专业英语论文草稿

2021年1月25日发(作者：头皮发麻)
Using Zigbee to Integrate Medical Devices
Paul Frehill, Desmond Chambers, Cosmin Rotariu
Abstract
—

Wirelessly enabling Medical Devices such as Vital Signs Monitors, Ventilators
and Infusion Pumps allows central data collection. This paper discusses how data from these types
of devices can be integrated into hospital systems using wireless sensor networking technology.
By integrating devices you are protecting investment and opening up the possibility of networking
with similar devices.
In this context we present how Zigbee meets our requirements for bandwidth, power, security
and mobility. We have examined the data throughputs for various medical devices, the
requirement of data frequency, security of patient data and the logistics of moving patients while
connected to devices.
The paper describes a new tested architecture that allows this data to be seamlessly integrated
into a User Interface or Healthcare Information System (HIS). The design supports the dynamic
addition of new medical devices to the system that were previously unsupported by the system. To
achieve this, the hardware design is kept generic and the software interface for different types of
medical devices is well defined. These devices can also share the wireless resources with other
types of sensors being developed in conjunction on this project such as wireless ECG
(Electrocardiogram) and Pulse- Oximetry sensors.
Keywords
—
Biomedical
Telemetry,
Medical
Devices,
Bioinformatics,
Wireless
Sensor
Networks, Healthcare Information Systems.
I. INTRODUCTION
MANY devices that exist today by the bedside in the hospital ward, intensive care unit or
other clinical setting have data output features over serial ports and other types of interfaces such
as USB. These devices are usually considered a significant investment and are usually purchased
in an ad hoc fashion as required when finance becomes available. The consequence of this is that
devices are often
from different manufacturers that don’t support any standard
protocol. This can
make integrating these devices into a single network difficult.
In the hospital ward Vital Signs monitors, Ventilators and Infusion Pumps of many different
brands are usually portable and wheeled from patient to patient as required. By networking these
devices the hospital gains all the advantages associated with storing patient data centrally in
electronic records. By making the device part of a wireless sensor network such as a Zigbee [1]
network there are several more advantages including, cable replacement, mobility and location
management. Once these devices are networked they can also use the infrastructure of other
deployments of similar wireless sensor networks in the surrounding environment.
To achieve this type of solution each device must be fitted with a piece of hardware that will
act as a serial to wireless bridge, a Medical Device Interface (MDI). This MDI will allow the
device to receive and transmit data within the wireless sensor network. This inexpensive hardware
will be generic to fit a wide range of medical devices. Similarly the firmware can be kept generic
and any specific device communication protocols can be implemented on a server on the network
backend.
The work described in this paper is part of a larger project,the goal of which is to provide a
complete patient monitoring system. Other features of the overall system will be to provide ECG
(Electrocardiogram) and Pulse-Oximetry data in a novel way over a wireless sensor network using
expertise gained on prior projects [2].
II. RELATED WORK
The concept of using wireless sensor networks for Medical Care and wireless patient
monitoring has been explored by others but integrating data from other devices is generally not
discussed. There is ongoing related work in patient monitoring using wireless sensors such as the
“CodeBlue”project at Harvard [3]. Others have also proven successful
with wireless sensor
networks designs for medical sensors [4] and in the management of sensor data [5]. It has been
identified that it is desirable to wirelessly enable existing medical devices that provide vital signs
data using technologies such as Zigbee [6], [7]. The research described in this paper aspires to
meet these requirements. The use of wireless sensor networks within the hospital has been
extensively examined. Moreover, other wireless technologies within the same frequency band,
such as IEEE 802.11 [8], have existed within the hospital for some time [9].
III. REQUIREMENTS ANALYSIS
A. Wireless Technologies
Established standards for wireless applications, such as Bluetooth [10] and IEEE 802.11,
allow high transmission rates, but at the expense of power consumption, application complexity,
and cost. Zigbee offers low cost, low power devices that can communicate with each other and the
outside world. ZigBee's self- forming and self-healing mesh-network architecture lets data and
control messages pass from one node to another by multiple paths. This is particularly useful in a
hospital environment where interference from walls, people and general obstacles is a major issue.
Zigbee is based upon the IEEE standard 802.15.4 [11] for radio hardware and software
specification.
B. Mobility
Zigbee enabled devices support a sleep mode. An off-line node can connect to a network in
about 30 ms. Waking up a sleeping node takes about 15 ms, as does accessing a channel and
transmitting data. If the requirement is to collect data once a minute the device can be placed in a
power saving mode saving significant amounts of energy and increasing the battery life. In sleep
mode a zigbee chip can assume as little as 1.0uA [12]. This is particularly important in a medical
setting where patients are often on the move while still attached to medical devices.
C. Co-existence
Both Zigbee and IEEE802.11 operate in the license-free industrial scientific medical (ISM)
2.4GHz frequency 802.11 is already in widespread use within hospitals which would
encourage the adoption of Zigbee solutions in the same environment. However care has to be
taken to avoid interference between these 2 neighbouring technologies as described in the paper
entitled “Coexistance of IEEE802.15.4
with other systems in the 2.4GHz- ISM-
band” [13]. By

