IEEE TRANSACTIONS ON INFORMATION TECHNOLOGY IN BIOMEDICINE, VOL. 8, NO. 4, DECEMBER 2004 439
A Wireless PDA-Based Physiological Monitoring
System for Patient Transport
Yuan-Hsiang Lin, I-Chien Jan, Patrick Chow-In Ko, Yen-Yu Chen, Jau-Min Wong, and Gwo-Jen Jan
Abstract—This paper proposes a mobile patient monitoring
system, which integrates current personal digital assistant (PDA)
technology and wireless local area network (WLAN) technology.
At the patient’s location, a wireless PDA-based monitor is used
to acquire continuously the patient’s vital signs, including heart
rate, three-lead electrocardiography, and SpO
2
. Through the
WLAN, the patient’s biosignals can be transmitted in real-time to
a remote central management unit, and authorized medical staffs
can access the data and the case history of the patient, either by
the central management unit or the wireless devices. A prototype
of this system has been developed and implemented. The system
has been evaluated by technical verification, clinical test, and user
survey. The evaluation of performance yields a high degree of
satisfaction (mean
=464
, standard deviation—SD
=0
53
in a
five-point Likert scale) of users who used the PDA-based system
for intrahospital transport. The results also show that the wireless
PDA model is superior to the currently used monitors both in
mobility and in usability, and is, therefore, better suited to patient
transport.
Index Terms—Mobile vital signs monitor, patient transport,
personal digital assistant (PDA), physiological monitoring, wire-
less local area network (WLAN), wireless patient monitoring,
wireless telemedicine.
I. INTRODUCTION
T
ODAY, MORE and more intrahospital transport of patients
is required in order to perform special examination or
therapy [1]. The key to success of all critical care transport is the
continuous monitoring of vital signs including single-strip elec-
trocardiography (ECG), oxygen saturation by pulse oximetry
SpO , heart rate (HR), and blood pressure [2]. Knowing
the physiological changes of patients while they are being
transported supports a preventive and early treatment strategy
that makes transport safe and smooth. In cases of intrahospital
or interhospital transport, patients are generally confined in
a small carrier space such as an ambulance, a stretcher, or a
wheelchair. In our experience, health-care personnel are often
confronted by several inconveniences associated with the use
Manuscript received August 29, 2003; revised April 20, 2004. This work was
supported in part by the National Taiwan University Hospital under Research
Grant NTUH92N007.
Y.-H. Lin, I-C. Jan, and Y.-Y. Chen are with the Department of Electrical En-
gineering, National Taiwan University, Taipei 10617, Taiwan, R.O.C. (e-mail:
f86921008@ntu.edu.tw; f86008@mail.ee.ntu.edu.tw).
P. C.-I. Ko is with the Department of Emergency Medicine, National Taiwan
University Hospital, Taipei 100, Taiwan, R.O.C.
J.-M. Wong is with the Institute of Biomedical Engineering, National Taiwan
University, Taipei 100, Taiwan, R.O.C., and also with the Department of Internal
Medicine, National Taiwan University Hospital, Taipei 100, Taiwan, R.O.C.
G.-J. Jan is with the Department of Electrical Engineering and Graduate Insti-
tute of Electro-Optical Engineering, National Taiwan University, Taipei 10617,
Taiwan, R.O.C. (e-mail: gjjan@cc.ee.ntu.edu.tw).
Digital Object Identifier 10.1109/TITB.2004.837829
of monitoring equipment during transport. First, the bulkiness
of the monitor makes it difficult to lift and transport. Second,
since the monitors are usually put on a trolley or at the end
of the stretcher and the leads between the patient and the
equipment are frequently wrapped around intravenous lines or
other tubes, it can easily lead to disconnection during transport.
Moreover, when patients receive radiographic examination, the
monitors must be placed beside them during radiation process,
and health-care personnel cannot remain in the control room to
monitor the physiological data on the monitor screen.
