Bluetooth as the preferred wireless connection for medical equipment
Wireless communication opens up completely new
possibilities and application areas for medical technology. Bluetooth seems to
be establishing itself more and more as the standard.
Demographic change is in full swing. As early as 2035,
Germany will have one of the oldest populations in the world alongside Japan.
This shift represents one of the biggest social challenges of the coming decades
but admittedly also offers huge market opportunities for companies active in the
medical technology and health care sectors.
For example, the Parks Associates analysts have predicted a
compound annual growth rate of more than 80% for the next five years in their
current Wireless Healthcare report. According to the study, the wireless
technologies will benefit most of recent and future developments in the
Telehealth technologies. One pre-condition is, however, not only standardisation
between various manufacturers’ different devices but also different classes of
device. So-called Ambient Assisted Living (AAL), for example, uses electronics
and micro-system and information technology components in combination with
services in order to be able to offer cost-efficient solutions in the health
sector.
Typical applications from the medical field are, for example,
assistance systems for the chronically sick persons, patient monitoring for the
critically ill patients, monitoring for old people with dementia and Alzheimer’s
and the overweight, implant monitors, regular and automated inter-disciplinary
data exchange between medical specialists, monitoring or fitness data and also
medication control and reminders for senior citizens and the chronically ill.
In order to initiate work towards the necessary
standardisations for the public health sector, the Institute of Electrical and
Electronic Engineers (IEEE) has already launched several standardisations.
Meanwhile, however, the non-profitmaking Continua Health Alliance, whose more
than 200 members have committed themselves to the standardisation of health care
and wellness equipment, has started to play an even more important role. Amongst
other things, their aim is the development of interoperable devices and
standards, quality improvement, more cost-efficiency in the health service and
also prevention and help for senior citizens and the chronically and critically
ill patients.
Figure 1 shows the typical structure of a Telehealth system,
consisting of LAN (Local Area Network) and PAN (Personal Area Network)
components, application host devices, WAN devices with the health databases
often integrated into them (Electronic/Personal Health Record Network = xHRN)
keeping patient-related health files.
The Continua Health Alliance initially focussed on PAN
devices and the xHRN interfaces. In future, the wireless interfaces in typically
mobile PAN devices or PAN devices acting as decentralised sensors/actuators will
enjoy the greatest significance; communication via Bluetooth plays a decisive
role here.
For this reason, 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.  Wireless
hardware modules such as Panasonic’s types PAN1455, PAN1555 (Figure 4) and PAN
1326, for example, which can support both the HDP Bluetooth Health Device
Profile and comply with IEEE11073 proved to be especially helpful and have some
parts already fully integrated. The modules fulfil not just all interface and
software stack requirements; they are also pre-certified, which helps the
customer to achieve a rapid time to market without high additional time and cost
demands. The modules are mainly integrated via serial or processor interfaces
and are relatively simple to realise.
A discretely set up and tailor-made wireless interface and
the required certification costs is generally 15 to 25 times more expensive than
such application-specific wireless hardware modules off the peg. The fastest,
most cost-efficient and low-risk way to implement wireless interfaces in medical
equipment is therefore the use of ready-made modules with integrated software
stacks.
|
Figure 5 shows the
block diagram of a typical Bluetooth medical application. At a minimum, these
consist of a host processor, memory, the power supply and the Bluetooth module.
Ideally, even the antenna can be integrated on to the module to make
certification even simpler. This depends, however, on the enclosure used.