https://doi.org/10.53964/jmnpr.2024015

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Journal ofModern Nursing Practice and Research
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ISSN 2708-2202 (Online)

Short Communication
Feasibility of Non-contact Noise Cancellation for Medical Device Alarms in Intensive
Care Unit: An In Vitro Experiment
Nao Sonoda1*, Kiyotaka Fujii2, Akiko Morimoto1
1

Graduate School of Nursing, Osaka Metropolitan University, Osaka, Japan

2*

School of Allied Health Sciences, Kitasato University, Kanagawa, Japan

Correspondence to: Nao Sonoda, PhD, RN, Graduate School of Nursing, Osaka Metropolitan University,
3-7-30 Habikino, Habikino-city, Osaka, 583-8555, Japan; Email: sonoda@omu.ac.jp
Received: June 4, 2024 Revised: July 11, 2024 Accepted: July 23, 2024 Published: August 6, 2024

Abstract
Objective: Medical device alarms in intensive care units (ICUs) are essential but their constant noise
contributes to sleep disturbance and delirium in patients, jeopardizing their health and recovery.
Therefore, improving the sound environment for patients in the ICU is crucial. This fundamental
experiment investigated the potential of non-contact noise cancellation to reduce the noise level frommedical device alarms in patients’ ears. We tested whether non-contact noise cancellation using aloudspeaker reduced the noise level of medical device alarms.
Methods: In Experiment 1, we measured and analyzed the electrocardiogram sounds (volume 2,
default setting) from a bedside monitor and the alarm sounds (volume 2, default setting) from a syringe
pump. Negative-phase sound waves were subsequently generated for each alarm type. In Experiment 2,
we tested whether non-contact noise cancellation using a loudspeaker reduced the noise level of each
alarm.
Results: The electrocardiogram sound from the bedside monitor was highest around 1kHz, while, thealarm sound from the syringe pump peaked around 4kHz. Non-contact noise cancellation using theloudspeaker reduced the electrocardiogram sounds emitted from the bedside monitor by more than 15
decibel (dB) and the alarm sounds from the syringe pump by more than 10dB.
Conclusion: A 10dB change doubles or halves the perceived loudness, making the over 10dB
reduction achieved for medical device alarms in this study highly significant. The results of thisexperimental study demonstrate the promising potential of noise-cancelling loudspeakers for
improving patient comfort and well-being in ICUs.
Keywords: Noise, sound environment, non-contact noise cancellation, medical device alarm, ICU
Citation: Sonoda N, Fujii K, Morimoto A. Feasibility of Non-contact Noise Cancellation for Medical Device Alarms in Intensive
Care Unit: An In Vitro Experiment. J Mod Nurs Pract Res, 2024; 4(3): 15. DOI: 10.53964/jmnpr.2024015.
Copyright © 2024 The Author(s). This open-access article is licensed under a Creative Commons Attribution 4.0 International License(https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, sharing, adaptation, distribution, and reproduction in any
medium, provided the original work is properly cited.

