percutaneous puncture and closure using a suture-mediated closure device. The study group received additional hands-on training on a pulsatile flowmodel of the groin and the performance of both groups was then graded. Study group participants were timed during and after their training on the model. The study group achieved higher overall grading than the control group on a 5-point scale with higher scores indicating a better performance (mean overall scores 4.0 ± 0.7 versus 2.8 ± 1.0, respectively; p = 0.03). Experienced participants (more than 20 punctures performed before the study) achieved higher overall scores than trainees (3.8 ± 0.4 versus 2.5 ± 0.8, respectively; p = 0.01). Five participants in the study group could deploy and close the ProGlide closure device correctly without the help of a tutor while being graded (71% in the study versus 0% in the control group; p = 0.02). Study group participants improved their overall score from 3.2 ± 0.9 to 4.0 ± 0.7 during training (p = 0.02). Time needed to complete the puncture and closure reduced from 456 seconds on average before, to 302 seconds after training (p < 0.001). Study group participants could improve their overall score while working on the simulator. More experienced participants performed better during the simulation, which may indicate the model to be life-like and a potential skills assessment tool. Simulation training may be a valuable adjunct to traditional forms of training when teaching an endovascular technique but is limited by its reliance on simulators and demo devices.

Treatment of Tricuspid Regurgitation at Subvalvular Level: Hemodynamic and Morphological Assessment in Ex-Vivo Beating Heart Model

ABSTRACT Background: Functional tricuspid regurgitation (FTR) treatment is challenging and most therapies targeting tricuspid valve (TV) annulus have shown limited durability with high rate of residual and recurrent regurgitation. In fact, right ventricular (RV) dilatation, which is another important determinant of FTR, remains unaddressed with these procedures. The aim of this study was to assess the effects of RV free wall approximation (FWA) toward the septal wall in an ex-vivo pulsatile model of FTR. Methods: FWA was simulated in 15 porcine right hearts by approximating RV free wall at the anterior papillary muscle level toward the septal wall in three different directions. Results: The treatment induced 19% decrease of regurgitation fraction with respect to pre-treatment and changes in TV morphology including reduction of TV tenting volume (up to 47%) and annulus size (up to 18%) as assessed via 3D computational reconstructions from echocardiographic volumetric data. The procedure success was significantly correlated (R2 = 0.91) with TV annulus size (p = 0.02) when corrected for pre-treatment cardiac output. Conclusions: As evaluated in the FTR experimental model, FWA significantly reduced TV regurgitation, leaflet tenting and annular dimension. Concomitant annular stabilization could improve the results as the pre-treatment dimension of TV annulus had an impact on FWA outcome.

Artificial pulsatile blood vessel model for medical phantom

Artificial pulsatile blood vessel model for medical phantom

Potential utility of new surgical hemostatic film using Hydrofit®: a preliminary study.

We developed a surgical hemostatic film using Hydrofit® (Hydrofit® film). This film is prepared by reacting Hydrofit® with water in advance, and it can be used in the same way as an accessory silicone sheet. In addition, unlike the silicone sheet, there is no need to remove the Hydrofit® film from the body. In the present study, we describe the hemostatic effect of our new method using Hydrofit® film. We created a pulsatile flow circuit model using a ventricular assist device and a vascular graft. The circuit was filled with water, and the systolic pressure was adjusted to ≥ 130mmHg. The artificial blood vessel was punctured by an 18-G needle. Operations to prevent water from leaking were attempted through either a conventional method using a silicone sheet or our new method using Hydrofit® film. In the 180-s trial, 14 attempts (93.3%) with the Hydrofit® film were successful. In the silicone sheet group, 13 attempts (86.7%) were successful before the silicone sheet was peeled off, and hemostasis was maintained in 10 (66.5%) cases after the silicone sheet was removed. After short-duration hemostasis for 60s, good waterproofing was obtained in the Hydrofit® film group (success in 17 cases [85%]). In contrast, in the silicone sheet group, 10 attempts (50%) were successful before the silicone sheet was peeled off, and hemostasis was maintained in only 7 (35%) cases after the silicone sheet was removed. Hydrofit® film showed good hemostatic performance in the pulsatile flow circuit model.

