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Proceedings of the Human Factors and Ergonomics Society 2017 Annual Meeting
Redesign process of a semi-powered patient transfer device
Jeongmin Park1, Hyun-hwa Hong2, Eunji Kim1, Gwanseob Shin1
Department of Human Factors Engineering, Ulsan National Institute of Science and Technology, Korea
Medical System Research Department, Hyundai Heavy Industries, Korea
Intra-facility patient transfer poses substantial risks of patient falls and care-giver’s musculoskeletal injuries.
Several patient lifters and aid devices have been introduced but they have not been widely used due to their
bulky size and slow operation. A prototype of new patient transfer aid device has been developed to help
care-givers transfer patients safely and more efficiently than conventional manual transferring or the use of
powered patient lifters. This study was aimed to explain how the new patient transfer aid device has been
developed, evaluated and redesigned to improve its safety, functionality and usability. Both laboratory
experiment using a quantitative assessment method and field user research by interview and shadowing have
been conducted to evaluate ergonomic advantages and to identify usability issues when transferring patients
using the new aid device. Then, the initial prototype has been redesigned to address the issues and improve
overall usability.
Copyright 2017 by Human Factors and Ergonomics Society. DOI 10.1177/1541931213601872
Safe intra-hospital patient transfer is an important issue
for health-care providers. Patient falls during transfer from and
to a bed can cause serious injuries such as fracture and subdural
hematomas, leading to additional hospitalization and related
extra costs (Bergland & Wyller, 2004; Coussement et al., 2008).
Care-givers including nurses also experience risks for
musculoskeletal injuries due to heavy manual lifting, pushing
and pulling in awkward postures while transferring a patient
from and to a bed (Knibbe and Friele, 1996).
Transferring a patient between bed and a wheelchair
requires the care-giver to lift the patient manually and carry the
patient to the bed or wheelchair. It has been considered one of
the most stressful tasks for nurses or nurse aids (Grag and Owen,
1992), and it is known that one of three care-givers in healthcare facilities experience musculoskeletal injuries due to
repetitive manual patient transfer in U.S. (Pormpeii at al., 2009).
Various powered patient lifters or transfer aid devices
have been developed and used to help care-givers transfer a
patient more safely with less physical efforts (Fig. 1). Most of
them are equipped with powered or semi-powered lifters that
eliminate the manual lifting efforts of care-givers. Although
their lifting aid features can address the risk of care-givers and
also improve the safety of patient, their bulky size and slow
operation have been the main obstacles of their wide adaptation.
Figure 1. Existing patient transfer aid devices.
To overcome such limitations of existing patient lifters,
a prototype of a semi-powered patient transfer device, named
‘CarryBot’ has been developed for laboratory and field
evaluation (Fig. 2). This device is equipped with a powered
drive mechanism, a forward leaning cushion seat with powered
height and angle adjustability. It was designed to transfer a
patient not by lifting but by sliding toward the seat and carry the
patient while seated. It may not entirely eliminate care-giver’s
physical efforts, but the smaller size and faster operation may
be more suitable to some facilities that need a faster and smaller
patient transfer aid device.
Proceedings of the Human Factors and Ergonomics Society 2017 Annual Meeting
female patient was also recruited to play a role of a patient who
could not stand or move without an external aid of care-giver.
Table 1. Participant information (mean and standard
Figure 2. CarryBot (manufacturer: Hyndai Heavy
Industries Co., Ltd., Korea).
In this study, the ergonomics of the patient aid device has
been evaluated both by a laboratory experiment and field user
research to confirm the product functionality and understand
users’ additional needs. Then, the prototype has been
redesigned to meet the needs. The objective of this study was to
introduce the key processes of the ergonomic evaluation and
user research, and how the outcomes of the evaluation have
been applied to the redesign of the prototype.
22.2 (1.5)
158.0 (7.5)
54.1 (6.6)
Each participant performed the four patient transfer tasks
three times each (3 repetitions x 2 methods x 2 scenarios) while
the EMG signals from superficial muscles of the upper
extremities and lumbar spine were collected. The order of the
four task conditions was randomized and balanced between
twenty participants.
Ergonomic performance of this prototype has been
evaluated both quantitatively and qualitatively. Quantitative
evaluation was conducted in a laboratory to determine whether
the use of the prototype would reduce the physical risks of
musculoskeletal injuries of care-givers. The amount of physical
efforts when transferring a patient using the prototype was
compared with that of a conventional manual wheelchair.
Qualitative evaluation was conducted by user interview and
shadowing at hospitals to understand how easy or difficult to
use the prototype in real working environments and to
determine how to improve the design of the prototype.
Quantitative Evaluation
Ergonomic benefit of using the prototype for patient
transfer was quantitatively evaluated by comparing the
myoelectric muscle activities (EMG amplitudes) between the
use of a conventional wheelchair and the use of the prototype
in two transfer scenarios (transfer from bed and transfer to bed)
(Fig. 3).
Twenty female participants who had no previous and
current musculoskeletal problems participated in the laboratory
experiment (Table 1). Prior to the experiment, they provided
informed consent on a protocol approved by the university’
institutional review board.
Each participant was trained for manual patient transfer
protocols from and to a conventional wheelchair as well as for
the operation of the prototype prior to the experiment. The
training protocol was prepared by experienced care-givers
(three registered nurses) prior to the experiment. A proxy
Figure 3. Patient transfer to the prototype.