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1 INTRODUCTION
Medical device alarms in intensive care units (ICUs)
are essential. However, their constant noise contributes tosleep disturbance and delirium in patients, jeopardizing
their health and recovery[1-6]. Patients with delirium are at
an increased risk of dying during admission, longer stays
in the hospital, and cognitive impairment after discharge[7].
Therefore, it is important to improve the sound environment
for patients in the ICU.
The World Health Organization recommends that noiselevels (LAeq) should not exceed 35 decibel (dB) during
the day and 30-40dB at night in hospital environments[8].
However, LAeq in the ICU are frequently reported to be in
the range of 45-70dB, with peaks exceeding 85dB[4-6,9-13].
Although the alarm volume can be reduced from the default
setting in the ICU, where patients are usually in criticalcondition, low-volume alarms may miss vital alerts, making
medical professionals such as nurses anxious[14]. Therefore,
it is necessary to reduce LAeq perceived by patients withoutcompromising medical professionals’ awareness.
Noise reduction strategies include passive noise
cancellation (e.g., earplugs), which physically prevents
outside sounds from entering the ear, and active noise
cancellation, which reduces the noise level in a particulararea by sending a negative-phase sound. Earplugs are thecommonest measure; however, the majority of studies related
to the use of earplugs have found no benefit on objective sleep
outcomes[15]. Conversely, regarding active noise cancellation,
an experimental study reported that commercially available
noise-cancelling headphones reduced LAeq in an ICU
environment by 6.8dB[16]. However, noise-cancelling
headphones and earphones are not suitable for patients in
the ICU with poor general condition, who are at risk ofdeveloping pressure ulcers, or for those with head trauma.
Sound is a pressure wave consisting of alternating
periods of compression and rarefaction. The active noise
cancellation concept relies on the superposition principle: anoise-cancelling loudspeaker emits a sound wave with thesame amplitude but with an inverted phase (negative-phasesound) relative to the original sound (positive-phase sound).
The waves combine to form a new wave in a process calledinterference and effectively cancel each other out (Figure 1).
A loudspeaker may enable non-contact noise cancellation inpatients in the ICU.
As a fundamental experiment for developing non-contact
noise cancellation to reduce the medical device alarm LAeq
around patients’ ears, our study tested whether non-contact
noise cancellation using a loudspeaker reduced the noiselevel of medical device alarms.
2 METHODS
We measured and analyzed medical device alarmInnovation Forever Publishing Group Limited

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sounds in Experiment 1 and created negative-phase sounds.
In Experiment 2, we tested whether non-contact noise
cancellation using a loudspeaker reduced the noise level of
medical device alarms.
2.1 Experiment 1 (Characterization of Alarm Sounds)
2.1.1 Experiment Location
Experiment 1 was conducted in a simulated ICU
environment (ICU Room at the Kobe International Living
Medical Center, Hyogo, Japan) (Figure 2) in March 2020.
2.1.2 Medical Device Alarms
We measured the electrocardiogram sounds (volume
2, default setting) from a bedside monitor and alarmsounds (volume 2, default setting) from a syringe pump,
representing high-frequency and simple alarm sounds
commonly used in ICUs.
2.1.3 Measurement and Analysis
On the day of the measurement, no one was allowed on
the floor except for the investigators. Additionally, all air
conditioners and devices on the floor were turned off except
for the medical devices to be measured. Measurements
were recorded 100cm from the loudspeaker of each medical
device (pillow position on the bed) (Figure 3). Further, each
alarm sound was recorded for 10s using a sound level meter(NL-22, RION Corporation, Tokyo, Japan), and the LAeq(dB) and LAeq (dB) per frequency band were calculated.
LAeq is the A-weighted equivalent continuous sound level(dB), and is a measure averaging noise exposure over agiven period of time. Measurements were repeated thrice inthe same environment.
2.2 Experiment 2 (Non-contact Noise Cancellation Test)
2.2.1 Experiment Location
Experiment 2 was conducted in an anechoic chamber(Hyogo, Japan) in December 2020 to experimentally andaccurately evaluate noise reduction.
2.2.2 Positive-phase and Negative-phase Sounds
We used the electrocardiogram sounds from the bedsidemonitor and alarm sounds from the syringe pump obtainedin Experiment 1. Negative-phase sounds were created foreach alarm sound obtained in Experiment 1 using Audacity(version 2.1.3) (Audacity, New Delhi, India).
2.2.3 Measurement and Analysis
We tested whether non-contact noise cancellation using
a loudspeaker reduced the noise level of each alarm. The
following devices and software were used in the experiment:
two loudspeakers (MSP3, Yamaha Corporation, Hamamatsu,
Japan), a sound playback software (Live 9.7.7, Ableton
Corporation, Berlin, Germany), a measurement microphone(Type4007, Bruel & Kjaer Corporation, Nærum, Denmark),
and a sound measurement software (Smaart 8.4.3.1, RationalAcoustics Corporation, Woodstock, CT, USA). The two

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Figure 1. A noise reduction method using a noise-cancelingloudspeaker.

Figure 2. A simulated ICU environment.

Figure 3. Recording environment.

Figure 4. Placement of two loudspeakers in the anechoic
chamber.

