A Method for a Simulation of Continuous Intracranial Pressure Curves

The study introduces a method to simulate continuously an intracranial pressure (ICP) wave form. In a system analysis approach the intracranial compartment was viewed as a black box with arterial blood pressure (ABP) as an input signal and ICP as an output. A weight function was used to transform the ABP curve into the ICP curve. The output ICP waveform was generated using a weight function derived from the transcranial Doppler blood flow velocity (FV) and ABP curves. In order to establish the relationship between TCD characteristics and weight functions simultaneous recordings of FV, ABP, and ICP curves of a defined group of patients were used. A linear function between the TCD characteristics and the weight functions was obtained by calculating a series of multiple regression analyses. Given examples demonstrate the procedure's capabilities in predicting the mean ICP, the pulse and respiratory waveform modulations, and the trends of ICP changes.     

Simulation of cerebrospinal fluid transport

The pulsatile nature of the CSF movement is a result of the cardiac-related pulsations in blood volume in cranial region. According to Monro–Kellie Doctrine, the net inflow of arterial blood during systole is compensated by an equal outflow of venous blood and by caudal displacement of the CSF. Knowledge of the distribution of physical properties (compliance, resistance) along the craniospinal system is crucial for understanding of the CSF hydrodynamics. The synthesis of both invasively and non-invasively obtained data is needed. The aim of our project was to develop a lumped-parameter compartment model of the craniospinal system and, in relation to the cardiac-related blood-volume pulsations, to describe its basic hydrodynamic properties. The model consists of six compartments representing major parts of the craniospinal system. Each compartment has its own set of physical properties which describe its behavior. The pressure transmission from head arteries to the brain compartment serves as a source of pulsations. The simulation tightly mimics pressure waves of the CSF and thus the flow characteristics and magnitudes. The fitted compliance of the spinal compartment in our model was two orders higher (9 × 10⁻¹⁰ m³/Pa) then the cranial compartment (5.2 × 10⁻¹² m³/Pa): only in this adjustment pulsations were present. It makes 99.5% of compliance related to the spinal canal and 0.5% to the intracranial structures. Our fitting showed that this model might be used in medical education as well as in medical practice.     

基于非线性动力学的脑血流自动调节能力评估

脑血流自动调节能力反映了循环系统的代偿能力,它的量化评估对脑血管疾病治疗与预防具有重要研究意义。本文利用非线性动力学中的互近似熵对脑血流自动调节能力进行了研究。实验结果发现该方法能实现实时、连续量化评估脑血流自动调节能力,为脑血流自动代偿能力及脑血管病的预后评估提供了一种有益的方法。     

基于弹性腔模型的下肢脉动信号仿真

脉搏波包含人体的重要生理信息,对下肢脉动信号进行仿真研究,有助于辅助临床诊断和疾病预测。根据电网络模型理论,将下肢各段动脉等效为串并联弹性腔,建立了下肢动脉仿真模型。通过matlab/simulink对该模型的脉搏波在不同动脉顺应性和外周阻力的条件下进行仿真分析,得到正常与病理状态下足背动脉脉搏波的仿真波形。结果显示,当血管顺应性减小时,收缩压升高,主波波峰前移,脉压差增大;外周阻力增大时,脉搏波上升支的幅度与斜率均增大,脉压差增大,仿真结果与实测基本吻合。该模型能较有效模拟血管不同生理参数下的脉搏波,对血管疾病的诊治和相关医疗仪器的开发具有一定应用价值。     

Model-based synthetic fuzzy logic controller for indirect bloodpressure measurement

