Venous ultrasound catheter-tip technique for evaluation of arterial hemodynamics.

A variety of devices has been used for measuring flow properties of deep-lying arteries, but many have limitations. This paper describes a relatively nontraumatic intravenous approach which uses a catheter in connection with a pulsed ultrasonic Doppler velocity meter (PUDVM) and an ultrasound echo track. The venous ultrasound catheter (VUC) has permitted measurements of local instantaneols blood velocity, flow, and wall motion in the abdominal aorta and iliac arteries of beagle dogs; evaluation studies have been conducted to compare the VUC recordings with an independent method for measuring blood flow and wall motion. Coupling of this catheter-tip device with the PUDVM and echo track provides chronic measurements of hemodynamic parameters in these deep vessels which were virtually impossible to obtain previously. This technique may prove useful in monitoring vessel pathology longitudinally as well as in basic experimental situations requiring flow and arterial wall mechanical properties.     

Study of the trajectory of erythrocyte movement in microvessels using a method of automatic image analysis

Many physiological and pathological processes in the circulation are related to changes of blood rheological properties. Since blood represents a specific suspension of cells in plasma the mentioned changes are to a great degree dependent on behavior and interaction of red blood cells (RBC). For investigation of blood flow structure in microvessels we developed an algorithm and worked out a program for automatic treatment of RBC movement on the basis of automatic image analysis system "Leitz-TAS" (Ernst Leitz, FRG). The program was based on computation of coordinates of blood cell centers. Further we calculated the following values: the vector of displacements (S), its projection on both axes (dx, dy), their relationship (dy/dx), the relationship of RBC radial coordinate to vessel radius (y/R), and the velocity of RBC movements (V). Proceeding from these data we obtained such parameters, as e.g., the velocity profile, the radial displacements of red cells, etc. by which we could judge on the blood flow regime, the flow structure and changes of blood rheological properties.     

Fiber-optic transmission catheter for regional venous oxygen saturation and blood flow.

We have developed a method for monitoring regional venous oxygen saturation. The key feature of this system is the use of highly flexible polymer fiber optics, and this flexibility allowed the production of a new fiber-optic transmission catheter. The space between the "face-to-face" positioned fiber-optic tips forms a remote catheter-based transmission cell. Our method applies Twersky's theory, in which absorption and scattering can be treated independently. Fresh rabbit blood was pumped through a disk oxygenator in which gas exchange occurred and passed the catheter. Simultaneous results obtained by the catheter and a cuvette oximeter were excellent (r = 0.99, SD = 1.1%). Oxygen saturation measured by this catheter was independent of vessel wall artifacts, blood pH, and flow velocity. Another application of this method is measurement of blood flow by the dye- (indocyanine green) dilution technique. The results of flow measurements by the catheter appeared to be satisfactory (r = 0.99, SD = 1.7%). This study concludes that our method is effective for monitoring the balance between regional oxygen supply and demand.     

Conductance catheter measurements of lumen area of stenotic coronary arteries: theory and experiment

An injection of saline solution is required for the measurement of vessel lumen area using a conductance catheter. The injection of room temperature saline to displace blood in a vessel inevitably involves mass and heat transport and electric field conductance. The objective of the present study is to understand the accuracy of conductance method based on the phenomena associated with the saline injection into a stenotic blood vessel. Computational fluid dynamics were performed to simulate flow and its relation to transport and electric field in a stenotic artery for two different sized conductance catheters (0.9 and 0.35 mm diameter) over a range of occlusions [56-84% cross-sectional area (CSA) stenosis]. The results suggest that the performance of conductance catheter is dependent on catheter size and severity of stenosis more significantly for 0.9 mm than for 0.35 mm catheter. Specifically, the time of detection of 95% of injected saline solution at the detection electrodes was shown to range from 0.67 to 3.7 s and 0.82 to 0.94 s for 0.9 mm and 0.35 mm catheter, respectively. The results also suggest that the detection electrodes of conductance catheter should be placed outside of flow recirculation region distal to the stenosis to minimize the detection time. Finally, the simulations show that the accuracy in distal CSA measurements, however, is not significantly altered by whether the position of detection electrodes is inside or outside of recirculation zone (error was within 12% regardless of detection electrodes position). The results were experimentally validated for one lesion geometry and the simulation results are within 8% of actual measurements. The simulation of conductance catheter injection method may lead to further optimization of device and method for accurate sizing of diseased coronary arteries, which has clinical relevance to percutaneous intervention.     

