Pulsating Blood Flow Research Articles

A parametric model for analysing atherosclerotic arteries: On the FSI coupling

There are many evidences that coronary plaque is not only dependent on the formation and progression of atherosclerosis, but also on the vascular remodelling response. If the local wall shear stress is low, a proliferative plaque may develop. Local inflammatory response will stimulate the formation of a plaque prone to rupture with superimposed thrombus formation (vulnerable plaque). Furthermore, the role of the wall shear stress in the genesis and the development of atherosclerotic diseases has been recently intensively investigated, examining its relationship with the presence of lesions and the intima media thickness. Due to the important role of pulsating blood flow, pressure and hemodynamics factors in atheroma growth, a Fluid Structure Interaction (FSI) parametric study of a 3D atherosclerotic artery has been carried out, with aim of studying the main geometrical risk factors in terms of plaque vulnerability.

OC-095 Performance of a novel optical sensor for intraoperative assessment of intestinal viability – ‘proof of principle’ study

Introduction Objective assessment of intestinal viability during surgery will allow surgeons to make informed decisions on the safety of intestinal anastomosis and to predict anastomotic related complications. 1 We investigated the performance of a novel dual sensor incorporating two established methods – photoplethysmography (PPG) and laser Doppler flowmetry (LDF) in a ‘proof of principle’ study. Method Using the new probe, infrared and red PPG amplitude and LDF flux of the bowel surface were recorded by LDF and PPG simultaneously in 30 patients undergoing large bowel resection with or without anastomosis. Each patient had measurements at eight different time points: before and after colonic mobilisation, over the tumour, before and after ligation of major vascular pedicle, immediately before and after anastomosis (+/- 5 min) at distal and proximal limbs. Both laparoscopic and open resectional cases were included. The differences between the mean amplitude and flux between different measurements were analysed. Results Twenty four laparoscopic and six open bowel resection cases had a total of 121 measurements recorded using the new probe. The mean IR AC amplitude in pre-ligation was 433 (± 189) mV and the mean IR AC in post ligation was 301 (± 152) mV. A statistically significant difference ( P = 0 .047) was observed between pre-ligation and post-ligation for the mean infrared PPG amplitude (student’s t-test). A considerable difference in mean amplitude between pre and post ligation for the red PPG was also observed (the mean amplitude for the red PPG fell by –25.6%). The amplitude of the infrared PPG increased after anastomosis by 38.2% at the proximal site and by 37.8% at the distal site. The amplitude of the red PPG also increased after anastomosis (by 6.3%) at the proximal site although the equivalent increase was not seen at the distal site. The LDF measurements did not follow the same pattern of the changes seen in PPG amplitude. Conclusion The preliminary results show that simultaneous PPG/LDF measurements from a combined sensor is feasible and provide useful information on changes in pulse volume and blood flow. Although the differences in PPG amplitude achieved statistical significance, the LDF measurements produced confounding results, perhaps explained by motion artefacts. Further refinements in design of the probe are required to improve the probe-tissue optical interface and reduce motion artefact. Disclosure of interest None Declared. Reference Urbanavicius L, Pattyn P, Van de Putte D, Venskutonis D. How to assess intestinal viability during surgery: a review of techniques. World J Gastrointest Surg. 2011;3(5):59–69

One-Dimensional Model of Viscoelastic Blood Flow Through a Thin Elastic Vessel

Based on the three-dimensional Oldroyd viscoelastic fluid model, we develop a simple linear one-dimensional model of blood flow through a thin blood vessel with an elastic multilayer cylindrical wall. Unlike known models, the obtained system of integrodifferential equations with respect to the variables z and t (the longitudinal coordinate ant time) includes the Volterra operator in t, which takes into account the relaxation effect of stresses in a pulsating flow of blood regarded as a many-component viscoelastic fluid. We construct a simplified differential model corresponding to “short-term memory.” We study the effect of high-amplitude longitudinal oscillations of wall under a dissection (lamination). Bibliography: 24 titles. Illustrations: 1 figure.

