HUMAN-CENTERED PHONE OXIMETER INTERFACE DESIGN

FOR THE OPERATING ROOM

Pulse Oximeter Interfaced to a Mobile Device for Anesthesia Monitoring

in the Developing World

Walter Karlen, Guy Dumont

Electrical and Computer Engineering in Medicine (ECEM), The University of British Columbia, Vancouver, Canada

Chris Petersen, Jennifer Gow, Joanne Lim, Jules Sleiman, J. Mark Ansermino

Pediatric Anesthesia Research Team (PART), BC Children’s Hospital, Vancouver, Canada

Keywords:

Mobile phones, Pulse oximeter, Interface design, Photoplethysmography, Human-centered, Anesthesia.

Abstract:

Mobile phones offer huge potential as platforms for clinical decision making in resource-poor and remote

areas. We present methods for the development of a human-centered interface for anesthesia monitoring

that is targeted to remote operating rooms in developing countries. The Phone Oximeter is compatible with

major PC and mobile phone operating systems and is optimized for small phone screens. It displays vital

physiological parameters in the corresponding clinical colours. Combined with an easily identiﬁable icon, this

guarantees that accessibility is language-independent. To evaluate the acceptance and usability of the initial

prototype of the Phone Oximeter, the Think Aloud process while completing a speciﬁc Task List, followed

by the Mobile Phone Usability Questionnaire (MPUQ) were tested on 20 subjects with varying medical and

mobile phone experience. The acceptance rate of 81.9 % from the MPUQ questionnaire clearly demonstrates

the usability of the Phone Oximeter. The incorporation of the most relevant errors and complaints into the

design of the next iteration of the Phone Oximeter prototype enhanced its capabilities further.

1 INTRODUCTION

Over two billion people do not have access to ad-

equate surgical care (Funk et al., 2010). Operat-

ing rooms (OR) in developing countries often lack

the expertise and essential equipment required to

safely monitor patients during anesthesia and surgery

(World Health Organisation, 2008). For example,

continuous blood oxygen saturation (SpO

) measure-

ment is considered to be a minimum standard in the

developed world but it is used in 50 % or less surg-

eries in many countries of the developing world (Funk

et al., 2010). Limited access to such medical devices

and the expertise needed to effectively use them con-

strains safe surgery.

We are taking a highly innovative and creative ap-

proach to address this issue by developing the Phone

Oximeter

(Figure 1). Our novel software, which is

hosted by a mobile phone connected to a pulse oxime-

http:///www.phoneoximeter.org

ter, creates a unique stand-alone medical device. At

low cost, it is capable of monitoring SpO

and guid-

ing anesthesia technicians in the safe management of

their patients. Using established clinical guidelines,

the software translates the clinical data it has extracted

from the pulse oximeter into easily understood mon-

itoring parameters and warning signals. Encoded ex-

pert advice will facilitate life saving decision support.

The intuitive and human-centered display of symbols

on the phone ensures that it is easy to use, regardless

of literacy level or language. This monitoring will

prevent clinical deterioration and save lives, as well

as reducing device costs.

2 DESIGN REQUIREMENTS

Unlike currently used clinical pulse oximeters, be-

cause of its portability and battery-run operation,

the inexpensive Phone Oximeter will be able to be

433

Karlen W., Dumont G., Petersen C., Gow J., Lim J., Sleiman J. and Mark Ansermino J..

HUMAN-CENTERED PHONE OXIMETER INTERFACE DESIGN FOR THE OPERATING ROOM - Pulse Oximeter Interfaced to a Mobile Device for

Anesthesia Monitoring in the Developing World.

DOI: 10.5220/0003335204330438

In Proceedings of the International Conference on Health Informatics (HEALTHINF-2011), pages 433-438

ISBN: 978-989-8425-34-8

 2011 SCITEPRESS (Science and Technology Publications, Lda.)

Figure 1: First prototype of the Phone Oximeter.

used anywhere. Indeed, our innovative use of a mo-

bile phone platform takes advantage of the already

widespread distribution of these phones across the de-

veloping world. While pulse oximeters have been

previously connected to mobile phones (Black et al.,

2009; Moron et al., 2005), they have not been de-

signed for use in the OR, do not meet current pulse

oximeter design standards, nor do they include a goal

oriented interface design. In addition, speciﬁc phone

and language requirements limit the accessibility of

these designs to the developing world.