In this paper, a new measurement system for the noninvasive monitoring of the continuous blood pressure waveform in the radial artery is presented. The proposed system comprises a model-based fuzzy logic controller, an arterial tonometer and a micro syringe device. The flexible diaphragm tonometer registers the continuous blood pressure waveform. To obtain accurate measurement without distortion, the tonometer's mean chamber pressure must be kept equal to the mean arterial pressure (MAP), the so-called optimal coupling condition, such that the arterial vessel has the maximum compliance. Since the MAP cannot be measured directly, to keep the optimal coupling condition becomes a tracking control problem with unknown desired trajectory. To solve this dilemma, a model-based fuzzy logic controller is designed to compensate the change of MAP by applying a counter pressure on the tonometer chamber through the micro syringe device. The proposed controller consists of a model-based predictor and a synthetic fuzzy logic controller (SFLC). The model-based predictor estimates the MAPs changing tendency based on the identified arterial pressure-volume model.     

A numerical model on pulsatile flow of magnetic nanoparticles as drug carrier suspended in Herschel–Bulkley fluid through an arterial stenosis under external magnetic field and body force

ABSTRACT

A theoretical model for blood flow through an artery with stenosis carrying magnetic particles in the presence of magnetic field and periodic body acceleration is analysed. In the present study, blood is assumed to be Herschel–Bulkley fluid carrying iron oxide nanoparticles. The governing equations are highly non-linear and were solved numerically. The effects of model parameters are investigated and the results are represented graphically. The shear stress at the arterial wall and resistive impedance increases with enhancing values of stenotic height, yield stress, flow behaviour index, consistency index, pulsatile Reynolds number, amplitude of body acceleration, particle concentration and particle mass parameters. In order to treat the circulation disorders, control of the parameters involved in blood flow is necessary. The present model is useful in normalizing the parameter values and hence it can be applied in the field of medicine. The study has significant applications in drug delivery for treating cancer.     

A Computer Model of Intracranial Dynamics Integrated to a Full-Scale Patient Simulator

The ability to visualize intracranial dynamics during simulated clinical scenarios is a valuable tool for teaching brain physiology and the consequences of different medical interventions on the brain. Studies have isolated physiologic variables and shown their effects on brain dynamics. However, no studies have shown the combined effects of these variables on intracranial dynamics. This brain model offers one approach that brings all these relationships together and shows how they affect the dynamics of the brain. The brain model obtains its physiologic inputs from a full-scale patient simulator which responds to clinical interventions. This integration allows individuals working on the patient simulator to see the effects of their actions on brain dynamics. The brain model gives a real-time display of intracranial events (cerebral metabolic rate, cerebral blood flow, cerebral blood volume, cerebral perfusion pressure, and intracranial pressure) and responds to changes in the pulmonary and cardiovascular condition of the patient simulator.     

Oxygen transport: an analysis of short-term blood flow autoregulation

A model for studying oxygen transport was used to examine the acute blood flow autoregulation phenomenon and its effectiveness for maintaining tissue oxygenation under different physiological conditions. The effectiveness of tissue oxygenation was judged by the level of venous blood oxygen tension, PVo2. Three sets of conditions were studied with, and again without, autoregulation present. First, arterial blood oxygen tension, Pao2, was lowered in steps while changes in PVo2 and blood flow were recorded. Second, blood hemoglobin concentration was lowered in steps while Pao2 remained normal. Finally, the rate of oxygen consumption was increased, simulating the increase in metabolism that occurs during strenuous exercise. Although the basic negative feedback gain had been set at the same level in each case, in comparing the results of the different simulations it became apparent that there were notable differences in each of the autoregulatory responses. These observations indicated that the overall effectiveness and the total feedback response of autoregulation could be highly variable, depending on the conditions.     

Blood flow velocity waveforms in the middle cerebral artery at rest and during exercise

Blood flow velocities in the middle cerebral artery (MCA) were measured under steady-state and incremental cycle exercises using a transcranial Doppler ultrasound velocimeter. The peak systolic velocity was found to rise markedly under exercise, while the end diastolic velocity tended to remain at the resting value. The relationship between peak systolic velocity and systolic blood pressure, and that between peak systolic velocity and heart rate were found to show a statistically significant correlation. The mean MCA blood velocity also showed a significant correlation with the mean arterial pressure and heart rate. The fluctuations of velocity and the resistance index were calculated in order to evaluate the hemodynamic load on the vessel wall; these also increased markedly under exercise. Such hemodynamic changes in activity might be important in understanding the genesis of vascular diseases, as well as the physiology of cerebral circulation.     

