Modeling of the aorta artery aneurysms and renal artery stenosis using cardiovascular electronic system

The cause of vasomotor symptoms: Resonance phenomena in the vascular bed

This paper describes the probable cause of vasomotor symptoms during climacterics and before menstruation/ovulation. We propose that sex hormones imbalance changes the elasticity, resonance frequencies, and resonance peaks of vascular beds primarily in the uterus/intestines. It is also explained that vasomotor symptoms occur in the locations which resonate blood flow from the uterus/intestines for the above reason.

Causal Relationship between Celiac Stenosis and Pancreaticoduodenal Artery Aneurysm: Interpretation by Simulation Using an Electric Circuit

Pancreaticoduodenal artery (PDA) aneurysm and celiac artery (CA) stenosis are rare diseases in themselves. Interestingly, however, there are more cases documented in the literature in which these two disease entities occurred together than could be coincidental, and CA stenosis has been suggested as the provocative condition in developing PDA aneurysm. This study is aimed at examining the causal relationship between CA stenosis and PDA aneurysm by simulating the splanchnic circulation with an electric circuit. A patient with multiple PDA aneurysms and collaterals with CA stenosis was treated in our institution using hybrid techniques. The patient's pre- and postoperative status was simulated using an electric circuit, and the two possible scenarios were tested for compatibility: the stenosis-first scenario vs. the aneurysm-first scenario. The simulation was performed in two ways: using Simulink® software (MATLAB® Release 2018b) and actual circuit construction on a breadboard. The stenosis-first scenario showed that as the CA stenosis progresses, the blood flow through PDA increases, favoring the development of an aneurysm and/or collaterals if the artery was already compromised by a weakening condition. On the other hand, the aneurysm-first scenario also showed that if the aneurysm or collaterals developed first, the aneurysm will steal the blood flow through the CA, causing it to collapse if the artery was already compromised by increased wall tension. Contrary to the common belief, this study showed that in patients suffering from concurrent CA stenosis and PDA aneurysm, either condition could develop first and predispose the development of the other. The simulation of splanchnic blood flow with an electric circuit provides a useful tool for analyzing rare vascular diseases that are difficult to provoke in clinical and animal studies.

Modeling photoplethysmographic signals in camera-based perfusion measurements: optoelectronic skin phantom

The remote acquisition of photoplethysmographic (PPG) signals via a video camera, also known as photoplethysmography imaging (PPGI), is not yet standardized. In general, PPGI is investigated with test persons in a laboratory setting. While these in-vivo tests have the advantage of generating real-life data, they suffer from the lack of repeatability and are comparatively effort-intensive because human subjects are required. Consequently, studying changes in signal morphology, for example, due to aging or pathological effects, is practically impossible. As a tool to study these effects, a hardware PPG simulator has been developed: this is a phantom which simulates and generates both 1D and locally resolved 2D optical PPG signals. Here, we demonstrate that it is possible to generate PPG-like signals with various signal morphologies by means of a purely optoelectronic setup, namely an LED array, and to analyze them by means of PPGI. Signals extracted via a camera show good agreement with simulated generated signals. In fact, the first phantom design is suitable to demonstrate this qualitatively.

Application of 0D model of blood flow to study vessel abnormalities in the human systemic circulation: An in-silico study

In this paper, a multi-compartment 0D model of the blood flow is considered to study the vessel abnormalities (stenoses and aneurysms) in the human systemic circulation (SC). In the complete SC, different levels of stenosis and aneurysms are artificially created by decreasing and increasing the vessel diameters respectively and their effects on pressure and flow are studied using sensitivity analysis (SA). Normalized local sensitivity analysis (LSA) is used to study the impact of stenosis and aneurysms on pressure and flow wave pattern. Furthermore, global sensitivity analysis (GSA), Sobol’s method is used to quantify the overall influence of stenoses and aneurysms in the complete SC.

The results of global sensitivity analysis revealed that the impact of both stenoses and aneurysms is strong within the individual structures (arm, legs, carotid bifurcation, aorta), while, aortic stenoses and aneurysms have effect on almost all downstream nodes. Moreover, the study could be useful for medical doctors, teachers and students to observe the hemodynamical changes in the SC with respect to vessel abnormalities, which could further help in making any clinical decision for patients having different levels of vessel abnormalities in any part or structure of the SC.