Cardiovascular dynamics during head-up tilt assessed via pulsatile and non-pulsatile models.

This study develops non-pulsatile and pulsatile models for the prediction of blood flow and pressure during head-up tilt. This test is used to diagnose potential pathologies within the autonomic control system, which acts to keep the cardiovascular system at homeostasis. We show that mathematical modeling can be used to predict changes in cardiac contractility, vascular resistance, and arterial compliance, quantities that cannot be measured but are useful to assess the system's state. These quantities are predicted as time-varying parameters modeled using piecewise linear splines. Having models with various levels of complexity formulated with a common set of parameters, allows us to combine long-term non-pulsatile simulations with pulsatile simulations on a shorter time-scale. We illustrate results for a representative subject tilted head-up from a supine position to a [Formula: see text] angle. The tilt is maintained for 5min before the subject is tilted back down. Results show that if volume data is available for all vascular compartments three parameters can be identified, cardiovascular resistance, vascular compliance, and ventricular contractility, whereas if model predictions are made against arterial pressure and cardiac output data alone, only two parameters can be estimated either resistance and contractility or resistance and compliance.

Endovascular and Microsurgical Aneurysm Training in a Chicken Thigh and Leg Pulsatile Model

Neurovascular training models include animal models, synthetics, or computer simulation. In vivo models are expensive and require significant resources. Synthetic/computer models do not reflect theelasticity of fresh vessels. We describe an endovascular and microsurgical training model using a chicken thigh/leg. A total of 20 chicken thigh/leg models were obtained. Angiography was used to understand the anatomy. Proximal cannulation with a 5-French catheter was achieved and connected to a hemostatic valve with a pump to simulate pulsatile flow. Aneurysms were created at the thigh-leg junction. For clipping training, 3 types of aneurysms were created to reproduce anatomy seen in middle cerebral, anterior communicating, and posterior communicating aneurysms. The average cost per specimen was $1.70 ± $0.30. The diameter of the proximal femoral artery was 2.4 mm ± 0.2 mm. The length from the proximal femoral artery to the aneurysm was 9.5 cm ± 0.7 cm. Distal catheterization was successful in all cases (n= 6). Successful deployment of coils and a stent was achieved under fluoroscopic guidance. Gross oversizing of coils and other mistakes led to aneurysm rupture. Each examiner performed an exploration of the pulsatile aneurysm, application and reapplication of a variety of clips, and then the final inspection of branching vessels to confirm patency. The chicken thigh/leg model provides training opportunities in microsurgical suturing, endovascular techniques for aneurysm obliteration, and microsurgical reconstruction of aneurysms. It combines affordability, time efficiency, and reproducibility. Further studies measuring improvement in technical aneurysm management and comparison with other training models are warranted.

Effect of pulsatile blood flow on LDL transport in arterial layers

Considering the pulsatile nature of blood flow, the transport of low density lipoprotein (LDL) species in the arterial wall has been numerically analysed. A straight axi-symmetric arterial segment with four arterial porous layers vis. endothelium, intima, internal elastic lamina and media has been taken into consideration. These layers are considered porous in nature. For modelling the fluid flow in the lumen and the arterial wall, Navier-Stokes equation and Darcy's equation have been used respectively. The solute flow modelling in the lumen and in the arterial wall has been done by using convection-diffusion equation and convection-diffusion-reaction equation respectively. Simple pulsatile and physiological pulsatile model of blood flow have been considered in the present analysis. The present study shows that the physiological pulsatile flow is having more impact on the radial filtration velocity at lumen-endothelium interface than that of the case for simple pulsatile nature of flow. Therefore, the possibility of enhancement in solute transport in the arterial wall is more in case of physiological pulsatile nature of flow.

