Effects of changes in the volume ofautomated external defibrillator
audio guidance on audibility: a pilot
usability study
Original ResearchpISSN 2671-793X eISSN 2671-7948
J EMS Med 2024;3(3):68-73
https://doi.org/10.35616/jemsm.2024.00087

Received: January 23, 2024
Revised: April 11, 2024
Accepted: April 22, 2024
Correspondence to:
Koshi Nakagawa
Department of Integrated Scienceand Engineering for Sustainable
Societies, Faculty of Science andEngineering, Chuo University, 1-1327, Kasuga, Bunkyo-ku, Tokyo 1128551, Japan
E-mail: knakagawa493@g.chuo-u.ac.jp

Koshi Nakagawa1, Etsuko Sone2, Manabu Oki2, Shumpei Omori3,
Masaya Tanaka4, Ryu Kimura4, Hinata Kijima4, Hatsumi Yanagisawa4,
Taku Harigaya4, Hideharu Tanaka2,3,4
1

 epartment of Integrated Science and Engineering for Sustainable Societies, Faculty ofD
Science and Engineering, Chuo University, Tokyo, Japan
2
Research Institute of Disaster Management and EMS, Kokushikan University, Tokyo, Japan3
Department of Sport and Medical Science, Kokushikan University, Tokyo, Japan
4
Graduate School of Emergency Medical System, Kokushikan University, Tokyo, Japan
Objective: To evaluate whether automatically adjusting the volume of automated external
defibrillator (AED) audio guidance to match the environmental noise level made hearing innoisy environments easier for AED users.
Methods: A pilot usability study was conducted. We included three emergency life-saving
technicians and nine university students who assigned medical support to spectators at
the Japan Rugby League One match. Participants first used the AED without a volume-change function (no-change) and then used the AED with a volume-change function(change) in a noisy environment. The primary outcome was subjective audibility (7-point
Likert scale). Secondary outcome was recognition of audio guidance (yes/no).
Results: The mean point in subjective audibility was 4.83 in change and 2.50 in nochange; high subjective audibility was shown in change (difference, 2.33; 95% confidence
interval, 1.02 to 3.64). The number of participants who were able to recognize audio guidance was 11 in the change group and six in the no-change condition, indicating that alarge number of participants were able to recognize audio guidance (κ=0.36; 95% confidence interval, –0.16 to 0.88).
Conclusion: The results of this study indicate that this function increased subjective audibility, and 91.2% of participants recognized the AED’s audio guidance. In the future, it will
be necessary to develop and disseminate AEDs that are easy to use in any environment.
Keywords: Automated external defibrillator; Basic life support; Audibility, Usability; Bystander effect© 2024 Korean Association of EMS Physicians/
Asian Association for Emergency Medical Services
This is an Open Access article distributed under
the terms of the Creative Commons Attribution
Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits
unrestricted non-commercial use, distribution,and reproduction in any medium, provided theoriginal work is properly cited.

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INTRODUCTION
Approximately 130,000 out-of-hospital cardiac arrest (OHCA) cases occur annually inJapan, and although the survival rate is increasing each year, it remains low [1,2]. In orderto improve post-OHCA outcomes, the chain of survival has been emphasized [3], especially cardiopulmonary resuscitation (CPR) and automated external defibrillators(AEDs), which can be performed within a short period after the onset of OHCA [4].

