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At least 631 records · Page 35Linked to original sources
PubMed2002

Terminal gas velocity during laparoscopy.

STUDY OBJECTIVE: To assess the effect of port size in relation to laparoscopic gas flow and to determine the terminal velocity of gas flow during insufflation. DESIGN: Analysis and mathematical modeling of gas flow characteristics. SETTING: University biomedical engineering department. INTERVENTION: Analytic calculations including Bernoulli's equation to describe gas volumetric flow and velocity as it exits laparoscopic intraabdominal entrance sites. MEASUREMENTS AND MAIN RESULTS: Mathematical modeling showed that terminal velocity of gas entering the abdomen through needles or trocars reaches a practical limit depending on size and configuration of the gas exit site, amount of turbulence, length of delivery port, and gas flow. Flow rate was evaluated for circles of 2, 5, and 10 mm and annular slots of 0.1- to 0.01-mm thickness. CONCLUSION: Resistance to gas flow increases and gas exiting terminal velocity increases as the effective area of the gas exit site decreases. Depending on the configuration of variable parameters, gas flow can reach 30 m/second.

Biophysical Phenomena↗
PubMed2006

Diblock copolymers based on dihydroxyacetone and ethylene glycol: synthesis, characterization, and nanoparticle formulation.

Polymeric biomaterials have played an integral role in tissue engineering, biomedical devices, and targeted drug delivery. Block copolymers are especially important because their physical and chemical properties can be controlled by adjusting the ratio, size, and type of constituting blocks. Herein, the synthesis and characterization of diblock copolymers composed of poly(ethylene glycol) and a polycarbonate based on the metabolic intermediate, dihydroxyacetone, are reported. The length of the dihydroxyacetone-based block was controlled by adjusting the reactant feed ratios and initiator injection conditions. Intermediates and final products were characterized via (1)H NMR, GPC, DSC, TGA, and diffusion-ordered NMR spectroscopy. The dihydroxyacetone-based hompolymer is insoluble in water and most organic solvents, but is hydrophilic in nature. This, coupled with poly(ethylene glycol)'s solubility characteristics, allows the block copolymer to form nanoparticles in aqueous and organic anti-solvents. Dynamic light scattering and TEM results indicated the formation of spherical nanoparticles.

Calorimetry, Differential Scanning↗
PubMed1996

Current status of mechanical ventilation decision support systems: a review.

Objectives of computerized decision support systems for mechanical ventilation are discussed. Questions considered are: Why is computerized decision support for mechanical ventilation important? What parameter(s) should be optimized? What are the differences between a single attribute and a multiattribute value function used for optimization? How is it possible to achieve optimization in clinical practice with existing ventilators? How does one solve the problem of acquiring measurement of data needed for closed loop control? The possibilities and limitations of three existing decision support systems are discussed. 1) Computerized protocols from LDS Hospital in Salt Lake City, Utah, USA. 2) Optimization Program (OPTPROG) developed jointly at the Institute of Biocybernetics and Biomedical Engineering, Polish Academy of Sciences, Warsaw, Poland and Medical Intensive Care Unit, Department of Medicine at Karolinska Institute, South Hospital, Stockholm, Department of Medical Informatics Linkoping University, Sweden. 3) Ventilator Therapy Planner (VENT-PLAN) from the Section on Medical Informatics at Stanford University, Palo Alto, California, USA. Strategies leading to an optimal computerized decision support system are proposed. These strategies include development of better measurement methods for blood gases and cardiac output, improvement of man-machine and machine-machine interaction and the selection of optimization criteria. Finally, research directed towards building quantitative, dynamic patient models based on computerized databases of mechanically ventilated patients are discussed.

Algorithms↗
PubMed2004

The new Silk Road.

Explore the source record for details and available documents.

Academies and Institutes↗
PubMed2005

Millisecond-timescale, genetically targeted optical control of neural activity.

Temporally precise, noninvasive control of activity in well-defined neuronal populations is a long-sought goal of systems neuroscience. We adapted for this purpose the naturally occurring algal protein Channelrhodopsin-2, a rapidly gated light-sensitive cation channel, by using lentiviral gene delivery in combination with high-speed optical switching to photostimulate mammalian neurons. We demonstrate reliable, millisecond-timescale control of neuronal spiking, as well as control of excitatory and inhibitory synaptic transmission. This technology allows the use of light to alter neural processing at the level of single spikes and synaptic events, yielding a widely applicable tool for neuroscientists and biomedical engineers.

Action Potentials↗
PubMed1984

Simple devices for the physically disabled.