Real-time determination of the position and shape of the plasma column from external magnetic measurements in the GLOBUS-M tokamak

A fast algorithm is elaborated for determining the position and shape of the plasma column from measurements performed with magnetic probes located outside the vacuum vessel of the GLOBUS-M tokamak. The algorithm is based on the modeling of the plasma current by movable current filaments and allows one to take into account the effect of eddy currents induced in the vacuum vessel. The algorithm was tested in a series of model discharges under conditions characteristic of the GLOBUS-M tokamak and serves now as a software component of its magnetic diagnostic system. By employing a conventional PC (Pentium 1 GHz, 200-MHz data bus), the calculation time of the plasma column parameters at one instant in time does not exceed 3 ms, which offers the possibility of controlling the plasma parameters during a discharge.     

Doppler Optical Coherence Tomography of Retinal Circulation

Noncontact retinal blood flow measurements are performed with a Fourier domain optical coherence tomography (OCT) system using a circumpapillary double circular scan (CDCS) that scans around the optic nerve head at 3.40 mm and 3.75 mm diameters. The double concentric circles are performed 6 times consecutively over 2 sec. The CDCS scan is saved with Doppler shift information from which flow can be calculated. The standard clinical protocol calls for 3 CDCS scans made with the OCT beam passing through the superonasal edge of the pupil and 3 CDCS scan through the inferonal pupil. This double-angle protocol ensures that acceptable Doppler angle is obtained on each retinal branch vessel in at least 1 scan. The CDCS scan data, a 3-dimensional volumetric OCT scan of the optic disc scan, and a color photograph of the optic disc are used together to obtain retinal blood flow measurement on an eye. We have developed a blood flow measurement software called "Doppler optical coherence tomography of retinal circulation" (DOCTORC). This semi-automated software is used to measure total retinal blood flow, vessel cross section area, and average blood velocity. The flow of each vessel is calculated from the Doppler shift in the vessel cross-sectional area and the Doppler angle between the vessel and the OCT beam. Total retinal blood flow measurement is summed from the veins around the optic disc. The results obtained at our Doppler OCT reading center showed good reproducibility between graders and methods (<10%). Total retinal blood flow could be useful in the management of glaucoma, other retinal diseases, and retinal diseases. In glaucoma patients, OCT retinal blood flow measurement was highly correlated with visual field loss (R²>0.57 with visual field pattern deviation). Doppler OCT is a new method to perform rapid, noncontact, and repeatable measurement of total retinal blood flow using widely available Fourier-domain OCT instrumentation. This new technology may improve the practicality of making these measurements in clinical studies and routine clinical practice.     

System for flow sorting chromosomes on the basis of pulse shape

Sorting on the basis of the complex features resolved by chromosome slit-scan analysis requires rapid and flexible pulse shape acquisition and processing for determining sort decisions before droplet breakoff. Fluorescence scans of chromosome morphology contain centromeric index and banding information suitable for chromosome classification, but these scans are often characterized by variability in length and height and require sophisticated data processing procedures for identification. Setting sort criteria on such complex morphological data requires digitization and subsequent computation by an algorithm tolerant of variations in overall pulse shape. We demonstrate here the capability to sort individual chromosomes based on their morphological features measured by slit-scan flow cytometry. To do this we have constructed a sort controller capable of acquiring an 128 byte chromosome waveform and executing a series of numerical computations resulting in an area-based centromeric index sort decision in less than 2 ms. The system is configured in a NOVIX microprocessor, programmed in FORTH, and interfaced to a slit-scan flow cytometer data acquisition system. An advantage of this configuration is direct control over the machine state during program execution for minimal processing time. Examples of flow sorted chromosomes are shown with their corresponding fluorescence pulse shapes.     

