How does 'AIDA on-line' work?
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This Web page provides an overview of how the ‘AIDA on-line’ interactive educational diabetes simulator actually works.
AIDA is an interactive educational diabetes simulator which contains a model of glucose-insulin interaction in the human body . It simulates the effects of changes in insulin and diet on the blood glucose profile of a typical ‘virtual diabetic patient’ - as either a self-learning or demonstration exercise. Using AIDA as an example, ‘AIDA on-line’ has set out to show how it is possible to move from purely static, informational resources on the Web - to using the Internet to provide more interactive and dynamic information about clinically relevant situations in diabetes care.
The AIDA PC software is freely available for download without charge from this Website. While the program has been quite widely applied, there are a number of practical and theoretical limitations to the AIDA PC software approach. (i) People who wish to make use of the program need to download an archive file and then install it on their hard disk. This requires a certain modicum of computer knowledge or experience. (ii) Some people might be concerned about the theoretical risk of receiving some sort of virus when downloading an executable file from the Internet (notwithstanding the fact that the AIDA PC software has repeatedly been shown to be virus free). (iii) The software requires an IBM-compatible DOS / Windows PC (or an Apple Mac running SoftWindows or a PowerPC Macintosh). People who do not have access to one of these computers or operating systems cannot run the AIDA PC software. (iv) The availability of enhancements or upgrades to the PC software can take time to reach end-users, since further downloads and local installation are required to obtain the latest version. (v) The PC software, being DOS-based, has a user interface that is not totally adherent to the principles of a Windows graphical user interface (GUI) with which end-users will be most familiar.
Therefore, although over downloads of the AIDA PC software have taken place since its release on the Internet, it was hypothesised that an even wider audience might benefit from the AIDA diabetes-simulation approach if it did not require any local download or installation, could run on a wider range of computers, and would offer a standard Windows GUI for user interaction. To address these points, a version of the AIDA diabetes simulator, called ‘AIDA on-line’, has been developed that is totally Web-based and which therefore can operate from any computer, anywhere in the world, provided it is connected to the Internet and has a graphical display. Enhancements and upgrades can be made available instantaneously, worldwide. Furthermore, no download or local installation is required. In fact, it is not even necessary to have a computer to use ‘AIDA on-line’ - usage has even been reported from people with diabetes using WebTV!
Designed to be accessible and usable by anyone who desires to learn more about diabetes, 'AIDA on-line' has been made available via this Website at: http://www.2aida.net. ‘AIDA on-line’ allows users to make modifications to the insulin regimen and diet of 40 different pre-stored ‘virtual diabetic patients’ or create new ‘patients’ with user-generated regimens. Multiple simulations can be run for educational purposes in order to compare the results of changes in insulin therapy or diet. The results are viewed through the use of several graphs that display steady-state blood glucose and plasma insulin concentrations over a 24-hour period. The graphs can also display the different glucose fluxes underlying the simulations (net hepatic glucose balance, peripheral glucose utilization, glucose absorption from the gut, and renal glucose excretion into the urine).
Educational models written in Java or Perl allow a wide variety of Internet browsers to access and run simulations without requiring time-consuming downloading of lengthy files, utilizing compilers, or using local disk storage space. Perl v5.0 was selected for this work because it places a minimal load on the user’s system and is compatible with nearly every major Web browser that is currently in use.
Perl is a general purpose non-proprietary scripting language that can be used without modification on multiple computing platforms. It is maintained by a worldwide network of volunteers - a factor which contributed to its choice for the implementation of ‘AIDA on-line’ - which is itself a free Web resource implementation of a freeware PC program.
An often asked question is how does ‘AIDA on-line’ actually work? For instance, how is it possible to run a diabetes simulation from, for example, Auckland, New Zealand - simultaneously with a simulation from Basel, Switzerland and another from Durham, North Carolina - on a computer in London, England - all in a matter of seconds?