Study of arterial blood pressure by a Windkessel-type model: influence of arterial functional properties.

OBJECTIVE: To analyse the performance of a Windkessel blood pressure (BP) modeling of arterial compliance adjusted in a dynamic fashion according to a non-linear relationship between the arterial compliance (AC) and BP. Non invasive measurements of the radial BP waveform (MILLAR tonometry) were compared to those constructed by an electric simulator reproducing the model in a symmetrical network subdivided into 121 segments. We introduced at cardiac level the aortic stroke volume (Doppler echocardiography) and the dynamic values of compliance (relation of compliance-to pressure, constant or variable) whether the model was linear or non linear, measured by high resolution Doppler (NIUS 02) for each subject. RESULTS: At the radial artery segment the modelled BP obtained by the non linear model of AC was not significantly different from the measured BP wave, while in the linear model (AC constant at mean BP level) the systolic BP was significantly underestimated. (*P < 0.05). CONCLUSION: This work shows the limits inherent in simplification of arterial compliance in the Windkessel model using constant parameters. This demonstrates the influence of the dynamic properties of the arterial wall in a conduction artery on the level of systolic and diastolic BP.     

Blood flow dynamics and arterial wall interaction in a saccular aneurysm model of the basilar artery

Blood flow dynamics under physiologically realistic pulsatile conditions plays an important role in the growth, rupture and surgical treatment of intracranial aneurysms. This paper describes the flow dynamics and arterial wall interaction in a representative model of a terminal aneurysm of the basilar artery, and compares its wall shear stress, pressure, effective stress and wall deformation with those of a healthy basilar artery. The arterial wall was assumed to be elastic or hyperelastic, isotropic, incompressible and homogeneous. The flow was assumed to be laminar, Newtonian, and incompressible. The fully coupled fluid and structure models were solved with the finite elements package ADINA. The intra-aneurysmal pulsatile flow shows single recirculation region during both systole and diastole. The pressure and shear stress on the aneurysm wall exhibit large temporal and spatial variations. The wall thickness, the Young’s modulus in the elastic wall model and the hyperelastic Mooney-Rivlin wall model affect the aneurysm deformation and effective stress in the wall especially at systole.     

Automatic detection of ophthalmic artery stenosis using the adaptive neuro-fuzzy inference system

In this study, a new approach based on an adaptive neuro-fuzzy inference system (ANFIS) was presented for detection of ophthalmic artery stenosis. The ANFIS was used to detect ophthalmic artery stenosis when two features, resistivity and pulsatility indices, defining changes of ophthalmic arterial Doppler waveforms were used as inputs. The ophthalmic arterial Doppler signals were recorded from 115 subjects, of whom 52 suffered from ophthalmic artery stenosis and the rest were healthy. The proposed ANFIS model combined the neural network adaptive capabilities and the fuzzy logic qualitative approach. Some conclusions concerning the impacts of features on the detection of ophthalmic artery stenosis were obtained through analysis of the ANFIS. The performances of the classifiers were evaluated in terms of training performance and classification accuracies and the results confirmed that the proposed ANFIS classifier has potential in detecting the ophthalmic artery stenosis.     

连续测量血氧饱和度的视觉方法

血氧饱和度是人体的重要生命体征指标.文章通过深入分析基于动脉血液容积脉搏波的生理活动机理,及基于容积脉搏波的血氧饱和度测量原理和方法,提出了一种基于视频的无创连续测量血氧饱和度的新方法.该方法通过混合光照射动脉血液,并采用摄像头捕获血流视频,最终根据血流容积和血液颜色的连续变化来逐拍计算出血氧饱和度.结果显示,与专业设备所测数据相比,该方法测量结果准确性高、稳定可靠.     