Blood Tracer Kinetics in the Arterial Tree

Evaluation of blood supply of different organs relies on labeling blood with a suitable tracer. The tracer kinetics is linear: Tracer concentration at an observation site is a linear response to an input somewhere upstream the arterial flow. The corresponding impulse response functions are currently treated empirically without incorporating the relation to the vascular morphology of an organ. In this work we address this relation for the first time. We demonstrate that the form of the response function in the entire arterial tree is reduced to that of individual vessel segments under approximation of good blood mixing at vessel bifurcations. The resulting expression simplifies significantly when the geometric scaling of the vascular tree is taken into account. This suggests a new way to access the vascular morphology in vivo using experimentally determined response functions. However, it is an ill-posed inverse problem as demonstrated by an example using measured arterial spin labeling in large brain arteries. We further analyze transport in individual vessel segments and demonstrate that experimentally accessible tracer concentration in vessel segments depends on the measurement principle. Explicit expressions for the response functions are obtained for the major middle part of the arterial tree in which the blood flow in individual vessel segments can be treated as laminar. When applied to the analysis of regional cerebral blood flow measurements for which the necessary arterial input is evaluated in the carotid arteries, present theory predicts about 20% underestimation, which is in agreement with recent experimental data.     

Fast blood-flow simulation for large arterial trees containing thousands of vessels

Blood flow modelling has previously been successfully carried out in arterial trees to study pulse wave propagation using nonlinear or linear flow solvers. However, the number of vessels used in the simulations seldom grows over a few hundred. The aim of this work is to present a computationally efficient solver coupled with highly detailed arterial trees containing thousands of vessels. The core of the solver is based on a modified transmission line method, which exploits the analogy between electrical current in finite-length conductors and blood flow in vessels. The viscoelastic behaviour of the arterial-wall is taken into account using a complex elastic modulus. The flow is solved vessel by vessel in the frequency domain and the calculated output pressure is then used as an input boundary condition for daughter vessels. The computational results yield pulsatile blood pressure and flow rate for every segment in the tree. This solver is coupled with large arterial trees generated from a three-dimensional constrained constructive optimisation algorithm. The tree contains thousands of blood vessels with radii spanning ~1 mm in the root artery to ~30 μm in leaf vessels. The computation takes seconds to complete for a vasculature of 2048 vessels and less than 2 min for a vasculature of 4096 vessels on a desktop computer.     

Ultrasound imaging

Modern ultrasonic transducers mainly employ lead zirconate titanate (PZT) but vinylidene fluoride trifluoroethylene copolymer (P (VDF-TrPE)) is becoming more competitive. The static scanner is now largely replaced by mechanical or electronically controlled array real time systems; the speed of scanning is limited by the speed of sound and the resolution depends on the wavelength and so, ultimately, on the attenuation in tissue. Tissue inhomogeneities degrade the resolution. Intraoperative and intracavitary scanners have advantages in some anatomical situations and ultrasonic imaging can guide extracorporeal shock wave lithotripsy. Inexpensive battery powered scanners will soon become available. Duplex scanners are used to localize the acquisition of Doppler signals; blood flow volume rate can be estimated from measurements of blood velocity and vessel cross-sectional area, or by the attenuation-compensated technique which avoids the main sources of error. Colour flow mapping combines real time imaging with Doppler information, but has limited scanning speed. Computed tomography and acoustical microscopy are feasible. Speckle arises from the coherent nature of ultrasound and can be suppressed by summing uncorrelated images or by filtering. Image manipulation and display techniques are being developed to cope with three dimensional scan data and the approach is compatible with picture archiving and communication systems (PACS). Tissue characterization based on the measurement of properties has been disappointing but blood flow analysis and contrast agents are promising. Quality assurance programmes are crucial; ultrasonic diagnosis appears to be free from hazard and prudent use is determined by cost-benefit considerations.     

