The Hewlett-Packard (HP) Serial Distribution Network (SDN) is a popular system of bedside patient monitoring used in hospitals throughout the world. The system is robust and reliable, but access to the numeric data and real-time waveform data for clinical research requires a proprietary programmable network interface board. This project describes the design and implementation of a simple parameter data acquisition program for the HP 'Careplane' board. The application conforms to the 3-layer model suggested by HP. The Data Link Layer is implemented in IBM-PC assembler and the Session and Application layers are programmed in C++. Functional design predominates for the Data Link and Session layer modules, but object-oriented design is used for the Application Layer modules. The target is an MS-DOS executable. The application was tested on an IBM-compatible PC linked to an SDN with 15 nodes.
Recording and display of information from bedside patient monitors is now routine practice in many hospital areas, such as the operating theatre, intensive therapy unit (ITU) and coronary care unit. Manufacturers offer monitoring systems of varying complexity. The ITU in Edinburgh Royal Infirmary uses a proprietary system from Hewlett-Packard (HP) with bedside monitors linked on a Serial Distribution Network (SDN). Using an appropriate network interface, parameter data such as heart rate and arterial pressure may be recorded and displayed in a remote location.
To date there has been little effort by manufacturers to standardise the interface to medical devices. The IEEE Medical Information Bus (MIB) standard has been in development since 1980 [1], but the first two standard documents have only recently been approved for use. This represents an important step toward a standard interface, but it remains to be seen whether manufacturers will implement the IEEE recommendations. This is unfortunate, as automatic data acquisition by computer is important in clinical research, removing the tedium of manual bedside recording and allowing the researcher to use his or her time more productively.
At present, one can find various data acquisition programs in use in research centres around the world, but there is no central database of applications. This situation discourages software reuse, and efforts are being made by doctors in Glasgow to compile an archive of data acquisition applications from sources in the UK.
To design and build a data acquisition application for the SDN in the Royal Infirmary, Edinburgh. The application should:
The application developed for this project is an MS-DOS executable. The virtual memory mapping system of Windows makes it difficult (although not impossible) to develop a Windows application. HP specifies that the Careplane board must be installed in an IBM-compatible PC. The application could (in theory) be ported to Linux but this is left as an exercise for the more enthusiastic.
A library containing functions for initialising Careplane and reading from/writing to the shared memory was available
at the outset of the project. This code is referred to extensively in the Data Link Layer chapter. Several minor modifications were made to the library, including the substitution of simplified segment directives for conventional and the inclusion of a short pause during the initialisation procedure. A function-oriented design was used for the session layer module, as the simplicity of the code did not seem to merit an object-oriented approach.
For the application layer, a functional approach was taken to the module for reading data messages, but
object-oriented design predominated for the actual processing and storage of the data. The code is more readable,
and easier to modify as a result.