The approach makes use of standard Web-based Hypertext Markup Language (HTML) forms that post information directly as input to programs stored in a Common Gateway Interface (CGI) area of the host (‘AIDA on-line’) Web server. The CGI Perl scripts (programs) which actually run the simulations have been set up to accept input from the Web sever (HTML form submission) as well as from static text files stored at the Website. The main output from these scripts is formatted in HTML. This allows the user’s Web browser to view and download the output of the ‘AIDA on-line’ script. The HTML output does not actually exist physically as files but rather is created dynamically in real-time, upon demand. The Perl scripts’ other outputs include physical text files that store data used in the generated plots. There are a total of three scripts used to generate the ‘AIDA on-line’ simulations. Two scripts are used to process user preferences in order to set up forms for the users’ input. The third script actually generates the simulations.
The simulator requires several parameters that allow users to customize their session. For example, visitors can select their preferred units for blood glucose measurement (mmol/l vs mg/dl), select the insulin types to be used, decide whether or not they would like to see the advanced flux plots (net hepatic glucose balance, peripheral glucose utilization, renal excretion of glucose, and glucose absorption from the gut) as part of their simulation runs, and / or display user-defined upper & lower normoglycaemic ranges / limits on the blood glucose simulation curves.
As with the AIDA PC software, users can choose from 40 existing, pre-stored scenarios or create a new case from ‘scratch’. An abbreviated description of the cases is provided initially. However, if the user needs a further description, a link is given to a Web page where each of the 40 sample cases is described in full.
Once the user has selected a case, a CGI Perl script is invoked. This script is passed the preferences of the user and the sample case, if one has been chosen. If an existing case is chosen, the script populates an HTML form template with data for that case, which are extracted from static text files. This form would be left blank if the user decides to start a new case.
When the user actually opts to run a simulation, this HTML form data and the user’s preferences are passed to the simulator. The simulation engine - implemented in Perl - makes use of an identical model to that adopted for the AIDA PC simulator  to generate the blood glucose and plasma insulin profiles. The simulation engine calculates the blood glucose and plasma insulin levels as well as each of the four glucose fluxes at 15-minute intervals during a simulated 24-hour day. With all the calculations and plot creations completed, the simulator displays its output in HTML format to the user’s Web browser. The HTML output automatically contains references to the newly created plots and data files for the user’s browser to display.
A key feature of the ‘AIDA on-line’ diabetes simulation approach is the ability to compare simulation results before and after a change in regimen. Therefore, an HTML form identical to the previously submitted one is displayed below the simulation graphs. This enables the user to make changes to the original input. Again, the user can submit the changed data to the simulator. This time, however, the user will be submitting not only the changed data and preferences but also references to the data files that were produced during the original simulation run. The simulator then goes through the same process as the original run. However, this time, the previously stored data files are passed with the new data to the plotting program. The new graphs will then contain values for the two different simulations. This allows the user to see the changes made from the previous run.
‘AIDA on-line’ runs on a Linux Apache World Wide Web server on a Pentium III / 650MHz PC and utilizes a multi-threading algorithm that allows multiple simultaneous simulations to be run. When the simulator is invoked, a Process Identification (PID) number is assigned. The files (graphics and data) are stored uniquely with the PID as part of the file name - so even if multiple users from different parts of the world submit simulations at the same time, they can all be processed separately.
The simulations can be run from any computer (PC, Apple Mac, Linux machine, Unix server, NT server, etc) from anywhere in the world - provided the computer has access to the Internet and a graphical display. There is also a registration and announcement list that 'AIDA on-line' users can subscribe to at the Website (or by emailing: email@example.com) so that they can be immediately notified by email about any enhancements or modifications to the system as they become available worldwide.
The total elapsed time for a single simulation varies. There are basically two periods of delay between data being submitted by the user and the full results being presented back. First, the time for the simulator to be invoked and run depends on the amount of load on the server. However, the time used by the simulator is rarely over one second. Secondly, there is a time delay for the transfer of the HTML page and graphics files back to the end-user. The HTML (text only) file itself is only approximately 9 kilobytes (Kb) in size. By contrast, the standard simulation produces approx. 17 Kb and the advanced (fluxes) simulation produces approx. 25 Kb of graphics data. Therefore the total elapsed time for the end-user depends greatly on the speed of the connection to the Internet, and geographical location, since the ‘AIDA on-line’ server is located in Europe. However, these file sizes are tiny compared with usual Web transfers so apparent simulator response times for end-users are generally very rapid.
