A five compartment mathematical model of the cerebrospinal fluid (CSF) system has been developed to allow analysis of system control mechanisms, to aid in the understanding of hydrocephalus, and to facilitate the design and selection of shunt devices for treatment of this disorder [l]. In order to maximize desirable software features of this model, such as usefulness, reliabilty, and flexibility, two software languages were compared. The first, a high level language, Advance Continuous Simulation Language (ACSL) [6] implemented on both the VAXstation I1 and 80286 PC based system was used as the standard. The second software simulation language, Simulation Control Program (Stop) [ 7 ] , was run on a 80286 PC system and contrasted with ACSL. The PC ACSL model duplicated the VAX ACSL model and in most instances, similar SCoP results can be achieved on the PC system with the advantage of lower cost. OBJECTIVESThe goal of this study is to mathematically characterize selected shunt devices, incorporate them into the five compartment model developed in our laboratory, and implement the model on a PC based system. The analysis will result in the estimation of shunt performance through non-invasive means, and allows for comparison of various shunt designs. In general, a computer modeling approach should reduce the number of animal and clinical trials, and can be implemented on a PC based modeling system at a lower cost relative to other packages and systems.
Network performance analysis is an important part of PACS implementation. An understanding of the operational PACS -is necessary for the development of a realistic computer model of the system. Subsequent simulations of the model will help locate under and over utilized nodes and predict the effect of changes to the network. At Georgetown, we have started a model of our AT &T PACS, by first studying the acquisition aspect of the PACS in detail and developing a computer model using PAW simulation software.
In expanding our image management and communications system (IMACS) to include a new machine in the Ultrasound Section, we first modeled the impact of attaching the unit to either of our two acquisition modules (AM). Using the software package available to us, we could predict image queue lengths and average image waiting times (before transmission to the central archive). The AMs have attached a variety of devices with differing image production loads. The modeling allowed us to select the AM which would be least impacted (in terms of resoponse time to the devices sending data to the AM) by the added ultrasound machine.We found that though the input response times would not change much with the ultrasound machine connected to either AM, there was a significant impact on the predicted output queue length, with the more heavily loaded AM suffering larger increases in output queue dwell time if the new machine were connected to it. Based on these results, we elected to redistribute the AM loads, and connect the ultmsound machine so as to maintain a relatively balanced load.We tested certain parameters of the model by measuring input and output response times ofan AM under different, artificially induced, acquisition loading. The changes predicted by the model agreed with those measured in order-ofmagnitude terms.
A five compartment mathematical model of the cerebrospinal fluid (CSF) system has been developed to allow analysis of system control mechanisms, to aid in the understanding of the pathogenesis of hydrocephalus, and to facilitate the design of shunt devices to treat this disorder.The CSF system is modeled using a five compartment electric circuit analog (Figure l), which divides the CSF flow pathway into the four ventricles and the subarachnoid space. pressure-sensitive elements of the CSF flow system, which include ventricular compliance, outflow resistance, and CSF formation. In addition, age-dependent relationships further characterizing the pressure-volume index ( P W ) and the CSF formation rate (QN), are added to the model. ObjectivesThe model incorporates the The goals of this study are two-fold. First, to develop the mathematical characterization of the CSF system for a child, including the age-dependent relationships for the pressure-volume index and for the CSF formation rate. mathematically characterize selected shunt designs, and to incorporate them into the computer model. This analysis will result in the establishment of shunt performance criteria, permitting the evaluation of shunt performance through noninvasive means, and allowing one to compare various shunt designs. In addition, the effects of shunt siphoning due to changes in M y position can be estimated. In general, this computer modeling approach can reduce the number of animal and clinical trials and can be used to evaluate designs prior to prototype development. Thus, the overall cost to the health care system of bringing a new shunt design into clinical use can be markedly reduced. A second goal of the study is to BackgrollndOur research group began using computer modeling to study CSF flow in 1978 [l-31. At that time, a one compartment model of the CSF flow pathway was generated using an electric circuit analog to structure computer simulation software. In addition, animal experimentation and clinical studies helped to establish the complex relationships between system parameters [41. A two compartment model of the system was subsequently developed [5], and currently, a five compartment model, representing the four ventricles and the subarachnoid space, is employed I I Fig. 1 Five Compartment Model (Figure 1). A high level simulation language, Advanced Continuous Simulation Language (ACSL), is used, which allows for simplified encoding of the model.Employing the two compartment model, we investigated the dynamics of specific feedback mechanisms which act to minimize ventricular volume under high pressure conditions, including a decrease in ventricular compliance, lower CSF formation, and a decrease in CSF outflow resistance. The first two mechanisms reduce the potential for ventricular dilatation, while the third may result in ventricular enlargement when substantial intercompartmental resistance exists. between the degree of intercompartmental obstruction, ventricular compliance, and ventricular dilatation, the model demonstrates that a...
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