A report is given on a number of devices for the disabled that have been developed in the Biomedical Engineering Department at the Mississippi Methodist Rehabilitation Center. The primary criteria used in selection of devices to be included use simplicity, ease of fabrication and low cost.

Automobile Driving↗
PubMed2006

Gold nanostructures: engineering their plasmonic properties for biomedical applications.

The surface plasmon resonance peaks of gold nanostructures can be tuned from the visible to the near infrared region by controlling the shape and structure (solid vs. hollow). In this tutorial review we highlight this concept by comparing four typical examples: nanospheres, nanorods, nanoshells, and nanocages. A combination of this optical tunability with the inertness of gold makes gold nanostructures well suited for various biomedical applications.

Biomedical Engineering↗
PubMedDate not supplied

History of mechanical circulatory support.

End-stage heart failure exerts a tremendous impact on individuals and society in terms of personal and economic suffering. The development of mechanical circulatory support devices has been driven by the shortage of donor organs for heart transplantation. Collaborative efforts in the fields of surgery, medicine, and biomedical engineering, sponsored by both government and industry, have led to devices capable of providing reliable circulatory support. Future mechanical cardiac assist devices will likely play an important role in the treatment of an ever-growing population of patients with end-stage heart failure.

Cardiopulmonary Bypass↗
PubMed2001

[Tracheostomy valve with integrated cough flap for improving hands-free speech in laryngectomized patients--development and clinical applications].

BACKGROUND: Following successful voice restoration after laryngectomy either by a voice prosthesis, a surgical shunt or microvascular laryngoplasty, a further goal in rehabilitation is the insertion of a tracheostoma valve, which enables the patient to speak without using his fingers for closure of the tracheostoma. One important disadvantage of the tracheostoma valves, which are available today, is the necessity of removal of the valve in case of coughing, because the valve could be thrown from the stoma by the strong air flow during coughing. As many laryngectomies suffer from chronic bronchitis, this coughing problem is one of the reasons why only few patients could be provided with this useful aid. METHOD: At the department of biomedical engineering of the faculty of medicine at the university of Groningen, the Netherlands, 1994 two prototypes of a tracheostoma valve with an integrated cough lid were developed. These devices contain two separate valve systems: the normal speaking valve and a special coughing valve, which opens at a certain air flow and closes automatically after the coughing attack. Thus no manipulations are necessary during coughing, the patient can speak undisturbed. The ADEVA company (Lübeck, Germany) undertook the industrial production of this new type of tracheostoma valve creating different modifications of the prototype #2. PATIENTS: In four series with 6-8 patients per group the modified tracheostoma valves were tested clinically and the occurring faults or lack of correct function eliminated by small changes in the production. RESULTS: Meanwhile a suitable model for routine use is available, which was tested in 30 patients so far. This suitability was achieved by improvements in the valve mechanism, the valve seal and the adjustment mechanisms for the individual pressure level of the speaking and the coughing valve. CONCLUSION: The newly developed tracheostoma valve with integrated coughing lid (Window, ADEVA-medical Company, Lübeck, Germany) provides further improvement in speech rehabilitation of laryngectomies. The low acceptance of tracheostoma valves, which enable the patient to speak without using his fingers for closure of the tracheostoma, possibly may be raised by this new aid.

Bronchitis↗
PubMedDate not supplied

Creation of a neonatology facility in a developing country: experience from a 5-year project in China.

In 1983, Project HOPE was invited by Zhejiang Medical University to collaborate in developing a neonatal intensive care unit (NICU) at the Children's Hospital in Hangzhou, China. The initial approach involved renovating facilities, purchasing equipment and supplies, placing short-term consultants in the unit as teachers, and bringing selected leaders to the United States for brief fellowships. An evaluation at 18 months disclosed poor organization and leadership, inconsistent clinical care, and unsatisfactory utilization and maintenance of facilities and equipment. Therefore the strategy was revised to include long-term physician and nursing consultants, establishment of ties with HOPE Biomedical Engineering projects, and development of formal education programs. The unit was transferred to the Chinese after 4 years and an evaluation 1 year after transfer revealed an actively functioning independent NICU with evolving effective leadership, established purchasing and preventive maintenance programs, and continuing formal education activities. Unsatisfactory progress was found with the development of a transport system, some laboratory capabilities, adherence to admission and discharge policies, and various other administrative issues. Although the goal of establishing an independent NICU was realized, perhaps the most lasting accomplishment was the establishment of a facility and a format for development of a transportable education program aimed at improving neonatal care practices throughout a larger region of China.

China↗
PubMed2004

Using nanoparticles to create self-healing composites.

