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doi: 10.1177/003754979606600404pmid: N/A
Discrete event simulation has been used to explore different models of screening for diabetic retinopathy. Diabetic retinopathy is a common complication of diabetes and can cause blindness. The risk of blindness can be significantly reduced by screening and timely laser treatment. The simulation has been written in Pascal, using an extended version of Pascal_SIM, to explore the costs and benefits. The simulation models patients' disease progression and their screening, followed by treatment. The results shown are for patients with insulin- dependent diabetes.
Thomaseth, Karl; Boniollo, Barbara
doi: 10.1177/003754979606600406pmid: N/A
Therapy of occlusive pathologies of blood vessels, like acute myocardial infarction, is commonly based on administration of thrombolytic enzymes that accelerate the dissolution of thrombi, but that increase also the risk of bleeding through their activity on specific plasma substances. In order to gain insight regarding the relative importance of various processes on the dynamics of these plasma substances we developed a math ematical model of biochemical reactions occurring in plasma during therapy with the thrombolytic agent rt-PA ( recombinant tissue-type Plasminogen Activator). On the basis of in vitro knowledge a preliminary model was formulated and simulation studies were performed to analyze in detail the various processes. During the validation of the model some novel hypotheses emerged regarding the importance of specific biochemical reactions in vivo. A revised model was then formulated which well describes experimental observations reported in literature.
Amoore, John N.; Santamore, William P.
doi: 10.1177/003754979606600407pmid: N/A
Respiratory variations in blood flow are initiated by the changing pressures within the intrathoracic and abdominal cavities, thereby altering the pressure gradients for blood flow into and out of the thoracic cavity. The respiratory venous return variations alter the right ventricular volume which directly affects left ventricular function through ventricular interdependence. Variations in right ventricular output affect, after transmission through the pulmonary circulation, left atrial inflow and hence left ventricular (LV) output. LV output is also directly affected by respiratory variations in the pressure gradient between the left ventricle and the systemic circulation. Any respiration-induced variations in the haemodynamic impedance to blood flow (collapse of the great veins, variations in pulmonary vascular impedance) will also contrib ute to flow variations. The heart rate changes with respiration affecting heart chamber filling and output.The wide variety of factors contributing to respira tory blood flow variations complicates its analysis. However, by enabling the individual factors to be separately considered, model studies provide a convenient method of analysing the effects of the different factors involved.
doi: 10.1177/003754979606600408pmid: N/A
Many biomedical problems, including diabetes, hypertension, and drug tolerance, are fundamentally problems of biological control systems. Computer modeling and simulation constitute an effective tool for the systematic study of such systems. In particular, System Dynamics provides a graphical interface which allows one to develop a model structure using a parsimo nious set of symbols. The structural diagram is linked with a set of equations to quantitatively describe each component in the system. Simulations can then be conducted to examine the behavior of the system under a variety of circumstances. Once models are developed, they may be used by a larger audience after only a few hours' training. It soon becomes evident that a given model may be applied to a surprisingly wide variety of biological systems. Finally, System Dynamics models may be readily modified, adapted, and expanded, leading to a growing body of models which are relevant to the biomedical community.
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