Non-Newtonian pulsating blood flow-induced dynamic instability of visco-carotid artery within soft surrounding visco-tissue using differential cubature method

The high blood rate that often occurs in carotid arteries may play a role in artery failure and tortuosity which leads to blackouts, transitory ischemic attacks, and other diseases. However, dynamic analysis of carotid arteries conveying blood is lacking. The objective of this study was to present a biomechanical model for dynamic instability analysis of the embedded carotid arteries conveying pulsating blood flow. In order to present a realistic model, the carotid arteries and tissues are assumed viscoelastic using Kelvin–Voigt model. Carotid arteries are modeled as elastic cylindrical vessels based on Mindlin cylindrical shell theory (MCST). One of the main advantages of this study is considering the pulsating non-Newtonian nature of the blood flow using Carreau, Casson, and power law models. Applying energy method, Hamilton’s principle and differential cubature method (DCM), the dynamic instability region (DIR) of the visco-carotid arteries is obtained. The detailed parametric study is conducted, focusing on the combined effects of the elastic medium and non-Newtonian models on the dynamic instability of the visco-carotid arteries. It can be seen that with increasing the tissue stiffness, the natural frequency of visco-carotid arteries decreases. The current model provides a powerful tool for further experimental investigation about arterial tortuosity.

New type of pump for the heart-lung bypass system

Objective: Complications arising from roller pump usage in modern heart-lung bypass (HLB) systems are widely known. Alternative to roller pumps has existed as various devices. This work is dedicated to developing new, considerably simpler and less expensive pump device for HLB systems, which provides maximally physiological pulsating blood flow. Material and Method: We used pediatric cardiotomy reservoirs of HLB systems as blood chambers. Two such reservoirs were placed in front of the oxygenator, with their in-flow tubes connected to the venous blood tubes, and the outflow tubes – to the entry to the oxygenator. In each reservoir, 2 air outlets tubes were connected to pneumo-receivers of positive and negative pressure. We filled up one of the reservoirs whith closed of exit blood tube by creating negative pressure in it. Simultaneously, with closed entry blood tube of the second reservoir, we ejected blood from it by created positive pressure. Used external pulsator. Results: In stand testing under re-circulation regime, productivity of the device was 12,5 liters/minute. Pressure on exit blood pump was within 0 to 300mm.Hg. The pump operating system enabled laminar, as well as pulsating flow of liquid, with frequency of 0-200 pulses/minute. Research is based on experiments conducted on 14 mongrel dogs weighing 20 kg. Standard methodology was used to cannulate Venae cavae and aorta, and to connect perfusion system to body. Duration of complete HLB reached 2 hours. Systolic pressure was maintained within 120-130mm.Hg.; diastolic – 70-80 mmHg. Velocity of blood flow in the aorta arc fluctuated within 950-1100 ml/min; in the femoral artery – within 60-80 ml/min. Conclusion: Preliminary tests of the new pump indicate that its hemodynamic characteristics are maximally approximated to physiological ones. In comparison to modern machines, a perfusion system with new pump type has minimal volume of fill-up and does not damage formative elements of blood.

Modeling and simulation of multi-physics multi-scale transport phenomenain bio-medical applications