Topology optimization study of arterial bypass configurations using the level set method

We studied the arterial bypass design problem using a level set based topology optimization method. The blood flow in the artery was considered as the non-Newtonian flow governed by the Navier–Stokes equations coupled with the modified Cross model for the shear dependent viscosity. The fluid–solid interface is immersed in the design domain by the level set method and the fictitious porous material method. The sensitivity velocity derived by the level set based continuous adjoint method was utilized to control the evolution of the level set function. In order to accommodate the irregular analysis domains, the flow equations and the level set equations were computed on two different unstructured grids respectively. Three idealized arterial bypass configurations problems with the minimum flow shear stress objective were studied in the numerical examples. The results indicated that the optimal arterial bypass designs can effectively reduce integral of the squared shear rate in the artery and have a superior performance for the arterial grafting.     

Analysis of cerebral blood flow by pneumatic-valves-controlled microfluidic device: risk assessment of infarction correlated with morphometric variation of cerebral vascular system

Although cerebral blood flow is the crucial factor for cerebral infarction and the circle of Willis (CoW) is considered the primary control structure for cerebral hemodynamics, risk of cerebral infarction caused by the morphological variation in the CoW has never been studied due to lack of proper tools. Here, the alteration of cerebral blood flow in CoW variation was quantitatively assessed by a new analysis method using a microfluidic device that was controlled by pneumatic valves. Using this device, the occlusion of diverse major arteries was realized by closing the channel with pneumatic valves. The morphological variations of the CoW and their hemodynamics were designed and analyzed after occlusion of the major arteries. While the differences in hemodynamics of CoW variants were not statistically significant compared with a complete CoW without occlusion or with occlusion of the efferent arteries, the occlusion of afferent arteries such as common carotid artery and vertebral artery severely affected the flow rate (28.4–48.8 %) and related arterial pressure of efferent arteries (48.6 ± 6.7–36.0 ± 1.4 mmHg) in CoW variants where the posterior communicating artery and the P1 segment are absent, which is associated with cerebral ischemic infarction. The novel analysis system using microfluidics provides a robust and accurate method, in which the hemodynamics of individual morphological variation and stenosis, and occlusion of vessels can be analyzed. Thus, this method is particularly suitable for personalized analysis of hemodynamics and may find new applications in biomedical researches.     

Mathematical Analysis of Coronary Autoregulation and Vascular Reserve in Closed-Loop Circulation

The autoregulatory capacity of the coronary circulation has traditionally been studied in open-loop animal models where the coronary circulation was decoupled from the systemic circulation. In the closed-loop circulation, changes in arterial pressure alter coronary flow. Pressure variations can be caused by changes in cardiac contractility, preload, afterload, and heart rate. These changes also affect myocardial oxygen consumption. To maintain equilibrium between oxygen supply and consumption, coronary flow is altered by the autoregulation mechanism. Coronary resistance must change to produce the required change in coronary flow. The direction of change in coronary resistance is not directly predictable. Increased arterial pressure may result in either increased or decreased coronary resistance. To study the changes in coronary resistance in response to changes in arterial pressure that are produced by circulatory parameters, we used mathematical models. Coronary resistance was calculated to obtain equilibrium between ventricular oxygen consumption and supply for different values of contractility, preload, afterload, and heart rate. Maximum coronary resistance, indicating largest coronary vascular reserve and highest efficiency of arterial pressure generation, was defined as an optimal condition. The model predicted that the optimal value of cardiac contractility is its resting value. Minimizing end-diastolic volume and heart rate and maximizing peripheral resistance were shown to improve ventricular coronary vascular reserve. These observations suggest that afterload reduction therapy may not be beneficial for improving myocardial oxygen balance while venous vasodilatation and heart rate reduction result in greater coronary reserve.     