Recently, the fast development of mobile technologies, in-
cluding increased communication bandwidth and miniaturiza-
tion of mobile terminals, has accelerated developments in the
field of mobile telemedicine [3]. Wireless patient monitoring
systems not only increase the mobility of patients and medical
personnel but also improve the quality of health care [4]. With
respect to the remote monitoring of patients, many groups have
demonstrated the transmission of vital biosignals using global
system for mobile communication (GSM) technology [5], [6].
Some researchers have used cellular phones to transmit vital
signs from the ambulance to the hospital, either in store-and-for-
ward mode [7] or in real-time mode [8].
However, few attempts have so far been made to telemon-
itor patients continuously during intrahospital transport. Trans-
fers from one location within a hospital to another are some-
times confronted with temporary loss of the current state of
patients’ condition, a situation which can readily be alleviated
via the use of a wireless device [9]. In this paper, we devel-
oped a wireless patient monitoring system which integrates cur-
rent personal digital assistant (PDA) [10] and wireless local
area network (WLAN) [11] technology, which also enables con-
tinuous monitoring during intrahospital patient transport. The
PDA-based monitoring system has been preliminary evaluated
and compared with the present system, from the perspective of
its operators.
II. M
ETHODS
A. Overview of the System
The aim of this study is to design and implement a mobile
system for monitoring vital signs, and to facilitate the contin-
uous monitoring of patients during transport. Fig. 1 shows the
architecture of the proposed system. The telemedicine system
consists mainly of two parts—1) the mobile unit, which is set
up around the patient to acquire the patient’s physiological data,
and 2) the management unit, which enables the medical staffs
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440 IEEE TRANSACTIONS ON INFORMATION TECHNOLOGY IN BIOMEDICINE, VOL. 8, NO. 4, DECEMBER 2004
Fig. 1. Architecture of the wireless telemedicine system.
to telemonitor the patient’s condition in real-time. The manage-
ment unit is from either a fixed computer within an existing hos-
pital network or a mobile laptop via WLAN.
The major design requirements of the mobile unit are as fol-
lows: 1) it should be portable and lightweight, which means
easy to carry; 2) it should have power autonomy of more than
60 min to support patient transport; 3) it should have a user-
friendly interface; 4) it should collect and display critical biosig-
nals, including three-lead ECG, HR, and SpO
; 5) it should
record patient information and data; and 6) it should support
wireless communication. On the other hand, the design require-
ments of the management unit are as follows: 1) it must have
an easy-to-use interface; 2) it must display critical biosignals
and analysis of data; 3) it must record, retrieve, and manage
patient information and data (local database); and 4) it must
be connectable to the Internet to transmit data and distribute
information.
Furthermore, at the consultation terminals such as wireless
PDAs or laptops, the medical staffs can use them either to mon-
itor the physiological parameters and waveforms of a remote
patient online or to access his or her case history through the
wireless connection to the management unit.
Wireless connection in the studied hospital has been estab-
lished by WLAN technology (IEEE 802.11b) [12] with speeds
up to 11 Mb/s. An access point acts as a wireless bridge for
the network data to be transmitted to and received from the
existing wired hospital network. With multiple access points
linked to a wired network, it allows efficient sharing of network
resources throughout an entire building. The distance set be-
tween each access point was less than 30 m because of the radius
of indoor coverage for typical WLAN and regional geography
limitation. Devices with WLAN interface can roam among the
access points.
The transmission of data between a mobile unit and a man-
agement unit is implemented by the client server architecture.
In the proposed design, the mobile unit serves as the client end
and the management unit serves as the server end. Commu-
nication depends on the transmission control/Internet protocol
for error-free medical data transmission. A specific service set
identifier (SSID) and the 40-bit wired equivalent privacy (WEP)
model of the IEEE 802.11b are used to protect data during trans-
mission. All users are required to enter a user name and pass-
word to the system via a remote authentication dial-in user ser-
vice server. In addition, a robust advanced encryption standard
(AES) algorithm [13] is implemented in the designed C++ pro-
gram, permitting both mobile unit and management unit to per-
form end-to-end encryption.
B. Mobile Unit
The mobile unit in this study is comprised of a designed
vital-sign signals acquisition module and a Pocket PC (HP
iPAQ H5450). Multiple vital-sign parameters, which include
the three-lead ECG, SpO
, and HR, can be measured by this
unit. Fig. 2 shows the design architecture of this mobile unit.