We are harnessing the inherent computing power,

peripheral resources (LCD display, audio, serial and

USB connectivity) and energy storage of mobile

phones to develop a medical monitoring device that

can be easily deployed in the developing world at low

cost. However, several engineering challenges must

be overcome: 1) power consumption has to be min-

imized for maximal device efﬁciency and autonomy;

2) the user interface must be optimized for relatively

small screen displays; and 3) the device must be opti-

mized for use across a diverse range of hardware (e.g.

peripheral connectors) and operating systems (OS) to

ensure its portability between phone brands. In addi-

tion to these constraints, the successful design of the

pulse oximeter interface for the OR must meet sev-

eral design speciﬁcations: 1) adherence to standards

for pulse oximetry (e.g. ISO 9919 - 05); 2) auditory

and visual information and alerts to attract the atten-

tion of the clinician; 3) user friendly alert control

and adjustment; 4) display of the raw photoplethys-

mographic (PPG) waveform to allow for the manual

inspection of signal quality and feature interpretation;

5) signal quality indication; and 6) colour coding for

the easy identiﬁcation of vital signs. Additional re-

quirements of this mobile phone application for the

OR in developing countries are: 1) ease of use and

navigation (usability); 2) low learning curve; 3) low

risk for misinterpretation and error; and 4) provi-

sion of decision support. Speciﬁc capabilities of the

mobile phone user interfaces and operating sequences

will be integral to achieving these objectives. In this

manuscript, we will focus on the human-centered in-

terface design of the Phone Oximeter, and the evalua-

tion and improvement thereof.

3 DEVICE DEVELOPMENT

3.1 Software

The software implementation is designed to allow

the majority of development to be performed outside

of the proprietary software development kit (SDK)

frameworks. This maximizes portability across the

most common mobile phone platforms currently

available. The algorithms are implemented in C and

the graphics rendering is performed in OpenGL, using

only thin platform-speciﬁc wrappers to integrate with

the underlying operating systems. The beneﬁts of this

are: 1) use of compiled C binaries will ensure that the

algorithms maximally utilize the limiting processing

power of the devices; 2) OpenGL hardware acceler-

ation contained within the devices will greatly reduce

the processing overhead associated with the graphical

interface; and 3) ubiquity of C and OpenGL software

elements in modern computing devices will make the

prototype system easily portable to many other cur-

rent and future platforms, and capable of leveraging

a large body of existing and proven signal processing

and interfacing algorithms.

The developed software application compiles to

highly optimized ANSI-C. The application currently

compiles on the principal OS like MAC OS X, Win-

dows, Linux, and OpenBSD, and several of the most

widely used mobile platforms including iOS, An-

droid, and Maemo (Nokia) (Cozza et al., 2010). Ports

to Symbian, currently the most widely used phone OS

(Cozza et al., 2010), and Windows Mobile platforms

are in progress.

The Phone Oximeter software is interoperable be-

tween 8 bit and 16 bit pulse oximeter devices from

Nonin (Plymouth, USA) and automatically detects

the correct protocol upon connection. It collects the

PPG waveform and sensor alarms and stores them in

a ﬁle on the device. This can be retrieved from the

phone using a ﬁle transfer application for subsequent

processing and display. The software is fault tolerant,

and allows the pulse oximeter sensor to be inserted

and removed on the ﬂy.

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434

3.2 Hardware

The hardware used in this study is an iPod Touch

(Apple, Cuppertino, USA) hardwired via the serial

port through the dock connector to a certiﬁed 8 bit

OEM Nonin Xpod pulse oximeter sensor. Assuming

that touch-screen technology will soon dominate the

global market, we selected a more recent generation

mobile device like the iPod Touch. Our iPod Touch is

running iOS 3.1.3 and offers similar functionality as

the iPhone, but at a lower cost. The large and bright

LCD display makes it ideal for development in the

OR. The Xpod pulse oximeter sensor provides the raw

PPG waveform and processed trend values for SpO

and heart rate (HR).

The iPod connector provides a 3.3V UART con-

nection that is directly compatible to the sensor

pinout. The hardwire connection solution from the

pulse oximeter to the iPod increases the connection

reliability and powers the pulse oximeter sensor di-

rectly from the device. While a wireless solution

(e.g Bluetooth) is also technically possible, it would

be heavily dependent on interface and protocol, and

would be supported by far fewer devices. For exam-

ple, the iPhone Bluetooth stack is heavily restricted,

and does not currently support the necessary Serial

Port Proﬁle (SPP). A challenge of our wired solution

is to build adapters for varying connectors on the dif-

ferent phone systems.