selecting an appropriate channel, after performing a simple site survey, these problems can be
easily avoided.
D. Device Parameters
Typical readings available on a ventilator are
Inspiratory Tidal Volume, Expiratory Tidal
Volume, O2 concentration,Respiratory Rate, Peak Pressure, Expired Minute Volume and Mean
Airway Pressure.
The settings on the ventilator are also

of interest to medical staff. The most
typical settings we’ve

chosen are
Inspiratory Tidal Volume, Minute Volume, O2 Concentration,
I:E Ratio, Breath Duration and Inspiratory Flow.
Similarly we have chosen some common parameters for Vital Signs Monitors. These are
Respiratory Rate, Non Invasive

Blood Pressure, SPO2 and Temperature.
The third device we
selected parameters for is the Unfusion Pump. The common parameters we are most interested in
here are
Volume, Time, Ramp and Occlusion Pressure.
Further parameters can be easily added to
the system in the future.




E. Bandwidth
For development purposes we analysed a Maquet Servo-I [14] which supports all the
ventilator parameters described above. This ventilator works in a command response
initial configuration has taken place 2 commands which are 7 bytes long each will
produce 2 responses of 67 bytes each. Therefore even in a multi hop mesh network it is anticipated
we would be able to support several of these devices plus other types of devices on the same
802.15.4 channel.




F. Scalability



The ventilator, having the most parameters of the devicesstudied, requires the most bandwidth.
Experiments carried outon a CSI Vital Signs Monitor [15] show that 44 bytes of data will produce
all the information we are interested in. A BraunInfusion Pump [16] exports 24 bytes of data to
produce the 4 parameters we need. For any of the medical devices we are concerned with, the
readings are typically only required once aminute in a hospital environment. All these devices
have their own alarm mechanisms built in; we are purely providing a means of exporting the data
automatically. Theoretically a single Zigbee network could have above and beyond 600
Ventilators as each device only requires less than 1KB of bandwidth per minute. The frequency at
which we capture the data is decided upon by the clinical staff themselves. A 1 minute interval is a
typical value, however even if they were to require the data every few seconds it is clear the
network could still support a large number of devices.




IV. SYSTEM ARCHITECTURE



A. High-Level Architecture



The overall System Architecture consists of a Wireless Personal Area Network (WPAN) and a
Local Area Network. The WPAN implemented as a Zigbee network communicates with the LAN
via a gateway. This gateway also serves as the WPAN coordinator which is responsible for
forming the network.

Each medical device has a Zigbee node attached(MDI) which enables data
to be transmitted wirelessly to the
Gateway and then onto a Server existing on the LAN. See
Fig. 1 below for a graphical representation of this. When an MDI is powered on it automatically
joins the network and makes itself known to the Server. A user can then associate
this device with a patient using a GUI client. Once an association has been completed the MDI
will be notified to begin transmitting data. Data received by the server will be stored in the
Electronic Health Record (EHR) for that patient and displayed on any GUI Client that is
subscribed.