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J EMS Med 2024;3(3):68-73

While the rates of bystander CPR and public access defibrillation(PAD) in Japan have been increasing annually [5,6], the PAD
implementation rate in 2022 was only 4.2% [1]. Furthermore,
the COVID-19 pandemic has negatively impacted the PAD implementation rate, necessitating a nationwide effort to increase
PAD implementation.
Some AEDs provide visual and audible operational guidance,
which simplifies their use [7]. However, there have been instanceswhere the shock was not delivered despite the announcement[8,9]. The effectiveness of AED operational guidance can becompromised by environmental factors at the scene of a cardiac
arrest and the user's skill level. Public places, for example, tend to
be noisier than residential areas, increasing the likelihood that theuser may not hear the AED's audio instructions and may operate
the device incorrectly. Despite these challenges, OHCA occurrences in public places are expected to have favorable outcomes[6,10-12]. Therefore, reliable and rapid defibrillation is crucial.
To address this problem, ClearVoice technology was developed(Stryker). This technology adjusts the frequency of voice guidance and modifies the volume incrementally to adapt to environmental noise during AED use, with the goal of improving the audibility of AED audio guidance in noisy settings, such as those encountered during medical support at sporting events—an areathat has gained increasing importance in recent years [13,14].
However, there has been no research on whether altering the volume of the AED's audio guidance actually improves its audibility
in real-world noisy environments. As AED installations continue
to increase, this study could provide valuable insights into which
AED functions are best suited for specific environments.
We aimed to assess whether automatically adjusting the volume of AED audio guidance to match the environmental noiselevel would facilitate easier auditory comprehension for AED users in noisy settings.

METHODS
Study design

We conducted a pilot usability study. This study was approved by
the Ethics Committee of Kokushikan University (No. 23001).

Study setting

The study periods were April 8, 16, and 22, 2023. Measurements
were conducted during the warm-up period before the Japan Rugby League One match, where Kokushikan University was responsible for providing medical support to spectators. Additionally,
emergency life-saving technicians (ELST) and ELST students

https://doi.org/10.35616/jemsm.2024.00087

from Kokushikan University were tasked with offering medical assistance. The measurement setting was an outdoor rugby stadium,accompanied by background music and announcements. The
mean sound pressure level recorded was 80 dB (range, 60–98 dB).
Weather conditions during the measurement times included sunnyskies on April 8 and intermittent rain on April 16 and April 22.

Participants

Medical staff from Kokushikan University who provided medical
support to spectators were eligible for inclusion. The exclusion
criteria were as follows: (1) lack of consent to participate in the
study; (2) inability to use an AED due to health or mental status;(3) failure to perform the measurement properly due to equipment malfunction; and (4) improper administration of questionnaire responses. Due to the constraints of the pilot study and thelimited opportunities to use AEDs in a sports event environment,
where real noise was present and proper randomization and collection of participants were not feasible, measurements wereconducted on a small number of participants.
Sports medical support at Kokushikan University is provided
by ELSTs and individuals trained in basic life support (BLS). We
selected this participant due to our keen interest in exploring thepotential integration of the LIFEPAK CR2 (CR2; Stryker) into
our university's sports medical support framework. Additionally,
it is anticipated that the device will be adopted in various sports
settings, where nurses, ELSTs, athletic trainers, and others with
BLS training frequently operate. Therefore, we considered the usability of CR2 by BLS-trained participants to be of substantial interest to them.

Intervention

We utilized the CR2 (Fig. 1), which automatically activates the
AED upon opening the lid. Operational instructions are provided
on the back of the lid and on the defibrillation pad. The CR2 iscapable of recognizing environmental sounds, and the frequencyof the voice guidance can be adjusted. Additionally, the volume of
the audio guidance can be incrementally increased to a maximumof 95 dB. Adjusting the sound volume takes time to assess the environmental noises and may require several seconds to a dozen
seconds to reach the desired volume. The study commenced after
obtaining oral and written informed consent from the participants. Initially, participants operated the AED in a noisy environment without the volume-change function (no-change). Subsequently, they completed a questionnaire (Supplementary Material). Then, they used the AED with the volume-change function(change) and completed the same questionnaire after the session.

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Nakagawa K et al.

Effects of changes in volume of AED

In this study, participants activated the AED, listened to the audio
guidance, and prepared to apply the AED pad in a noisy setting.
However, they did not actually apply the AED pad to a mannequin or perform defibrillation. Participants were not previously
informed that the volume of the AED would be adjusted.