3.3 Interface Evaluation

The user interface design process was started by

assembling 20 cardboard prototypes with differing

printed oximeter interface concepts and the same

physical dimensions as the actual iPod Touch device.

Through a participatory design process that included

discussions with stakeholders, these cardboard mock-

ups served to deﬁne the initial layout of the ﬁrst soft-

ware prototype of the Phone Oximeter.

Following institutional ethics approval and in-

formed consent, 20 subjects (Table 1) working in a

hospital environment were recruited for a usability

study of the Phone Oximeter for anesthesia to identify

design ﬂaws and opportunities for design improve-

ments. Demographic information, including expe-

rience with the iPod (or any other iOS device) and

pulse oximetry, was collected (Table 1). Familiarity

with mobile phone use was evaluated by asking sub-

jects to choose a label from the IDC mobile phone

user label (Table 2, International Data Corporation,

2003). Users were given a 23-item Task List (Table

3) to complete with the Phone Oximeter and were not

given any training or instruction. An audio record-

ing was taken during the evaluation and subjects were

asked to Think Aloud (Someren et al., 1994). The ex-

periment was conducted in a quiet room with a mod-

erator and observer. The errors (tasks that required

more than one attempt and/or requests for assistance)

and time taken for each task were recorded. Four

de-brieﬁng questions and a 55-item modiﬁed Mo-

bile Phone Usability Questionnaire (MPUQ, Ryu and

Smith-Jackson, 2006) was administered following the

completion of the Task List. The MPUQ was ana-

lyzed using categorical response data (5 = Strongly

Agree to 1 = Strongly Disagree). The categorical vari-

ables were reversed (i.e. most desirable response was

1 rather than 5) for three questions. For these reversed

questions, the response was subtracted from 5 to al-

low for summary analysis.

Table 1: Demographics of the study subjects. Medical

Doctor (MD), Registered Nurse (RN), Anesthesia Assistant

(AA), Anesthesia Resident (R), Medical student (MDS).

MD RN AA R MDS

Nb. 10 5 2 2 1

Age (mean) 45.2 46 41 33 27

Age (SD) 9.0 12.6 5.7 5.7 0.0

Table 2: Subject responses to the IDC mobile phone user

metric (International Data Corporation, 2003): Display

Maven (DM), Mobile Elite (ME), Minimalist (M), Voice

and Text Fanatic (FA).

IDC

Label

DM ME M FA DM+

ME+ FA

M+

ME+

Nb. 1 0 11 1 1 4 2

4 RESULTS

4.1 Interface Evaluation

All subjects had previously used a pulse oximeter

but nine had never used an iPod Touch. All sub-

jects required more than one attempt to complete at

least some of the tasks. Ten of the 23 tasks required

more than one attempt by at least one subject (Table

3). A failed attempt was deemed to be any erroneous

touch, menu selection, navigation, or identiﬁcation.

The number of errors observed between subjects with

or without iPod Touch experience was similar (3 ±

0.5 vs 3.4 ± 1.8 respectively, per subject). The task

that most commonly required more than one attempt

was “Task 10: Changing the weight of the patient”.

All but one subject needed more than one attempt to

complete this task (Table 3). This was the ﬁrst time

that subjects encountered the Settings screen, as well

HUMAN-CENTERED PHONE OXIMETER INTERFACE DESIGN FOR THE OPERATING ROOM - Pulse Oximeter

Interfaced to a Mobile Device for Anesthesia Monitoring in the Developing World

435

Table 3: 23-item Task List and results of the study sub-

jects. The second column presents the number of subjects

that were not able to complete the task on the ﬁrst attempt

or required assistance. The third column presents the mean

± SD completion time for each task.

Task Users

with

>1 try

Completion

Time mean

± SD [s]