Transcatheter Edge-to-Edge Treatment of Functional Tricuspid Regurgitation in an Ex Vivo Pulsatile Heart Model

BackgroundAlthough associated with left heart pathologies, functional tricuspid regurgitation (FTR) is often left untreated during left heart surgery. Hence, owing to its degenerative character, reoperation is often needed, encompassing an impressive (25% to 35%) mortality rate. Thus transcatheter approaches to FTR are raising great interest. ObjectivesThe authors evaluated the post-treatment effectiveness of the edge-to-edge technique using the percutaneous mitral valve repair device in an ex vivo pulsatile model of FTR. MethodsThe devices were implanted in 11 porcine hearts simulating FTR. In each heart, single-clip treatments involved grasping leaflet pairs in the medial or commissural position (6 combinations). Two-clip treatments were then performed considering all possible 15 combinations of leaflet pairs and medial/commissural grasping. Cardiac output, mean pulmonary pressure, and mean diastolic valve pressure gradient were evaluated in physiological and simulated pathological conditions (FTR), and post-treatments. ResultsGrasping the septal and anterior leaflets allowed for the best post-procedural outcome, ensuring a complete re-establishment of physiological-like hemodynamics. Septal and posterior grasping induced a significant recovery from FTR, although less marked. Conversely, grasping the anterior and posterior leaflets did not reduce FTR, and was detrimental in some specific cases. ConclusionsThis experimental work demonstrated that the transcatheter edge-to-edge repair technique is a feasible approach for FTR. The study investigated this approach to develop a selective, specific structural intervention methodology for treating FTR, considering the several biomechanical factors that alter proper functionality of valvular substructures. These results can be used to guide the development of edge-to-edge repair techniques in treatment of FTR.

Critical evaluation of three hemodynamic models for the numerical simulation of intra-stent flows

We evaluate here three hemodynamic models used for the numerical simulation of bare and stented artery flows. We focus on two flow features responsible for intra-stent restenosis: the wall shear stress and the re-circulation lengths around a stent. The studied models are the Poiseuille profile, the simplified pulsatile profile and the complete pulsatile profile based on the analysis of Womersley. The flow rate of blood in a human left coronary artery is considered to compute the velocity profiles. “Ansys Fluent 14.5” is used to solve the Navier–Stokes and continuity equations. As expected our results show that the Poiseuille profile is questionable to simulate the complex flow dynamics involved in intra-stent restenosis. Both pulsatile models give similar results close to the strut but diverge far from it. However, the computational time for the complete pulsatile model is five times that of the simplified pulsatile model. Considering the additional “cost” for the complete model, we recommend using the simplified pulsatile model for future intra-stent flow simulations.

Abstract 20132: Quantification of Multiple Mitral Regurgitant Jets: An in vitro Assessment of Doppler Methods Pertaining to MitraClip

Introduction: Mitraclip deployment creates a double orifice valve with multiple regurgitant jets making quantification of mitral regurgitation (MR) difficult. Hypothesis: Our objective was to evaluate the accuracy of double jet MR quantification by summation of individual jet 3D echo-derived vena contracta area (VCA) or 2D proximal isovelocity surface area (PISA) estimation of regurgitant volume (RV). Methods: In a pulsatile flow loop model, six valve constructs were evaluated with RV of 25 ml, 45 ml, and 65ml/beat. Regurgitant orifices tested were: a single circular hole (n=6), two symmetric circular holes (n=6), and an asymmetric configuration with a circular hole and an elliptical hole (n=6). RV was compared with true flow measurements from in vitro flow transducers. RV was calculated as: 1) PISA-Effective regurgitant orifice area x Doppler time velocity interval (TVI) or 2) VCA x Doppler TVI. Results: RV derived by PISA method correlated well with reference standard flow measures for both single orifice and double orifice valve constructs (R=0.96 vs R=0.90, p&lt;0.0001, respectively). PISA-RV also demonstrated a good correlation to true RV when tested through symmetric or asymmetric double orifice disks (R=0.96 vs R=0.87,p&lt;0.0001). 3D-VCA derived RV showed a superior correlation using the symmetric vs asymmetric disks (R=0.946 vs R=0.63,p&lt;0.001). Conclusions: In a pulsatile model of double orifice MR, total RV is accurately measured by summation of PISA-derived RV or VCA -derived RV from each orifice. These methods deserve further evaluation in the clinical setting.