Participants’ characteristics

Outcomes

Outcomes

The primary outcome was subjective audibility (7-point Likert
scale). The secondary outcomes were subjective usability(7-point Likert scale) and recognition of audio guidance (yes/no). CR2 is anticipated to be extensively utilized in noisy settings.
Therefore, to determine whether audio guidance is audible to
AED users in these environments, we concentrated on subjective
audibility in a real-world setting.

Statistical analysis

The characteristics of the participants are summarized using means
and standard deviations (SDs) for continuous variables, and counts
and percentages for categorical variables. We calculated mean differences and 95% confidence intervals (CIs) for outcomes involving
continuous variables, and kappa coefficients and 95% CIs for outcomes involving categorical variables. The sample size of the pilot
study was small; consequently, we conducted an exploratory analysis instead of a superiority test [15]. R (R Foundation for StatisticalComputing, version 4.1.2) was used for all analyses.

RESULTS
Participant flow and recruitment

The flow chart of the study participants is shown in Fig. 2. All 12
participants provided consent for participation. No participants
met the exclusion criteria.

Participants’ characteristics are presented in Table 1. The mean
age of the participants was 24.1 years. The participants included
three ELSTs and nine ELST students, all of whom had received
CPR training within the past 2 years.

The results of this analysis are shown in Table 2. For subjective
audibility in the primary outcome, the mean ± SD score was
4.83 ± 2.12 in the change group and 2.50 ± 1.83 in the no-changegroup; higher subjective audibility was observed in the changegroup (difference, 2.33; 95% CI, 1.02 to 3.64). For subjective us-

12 Participants wereassessed for eligibility
0 Participant were
excluded
12 Participants were includedin the measurements (100%)

Measurement 1
AED use without volume change

5-min breakMeasurement 2
AED use with volume change

12 Participants were includedin the analysis (100.0%)

Fig. 2. Participant flow diagram and study sequence.
Table 1. Participants’ characteristics (n=12)
Characteristic
Male sexAge (yr), mean ± SD
Qualification
Emergency life-saving technician
University student
Previous CPR training within 2 yr

Fig. 1. LIFEPAK CR2. Image provided by Stryker K.K.

70

No. (%)
6 (50)
24.1 ± 9.0
3 (25)
9 (75)
12 (100)

SD, standard deviation; CPR, cardiopulmonary resuscitation.

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J EMS Med 2024;3(3):68-73

Table 2. The results of the usability measurements
Outcome
Subjective audibility, mean ± SD
Subjective usability, mean ± SD
Audio recognition, No. (%)

No-change (n = 12)
2.50 ± 1.83
5.00 ± 1.35
8 (66.7)

Change (n = 12)
4.83 ± 2.12
4.92 ± 1.51
11 (91.2)

Difference (95% CI)
2.33 (1.02 to 3.64)–0.08 (–0.77 to 0.61)
0.36a) (–0.16 to 0.88)

SD, standard deviation; CI, confidence interval.
a)Kappa (κ).

ability, the mean ± SD score was 4.92 ± 1.51 in the change groupand 5.00 ± 1.35 in the no-change group, indicating nearly identical subjective usability for both functions (difference, –0.08; 95%
CI, –0.77 to 0.61). In terms of recognizing audio guidance, 11participants (91.2%) in the change group and eight participants(66.7%) in the no-change group were able to do so, demonstrating that a significant number of participants could recognize audio guidance (κ = 0.36; 95% CI, –0.16 to 0.88).

DISCUSSION
We assessed whether automatically adjusting the volume of the
AED's audio guidance based on the environmental noise level
improved audibility for users in noisy settings. The results indicated that this feature increased subjective audibility, with 91.2%
of AED users reporting clear recognition of the audio guidance.
This study suggests that adjusting the volume of the operational audio guidance on an AED can be beneficial when the device
is used in noisy environments. Typically, AEDs are equippedwith visual aids, such as illustrations or LCD screens. However,given the urgency when using an AED, it can be challenging tofocus on visual instructions. In these situations, audio guidance
proves to be effective, facilitating the use of an AED without reliance on visual cues. Nevertheless, acute psychological stress, often experienced during AED use, can impair cognitive function.
This decline, coupled with environmental noise, may make iteven harder to hear audio instructions [16]. Moreover, with theincreasing adoption of fully automated defibrillators in recent
years [17,18], it has become increasingly important to provide
clear and audible audio guidance to AED users to help prevent
accidents, such as electrocution.
Although this study was limited to measurements at a sports
event, its findings might support the use of AEDs in a variety of
public places, including large sporting events such as the Olympic Games [19], as well as mid-sized community sporting eventsand general public gatherings. Since the noise level at crowded
events can vary widely depending on the size and number ofspectators, it is especially important for the AED audio guidance

