Three-phase CFD analytical modeling of blood flow

The behavior of blood cells in disturbed flow regions of arteries has significant relevance for understanding atherogenesis. However, their distribution with red blood cells (RBCs) and leukocytes is not so well studied and understood. Our three-phase computational fluid dynamics approach including plasma, RBCs, and leukocytes was used to numerically simulate the local hemodynamics in such a flow regime. This model has tracked the wall shear stress (WSS), phase distributions, and flow patterns for each phase in a concentrated suspension shear flow of blood. Unlike other computational approaches, this approach does not require dispersion coefficients as an input. The non-Newtonian viscosity model was applied to a wide physiological range of hematocrits, including low shear rates. The migration and segregation of blood cells in disturbed flow regions were computed, and the results compared favorably with available experimental data. The predicted higher leukocyte concentration was correlated with relatively low WSS near the stenosis having a high WSS. This behavior was attributed to flow-dependent interactions of the leukocytes with RBCs in pulsatile flow. This three-phase hemodynamic analysis may have application to vulnerable plaque formation in arteries with in vivo complex flow conditions.     

Fractal model for blood flow in cardiovascular system

Blood flow in the cardiovascular system is the central point of experimental and theoretical investigation. The objective of the study is to determine the blood flow in the cardiovascular system using Darcy's law, Reynold's number and Poiseuille's equation. A possible way of modeling of self-similar biological tree-like structure is proposed. Special attention is paid to the blood vessel system, with elaboration on a model with certain spatial arrangement of the vessels and reasonable dependence of the blood pressure on the vessels diameter such that the organism has a homogeneous oxygen supply. Flow analysis in the above systems is analyzed by invasion percolation. The blood flow in the cardiovascular system has been numerically calculated for both normal and abnormal patients. A new algorithm has been introduced to visit the blood vessels in a robust manner which avoids loops and provides us the results in a simple manner.     

A microcomputer system for assessment of peripheral blood flow. An example of nasal blood flow

We have designed and implemented a microcomputer system for studying the effect of various mediator substances on the nasal blood flow. The system uses an IBM PC/AT microcomputer, which is connected with a Laser Doppler Flowmeter (LDF) and an iontophoretic drug application system. The LDF measures flux from the tissue that in the example is the inferior nasal turbinate. The flux is converted to digital form by an analog-digital converter of 12 bits. The program is implemented in the Pascal language. In the analysis, a flux level, amplitude, rise time and decay time of the pulse wave are determined. The effect of drugs on the flux can be studied by applying them iontophoretically. In the program the length and number of the drug application periods as well as the recording period are user-driven. In the nasal blood flow iontophoretically administered adrenaline reduced significantly the flux parameters and histamine canceled this effect. Tachyphylalaxis was a frequent observation in repeated measurements. The system can be used to evaluate the role of different transmitters in the etiology of chronic rhinitis.     

CFD modeling of blood flow following coil embolization of aneurysms

In case of coil embolization of a giant or a multilobular aneurysm, it is difficult to fill an aneurysm sac completely with coils, therefore, partial blocking of an aneurysm sac is inevitable. Blood flow characteristics, which may influence embolization process of an aneurysm, are affected by the locations of coils for partially blocked aneurysms. Blood flow fields inside an aneurysm are also influenced by the geometry of a parent vessel. In order to suggest the coil locations effective for aneurysm embolization, the blood flow fields of lateral aneurysm models were analyzed for different coil locations and parent vessel geometries. Flow rate into an aneurysm sac from a parent vessel (inflow rate) and wall shear stress were also calculated. Inflow rates were smaller and low wall shear regions were larger in the distal neck blocked model comparing to the dome blocked models. In the distal neck blocked model, inflow volume was smaller by 31% (straight parent vessel model) and 34% (curved parent vessel model) comparing to other models. The time averaged values of normalized low wall shear regions were 4% and 12% greater in the distal neck blocked models with a straight and a curved parent vessel, respectively. Since smaller inflow and low wall shear stress provide hemodynamic environment promoting thrombus embolization, distal neck should be the effective coil location for aneurysm embolization.     

脉动流模拟系统血压波形相似度算法研究

目的研究表征血压波形间相似程度的量化指标,并应用到脉动流模拟系统中血压波形的分析。方法在对已有相似度算法进行研究的基础上,结合血压波形自身的特点,提出加权平均算法。该算法将相关系数法和特征参数法相结合,分别从整体和局部特征对波形进行相似性度量,兼具全局匹配和局部比较的优点。结果与夹角余弦法、平均绝对差法和数值型相似系数法相比,加权平均算法更适用于血压波形相似度的分析。结论加权平均算法可以表征不同血压波形之间的差异,比较不同脉动流装置之间的模拟性能,进一步完善后还可以用于其他生理波形的分析。     

An on-line system for acquisition and processing of cerebral blood flow data

Regional cerebral blood flow is measured by monitoring the clearance from the brain of the gamma emitting radioisotope ¹³³Xe following an intracarotid artery bolus injection. On-line data analysis, which is performed on a PDP $\text{12}\text{30}$ digital computer, involves exponential stripping to isolate grey and white matter flows and integration of the clearance curves to infinity to enable the mean flow to be calculated. The data is displayed in real time and stored on the PDP 12 Linc tapes as a permanent record.     