动脉硬化仿真模拟分析

目的：通过对血管中血液流动对血管的影响及血液内低密度脂蛋白（sLDL）微粒行为的模拟分析,研究动脉粥样硬化产生的血流动力学原因。方法：第一步,使用流体力学软件CFD,建立动脉血管弯曲分叉仿真模型;第二步,分析血液流动特性,跟踪血液中15—25纳米尺度范围类的sLDL粒子在动脉分叉模型中的流体力学行为,研究sLDL在血液流速稳定下在血管中的空间分布及流场特征分布。结果：血管起始段出现压强很高的区域。在动脉血管弯曲内侧处及分岔处的分支外侧血液流动较慢,并且在这些部位出现压强较高的区域。在血管弯曲外侧处及分岔点处,sLDL与血管壁发生碰撞的几率较其它位置较高,粒子在血管上沉积高发区域在这些部位呈斑块状分布。讨论及结论：在血管起始段的高压,可能是导致这一部分血管损伤,并进而引起动脉硬化形成的主要原因;在动脉血管弯曲外侧处及分岔点处出现的高压低速血流分布,一方面增大了血液中包括sLDL粒子在内的致病因子与血管壁的接触时间,另一方面则引起这些部位血清的侧漏加强,出现所谓的’浓度极化’现象,从而导致这些部位出现高浓度的sLDL分布,增大sLDL粒子与血管壁的接触几率;粒子在血管上沉积高发区域往往存在于动脉血管分岔点处,而在血管弯曲外侧处也有较高几率沉淀,呈斑状分布;长期性轻微性振动的剪切压力的作用使多数血管内皮细胞性质改变,促进动脉硬化形成。在动脉血管起始段、弯曲处及分岔点处血液的高压低速分布、sLDL粒子的高沉积率及低剪切应力等是动脉硬化产生及演化的重要因素.     

Evaluation of antifungal activity of antimycotics by automatic analyzing system

Antifungal activity of several antimycotics has been evaluated using an automatic analyzing system (AAS), which is composed of a specially designed reaction vessel, microscopic observation system, image analyzing system, and computer program for automatic tracing of hypha growth. The agar plate was prepared on the ceiling of the reaction vessel, and spore mass of a fungus (Aspergillus niger) was inoculated onto it. After the preincubation at 28 °C for 24 h the reaction vessel was set on a microscope stage and connected to the liquid flow system. An appropriate hypha was selected for the measurement of growth process during the following steps: first contact with saline for 30 min for the adaptation, the second contact with same saline for 30 min, contact with saline containing an antimycotic substance for 60 min, and contact with flushing saline for 60 min. During a sequence of these steps, the apical tip of a growing hypha displayed on a TV monitor was followed automatically. The dynamic response of hypha to an agent was analyzed by several parameters. Morphological changes of the hypha caused by respective agents were recorded on VTR for further analysis. By using this system, the antifungal activity of antimycotics could be quantitatively determined within several hours.     

A pulsed diagonal-beam ultrasonic airflow meter

The construction and specific function of a new ultrasonic flowmeter are described. The mean velocity of the respiratory airflow is calculated by measuring the transit times of short ultrasonic pulse trains, simultaneously transmitted upstream and downstream at a 500-Hz rate. The flowmeter system consists of a control unit and a separate flow head. The former includes the power supplies, a controlling microprocessor, most of the signal-processing circuitry, and three analog outputs for flow, volume, and temperature. The flow head contains the respiratory tube with a constant circular cross section (length 90 mm, diam 20 mm, dead space 35 ml), a fast temperature sensor, two electronic circuits for processing of flow and temperature data, and a sound transmission channel with two capacitive ultrasonic wide-band transducers. This respiratory airflow meter, suitable for spirometric maneuvers (vital capacity, forced vital capacity) as well as for long-term breath-by-breath respiratory analysis, is extremely fast (response time 1-2 ms) and accurate (volume accuracy with room air +/- 0.7%), with low noise (below 9 ml/s), a wide flow range (bidirectional from 0 to 9 l/s), and a flat frequency response up to 70 Hz.     