The need for viable materials for optical communications, display technologies, and biomedical engineering is driving the creation of multilayer composites that combine brittle materials, such as glass, with moldable polymers. However, crack formation is a critical problem in composites where thin brittle films lie in contact with deformable polymer layers. Using computer simulations, we show that adding nanoparticles to the polymers yields materials in which the particles become localized at nanoscale cracks and effectively form "patches" to repair the damaged regions. Through micromechanics simulations, we evaluate the properties of these systems in the undamaged, damaged, and healed states and determine optimal conditions for harnessing nanoparticles to act as responsive, self-assembled "band aids" for composite materials. The results reveal situations where the mechanical properties of the repaired composites can potentially be restored to 75%-100% of the undamaged material.

Journal Article↗
PubMed1998

A transient expansion of the native state precedes aggregation of recombinant human interferon-gamma.

Aggregation of proteins, even under conditions favoring the native state, is a ubiquitous problem in biotechnology and biomedical engineering. Providing a mechanistic basis for the pathways that lead to aggregation should allow development of rational approaches for its prevention. We have chosen recombinant human interferon-gamma (rhIFN-gamma) as a model protein for a mechanistic study of aggregation. In the presence of 0.9 M guanidinium hydrochloride, rhIFN-gamma aggregates with first order kinetics, a process that is inhibited by addition of sucrose. We describe a pathway that accounts for both the observed first-order aggregation of rhIFN-gamma and the effect of sucrose. In this pathway, aggregation proceeds through a transient expansion of the native state. Sucrose shifts the equilibrium within the ensemble of rhIFN-gamma native conformations to favor the most compact native species over more expanded ones, thus stabilizing rhIFN-gamma against aggregation. This phenomenon is attributed to the preferential exclusion of sucrose from the protein surface. In addition, kinetic analysis combined with solution thermodynamics shows that only a small (9%) expansion surface area is needed to form the transient native state that precedes aggregation. The approaches used here link thermodynamics and aggregation kinetics to provide a powerful tool for understanding both the pathway of protein aggregation and the rational use of excipients to inhibit the process.

Chromatography, Gel↗
PubMed2005

Shape optimization in steady blood flow: a numerical study of non-Newtonian effects.

We investigate the influence of the fluid constitutive model on the outcome of shape optimization tasks, motivated by optimal design problems in biomedical engineering. Our computations are based on the Navier-Stokes equations generalized to non-Newtonian fluid, with the modified Cross model employed to account for the shear-thinning behavior of blood. The generalized Newtonian treatment exhibits striking differences in the velocity field for smaller shear rates. We apply sensitivity-based optimization procedure to a flow through an idealized arterial graft. For this problem we study the influence of the inflow velocity, and thus the shear rate. Furthermore, we introduce an additional factor in the form of a geometric parameter, and study its effect on the optimal shape obtained.

Anastomosis, Surgical↗
PubMed2002

Stents: material, surface texture and design, in theory and practice.

Intravascular stenting has become standard practice in cardiology and interventional radiology. As part of their daily routine, interventional therapists have to choose from more than 50 different coronary stents for the optimal treatment of patients. Striking advances in biomedical engineering have triggered the production of numerous new and improved stent models, whose theoretical benefits have not yet been confirmed by large-scale clinical trials. Selecting appropriate stents for individual patients is frequently subject to the personal and, therefore, subjective experience of the interventional therapist. This paper reviews different stent materials and designs used in current trials and clinical practice. The theoretical benefits of individual parameters are discussed and correlated with up-to-date clinical results, particularly with a view to considering their favourable impact on intervention outcomes.

Journal Article↗
PubMedDate not supplied

MASTOS: Mammography Simulation Tool for design Optimization Studies.

Mammography is a high quality imaging technique for the detection of breast lesions, which requires dedicated equipment and optimum operation. The design parameters of a mammography unit have to be decided and evaluated before the construction of such a high cost of apparatus. The optimum operational parameters also must be defined well before the real breast examination. MASTOS is a software package, based on Monte Carlo methods, that is designed to be used as a simulation tool in mammography. The input consists of the parameters that have to be specified when using a mammography unit, and also the parameters specifying the shape and composition of the breast phantom. In addition, the input may specify parameters needed in the design of a new mammographic apparatus. The main output of the simulation is a mammographic image and calculations of various factors that describe the image quality. The Monte Carlo simulation code is PC-based and is driven by an outer shell of a graphical user interface. The entire software package is a simulation tool for mammography and can be applied in basic research and/or in training in the fields of medical physics and biomedical engineering as well as in the performance evaluation of new designs of mammography units and in the determination of optimum standards for the operational parameters of a mammography unit.

Algorithms↗