This signals acquisition module acquires the three-lead ECG
and dual-wavelength photoplethysmographic (PPG) signals,
and converts them into digital data. Through an RS232 con-
nection, the Pocket PC receives the physiological data and
computes the SpO
and HR parameters. According to user
commands, the mobile unit can display waveforms in real-time,
store data locally, and trigger an alarm. With regard to remote
monitoring, the Pocket PC transfers these physiological data to
a remote management unit in real-time by its built-in WLAN
device.
1) Module for Acquiring Vital-Sign Signals: Fig. 3 shows
the diagram of the designed vital-sign signals acquisition
module. The vital-sign signals acquisition module consists
of ECG signal conditioning circuits, pulse oximeter analog
circuits, and a microcontroller. This module is powered by four
rechargeable AA batteries and is packaged as a jacket of the
Pocket PC. The core control unit of the module is an 8-bit mi-
crocontroller, PIC16F877, which has an on-chip eight-channel
10-bit analog-to-digital converter (ADC). The three-lead ECG
signals were amplified with a gain of 700, filtered (0.5–50 Hz),
and then fed into the inputs of the ADC in the microcontroller.
The pulse oximeter analog circuits were designed based on the
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LIN et al.: WIRELESS PDA-BASED PHYSIOLOGICAL MONITORING SYSTEM FOR PATIENT TRANSPORT 441
Fig. 2. Design architecture in mobile unit.
Fig. 3. Block diagram of the designed vital-sign signals acquisition module.
principles of spectrophotometry and optical plethysmography
to measure SpO
[14], and a Nellcor oxygen sensor (DS-100A,
finger probe) was used to measure the PPG signals. The signals
determined by two light-emitting diodes (infrared and red)
are first demultiplexed, then separately amplified, and finally
separated into dc and ac components (IRAC, IRDC, RAC, and
RDC), which are used to calculate pulse rate and the oxygen
saturation in the blood.
The microcontroller digitizes the signals with a sampling fre-
quency of 200 Hz and transmits the ECG and PPG data to the
Pocket PC through the serial port. The baud rate is 115.2 kb/s.
Optical coupling is used in the serial communication to separate
the power supply of the signal acquisition module from that of
Pocket PC, reducing power interference. Fig. 4 illustrates the
mobile unit.
2) Program on the Pocket PC: A system program, devel-
oped by Microsoft embedded visual C++, was installed on the
Pocket PC to monitor the vital signs. This program records
users’ information and displays the HR, SpO
, ECG, and PPG
waveforms sent from the signal acquisition module. Raw data
can be stored into the built-in memory of the Pocket PC and
transmitted to a remote management unit via the WLAN. In
long-term store-and-forward mode, the raw data are stored
into the extended secure digital (SD) memory (256 MB) of
the Pocket PC. The waveforms are plotted in window with
an area of 200
150 pixels. The amplitude resolution is
0.04 mV/pixel for the three-lead display and 0.0125 mV/pixel
for the single-lead display. When the frame displays 4 s of ECG
data, the temporal resolution is 0.02 s/pixel. Besides, the sound
reflecting each heart beat can be pronounced by the speaker of
Pocket PC. In addition, this program is installed in the medical
staffs’ PDAs for receiving and displaying the physiological pa-
rameters and waveforms of a remote patient under monitoring
through the wireless connection to the management unit.
C. Management Unit
Fig. 5 shows the architecture of the management unit. The
management unit consists mainly of a fixed personal computer
or a laptop, and the management program. The management unit
can be set in many spots depending on different applications
of telemonitoring. It is normally located in the nurse’s station,
and provides a user-friendly interface for telemonitoring a pa-
tient’s vital-sign signals. The management terminal can receive
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442 IEEE TRANSACTIONS ON INFORMATION TECHNOLOGY IN BIOMEDICINE, VOL. 8, NO. 4, DECEMBER 2004
Fig. 4. Picture of the mobile unit.
Fig. 5. Architecture of the management unit.
patients’ physiological data from the remote mobile units via
the WLAN or the Internet.