Parallel computation and FASTA: confronting the problem of parallel database search for a fast sequence comparison algorithm

We have parallelized the FASTA algorithm for biological sequencecomparison using Linda, a machine-independent parallel programminglanguage. The resulting parallel program runs on a variety ofdifferent parallel machines. A straightforward parallelizationstrategy works well if the amount of computation to be doneis relatively large. When the amount of computation is reduced,however, disk I/O becomes a bottleneck which may prevent additionalspeed-up as the number of processors is increased. The paperdescribes the parallelization of FASTA, and uses FASTA to illustratethe I/O bottleneck problem that may arise when performing paralleldatabase search with a fast sequence comparison algorithm. Thepaper also describes several program design strategies thatcan help with this problem. The paper discusses how this bottleneckis an example of a general problem that may occur when parallelizing,or otherwise speeding up, a time-consuming computation. Received on July 25, 1990; accepted on October 15, 1990     

Minimally Invasive Monitoring of Chronic Central Venous Catheter Patency in Mice Using Digital Subtraction Angiography (DSA)

Background

Repetitive administration of medication or contrast agents is frequently performed in mice. The introduction of vascular access mini-ports (VAMP) for mice allows long-term vascular catheterization, hereby eliminating the need for repeated vessel puncture. With catheter occlusion being the most commonly reported complication of chronic jugular vein catheterization, we tested whether digital subtraction angiography (DSA) can be utilized to evaluate VAMP patency in mice.

Methods

Twenty-three mice underwent catheterization of the jugular vein and subcutaneous implantation of a VAMP. The VAMP was flushed every second day with 50 μL of heparinized saline solution (25 IU/ml). DSA was performed during injection of 100 μL of an iodine based contrast agent using an industrial X-ray inspection system intraoperatively, as well as 7±2 and 14±2 days post implantation.

Results

DSA allowed localization of catheter tip position, to rule out dislocation, kinking or occlusion of a microcatheter, and to evaluate parent vessel patency. In addition, we observed different ante- and retrograde collateral flow patterns in case of jugular vein occlusion. More exactly, 30% of animals showed parent vessel occlusion after 7±2 days in our setting. At this time point, nevertheless, all VAMPs verified intravascular contrast administration. After 14±2 days, intravascular contrast injection was verified in 70% of the implanted VAMPs, whereas at this point of time 5 animals had died or were sacrificed and in 2 mice parent vessel occlusion hampered intravascular contrast injection. Notably, no occlusion of the catheter itself was observed.

Conclusion

From our observations we conclude DSA to be a fast and valuable minimally invasive tool for investigation of catheter and parent vessel patency and for anatomical studies of collateral blood flow in animals as small as mice.     

Nontraumatic aortic blood flow sensing by use of an ultrasonic esophageal probe.

The measurement of blood velocity fields, volume flow, and arterial wall motion in the descending thoracic aorta provides essential hemodynamic information for both research and clinical diagnosis. The close proximity of the esophagus to the aorta in the dog makes it possible to obtain such data nonsurgically using an ultrasonic esophageal probe; however, the accuracy of such a probe is limited if the angle between the sound beam and the flow axis, known as the Doppler angle, is not precisely known. By use of a pulsed Doppler velocity meter (PUDVM) and a triangulation procedure, accurate empirical measurement of the Doppler angle has been obtained, allowing quantification of blood velocity scans across the aorta. Volume flow is obtained by integration of blood velocity profiles and arterial wall motion is measured with an ultrasonic echo tracking device. Accuracy of the probe was substantiated by comparison with ultrasonic and electromagnetic implanted flow cuff measurements. Use of the probe in measurement of blood velocity, volume flow and arterial wall motion at various locations along the 8- and 10-cm length of the descending thoracic aorta in adult beagle dogs is detailed. The simplicity, accuracy, and nontraumatic aspect of the technique should allow increasing use of such a probe in numerous research and clinical applications.     