We present a short overview of some of our most recent work that combines the mathematical modeling, advanced computer simulations and state-of-the-art experimental techniques of physical transport phenomena in various bio-medical applications. In the first example, we tackle predictions of complex blood flow patterns in the patient-specific vascular system (carotid artery bifurcation) and transfer of the so-called "bad" cholesterol (low-density lipoprotein, LDL) within the multi-layered artery wall. This two-way coupling between the blood flow and corresponding mass transfer of LDL within the artery wall is essential for predictions of regions where atherosclerosis can develop. It is demonstrated that a recently developed mathematical model, which takes into account the complex multi-layer arterial-wall structure, produced LDL profiles within the artery wall in good agreement with in-vivo experiments in rabbits, and it can be used for predictions of locations where the initial stage of development of atherosclerosis may take place. The second example includes a combination of pulsating blood flow and medical drug delivery and deposition controlled by external magnetic field gradients in the patient specific carotid artery bifurcation. The results of numerical simulations are compared with own PIV (Particle Image Velocimetry) and MRI (Magnetic Resonance Imaging) in the PDMS (silicon-based organic polymer) phantom. A very good agreement between simulations and experiments is obtained for different stages of the pulsating cycle. Application of the magnetic drug targeting resulted in an increase of up to ten fold in the efficiency of local deposition of the medical drug at desired locations. Finally, the LES (Large Eddy Simulation) of the aerosol distribution within the human respiratory system that includes up to eight bronchial generations is performed. A very good agreement between simulations and MRV (Magnetic Resonance Velocimetry) measurements is obtained. Magnetic steering of aerosols towards the left or right part of lungs proved to be possible, which can open new strategies for medical treatment of respiratory diseases.

Performance analysis and parameter optimization of an inner spiral in-pipe robot

SUMMARYA novel micro in-pipe robot using an internally threaded profile for propulsion is proposed in this paper, and the dynamic model of the robot in the turbulent liquid pipeline is established, and the computational fluid dynamics method is used to solve the influence of environmental parameters and operating parameters on the robotic performance. By the orthogonal experimental optimization method, the optimal inner spiral structural parametrical combination is obtained. According to the working principle of the inner spiral robot, an inner spiral driving device is designed and fabricated, and the running experiment in the pipeline full of 201 methyl silicone oil verifies the feasibility of the proposed robot. Adopting the pulsating blood flow function as the inlet condition, in a pulsating period, the robotic performance is numerically analyzed.

Function of Circle of Willis

Nearly 400 years ago, Thomas Willis described the arterial ring at the base of the brain (the circle of Willis, CW) and recognized it as a compensatory system in the case of arterial occlusion. This theory is still accepted. We present several arguments that via negativa should discard the compensatory theory. (1) Current theory is anthropocentric; it ignores other species and their analog structures. (2) Arterial pathologies are diseases of old age, appearing after gene propagation. (3) According to the current theory, evolution has foresight. (4) Its commonness among animals indicates that it is probably a convergent evolutionary structure. (5) It was observed that communicating arteries are too small for effective blood flow, and (6) missing or hypoplastic in the majority of the population. We infer that CW, under physiologic conditions, serves as a passive pressure dissipating system; without considerable blood flow, pressure is transferred from the high to low pressure end, the latter being another arterial component of CW. Pressure gradient exists because pulse wave and blood flow arrive into the skull through different cerebral arteries asynchronously, due to arterial tree asymmetry. Therefore, CW and its communicating arteries protect cerebral artery and blood-brain barrier from hemodynamic stress.

Gas Exchange Efficiency of an Oxygenator with Integrated Pulsatile Displacement Blood Pump for Neonatal Patients

Oxygenators have been used in neonatal extracorporeal membrane oxygenation (ECMO) since the 1970s. The need to develop a more effective oxygenator for this patient cohort exists due to their size and blood volume limitations. This study sought to validate the next design iteration of a novel oxygenator for neonatal ECMO with an integrated pulsatile displacement pump, thereby superseding an additional blood pump. Pulsating blood flow within the oxygenator is generated by synchronized active air flow expansion and contraction of integrated silicone pump tubes and hose pinching valves located at the oxygenator inlet and outlet. The current redesign improved upon previous prototypes by optimizing silicone pump tube distribution within the oxygenator fiber bundle; introduction of an oval shaped inner fiber bundle core, and housing; and a higher fiber packing density, all of which in combination reduced the priming volume by about 50% (50 to 27 mL and 41 to 20 mL, respectively). Gas exchange efficiency was tested for two new oxygenators manufactured with different fiber materials: one with coating and one with smaller pore size, both capable of long-term use (OXYPLUS® and CELGARD®). Results demonstrated that the oxygen transfer for both oxygenators was 5.3-24.7 mlO2/min for blood flow ranges of 100-500 mlblood/min. Carbon dioxide transfer for both oxygenators was 3.7-26.3 mlCO2/min for the same blood flow range. These preliminary results validated the oxygenator redesign by demonstrating an increase in packing density and thus in gas transfer, an increase in pumping capacity and a reduction in priming volume.