1 Place sensor on ﬁnger 0 –

2 Start Phone Oximeter

from iPod menu screen

0 14.0±7.0

3 Identify what value is

alarming

2 5.5±4.4

4 Silence alarm generated 0 4.6±4.9

5 View alarm details 2 4.9±5.4

6 Identify the cause of the

alarm

1 9.5±11.3

7 Change patient mode from

neonate to adult

7 17.3±15.6

8 Back to Home screen 0 –

9 Identify the weight of the

patient from the Home

screen

0 1.7±0.9

10 Change weight from 70 kg

to 111 kg

19 41.6±25.5

11 Back to Home screen 0 –

12 Identify the heart rate UP-

PER Limit

0 6.1±8.1

13 Change heart rate UPPER

limit to 128 beats/min

3 18.5±11.8

14 Back to Home screen 0 –

15 Identify the relative signal

quality for heart rate

4 17.5±13.7

16 Change trend line length

to 3 min

6 27.5±19.8

17 Back to Home screen 0 –

18 Identify O2 saturation

LOWER limit

0 4.3±7.4

19 Change O2 saturation

LOWER limit to 85%

2 9.5±4.7

20 Restore the default values

for adult

9 17.4±15.3

21 Change patient mode to

child

0 3.8±3.4

22 Back to Home screen 0 –

23 Shut down Phone Oxime-

ter

0 –

as the ﬁrst experience with the spinning wheel. Ta-

ble 3 shows how subjects improved after completion

of this task by having lower completion times for the

following tasks. The mean time to complete the entire

Task List was 203.39 ± 56.4 s. The task of changing

an alarm limit took longer than the other tasks (Ta-

ble 3). The MPUQ analysis showed a high degree of

overall satisfaction with the use of the Phone Oxime-

ter (Table 4). Design improvements for the second

prototype of the Phone Oximeter interface were based

on the most frequent user errors (Table 5).

4.2 Second Design

Based on the subjects’ comments during the Think

Aloud process and the errors committed during the

experiments, we identiﬁed the most important and

frequent complaints regarding the Phone Oximeter

(Table 5). Based on these common errors, we mod-

iﬁed the interface to better satisfy the users’ needs

and to render the system more intuitive. The second

Phone Oximeter interface prototype consists of four

main tabs (Figure 2):

1) The Home screen displays the vital parame-

ters of HR, SpO

and respiratory rate (RR) in the

corresponding clinical colours and easily identiﬁable

icons. The raw PPG waveform is displayed in com-

bination with the SpO

parameter. A signal quality

index (SQI) represented by coloured bars and a trend

graph is displayed for each vital parameter. Within the

trend graph, the current alarm threshold settings are

displayed as horizontal lines. On the top bar, the pa-

tient demographics (age group and weight), and bat-

tery capacity are displayed. The bottom bar contains

the tabs to navigate between the screens.

2) Three buttons in the top bar of the Settings

screen allow switching between age groups (neonate,

pediatric, adult) and reset to the default settings. Spin-

ning wheels are used to input patient weight, upper

and lower alarm thresholds for each vital parameter,

and the window length for the trend graph.

3) The Messages screen displays the current time

on top. Messages are displayed in the main window

using red, orange and yellow colour codes to denote

importance (high, medium, low, respectively).

4) The fourth tab (as shown by an illumination

icon) allows the Phone Oximeter to enter a power

save mode and disables the LCD screen. The auditory

functions remain enabled which allows for low-power

operation without disrupting information transfer to

the user.

The Phone Oximeter software includes an audi-

tory interface consisting of a sounded heart rate with

SpO

modulated pitch in accordance with clinical

standards, and three priority levels of auditory alarms

following accepted standards for commercial physio-

logical monitors.

5 DISCUSSION

AND CONCLUSIONS

The Phone Oximeter for anesthesia provides a low

cost solution for monitoring pulse oximetry in ORs

around the world. It provides all of the important

features required to provide safer patient monitoring

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(a) Home screen (b) Settings screen (c) Messages screen

Figure 2: Revised Phone Oximeter interface featuring four screens (Home, Settings, Messages, and Powersave (not shown)).

Table 4: MPUQ analysis levels.

Factor

Nb. of

questions

Perfect

score

Total score

Satisfaction

[%]

Ease of Learning and Use (LEU) 21 2100 1747 83.19

Helpfulness and Problem Solving Capabilities 3 300 243 81.00

Affective and Aspect 2 200 185 92.50

Multimedia Properties (AAMP) 9 900 712 79.11

Commands and Minmal Memory Load (CMML) 6 600 480 80.00

Control and Efﬁciency (CE) 8 800 668 83.50

Typical Tasks for Mobile Phone 1 100 85 85.00

Typical Tasks for Phone Oximeter 5 500 386 77.20

Total 55 5500 4506 81.93

Table 5: Design improvements for the second Phone Oximeter prototype.

Error / complaint Nb. of subjects with

error / complaint

Improvement

Users were unclear which parameter

was alarming from the Home screen

10 Brighter, ﬂashing alarm state

Users tried to press the top bar in order

to access Settings screen

19 Touch functionality added to top bar of

the Home screen

Users were unclear which icon repre-

sented the trend line

14 New icon for trend line in Settings

screen

Users were unclear what the original

SQI symbols meant

11 Redesign of SQI to more closely re-

semble industry standards

Users felt that the alarm limits were

faint and unclear.