Ultrasonic monitoring of glycerol settling during transesterification of soybean oil

A low-intensity ultrasonic measurement system was used to monitor the products of transesterification of soybean oil in methanol to FAME (biodiesel). The byproducts of the transesterification reaction are methyl esters, glycerol and other products. During the transesterification reaction, the glycerol, having a higher density than the methyl ester, settles at the bottom of the reaction vessel. The aim of this study was to measure the glycerol deposition rate during transesterification and to assess the reaction rate and end time. Soybean oil was converted into biodiesel at four temperature levels. The amount of catalyst (KOH) used in the transesterification reactions was determined by titration. The ultrasonic waveforms captured during the reaction were recorded and analyzed automatically. The ultrasonic system monitored the effects of reaction temperatures on the glycerol settling rate and the reaction end times. The ultrasonic measurement of glycerol settling would be a useful non-destructive method for evaluating the effects of parameters such as catalyst amount, mixing time and temperature on transesterification reactions.     

A two-stage regulatory system for pressure-constant perfusion of coronary vessels

This paper describes a double-loop servo-controlled pump system for the constant-pressure perfusion of a coronary artery. Due to the transient nature of changes in coronary vasomotor tone, such a perfusion system must have a fast regulatory response. In the first stage, a servo-controlled pump primes a windkessel having a volume of 35 ml with blood. The pumping rate is electronically controlled to maintain a constant pressure within the windkessel max. 700 mmHg. The maximal flow rate is 300 ml/min. To reduce the high pressure in the windkessel to the desired coronary perfusion pressure, a variable flow resistance, comprising a clamped thin-walled silicone tube, is provided in the output line of the system. A fast servo-motor drives the clamp and is controlled by an electronic regulator, using a second feedback loop from the pressure signal measured at the tip of the perfusion cannula. The system stabilizes the coronary perfusion pressure within 300 ms. An additional modulation of the setpoint signal in synchrony with the cardiac cycle improves the phasic pattern of the blood flow, and thus prevents changes in transmural blood flow distribution. The dead volume of the overall system is about 60 ml. Hemolysis caused by this system during five hours of perfusion in vivo is negligible.     

Measurement of blood flow and oxygen consumption in the pelvic limb of fetal sheep

In order to determine blood flow and oxygen consumption in the pelvic limb of fetal sheep, we applied the Fick principle of measurement of oxygen consumption in seven paired experiments in seven fetal sheep under normal conditions and after treatment with pancuronium bromide. Catheterization procedures, which minimized interference with the study limb circulation, avoided changes of catheter tip position during fetal movements,n and prevented collateral circulation to and from tissues not located in the pelvic limb, were utilized. Blood flow through the external iliac artery was measured by means of a transit time ultrasonic method. Six sample sets for oxygen content were drawn from the external iliac artery and vein during 45-min control period and repeated after neuromuscular blockade. Normal oxygen consumption under these experimental conditions was determined to be 20.7 +/- 1.9 (mean +/- SEM) mumole.min-1.100 g-1. Neuromuscular blockade caused oxygen consumption to decrease significantly (P less than 0.01) by 12% to 18.1 +/- 2.1 mumole.min-1.100 g-1 and decreased the average coefficient of variation from 15 to 8%. The data demonstrate that spontaneous skeletal muscle activity accounts for a significant amount of oxygen consumption, the level of which can vary widely over brief periods of time. These results suggest that such tissues with significant spontaneous changes in metabolic activity require repeated blood flow measurements with simultaneous determination of substrate arteriovenous differences to best describe metabolism under normal conditions.     

Numerical modelling of blood clot extraction by aspiration thrombectomy. Evaluation of aspiration catheter geometry

Aspiration thrombectomy is one of the most effective systems for blood clot removal and vessel recanalization. We present the results of a study involving the modelling and extraction of blood clots in the arteries of the human body using the following computer tools: Bond-Graph methodology for the fluid domain and Multi-Body Simulation for the mechanical domain. The modelling for the mechanical domain focuses on the clot and the distal end section of an aspiration device. Our final model considers an elastic characterization of the blood clot with progressive detachment from the vessel wall. We conclude that the results of such modelling could potentially improve the effectiveness of blood clot removal by reducing the risk of clot fragmentation. Such modelling could also potentially provide an adjunct technique in improving recanalization of arteries over a range of given parameters (mechanical properties of the vessel, mechanical properties of the blood clot, blood clot length, suction pressure, catheter – clot distance, catheter shape, catheter diameter and vessel occlusion).