The management program is implemented on a Windows
2000 platform and developed by the Borland C++ builder. The
program receives the data from the mobile unit, displays HR,
SpO
, three-lead ECG, and PPG waveforms on the terminal
screen, and stores the data in the local database. In this work,
a MySQL database system is set up to manage the raw data
of ECGs and PPGs, patients’ information, and the doctors’
diagnosis. The database can also be accessed from authorized
terminals through the hospital network and the Internet. More-
over, the vital-sign signal can be delivered in real-time to a
mobile platform for sharing data. The waveforms are plotted in
a 600
448 pixels window, which shows 6 s of ECG data. The
default resolutions of amplitude and time are approximately
0.015 mV/pixel and 0.01 s/pixel, respectively. The program
also supports the selection of leads, the replay of waveforms,
analysis of raw data, and the scaling of amplitude and time.
Both mobile unit and management unit have an alarm set-
ting window which enables the medical staff to set up the alarm
threshold of SpO
and HR individually according to the physi-
ological status of the patient. When the recorded vital signs are
beyond the preset limits, the mobile unit would trigger an alarm
automatically and a warning message window will pop-up on
the screen.
D. Evaluation of System
The system was evaluated in the following phases.
1) Technical Verification: First, the developed pulse
oximeter was calibrated by an index pulse oximeter simu-
lator (Bio-Tek product; SpO
range: 35%–100%; HR range:
30–250 bpm), whereas the accuracy of the ECG monitor
was verified by the medSim 300 Patient Simulator (Dynatech
Nevada, Inc.). Then, the functions of the PDA-based pulse
oximeter and the ECG monitor, as well as the transmission
of data between the mobile unit and the central management
unit were tested. Twenty healthy volunteers, including eleven
males (with an average age of 29.7
11 years old) and nine
females (with an average age of 29.6
10 years old), were
involved in the test. Three-lead ECG signals and PPG signals
were acquired simultaneously. All results were recorded locally
and were transmitted to the remote central management unit
for 5 min to confirm the quality of the signals and the error
rate of data transmission between the two units. Two different
probes, one of the designed pulse oximeter and the other of
the commercial pulse oximeter BCI-3304 (product of BCI,
Inc.) were connected to different fingers of the same volunteer
and then operated simultaneously to compare SpO
and HR
readings over 5 min. During the first minute, the volunteers
breathed normally. They were then required to hold their breath
for one minute, and then breathe normally until the end of the
test.
2) Clinical Test and User Survey: The complete system was
demonstrated at National Taiwan University Hospital (NTUH).
In the test scenario, each patient was transported from the inten-
sive care unit (ICU) to a radiographic examination room. The
mobile unit was placed beside the patient, which enables the
medical personnel to observe the patient’s physiological con-
dition and check the connection of the electrodes. The mobile
unit transmits the patient’s vital-sign signals to the management
unit via the WLAN, allowing medical staffs to monitor online
the patient’s data during transport. During the radiographic ex-
amination, the mobile unit was placed next to the patient, and a
laptop was set up at the control station to monitor the real-time
data from the mobile unit.
According to the test scenario, a survey was conducted
to elicit the operators’ opinions on the wireless PDA-based
physiological monitoring system in three areas—1) mobility
(size and weight), 2) usability, and 3) performance of the
overall system on intrahospital transport. A questionnaire with
a five-point Likert scale (from 5 = completely satisfied to 1 =
completely unsatisfied) was used to rate the performance of the
overall system on intrahospital transport. Also, the mobility and
usability of the wireless PDA-based monitoring system were
compared with the currently used monitoring device (Agilent
M3046A) in intrahospital transport at NTUH. The satisfaction
of mobility was evaluated in relation to two statements of
weight and size and that of usability was estimated by easy
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LIN et al.: WIRELESS PDA-BASED PHYSIOLOGICAL MONITORING SYSTEM FOR PATIENT TRANSPORT 443
TABLE I
B
ATTERY LIFE OF
POCKET
PC (HP iPAQ H5450)
operation and easy monitoring. The outcomes of these four
statements were represented as a ten-point scale (from 1 = com-
pletely unsatisfied, to 10 = completely satisfied). Intrahospital
transport scenarios were tested over a one month period in the
emergency department. Fifty medical personnel, including 30
nurses and 20 doctors, used the wireless patient monitoring
system and answered the questionnaire. The staffs included 14
males and 36 females with ages in the range 23–50 years old
(mean
SD ) and with 1–25 years (mean
SD ) of experience in emergency medical care.