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to be clearly audible. Psychological effects, such as anxiety, andtechnical inexperience can prevent laypersons from initiating
BLS and AED use [20], and this stress can be particularly high ina noisy or crowded environment. However, confidence in the
AED is expected to reduce anxiety. Thus, the audibility of the
AED audio guidance is a very important feature. In recent years,
OHCA in public places has been reported to be associated withfavorable outcomes [6,10-12]. It is hoped that the widespread
implementation of AEDs, featuring both easy-to-hear audio
guidance and highly visible visual guidance, will enable everyone
to use an AED safely and effectively, even during emergencies.
This study has several limitations. First, as this was a pilot
study, it did not conclusively demonstrate the effectiveness of thefunction for adjusting the audio guidance volume. Further interventional studies based on the findings of this study are warranted. Second, the sound pressure level in the environment where
this study was conducted was not constant and varied over time.
Therefore, the noise level may have decreased at certain times,
making the audio guidance easier to hear. Third, all participantsin this study had completed a CPR course within the past 2 years.
Thus, the results may not be representative of laypersons who
have not undergone such training. It is crucial to include laypersons who are not trained in BLS in future studies. Fourth, thefunction used in this study to adjust the volume detects environmental sounds and changes the volume incrementally; thus, it
may take time to reach a volume level that is sufficiently loud tounderstand the AED guidance. As a result, we cannot assert that
this will lead to rapid defibrillation. Fifth, since all participants
initially used AEDs without the volume change and then withthe volume change, and because this study was not randomized,
there may have been residual order effects.
We assessed whether adjusting an AED’s audio guidance volume based on ambient noise levels facilitated easier auditory reception for users in noisy settings. The study demonstrated that
this feature improved subjective audibility, with 91.2% of participants able to discern the AED's audio instructions. Moving forward, it will be essential to develop and distribute AEDs that are
universally easy to operate in various environments.

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Effects of changes in volume of AED

FUNDING
None.

CONFLICT OF INTEREST
LIFEPAK CR2 used in this study was provided free of charge by
Stryker K.K. for research use. Except for that, no potential conflict of interest relevant to this article was reported.

AUTHORS’ CONTRIBUTIONS
Conceptualization: KN; Data curation: KN; Formal analysis:
KN; Investigation: all authors; Methodology: KN; Project administration: KN, ES; Software: KN; Supervision: HT; Visualization: KN; Writing-original draft: KN, MO; Writing-review &editing: HT; All authors read and approved the final version.

ORCID
Koshi Nakagawa, https://orcid.org/0000-0001-8738-1261
Etsuko Sone, https://orcid.org/0009-0001-3671-8415
Manabu Oki, https://orcid.org/0009-0002-7364-407X
Shumpei Omori, https://orcid.org/0009-0006-1367-3855
Masaya Tanaka, https://orcid.org/0009-0000-1507-8378
Ryu Kimura, https://orcid.org/0009-0003-8863-6643
Hinata Kijima, https://orcid.org/0009-0004-5085-1775
Hatsumi Yanagisawa, https://orcid.org/0009-0001-5888-7287
Taku Harigaya, https://orcid.org/0009-0008-3774-0068
Hideharu Tanaka, https://orcid.org/0000-0003-4565-0026

SUPPLEMENTARY MATERIAL
Supplementary materials can be found via https://doi.org/jemsm.
2024.00087

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