Influence of high-porosity mesh stent on hemodynamics of intracranial aneurysm: A computational study

This paper studies the influence of a High-Porosity Mesh (HPM) stent on the hemodynamic characteristics in the intracranial aneurysm based on the Computational Fluid Dynamics (CFD). An idealized basilar tip aneurysm model and a HPM stent model are built. The pulsating blood flow in a cardiac cycle is computationally simulated for non-stented and stented models, to provide a wealth of information of the spatio-temporally varying blood flow field. The influence of the stent placement on the hemodynamic characteristics is analyzed in terms of distributions of velocity, pressure, Wall Shear Stress (WSS) and Energy Loss (EL), which are believed to play an important role in the development and rupture of the aneurysm. The numerical results clearly show that the velocity, pressure, WSS and EL of the blood flow in the aneurysm are reduced by 30%–40% when the HPM stent is implanted. These computational results may provide valuable hemodynamic information for clinical neurosurgeon.

Asymmetric radial expansion and contraction of rat carotid artery observed using a high-resolution ultrasound imaging system

The geometry of carotid artery bifurcation is of high clinical interest because it determines the characteristics of blood flow that is closely related to the formation and development of atherosclerotic plaque. However, information on the dynamic changes in the vessel wall of carotid artery bifurcation during a pulsatile cycle is limited. This pilot study investigated the cyclic changes in carotid artery geometry caused by blood flow pulsation in rats. A high-resolution ultrasound imaging system with a broadband scanhead centered at 40MHz was used to obtain longitudinal images of the rat carotid artery. A high frame rate retrospective B-scan imaging technique based on the use of electrocardiogram to trigger signal acquisition was used to examine precisely the fast arterial wall motion. Two-dimensional geometry data obtained from nine rats showed that the rat carotid artery asymmetrically contracts and dilates during each cardiac cycle. Systolic/diastolic vessel diameters near the upstream and downstream regions from the bifurcation were 0.976±0.011/0.825±0.015mm and 0.766±0.015/0.650±0.016mm, respectively. Their posterior/anterior wall displacement ratios in the radial direction were 41.0±14.9% and 2.9±1.6%, respectively. These results indicate that in the vicinity of bifurcation, the carotid artery favorably expands to the anterior side during the systolic phase. This phenomenon was observed to be more prominent in the downstream region near the bifurcation. The cyclic variation pattern in wall movement varies depending on the measurement site, which shows different patterns at far upstream and downstream of the bifurcation. The asymmetric radial expansion and contraction of the rat carotid artery observed in this study may be useful in studying the hemodynamic etiology of cardiovascular diseases because the pulsatile changes in vessel geometry may affect the local hemodynamics that determines the spatial distribution of wall shear stress, one of important cardiovascular risk factors. Further systematic study is needed to clarify the effects of wall elasticity, branch angle and vessel diameter ratio on the asymmetric wall motion of carotid artery bifurcation.

Fluid-Structure Interaction Analysis of Pulsatile Blood Flow and Heat Transfer in Living Tissues During Thermal Therapy

The current numerical investigation tackles the fluid-structure interaction in a blood vessel subjected to a prescribed heating scheme on tumor tissues under thermal therapy. A pulsating incompressible laminar blood flow was employed to examine its impact on the flow and temperature distribution within the blood vessel. In addition, the arterial wall was modeled using the volume-averaged porous media theory. The motion of a continuous and deformable arterial wall can be described by a continuous displacement field resulting from blood pressure acting on the tissue. Moreover, discretization of the transport equations was achieved using a finite element scheme based on the Galerkin method of weighted residuals. The numerical results were validated by comparing them against documented studies in the literature. Three various heating schemes were considered: constant temperature, constant wall flux, and a step-wise heat flux. The first two uniform schemes were found to exhibit large temperature variation within the tumor, which might affect the surrounding healthy tissues. Meanwhile, larger vessels and flexible arterial wall models render higher variation of the temperature within the treated tumor, owing to the enhanced mixing in the vicinity of the bottom wall.