Stabilizing control for a pulsatile cardiovascular mathematical model.

In this paper, we develop a pulsatile model for the cardiovascular system which describes the reaction of this system to a submaximal constant workload imposed on a person at a bicycle ergometer test after a period of rest. Furthermore, the model should allow to use measurements for the pulsatile pressure in fingertips which provide information on the diastolic and the systolic pressure for parameter estimation. Based on the assumption that the baroreceptor loop is the essential control loop in this case, we design a stabilizing feedback control for the pulsatile model which is obtained by solving a linear-quadratic regulator problem for the linearization of a non-pulsatile counterpart of the pulsatile model. We also investigate the behavior of the model with respect to changes in the weight of the term in the cost functional for the linear-quadratic regulator problem which penalizes the deviation of the momentary pressure in the aorta from the pressure at the stationary situation which should be obtained.

Multidetector-Row Computed Tomography Allows Accurate Measurement of Mechanical Prosthetic Heart Valve Leaflet Closing Angles Compared With Fluoroscopy

The purpose of this study was to compare multidetector-row computed tomography (MDCT) leaflet restriction measurements with fluoroscopy measurements in commonly used mechanical prosthetic heart valves (PHVs). Four mechanical PHVs (ON-X, Carbomedics, St. Jude, and Medtronic Hall) were imaged in a pulsatile model using fluoroscopy and 64-detector-row computed tomography. Five image acquisitions of each PHV without (1) and with (4) restricted leaflet closure were made. Three observers measured closure angles on fluoroscopy and MDCT. Data were analyzed using intraclass correlation coefficient (ICC) and Bland-Altman plots. Interobserver agreement was high in restricted and non-restricted leaflets on both modalities (ICCs >0.995). MDCT and fluoroscopy showed high agreements (ICCs >0.989). Median MDCT closure angle measurements differed at most -2 to +2 degrees from fluoroscopy in the restricted and -1 to +2 degrees in the non-restricted leaflets. MDCT allows measurement of leaflet motion with a maximal median discrepancy of 2 degrees. Both MDCT and fluoroscopy detect restricted leaflet closure with great accuracy.

Experimental Foundation for In Vivo Measurement of the Elasticity of the Aorta in Computed Tomography Angiography

This study was performed to determine the feasibility of measuring the elastic properties of the arterial wall in vivo. To prove this concept, elastic parameters were calculated from an aortic model of elastic behavior similar to a human aorta using computed tomography angiography (CTA) images. We first constructed an aortic model from polydimethylsiloxane (PDMS). This model was inserted into a pulsatile flow loop. The model was then placed inside a computed tomography scanner. To estimate the elasticity values, we measured the cross-sectional area and the pressure changes in the model during each phase of the simulated cardiac cycle. A discrete wavelet transform (DWT) algorithm was applied to the CTA data to calculate the geometric changes in the pulsatile model over a simulated cardiac cycle for various pulsatile rates and elasticity values of the PDMS material. The elastic modulus of the aortic model wall was derived from these geometric changes. The elastic moduli derived from the CTA data were compared with those obtained by testing strips of the same PDMS material in a tensile testing machine. Our two aortic models had elastic values at both extremes of those found in normal human aortas. The results show a good comparison between the elastic values derived from the CTA data and those obtained in a tensile testing machine. In addition, the elasticity values were found to be independent of the pulsatile rate for mixing ratios of 6:1 and 9:1 (p = .12 and p = .22, respectively). The elastic modulus of a pulsatile aortic model may be measured by electrocardiographically-gated multi-detector CTA protocol. This preliminary study suggests the possibility of determining non-invasively the elastic properties of a living, functioning aorta using CTA data.

