An Evaluation of a Vibro-Tactile Display Prototype for
Physiological Monitoring
Jessie Y. C. Ng, MASc*,JoC.F.Man,MASc*, Sidney Fels, PhD, PEng*, Guy Dumont, PhD*, and
J. Mark Ansermino, MBBCh, MSc (Inf), FFA†
*Department of Electrical and Computer Engineering, University of British Columbia, Vancouver, Canada; †Department
of Anesthesia, University of British Columbia, Vancouver, Canada
Visual displays and auditory alarms are used to convey
information on physiological variables in an operating
room. However, the exponential growth in the number
of physiological variables and the high probability of
false alarms has amplified demands on the clinician’s
attention.We have extended existing tactile technology
to improve situational awareness and produce a practi-
cal clinical advisory device. A vibro-tactile display, us-
ing two vibratingmotors applied to the volar surface of
the forearm, was compared to an auditory alarm in a
simulated clinical environment. Compared with audi-
tory alarms, the vibro-tactile alarmwas as easy to learn
and had a better identification rate when used alone or
combined with the auditory alarm. Most users pre-
ferred the vibro-tactile alarm although the prototype
caused some discomfort. Furthermore, a combined
vibro-tactile and auditory alarm had reduced accu-
racy when compared with the vibro-tactile alarm
alone. The vibro-tactile modality shows considerable
promise for clinical practice but will require further
clinical testing and refinement, especially with re-
gard to user comfort.
(Anesth Analg 2005;101:1719–24)
T
he exponential growth in the number of moni-
toring devices within the operating room and
intensive care unit has amplified the clinician’s
cognitive load. Routine inclusion of monitoring vari-
ables such as electrocardiogram, invasive arterial
blood pressure monitoring, pulse oximetry, gas anal-
ysis, cardiac output monitoring, and electroencepha-
logram recordings make it difficult for the clinician to
simultaneously appreciate each variable over an ex-
tended period of time.
The presence of an abnormal clinical condition is
signaled in one of two ways: by a primitive alarm
system automatically triggered when a single variable
fluctuates beyond its preset threshold or by the anes-
thesiologist visually tracking changes to a signal pat-
tern over time. Known clinical interventions and arti-
facts resulting from diathermy interference or
movement exacerbate the complexity of this situation
to the extent that more than 90% of alarms currently
generated in the clinical environment can be dis-
missed as insignificant, with one third triggered by
artifacts (1). Responsiveness to auditory alarms dimin-
ishes with increased exposure to false alarms and with
escalating noise pollution of the operating room and
intensive care unit. However, if clinicians switch to an
increased reliance on visual cues, through an en-
hanced inspection of the monitor, they risk compro-
mising their careful clinical observation of the patient.
Tactile displays stimulate the skin’s sensory recep-
tors to give the illusion of direct contact with an object
(2), and are ideally suited to enhance situational
awareness, such as in a haptic navigation guidance
system (3). Suitable applications for these devices arise
whenever environmental or social factors make the
use of visual or auditory communication impractical,
or when continuous observation of, or the repeated
switching of attention to, a visual display might be
unsafe. This is precisely the situation found in the
clinical environment of the operating room. Such a
modality of communication does not detract from
other forms of social or patient interaction nor does it
disturb other individuals in the environment. As the
largest sensory organ in the body, the skin forms an
approximate surface area of 1.8 m
2
of mechanorecep-
tors (4), and responds to a number of physical prop-
erties including vibration, pressure, and temperature
with a high degree of precision and discrimination.
Accepted for publication June 16, 2005.
Address correspondence and reprint requests to Mark Anser-
mino, MBBCh, MSc (Inf), Director of Research Department of Pedi-
atric Anesthesia British Columbia Children’s Hospital Room 1L7,
4480 Oak Street, Vancouver, V6H 3V4 Canada. Address e-mail to
anserminos@yahoo.ca.
Mark Ansermino is the recipient of the Canadian Anesthesiolo-
gist’s Society Career Scientist Award.
DOI: 10.1213/01.ANE.0000184121.03150.62
2005 by the International Anesthesia Research Society
0003-2999/05 Anesth Analg 2005;101:1719–24 1719

Vibration is an ideal stimulus for the development of
a tactile display as it can be easily delivered by low-
power, tiny, and lightweight vibrating motors. Inte-
gration of wearable vibro-tactile displays with the hu-
man body that have previously been described
include: a feedback glove called CyberTouch™ (5), a
shoulder-pad insert (6), a tactile vest, and a conceptual
earpiece tactile display called The Sprout (7).
The aim of this study was to develop and test an
unobtrusive and lightweight vibro-tactile display to
be worn on the forearm in a simulated operating room
environment. The intention was to harness a largely
underutilized sensory organ, the skin, to convey phys-
iological information to attending clinicians. This
“touch on the arm” could provide subtle cues, rather
than outright alarms, to indicate monitoring changes
and should improve communication between the
monitoring system and the clinician.
Methods
The basic test device is a vibrating motor or vibro-
tactor. It has low power consumption (
100 mW) and
is lightweight (0.59 g) (8). The motor vibrates perpen-
dicularly to the skin surface at a frequency of 162 Hz,
close to the threshold of the skin’s Pacinian mechano-
receptors (200 Hz) (9). Each vibro-tactor is powered by
a current amplifier and mounted onto a metallic con-
tactor with a base area of 1.6 cm
2
to prevent interfer-
ence with the motor’s rotation.
Two vibro-tactors were applied to the volar surface
of the forearm: at the wrist and near the inner elbow,
respectively, with a 12-cm separation (Figs. 1 and 2).
Vibro-tactor locations were sited using results from
perception and psychophysical experiments con-
ducted by Cholewiak and Colins (10). Each vibro-
tactor was mounted using an adjustable elastic strap,
and a commercially available interface board, the
Phidget Interface kit (11), was used to provide com-
puterized control of the motors.
The alarm stimulus scheme is the pattern of vibra-
tions used to represent a change in a physiological
signal, in this instance, heart rate, for communication
to users via the vibro-tactile display. There were 6
types of alarm; 3 levels that correspond to 10% (Level
I), 20% (Level II), and 30% (Level III) change in heart
rate over the previous 5 s; with each category further
differentiated to distinguish between increasing and
decreasing heart rates (Fig. 3). A long initial pulse (600
ms) at the wrist indicated a decreasing alarm while a
long initial vibration near the elbow indicated an in-
creasing alarm. The number of subsequent short
pulses (200 ms each) at the other vibro-tactor locations
indicated the alarm level. The time separation be-
tween pulses for a level III alarm was shorter than
level II to emphasize the urgency of the alarm. We
decided to implement the alarm scheme with two
vibro-tactors instead of three after analyzing the re-
sults of a pilot study (12).
The practicality of the vibro-tactile device was eval-
uated using the following criteria:
Training—the ease with which subjects could learn
and remember different alarm patterns
Identification rate—the number of events detected
Accuracy—the number of alarm patterns correctly
classified under test conditions
Response time—the time taken from the end of the
alarm sequence to correctly identify an alarm scheme
Comfort and satisfaction—subjects’ perceptions of
the wearability and usefulness of the device
The vibro-tactile display was compared with an
auditory alarm similar to that routinely used in cur-
rent clinical practice, and the two modalities were
Figure 1. A vibro-tactile display comprised of two vibrating motors.
Figure 2. The vibro-tactile display applied to the forearm.
1720 TECHNOLOGY, COMPUTING, AND SIMULATION NG ET AL. ANESTH ANALG
TACTILE DISPLAY FOR PHYSIOLOGICAL MONITORING 2005;101:1719–24