Capillary resistance to flow of hardened (diamide treated) red blood cells (RBC)

Pressure-flow curves for control and hardened (diamide treated) human RBC's were obtained in capillaries of the isolated rat mesentery, in order to evaluate resistance to flow of hardened RBC's.Blood vessels were maximally dilated by an infusion of 10^–5 mol/l acetylcholine and isoprenaline and perfused with freshly collected human RBC's as well as with RBC's hardened by a treatment (hct 40%; pH 8.0; 37° C) with 0.5 mmol/l or 1.5 mmol/l diamide, respectively, suspended in Albumin (0.05%). — Ringer solution. The mesentery was perfused via a hydrostatic pressure reservoir. Arterio-venous pressure difference was varied from 4–10 kPa, and corresponding arteriolo-venular pressure gradients changed from about 200–500 Pa/mm. No significant difference in resistance to flow was observed between control and diamide treated cells over the whole pressure range. However, the flow through the microvascular bed was inhomogeneous upon perfusion with diamide treated cells, caused by a deceleration and stoppage of the cells at capillary narrowing (ratio of cell to vessel diameter >2). The time of stagnation increased with decreasing pressure gradient.This study was supported by the Minister für Wissenschaft und Forschung des Landes Nordrhein-Westfalen (06/0604/68511)Presented in part: XI European Conference for Microcirculation, Sept. 1980, Garmisch-Partenkirchen, FRG     

A microcomputer system for analysis of coronary artery calibre and blood flow

Measurement of myocardial blood flow and assessment of coronary calibre in man has important clinical and research value. An inexpensive microcomputer system has been developed to facilitate analysis of each of these. Coronary sinus and great cardiac vein blood flow are measured using the thermodilution technique. The output of the temperature measurement circuitry is digitized and used to calculate blood flows. For coronary artery calibre measurement, the outline of an arterial segment recorded during coronary arteriography is digitized manually. The microcomputer system provides a graphic display of the digitized artery and calculates diameters throughout its length. Excellent correlations were observed between computer and manual methods for both systems.     

Local versus regional cerebral blood flow in the rat at high (hypoxia) and low (phenobarbital anesthesia) flow rates

Local cerebral blood flow (CBF) was measured in rats, using an autoradiographic technique with ¹⁴C-iodoantipyrine as diffusible tracer, in situations with low, normal and high flow rates (phenobarbital anesthesia, analgesia with 75% N₂O, and hypoxia, respectively). A comparison of the results with previous data obtained in conscious rats (Sakurada et al. 1978) demonstrates that 75 % N₂O moderately reduces local CBF in some, but not all, cortical and subcortical areas, that phenobarbital anesthesia reduces local CBF to between 30 and 65 % of (conscious) control, and that pronounced hypoxia (arterial Po₂ about 25 mmHg) increases local CBF 3- to 4-fold. A comparison of the values obtained for cortical structures with those previously measured with a technique based on the Fick principle shows that the autoradiographic technique gives similar values at low and normal flow rates but that it moderately underestimates CBF at high flow rates, probably due to diffusion limitation.     

Regional blood flow in genetically obese (ob/ob) mice

1. Experiments have been undertaken on 11 decerebrate cats to investigate the effects of natural vestibular stimulation on the activity of cerebellar fastigial neurons. 2. From recordings in the rostral portion of the nucleus during sinusoidal lateral (roll) and horizontal (yaw) rotation, distinctive patterns of response were observed. 3. The majority of neurons sensitive to vestibular stimulation showed responses to a single modality of vestibular activation. During lateral tilt some neurones showed positional sensititivy, others gave responses related tothe velocity of movement. Other neurones responded in phase with the velocity of movement in the horizontal plane. 4. Aside from these neuronal responses, others provided indications of a convergence of inputs from different sets of vestibular receptors. In particular, several neurons showed a pattern of response that indicated tht they received inputs from otolith receptors and ampullar receptors of the vertical canal. At low velocities of movement their response was positional but with inreasing velocity the magnitude of the response increased and there was a marked phase shift of the discharge towards head velocity. 5. Neurons responding to horizontal rotation often showed positional responses during lateral tilt. There were also indications of a convergence of ampullar inputs from both vertical and horizontal canals. 6. The neural pathways mediating these resonses are discussed in consideration of previous neuroanatomical and neurophysiological data. We consider it likely that several pathways may act to evoke the patterns of response observed, and a role of the cerebellar cortex is indicated.     

A microcomputer system for on-line collection of blood flow and related physiological data

A multi-disciplinary approach is described for the development of a microcomputer based on-line data collection system for blood flow experiments. Well designed software provides a flexible approach to data collection, which is particularly suited to blood flow research laboratories. The choice of well supported hardware ensures ease of development with minimum time and cost.     

轴流式血泵无位置传感驱动控制系统设计

目的:设计一种无位置传感器轴流式血泵驱动控制系统,实现轴流式血泵的速度闭环控制、无线状态监测及动态调节控制。 方法:以STM32F103作为主控芯片,设计六臂全桥驱动电路,采用端电压过零检测实现转子位置和速度检测,并设计PI控制器实现闭环控制,使用无线蓝牙通讯实现泵状态监测及控制。 结果:驱动控制系统速度响应快,稳态误差小于1%,在8 000 rpm转速下,能够达到人体血液循环所需的流量及压差要求。 结论:系统实现了轴流式血泵无位置传感的启动及速度闭环控制,通过蓝牙模块实现对泵运行过程的电压、电流及流量进行监控和运行过程中根据病人生理情况动态调节泵转速。