In vitro strain measurements in cerebral aneurysm models for cyber‐physical diagnosis

The development of new diagnostic technologies for cerebrovascular diseases requires an understanding of the mechanism behind the growth and rupture of cerebral aneurysms. To provide a comprehensive diagnosis and prognosis of this disease, it is desirable to evaluate wall shear stress, pressure, deformation and strain in the aneurysm region, based on information provided by medical imaging technologies. In this research, we propose a new cyber-physical system composed of in vitro dynamic strain experimental measurements and computational fluid dynamics (CFD) simulation for the diagnosis of cerebral aneurysms. A CFD simulation and a scaled-up membranous silicone model of a cerebral aneurysm were completed, based on patient-specific data recorded in August 2008. In vitro blood flow simulation was realized with the use of a specialized pump. A vision system was also developed to measure the strain at different regions on the model by way of pulsating blood flow circulating inside the model. Experimental results show that distance and area strain maxima were larger near the aneurysm neck (0.042 and 0.052), followed by the aneurysm dome (0.023 and 0.04) and finally the main blood vessel section (0.01 and 0.014). These results were complemented by a CFD simulation for the addition of wall shear stress, oscillatory shear index and aneurysm formation index. Diagnosis results using imaging obtained in August 2008 are consistent with the monitored aneurysm growth in 2011. The presented study demonstrates a new experimental platform for measuring dynamic strain within cerebral aneurysms. This platform is also complemented by a CFD simulation for advanced diagnosis and prediction of the growth tendency of an aneurysm in endovascular surgery.

Pulsatile blood flow in human bone assessed by laser-Doppler flowmetry and the interpretation of photoplethysmographic signals

Human bone blood flow, mean blood speed and the number of moving red blood cells were assessed (in arbitrary units), as a function of time, during one cardiac cycle. The measurements were obtained non-invasively on five volunteers by laser-Doppler flowmetry at large interoptode spacing. The investigated bones included: patella, clavicle, tibial diaphysis and tibial malleolus. As hypothesized, we found that in all bones the number of moving cells remains constant during cardiac cycles. Therefore, we concluded that the pulsatile nature of blood flow must be completely determined by the mean blood speed and not by changes in blood volume (vessels dilation). Based on these results, it is finally demonstrated using a mathematical model (derived from the radiative transport theory) that photoplethysmographic (PPG) pulsations observed by others in the literature, cannot be generated by oscillations in blood oxygen saturation, which is physiologically linked to blood speed. In fact, possible oxygen saturation changes during pulsations decrease the amplitude of PPG pulsations due to specific features of the PPG light source. It is shown that a variation in blood oxygen saturation of 3% may induce a negative change of ∼1% in the PPG signal. It is concluded that PPG pulsations are determined by periodic ‘positive’ changes of the reduced scattering coefficient of the tissue and/or the absorption coefficient at constant blood volume. No explicit experimental PPG measurements have been performed. As a by-product of this study, an estimation of the arterial pulse wave velocity obtained from the analysis of the blood flow pulsations give a value of 7.8 m s−1 (95% confidence interval of the sample mean distribution: [6.7, 9.5] m s−1), which is perfectly compatible with data in the literature. We hope that this note will contribute to a better understanding of PPG signals and to further develop the domain of the vascular physiology of human bone.