EMG signals were collected from eight muscles at 2048
Hz using a surface EMG system (Flexcomp system, Thought
technology, Canada). Electrodes were attached bilaterally on
the biceps brachii (BB), lateral deltoid (LD), upper trapezius
(UT) and elector spinae at the level of L4 (L4) level, following
recommendations in literature. Raw EMG data were rectified
and band pass filtered (10Hz - 500Hz), notch filtered and
smoothed by the 2nd order Butterworth filter with a cut-off
frequency of 6 Hz to generate linear envelope EMG data (Kang
and Shin, 2017).
Then, the mean, peak and integrated amplitude of the
non-normalized EMG values were identified for each trial, and
the values from three repetitions were averaged. The averaged
mean, peak and integrated values were statistically compared
between the two transfer methods (wheelchair vs. prototype)
within each scenario using one-way repeated measures analysis
of variance (ANOVA). A significance criterion of p<0.05 was
Qualitative Evaluation
Proceedings of the Human Factors and Ergonomics Society 2017 Annual Meeting
Qualitative evaluation of the usability (easy of use) of the
prototype has been conducted by actual users (nurses) at
hospitals. Six nurses were recruited from two hospitals and one
nursing home in Korea. Hospitals included one respiratory
medicine ward and one orthopedics ward of two large general
hospitals (over 1500 beds). The participating nurses were fully
trained and certified nurses who routinely conduct (~ 30 times
per day) manual patient transfer tasks.
After an instruction and training session, a prototype was
provided to each hospital and the participating nurses used the
prototype for four weeks for their routine patient transfer tasks.
During the evaluation period, they were interviewed twice per
week regarding pros and cons of the prototype. In addition, at
each hospital visit, they were shadowed by experimenters, and
their usage pattern and behaviors during routine patient transfer
were monitored and recorded.
Quantitative Evaluation
When transferring from bed to the prototype, participants
spent 9.9 sec, while transferring to a wheelchair took 3.6 sec
more in average. Similarly, it took 11.4 sec in average when
transferring from the prototype to bed, and transferring from the
wheelchair took 1.6 sec more.
Significant effects of transfer method on mean EMG
amplitude were found on the right lateral deltoid and the right
upper trapezius muscles (Fig. 4). When transferring from bed
to the prototype, participants used the two muscles significantly
less than transferring to a wheelchair. To the contrary, when
transferring to bed, participant used the same muscles
significantly more when using the prototype (p<0.05).
Difference in the peak and integrated EMG between the
two methods was more pronounced when transferring from bed.
When transferring to the prototype, significantly less peak and
integrated EMG values were observed from all muscles but the
right biceps brachii and lumber extensor muscles (p<0.05).
Figure 4. Mean, peak, and integrated EMG amplitudes.
(A) Bed to prototype/wheelchair, (B) Prototype /
wheelchair to bed (* p<0.05).
Proceedings of the Human Factors and Ergonomics Society 2017 Annual Meeting
Qualitative Evaluation
All six participants (nurses) provided similar feedback
and opinions regarding the prototype during the periodic
interviews. They were positive about the forward leaning seat
design and height adjustability of the seat as it could reduce
care-giver’s physical efforts and improve patient’s comfort.
However, the bulky size, heavy weight and difficult
maneuvering (direction control) were reported as negative
aspects (Table 2). Observations from individual shadowing also
confirmed their opinions.
Following above principles, a new prototype has been
developed with below specific improvements (Fig. 5).
Table 2. Key issues identified by participating nurses.
Travel speed (2.4 km/h) of the power drive is too slow
for long distance travel within hospital.
Controlling moving direction (joystick, powered
control) is too difficult.
Powered drive mechanism has been removed, and four
caster wheels were installed instead to allow easier and
faster manual movement and control (A).
Side guards were added to avoid side falls and to allow
patient to hold during transfer (B).
Sectioned detachable cushion pads were used for the
seat to accommodate various patients by exchanging
specific sections (C).
Overall size and weight (18%) has been reduced for
easier maneuver by care-givers.
Future Plan
The newly developed prototype will be tested again at
various hospitals to confirm whether the design improvements
meet the needs of care-givers and patients. Additional design
changes may be made to further improve the safety, usability
and marketability of this product.
Seat does not fit to all types of patients.
Side supports are necessary for safe and easy
Safety belt is too high, stiff, and difficult to fasten.
Base frame is too large to safely move the prototype
inside a patient room.
Too heavy for manual movement (fine adjustment
near the patient bed) by female care-givers.
In this study, ergonomic advantage and usability of a
new patient transfer aid prototype has been evaluated to come
up with design improvement ideas. Both ergonomic evaluation
and qualitative user research indicated that the prototype could
help care-givers transfer patients more safely with less physical
efforts compared when transferring using a conventional
wheelchair. However, several critical usability issues have also
been identified from the user research, and design modifications
have been made to address those issues.
Design Modification
The prototype has been redesigned with below
Patient’s safety should be improved by providing
proper safety belt and side guards.
Care-givers should be able to more easily control and
maneuver the device when moving inside a tight
patient room.
Seat shape and dimension should be able to
accommodate various patients (gender, height, weight,
health condition).
Location and dimension of main handle, seat, safety
belt and side guards should be determined according
to the anthropometric data of target users.
Figure 5. Redesigned prototype.
Proceedings of the Human Factors and Ergonomics Society 2017 Annual Meeting
This paper is the result of research project of Future
Growth Engine Flagship Project (NTIS No: 1711034791) by
Minister of Science, ICT and Future Planning, supported by the
Korea Institute of S&T Evaluation and Planning.
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