THE EFFECTS OF IMPLANTING DIFFERENT STENTS ON THE BLOOD HEMODYNAMIC IN CORONARY ARTERIES

Stent implantation alters coronary artery hemodynamic and wall shear stress during cardiac cycles. In this study, three-dimensional models were used to analyze the effects of different stent designs and strut thicknesses on the hemodynamic of the artery. The flow was assumed to be pulsatile and stent models were expanded in the artery the same as angioplasty procedure that uses balloon. The data was applied to Fluent-ANSYS package as a UDF MATLAB code. A non-slip condition was applied to the artery walls. The pressure variation in different stents and the wall shear stress distribution were studied. Furthermore, the hemodynamic effects on the flow were investigated for two different thickness values of the same stent design. These results showed that stent implanting is one of the main parameters of pressure drop in the artery. Moreover, the surface of the stent is the location of maximum wall shear stress and the thicker stent strut did not vary this stress much. Our study implies that some design parameters such as thickness affect the hemodynamic factors of blood after stent implantation. Even stent implanting causes re-stenosis in the coronary artery. Using new real models is suggested to investigate new aspects of stent design and related effects on the hemodynamic of coronary arteries.

Rationale, scope, and 20-year experience of vascular surgical training with lifelike pulsatile flow models

Vascular surgical training currently has to cope with various challenges, including restrictions on work hours, significant reduction of open surgical training cases in many countries, an increasing diversity of open and endovascular procedures, and distinct expectations by trainees. Even more important, patients and the public no longer accept a "learning by doing" training philosophy that leaves the learning curve on the patient's side. The Vascular International (VI) Foundation and School aims to overcome these obstacles by training conventional vascular and endovascular techniques before they are applied on patients. To achieve largely realistic training conditions, lifelike pulsatile models with exchangeable synthetic arterial inlays were created to practice carotid endarterectomy and patch plasty, open abdominal aortic aneurysm surgery, and peripheral bypass surgery, as well as for endovascular procedures, including endovascular aneurysm repair, thoracic endovascular aortic repair, peripheral balloon dilatation, and stenting. All models are equipped with a small pressure pump inside to create pulsatile flow conditions with variable peak pressures of ~90 mm Hg. The VI course schedule consists of a series of 2-hour modules teaching different open or endovascular procedures step-by-step in a standardized fashion. Trainees practice in pairs with continuous supervision and intensive advice provided by highly experienced vascular surgical trainers (trainer-to-trainee ratio is 1:4). Several evaluations of these courses show that tutor-assisted training on lifelike models in an educational-centered and motivated environment is associated with a significant increase of general and specific vascular surgical technical competence within a short period of time. Future studies should evaluate whether these benefits positively influence the future learning curve of vascular surgical trainees and clarify to what extent sophisticated models are useful to assess the level of technical skills of vascular surgical residents at national or international board examinations. This article gives an overview of our experiences of >20 years of practical training of beginners and advanced vascular surgeons using lifelike pulsatile vascular surgical training models.

Pulsatile unsteady flow of blood through porous medium in a stenotic artery under the influence of transverse magnetic field

The periodic nature of the cardiac cycle induces a pulsatile, unsteady flow within the circulatory system. The pulsatile model of blood flow provides data to analyse the physiological situation in close proximity. The distribution of fatty cholesterol and artery-clogging blood clots in the lumen of the coronary artery is assumed as a porous medium. A mathematical model for pulsatile flow through an stenosed artery filled with porous medium in the presence of transverse static magnetic field has been formulated under the consideration of hematocrit dependent viscosity of blood that governed by Einstein equation. The velocity profile, volume flux, pressure gradient and wall shear stress are obtained and the effects of magnetic number, Darcy number, Womersely number are computed and represented through graphs.