VITAL FRAMEWORK INTERFACE FOR A FLEXIBLE PERSISTENCE OF MEDICAL DATA INFORMATION 
Matthias Struck, Svetoslav Pramatarov, Christian Weigand
Fraunhofer Institute for Integrated Circuits, IIS
INTRODUCTION The progress of information technology has become irreplaceable in the field of medical applications in the past few years. In both the intensive clinical and home care region the wireless communication between sensors acquiring physiological parameters and mobile stations allows a convenient monitoring of the patient vital signs. The trend of medical devices is from the isolated stand-alone ones towards a network of connected medical devices. The integration of such a network into a hospital information system provides the medical data information to be accessed by several physicians at different places. Essential requirements to integrate medical devices of different manufacturers in such a network are a standardized data representation and well-defined communication protocols. The purpose of the CEN ENV13734/35 standard for Vital Signs Information Representation (VITAL) is to define an object oriented model of medical devices and vital parameters that are identified by a unique nomenclature. Furthermore, it specifies a communication model that consists of protocols and services based on the ISO/OSI standard. The implementation of the standard results in a VITAL library, which is embedded into a generic and flexible framework. This framework defines interfaces for the integration of different medical devices, additional communication protocols, for example Bluetooth and WLAN,   graphical user interfaces to visualize vital signs and signal processing units. These modules can be implemented and integrated in form of plug-ins. At the current state-of-the-art, there is no interface for the persistence of the medical parameters represented by VITAL objects. In order to guarantee readability of patient related medical data information by several institutions in the future, standardized and efficient storing methods are indispensable. That is why we created a new user interface that allows a flexible real-time persistence of all data acquired in the medical workflow. In the following section, we describe the interface mechanism that can handle with different file formats in a homogenous manner. Afterwards, those file formats together with their benefits and disadvantages are presented, which come into question for the persistence.
METHODS There are lots of aspects that are of great importance when dealing with an interface for data persistence: on the one hand the interface has to define general methods, which only describe their achievement. The concrete functionality has to be implemented in a plug-in describing the properties of a specific file format. On the other hand the used file formats have to be independent of specific hardware technologies. Therefore, the interface has to incorporate with the byte order problem. Furthermore, the persistence should allow fast access to all pieces of data and the file formats should contain as less redundancy as possible. Concentrating on the choice of specific file formats, there are additionally requirements such as the degree of deployment of the file formats in the clinical routine and the quality of the tools for visualization of medical data information.  In order to give a conclusion about the suitability of different formats, the following data file formats have been evaluated: EDF, EDF+, FEF and SCIPHOX. The European Data Format (EDF) is a simple format for exchange and persistence of multi channel biological signals. In addition to the simple composition, the main advantages of EDF are its high distribution in hospitals and the existence of many non-commercial viewing tools. But it was not developed to store interrupted recordings of vital data streams. An extension of the EDF is the EDF+. The file structure of them is nearly the same. Both consist of a header followed by the data records. In contrast to the first version, EDF+ can deal with interrupted signals within the same file. Additionally, one of the EDF+ signals can be specially encoded to save medical alerts such as the battery status and different annotations, for example, made by the physician. The File Exchange Format (FEF) is much more universal than EDF/EDF+. It is based on the VITAL CEN ENV13734/35 and has become an own standard: CEN/TS 14271, which uses the same nomenclature and Domain Information Model (DIM) representing medical devices and vital parameters as the VITAL standard. That is why the persistence with the FEF is free of information loss in the sense of the VITAL standard. Consequently, it allows the complete reconstruction of the VITAL object hierarchy. Furthermore, the FEF standard defines a multimedia section, which can either contain multimedia data such as patient images and audio/video data or reference them. In contrast to the file formats discussed so far, the Standardized Communication of Information in Physician Offices and Hospitals using XML (SCIPHOX) is not a binary file format, but is based on the XML syntax. Because of the high redundancy resulting from the encoding of numerical data, it concentrates on demographic and administrative data. Nevertheless, a big benefit of SCIPHOX is that its contents can be interpreted by arbitrary XML parsers. In the following section we will give a summarized conclusion of the main aspects.   
RESULTS Due to the fact that FEF is the most universal file format, which is completely consistent to the VITAL standard, the persistence of medical data with the File Exchange Format is an adequate solution within the VITAL framework. Unfortunately, the FEF standard was first published after lots of "isolated applications" have already been introduced into the clinical workflow. Consequently, it is of limited practical use up to now.  That is why it is important that the persistence interface of the VITAL framework can also handle with the other described file formats without modifying the interface.
DISCUSSION In order to guarantee both the full information acquisition of the VITAL standard and also its immediate practical usage it is meaningful to store the data in FEF format and also provide a tool that can convert FEF to EDF/EDF+ file format. Therewith full information persistence as well as the consistence with existing clinical applications can be achieved.