隐蔽脉搏波潮波定位研究

中心动脉压的临床医学意义虽大于传统肱动脉和桡动脉血压,但其推算方法一直以来受基于有创伤数据的通用转换函数(General Transform Function,GTF)的建立和桡动脉脉搏波中隐蔽潮波位置的确定的约束。提出利用公开的有创伤中心动脉数据(麻省理工学院医学院的MIMIC重症监护数据,MIT MIMIC),通过傅里叶变换获得GTF,根据中心动脉收缩压数值,结合小波变换,反推脉搏波的隐蔽型潮波位置。研究发现,桡动脉脉搏波经小波sym4和haar变换后,其各自第3阶差值波的最大值后的第6个过零点为隐蔽型潮波位置。实验结果表明,利用所提方法获得隐蔽型潮波位置的识别准确率达到91.11%。     

A COMPUTER MODEL OF MYOCARDIAL SQUEEZING AND INTRAMYOCARDIAL FLOW DURING GRADED CORONARY ARTERY STENOSIS IN THE PRESENCE OF CORONARY SINUS INTERVENTIONS

A mathematical model of the left coronary circulation is used to calculate phasic arterial and intramyocardial flows under normal conditions, gradual stenosis, and full occlusion of the left anterior descending coronary artery. Experimental data reported in literature are compiled to derive a mathematical formula for the physiologic link between two model parameters: the resistance across the stenosis and the extravasal squeezing pressure within the LAD-dependent region of the myocardium. Matching pairs of resistance and decrease in squeezing form “infarction traces.” Model simulations yield the changes in coronary and intramyocardial flows along these infarction traces. The model was applied to alternating brief coronary sinus occlusions and coronary sinus release. The retrograde blood flow from the coronary veins to the capillaries during coronary sinus occlusion was estimated to range between 47% and 88% of the forward blood flow under patent coronary sinus conditions.     

鲁棒的超声多普勒肾动脉血流信号提取方法

声多普勒肾动脉血流速度信号是进一步提取血流速度信号特征的前提。而超声多普勒肾动脉血流速度信号特征是肾动脉狭窄早期诊断的重要手段。因强烈的斑噪影响和其它信息干扰,从超声图像中准确提取肾动脉血流速度信号是比较困难的。提出了局部自适应的置信连接分割方法,该方法用于分离信号区域和背景,在灰度分布不均匀和强噪声条件下仍能实现有效分割;然后使用连通域标号的方法填补小空隙,以消除干扰信息的影响,通过局部统计特性修正提取的信号并使用Mean Shift方法为信号降噪,最终实现了鲁棒的肾动脉血流速度信号的提取。实验结果显示,该方法能准确提取肾动脉血流速度信号,鲁棒性强。     

A model of ventilation of the healthy human lung

This paper presents a model of the lung mechanics which simulates the pulmonary alveolar ventilation. The model includes aspects of: the alveolar geometry; pressure due to the chest wall; pressure due to surface tension determined by surfactant activity; pressure due to lung tissue elasticity; and pressure due to the hydrostatic effects of the lung tissue and blood. The cross-sectional area of the lungs in the supine position derived from computed tomography is used to construct a horizontally layered model, which simulates heterogeneous ventilation distribution from the non-dependent to the dependent layers of the lungs. The model is in agreement with experimentally measured hysteresis of the pressure-volume curve of the lungs, static lung compliance, changes in lung depth during breathing and density distributions at total lung capacity (TLC) and residual volume (RV). In the dependent layers of the lungs, alveolar collapse may occur at RV, depending on the assumptions concerning lung tissue elasticity at very low alveolar volumes. The model simulations showed that ventilation increased with depth in the lungs, although not as pronounced as observed experimentally. The model simulates alveolar ventilation including all of the mentioned components of the respiratory system and to be validated against all the above mentioned experimental data.