The purpose of developing a World Wide Web-accessible glucose-insulin simulator was to provide an educational opportunity for as many people as possible (patients with diabetes, their relatives, students, and health-care professionals). In this respect, we have exceeded our expectations. Since we started keeping records in August 1998, nearly 140,000 interactive simulations have been run at ‘AIDA on-line’ @ http://www.2aida.net. Visits have been recorded from over 70 countries, and independent comments about the simulations have been very encouraging [2-4].
This work shows how it has been possible to make use of the Internet not just as a static repository of information but also as an interactive medium to perform quite complex dynamic simulations in a clinically useful manner. Writing the program in Perl and then utilizing a fast Web server has allowed many users to access ‘AIDA on-line’ simultaneously. We are not aware of any diabetes simulation facility as sophisticated as ‘AIDA on-line’ that is available anywhere else on the Internet.
The main educational utility of 'AIDA on-line' lies in the ability to rapidly compare results from different diabetes simulations. By modifying the simulated insulin injections, users can learn to exercise more control over the blood glucose level of the simulated patient. For instance, possible advantages of using multiple injections and different insulin types can become apparent as different therapeutic combinations are compared. Modifying carbohydrate inputs can also demonstrate the important contribution of diet to blood glucose control. In this respect, large swings in meal carbohydrate intake result in obvious swings in the blood glucose level which requires insulin injections to be adjusted for the simulated virtual diabetic patient. Having multiple, pre-stored example ‘patients’ allows users to see the effects of these changes on different patients with different sensitivities to insulin.
The hope is that patients, their relatives, and students can learn how to balance insulin and diet in diabetes by modifying the simulations. The concept underlying this diabetes simulation approach is that patients with diabetes may also improve their ability to actually manage their own diabetes by experimenting in this way. Clearly this hypothesis remains to be tested in a randomized controlled clinical trial setting. However it is hoped that the relatively widespread use - and widespread availability - of the AIDA PC and ‘AIDA on-line’ diabetes simulation approaches will encourage the undertaking of such clinical trials.
‘AIDA on-line’ can be accessed on the Internet at http://www.2aida.net where it is being made available, without charge, as a non-commercial contribution to continuing diabetes education. People who wish to be automatically informed about updates and enhancements to the ‘AIDA on-line’ Website can subscribe (for free) to the 'AIDA on-line' registration / announcement list by sending a blank email note to: firstname.lastname@example.org
 Lehmann ED, Deutsch T. A physiological model of glucose-insulin interaction in type I diabetes mellitus. J Biomed Eng 1992;14:235-242. Anon. The virtual diabetic patient: AIDA on-line. Diabetes/Metabolism Research and Reviews 1999;15:226.  Mendosa R. AIDA On-Line. Review available from the American Diabetes Association Website at: http://www.mendosa.com/aida.htm
 Lehmann ED. User reviews of AIDA online: a web-based interactive educational diabetes simulator. Diabetes Technol Ther 2000;2:329-342.
The overview of ‘AIDA on-line’ documented above is derived from an extended abstract entitled: "Dynamic Interactive Educational Diabetes Simulations Using the World Wide Web" by E.D. Lehmann, D.K. DeWolf, C.A. Novotny, R.R. Gotwals Jr., R.P. Rohrbach, and S.M. Blanchard which has been published in the journal Diabetes Technology & Therapeutics 2001; 3(1): A17-A20. © Mary Ann Liebert, publishers.
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Return to AIDA Website Home Page AIDA is a freeware diabetes software simulator program of glucose-insulin action + insulin dose & diet adjustment in diabetes mellitus. It is intended purely for education, self-learning and / or teaching use. It is not meant for individual blood glucose prediction or therapy planning. Caveats
This Web page was last updated on 19th October, 2003. (c) www.2aida.org, 2000. All rights reserved. Disclaimer. For the AIDA European Website, please click here. For the Diabetes / Insulin Tutorial, please click here.