URL : http://www.msc-ge.com/en/7653-www
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collaboration with the Bluetooth SIG has been initiated which then worked out the Health Device Profile (HDP) and the Stack extension Multi-Channel Adaptation Layer (MCAP) and also the Device ID Profile (DI) as a new standard for transmitting medical data via Bluetooth. There is a close link to the IEEE 11073 standard which determines the format of the medical data, in other words the structure.
These new standards work connection-oriented to detect connection losses quickly. The health device profile consists of two parts; the transfer protocol in the Bluetooth stack and the description of the data structure. For the transfer part, several new functions play an important role and make the HDP significantly different to all other Bluetooth profiles: in order to be able to securely connect either streaming devices (EEG, ECG etc.) or also non-streaming devices (glucose, pulse, oxygen meter etc.), a control channel and also one to two data channels (streaming channel) are set up. The device ID profile ensures unique identification for data retransfer, for example between the health centre and the patient.
For this, a so-called Multi-Channel Adaptation Layer (MCAP) was the additionally implemented protocol stack which permits simultaneous communication between several channels.
Apart from this significantly improved data transmission reliability, the time-synchronisation of data from different sources also plays an important role in order to permit precise assessment of the physiological data. The Multi-Channel Adaptation Layer not only guarantees reliable data transmission in streaming and non-streaming mode but also clock synchronisation between different data sources. A time stamp with a resolution of 1µs can be produced via the clock on the master and the offset on the slave.
Extensions were also added to the Logical Link & Adaptation Layer (L2CAP). Enhanced Retransmission Mode and the streaming mode channels are organised within this protocol.
In relation to the data formats for medical information, the Bluetooth SIG recommends the IEEE 11073 reference implementation of the Continua Health Alliance (Figure 2).
The ISO/IEEE 11073 family of standards defines the components of a system with which it is possible to exchange vital sign data between different medical devices, to assess it and to remotely control the devices.
Within this standard, nomenclature codes are set out with which objects and attributes can be subsequently uniquely identified in connection with the so-called OID Code. In addition, objects for transmitting vital sign data and their arrangement in a Domain Information Model are defined and a service model for communication is determined. The agent/manager principle is also defined here where the data provider is agent (e.g. a sensor, a measuring device, etc..) and the manager is a data collector, a remote monitor or a database.
The IEEE 11073-20601 standards define the protocol for data exchange and the IEEE 11073-104xx the specification of the different end devices (agents).
Some dedicated device specifications are shown in the following diagram (Figure 3).
The specifications define the maximum packet sizes for both sending and receiving and also the data for the description, the formats and the values.
The examples give an idea that a fair amount of practical expertise is necessary for a successful Bluetooth implementation. However, most medical device manufacturers either did not have to deal with the topic of communication technology at all to date, or if at all then at least only peripherally. In order to minimise the necessary investments and to exclude development risks as far as possible, particularly medium-sized equipment manufacturers are well advised here to fall back on the expertise of communications specialists.
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Conclusion: if some rules of the game are complied with, it is arguably not very difficult to integrate wireless technologies such as Bluetooth into medical equipment. It is, however, important to take care in advance that all standards and regulations are complied with and that the development risk, especially with HF interfaces, is minimised. In many cases, pre-validated and, if necessary, pre-qualified software modules which contribute towards reducing the time and effort involved in certification and thus time and costs to market can prove helpful.