III. R
ESULTS
A prototype of the overall system has been designed and
implemented. The mobile unit, which includes a vital-sign
signals acquisition module and a wireless PDA, is compact
cm and lightweight ( 500 g). Size of the
vital-sign signals acquisition module is small due to the using
of surface mount technology devices. The static current con-
sumption of the module is 50 mA, and the dynamic current
consumption is 80 mA. This module can continuously acquire
biosignals for over 7 h using 600-mAh AA batteries. The power
consumption and continuous in-use time of the Pocket PC (HP
iPAQ H5450 including the 1250-mAh lithium-ion polymer
battery) are tested. In real-time mode, data are displayed on
the Pocket PC’s screen and transmitted in real-time to the
remote management unit. The Pocket PC can run under its own
power for around 70 min in the worst case. In the store-and-for-
ward mode, the device remained active for approximately 2 h
recording around 20 MB of uncompressed raw data into the SD
memory. The brightness of the backlight and the power of the
wireless transmission of the Pocket PC strongly influence the
duration of the function of this mobile unit. Table I summarizes
the mean battery life in various test scenarios.
Fig. 6 presents the main control and display window of the
mobile unit. Both SpO
and HR are displayed in the upper area.
The middle area plots the ECG and PPG waveforms and also the
user can select to display individual waveform. The command
buttons are arranged in the lower area.
The technical verification revealed an error in SpO
of less
than
2%, and an error in HR of less than 2 bpm, between the
pulse oximeter that designed herein and the commercial pulse
oximeter BCI-3304. Fig. 7 shows a typical 5-min plot of SpO
and HR. During the initial 60 s, the examinee was breathing nor-
mally. The system recorded a stable SpO
of 96%–97% and an
HR of around 70 beats/min. Subsequently, the examinee started
to hold his breath. After about 30 s, which stands for the 90th
second in the whole process, the concentration of SpO
started
to decline and at the same time the heart beat rate became faster.
Fig. 6. Main control window and vital-sign signals display of the mobile unit.
After the 120th second, the examinee returned to normal status
with the HR at about 70 beats/min, and his SpO
also rose from
88% to 98%.
The wireless data transmission test reveals no error in the
real-time vital-sign transmission from the mobile unit to the
management unit. The management unit receives the data and
adequately displays the patient’s information. Fig. 8 presents
the test results, the main control, and the display window of the
management unit. The data of SpO
and HR are shown at the
right-hand side and the patient information is shown at the top.
The middle area displays the ECG and PPG waveforms, where
the user can select to display one specific waveform (ECG Lead
I, II, III, or PPG) and scale the time and amplitude. The com-
mand buttons are arranged at the right-hand side. The medical
staff can open the alarm-setting window to set up the thresholds.
Twenty doctors and thirty nurses who had used the
PDA-based monitoring system during patient transport an-
swered the questionnaire. The medical staffs highly rated the
overall system (mean
,SD )byafive-point
Likert scale (5: completely satisfied, 1: completely unsatisfied)
for performance on intrahospital transport. The mobility and
usability of the wireless PDA-based system were compared
with those of the currently used monitoring system for intra-
hospital transport at NTUH. The results in Table II indicate that
the wireless-PDA model outperforms the traditional monitors
in both mobility and usability (at a 95% confidence level).
IV. D
ISCUSSION
A prototype of this PDA-based telemedicine system has
been designed and tested. For intrahospital transport of critical
patients, experienced senior staffs could monitor the patients
online and advise for unexpected condition, and thus, may
prevent further deterioration of the patient condition. Under
such circumstances, online monitoring or consultation would
be helpful. Therefore, the remote monitoring during transport
would be beneficial for a better quality care of the patient.
We will discuss the following issues that relate to the wireless
patient monitoring system.
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