Theoretical mechanism of temporary renal function improvement after abdominal aortic aneurysm surgery: Applications for clinical imaging and laboratory data

We evaluated the effects of changes in blood flow due to abdominal aortic aneurysm (AAA) surgery by using a simple zero-dimension model and applied theoretical values to clinical data.The zero-dimension electronic circuit model and diagram of blood flow distribution were created by setting the resistance of the aorta, bilateral iliac arteries, renal arteries, and aneurysm. Resistance of the aneurysm and resistance of the aorta before surgery were compared with that of the aorta after surgery. We set the radius length of each anatomical parameter to calculate theoretical values.Renal flow increased 13.4% after surgery. Next, we analyzed contrast-enhanced computed tomography data of 59 patients who underwent AAA surgery. A total of 19 patients were treated with a Y graft and 7 patients were treated with a straight graft during open surgery. However, 33 patients were treated with a bifurcated stent graft. A significant linear relationship between the increased estimated glomerular filtration rate (eGFR) ratio and the decreased aneurysm ratio was found only for the straight graft group.Using a circuit model, renal blood flow theoretically increased after AAA surgery. Clinically, there was a correlation between volume regression and eGFR improvement only in the limited AAA group.

Recirculation zone length in renal artery is affected by flow spirality and renal-to-aorta flow ratio

Haemodynamic perturbations such as flow recirculation zones play a key role in progression and development of renal artery stenosis, which typically originate at the aorta-renal bifurcation. The spiral nature of aortic blood flow, division of aortic blood flow in renal artery as well as the exercise conditions have been shown to alter the haemodynamics in both positive and negative ways. This study focuses on the combinative effects of spiral component of blood flow, renal-to-aorta flow ratio and the exercise conditions on the size and distribution of recirculation zones in renal branches using computational fluid dynamics technique. Our findings show that the recirculation length was longest when the renal-to-aorta flow ratio was smallest. Spiral flow and exercise conditions were found to be effective in reducing the recirculation length in particular in small renal-to-aorta flow ratios. These results support the hypothesis that in renal arteries with small flow ratios where a stenosis is already developed an artificially induced spiral flow within the aorta may decelerate the progression of stenosis and thereby help preserve kidney function.

Spiral blood flow in aorta-renal bifurcation models

The presence of a spiral arterial blood flow pattern in humans has been widely accepted. It is believed that this spiral component of the blood flow alters arterial haemodynamics in both positive and negative ways. The purpose of this study was to determine the effect of spiral flow on haemodynamic changes in aorta-renal bifurcations. In this regard, a computational fluid dynamics analysis of pulsatile blood flow was performed in two idealised models of aorta-renal bifurcations with and without flow diverter. The results show that the spirality effect causes a substantial variation in blood velocity distribution, while causing only slight changes in fluid shear stress patterns. The dominant observed effect of spiral flow is on turbulent kinetic energy and flow recirculation zones. As spiral flow intensity increases, the rate of turbulent kinetic energy production decreases, reducing the region of potential damage to red blood cells and endothelial cells. Furthermore, the recirculation zones which form on the cranial sides of the aorta and renal artery shrink in size in the presence of spirality effect; this may lower the rate of atherosclerosis development and progression in the aorta-renal bifurcation. These results indicate that the spiral nature of blood flow has atheroprotective effects in renal arteries and should be taken into consideration in analyses of the aorta and renal arteries.

MODELING OF ILIAC ARTERY ANEURYSM USING FLUID–STRUCTURE INTERACTION

The aneurysm of iliac artery is a rare entity and there are few computational models that have studied the disease. In this study, we have presented the flow patterns in the aneurysmal artery using Fluid–structure interaction method. The blood was assumed Newotonian, pulsatile, laminar, incompressible, and homogenous. The geometry of the model was made based on CT images of clinical cases. Using the computational method, we have obtained the velocity and pressure contours, shear rates and vortices for the healthy and aneurysmal artery. The results show that a pressure maximum was found at the midpoint of the dilation. The vortices are formed in the aneurysmal area26 and shear rates do not change much. However, the rate increased in the neck of aneurysms. Furthermore, the aneurysm with bigger dilation tend to rupture due to more shear rates in the neck and the velocity at peak systole decreases in the aneurysmal area due to increase of the artery diameter. We have compared our results with some available relevant clinical data in discussion section.