7 Colour-coded alarm limits on Home

screen

through pulse oximetry. The major engineering chal-

lenge was to provide a human-centered, user-friendly

and language independent interface that is deployable

on a multitude of platforms and OS. This was ad-

dressed using OpenGL that can be embedded with

an OS-dependent hook into the native code. The in-

HUMAN-CENTERED PHONE OXIMETER INTERFACE DESIGN FOR THE OPERATING ROOM - Pulse Oximeter

Interfaced to a Mobile Device for Anesthesia Monitoring in the Developing World

437

terface design was improved based on usability stud-

ies using a task list and a modiﬁed MPUQ. Whereas

the study participants had a diverse range of experi-

ence and demographics that was helpful for interface

design improvement, we could not test the effect of

language or cultural barriers, as all subjects were En-

glish speaking and living in Canada. We are currently

conducting the same usability studies in Africa with

a wide range of potential end users (e.g. anesthesia

technician). The high acceptance rate obtained from

our Canadian study and the intentional minimal use of

English words in the Home and Settings screen sug-

gests that adoption could be universal.

The Phone Oximeter application prototype con-

sists of our developed software and interface, an iPod

Touch and a Nonin Xpod pulse oximeter. The iPod

Touch was able to provide power for the pulse oxime-

ter sensor for ﬁve hours, which included continuous

recording and display of data without dimming the

screen. Most phones have a substantially larger bat-

tery and will, therefore, be able to operate the applica-

tion for a longer period of time. This will be sufﬁcient

for most operating scenarios conducted in the devel-

oping world. If required, additional autonomy could

be provided by an additional battery pack to power

the pulse oximeter sensor independently.

The current prototype is based on a wired connec-

tion between sensor and phone. This is an advantage

for power consumption and designing the commu-

nication protocol, since less complex layers are re-

quired. However, our current implementation does

not provide the required electrical isolation between

the iPod Touch and oximeter device. This will be

solved in upcoming versions with an improved elec-

tronic isolation circuit or through wireless communi-

cation between sensor and display device. This will,

however, increase power consumption and costs, and

reduce autonomy.

Further work will include the improvement of the

embedded algorithms for the computation of HR, RR

and SQI. We also plan to include a clinical decision

support engine that will have the potential to increase

the reliability of the warning and alarm messages.

We have demonstrated an approach to design a

user interface for visualization of HR, RR, and SpO

data for use on a size-restricted mobile phone display

to be used in remote locations by healthcare workers

with little to no prior training. This will offer great

potential in deploying low-cost, life-saving devices in

the ORs of developing countries without signiﬁcant

investments in training and infrastructure.

ACKNOWLEDGEMENTS

The authors would like to thank all subjects for par-

ticipating in the interface evaluation study. Ali Buttar

and Shona Massey designed the cardboard mockups

for the participatory design process. Dr. Speciosa

Mbula Kimenye and Dr. Jacqueline Hudson assisted

in the usability study.

REFERENCES

Cozza, R., Milanesi, C., Nguyen, T. H., Vergne, H. J.

D. L., Zimmermann, A., Gupta, A., and Lu, C. (2010).

Competitive Landscape: Mobile Devices, Worldwide,

1Q10. Gartner Inc., Stamford, CT.

Funk, L. M., Weiser, T. G., Berry, W. R., Lipsitz, S. R.,

Merry, A. F., Enright, A. C., Wilson, I. H., Dziekan,

G., and Gawande, A. a. (2010). Global operating the-

atre distribution and pulse oximetry supply: an esti-

mation from reported data. The Lancet, 6736(10):1–9.

International Data Corporation (2003). Exploring Usage

Models In Mobility: A Cluster Analysis of Mobile

Users. Framingham, MA.

Moron, M., Casilari, E., Luque, R., and Gazquez, J. (2005).

A Wireless Monitoring System for Pulse-Oximetry

Sensors. 2005 Systems Communications (ICW’05,

ICHSN’05, ICMCS’05, SENET’05), pages 79–84.

Someren, M. W. V., Barnard, Y., and Sandberg, J. (1994).

The think aloud method: A practical guide to mod-

elling cognitive processes, volume 31 of Knowledge

Based Systems Series. Academic Press, San Diego,

CA.

World Health Organisation (2008). Safe surgery saves lives.

The second global patient safety challenge. Geneva,

CH.

HEALTHINF 2011 - International Conference on Health Informatics

438