On conditions of negativity of friction resistance for non- stationary modes of blood flow and possible mechanism of affecting of environmental factors on energy effectiveness of cardiovascular system function

It is shown that initiated by action of molecular viscosity impulse flow, directed usually from the moving fluid to limiting it solid surface, can, under certain conditions, turn to zero and get negative values in the case of non-stationary flow caused by alternating in time longitudinal (along the pipe axis) pressure gradient. It is noted that this non-equilibrium mechanism of negative friction resistance in the similar case of pulsating blood flow in the blood vessels, in addition to the stable to turbulent disturbances swirled blood flow structure providing, can also constitute hydro-mechanical basis of the observed but not explained yet paradoxically high energy effectiveness of the normal functioning of the cardiovascular system (CVS). We consider respective mechanism of affecting on the stability of the normal work of CVS by environmental variable factors using shifting of hydro-dynamic mode with negative resistance realization range boundaries and variation of linear hydro- dynamic instability leading to the structurally stable swirled blood flow organization.

Numerical Simulation of Pulsating Flow over Blood Vessel Robot

In order to study the influence of pulsating blood flow to robot and blood vessel, UDF programming of the inlet velocity is defined as the boundary condition, and the model simulate the turbulent blood flow. Moreover, in this situation, this paper analyzes the influence caused by blood parameters for the biggest surface pressure on robot. The results are showed that the variation of pressure and velocity is different on different position at 0.08s and 0.27s, and the surface pressure of the robot become greater by the increase of blood density or viscosity.

Fluid-dynamics modelling of the human left ventricle with dynamic mesh for normal and myocardial infarction: Preliminary study

Pulsating blood flow patterns in the left ventricular (LV) were computed for three normal subjects and three patients after myocardial infarction (MI). Cardiac magnetic resonance (MR) images were obtained, segmented and transformed into 25 frames of LV for a computational fluid dynamics (CFD) study. Multi-block structure meshes were generated for 25 frames and 75 intermediate grids. The complete LV cycle was modelled by using ANSYS-CFX 12. The flow patterns and pressure drops in the LV chamber of this study provided some useful information on intra-LV flow patterns with heart diseases.

Combination of Heterogeneous Features for Wrist Pulse Blood Flow Signal Diagnosis via Multiple Kernel Learning

Wrist pulse signal is of great importance in the analysis of the health status and pathologic changes of a person. A number of feature extraction methods have been proposed to extract linear and nonlinear, and time and frequency features of wrist pulse signal. These features are heterogeneous in nature and are likely to contain complementary information, which highlights the need for the integration of heterogeneous features for pulse classification and diagnosis. In this paper, we propose a novel effective method to classify the wrist pulse blood flow signals by using the multiple kernel learning (MKL) algorithm to combine multiple types of features. In the proposed method, seven types of features are first extracted from the wrist pulse blood flow signals using the state-of-the-art pulse feature extraction methods, and are then fed to an efficient MKL method, SimpleMKL, to combine heterogeneous features for more effective classification. Experimental results show that the proposed method is promising in integrating multiple types of pulse features to further enhance the classification performance.

Physical Model of the Pulmonary Circulation Designed for Investigation on Cardiac Output Measurement by Means of the Thermodilution Method

The “gold clinical standard” of cardiac output measurements is the thermodilution method, implemented by the Swan–Ganz catheter. The unreliability of obtained results is difficult to estimate experimentally, due to the lack of reference methods or the risk of serious interferences in the measured object. Moreover, the pulsating blood flow produced by the heart is difficult to measure. Therefore it is advisable to develop the physical model of the pulmonary circulation, designed to investigate the accuracy of cardiac output measurements by means of the thermodilution method.

심전도 게이트를 사용한 다관점 도플러 광 단층촬영법

The aim of this study is to point out the uniqueness of Doppler optical coherence tomography (DOCT) for use in a probe station for (in vivo) visualization of microscale flow and structure and to maximize the effectiveness of DOCT by overcoming its limitations. Conventional DOCT produces images of only one of the velocity components that is parallel to the incident light. In this study, a multi-angle DOCT to quantify a velocity vector field is proposed; this is an extension from a velocity scalar field to a vector field. Quantifying an instantaneous three-dimensional velocity field in a pulsating flow is another challenge because of its limited frame rate. The in-vivo pulsating blood flow is measured by using an electrocardiogram-gated multi-angle DOCT in a hamster cheek pouch model. It is shown that the aliasing problem caused by a relatively low frame rate is resolved by using this method of measurement.