MODELING OF SUPERIOR MESENTERIC ARTERY ANEURYSM USING FLUID–STRUCTURE INTERACTION

The aim of this study was to model the blood flow and predict related hemodynamics characteristics in healthy superior mesenteric artery (SMA) and saccular aneurysm cases. A fluid–structure interaction (FSI) method was performed, using an arbitrary Langrangian–Eulerian mesh. The computational mesh was generated using anatomical data from available human computed tomography (CT)-images. Combining constitution and momentum equations, projection method, the discretized resultant equation were numerically solved for velocity, pressure, shear stress and vortices for healthy/aneurysmal artery. The results including velocity contours, pressure contours, shear rate values, and vortices were obtained and analyzed for three main steps including peak systole, diastole, and end of cardiac cycle. Profiles show the varying velocity and pressure for a pulsatile flow input before and after aneurysms. They also show the formation of single or multiple vortices at aneurysmal area and decrease of wall shear stress with aneurysm enlargement. Furthermore, shear rate values at the neck of aneurysms exceed throughout the entire cardiac cycle. The outcome of the computational analysis is then compared to information available on pressure, vortices and wall shear stress from some clinical findings.

Morphological analysis of pressure wave in the arterial tree with stenosis - a modeling approach

This paper describes the morphological changes in peripheral signals due to arterial diseases with various severity conditions and site of stenosis using modeling approaches, and its effect in the morphological parameters of radial artery. As stenosis induces abrupt change in geometry and elastic properties of arterial tree (constitutes major reflection sites), hybrid model is well suited for studying the changes in shape of the pressure and flow wave transmitted through the stenosis. These morphological changes in wave shape of peripheral signal have significant diagnostic value in both modern and traditional medicine systems. It can be used for the quantitative assessment of the severity of the arterial diseases.

MODELING OF ABDOMINAL AORTA ANEURYSM AND STUDY OF THE PATHOLOGY USING COMPUTATIONAL FLUID DYNAMICS METHOD

In this paper, we have constructed a three-dimensional abdominal aorta aneurysm model based on the CT-scan/angiography images. The inlet velocity is pulsatile and the simulation was done by means of finite volume analysis. The velocity and pressure contours were obtained for four different aneurysm sizes in three sections. The results indicate that the velocity decreases in aneurysm wall but pressure increases in that area. Furthermore, the increase of the aneurysm diameter increases the rupture risk due to high pressure in the wall. The shear stress is high in the start point and end of the aneurysm's curvature. Our study indicates that the aneurysm diameter is directly related to the pressure. High blood pressure could be a risk factor in artery rapture. Our model can serve as a useful tool for the study of the aortic aneurysms.

Vasorelaxant effect of Cinnamomi ramulus ethanol extract via rho-kinase signaling pathway

The Rho-kinase (ROCK) signaling pathway is substantially involved in vascular contraction. This study investigated the vasodilatory effects and possible mechanisms of Cinnamomi ramulus ethanol extract (CRE), with the hypothesis that the CRE vasodilatory effect involves RhoA and the ROCK signaling pathway in rat aortic preparations. CRE (0.05-1 mg/ml) dose-dependently relaxed the vascular contraction induced by phenylephrine and calpeptin in an endothelium-independent manner. Measurement of the expression levels of ROCK-related signaling molecules in response to calpeptin revealed that CRE completely inhibited RhoA and ROCK2 protein expressions. Furthermore, CRE dephosphorylated the subsequent downstream targets myosin phosphatase targeting subunit 1 (MYPT-1), protein kinase C potentiated phosphatase inhibitor protein-17 kDa (CPI-17) and myosin light chain 20 kDa (MLC20). We conclude that the vasorelaxation effect of CRE occurs via downregulation of ROCK signal molecules.

Computational modelling of blood-flow-induced changes in blood electrical conductivity and its contribution to the impedance cardiogram

Studies have shown that blood-flow-induced change in electrical conductivity is of equal importance in assessment of the impedance cardiogram (ICG) as are volumetric changes attributed to the motion of heart, lungs and blood vessels. To better understand the sole effect of time-varying blood conductivity on the spatiotemporal distribution of trans-thoracic electric fields (i.e. ICG), this paper presents a segmented high-resolution (1 mm(3)) thoracic cardiovascular system, in which the time-varying pressures, flows and electrical conductivities of blood in different vessels are evaluated using a set of coupled nonlinear differential equations, red blood cell orientation and cardiac cycle functions. Electric field and voltage simulations are performed using two and four electrode configurations delivering a small alternating electric current to an anatomically realistic and electrically accurate model of modelled human torso. The simulations provide a three-dimensional electric field distribution and show that the time-varying blood conductivity alters the voltage potential difference between the electrodes by a maximum of 0.28% for a cardiac output of about 5 L min(-1). As part of a larger study, it is hoped that this initial model will be useful in providing improved insights into blood-flow-related spatiotemporal electric field variations and assist in the optimal placement of electrodes in impedance cardiography experiments.