Table 1. Electrocardiogram Sounds From the Bedside
Monitor and Alarm Sounds From the Syringe Pump

Finally, the difference (dB) between “the LAeq when only
the positive-phase sound was played” and “the LAeq whenboth positive- and negative-phase sounds were played
simultaneously” was calculated.

ElectrocardiogramSounds (Volume2, Default Setting)from the Dedside
Monitor

Alarm Sounds(Volume 2,
Default Setting)from the Syringe
Pump

LAeq for 10s (dB)
1st measurement

52.2

58.0

nd

52.1

58.9

rd

51.9

58.1

52.1±0.258.3±0.5

2 measurement
3 measurement
Mean LAeq of threemeasurements (dB)**

Notes: Mean ± standard deviation.

loudspeakers were placed in parallel (Figure 4), with themeasurement microphone in front of them. While one
loudspeaker played positive-phase sounds (alarm sounds
obtained in Experiment 1), the other loudspeaker played
negative-phase sounds.
First, the positive-phase sound pressure level was set to
60dB at the 50cm point, and the LAeq was measured every
10cm between 50cm and 100cm points when only the
positive-phase sound was played for 10s. Furthermore, theLAeq was measured at the same points with both positiveand negative-phase sounds playing simultaneously for 10s.

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3 RESULTS
3.1 Characterization of Alarm Sounds (Experiment 1)
Mean LAeq of three measurements for both electrocardiogram sounds and alarm sounds at 100cm from theirrespective loudspeakers exceeded 50dB (Table 1). Mean
LAeq of three measurements for each frequency band isshown in Figure 5. The electrocardiogram sound (volume
2, default setting) from the bedside monitor was high in dB
around 1kHz. Meanwhile, the alarm sound (volume 2, default
setting) from the syringe pump was high in dB around 4kHz.
LAeq is the A-weighted equivalent continuous sound level(dB), and is a measure averaging noise exposure over a given
period of time.
Measurements were performed at a distance of 100cm
from the loudspeaker of each medical device (pillow
position on the bed).
3.2 Non-contact Noise Cancellation Test (Experiment 2)
The degree of reduction in the noise level of each alarm
due to non-contact noise cancellation using a loudspeaker

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Figure 5. Mean LAeq of three measurements of each frequency band.

is shown in Table 2. The difference at the 100cm point
was -16.2dB for the electrocardiogram sounds from thebedside monitor and -11.2dB for the alarm sounds from thesyringe pump. Notably, both sounds experienced reductions
exceeding 15dB and 10dB, respectively, at all points
from 50cm to 100cm (average reductions: -17.3dB forelectrocardiogram, -14.3dB for alarm).
LAeq is the A-weighted equivalent continuous soundlevel (dB), and is a measure averaging noise exposure overa given period of time.
4 DISCUSSION
The electrocardiogram sounds (volume 2, default setting)emitted from the bedside monitor were characterized by ahigh dB level approximately 1kHz, exceeding 50dB at a
distance of 100cm from the monitor’s loudspeaker. Notably,
these sounds were reduced by more than 15dB owing to
non-contact noise cancellation while using the loudspeaker.
Similarly, the alarm sounds (volume 2, default setting)from the syringe pump, characterized by a high dB level

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approximately 4kHz and exceeding 50dB at a distanceof 100cm from the loudspeaker of the syringe pump,were attenuated by over 10dB through non-contact noise
cancellation.
Despite the increased emphasis on noise reduction in
hospitals, hospital noise, particularly in ICUs, is a steadily
worsening problem[17]. Previous studies have reported thatthe main noise sources in the ICU are medical device alarms
and the voices of medical professionals[14,18-22]. Additionally,
electronic sounds, such as alarms, have a greater negative
effect on sleep disruption compared to human voices[23].
Moreover, frequent sound peaks (abrupt sound elevation
exceeding 10dB) are the commonest cause of noise-induced
arousal[24]. Notably, a 10dB change doubles or halves
the perceived loudness, making the over 10dB reduction
achieved for medical device alarms in this study highly
significant. Our findings highlight the promising potential ofnoise-canceling loudspeakers to address this critical issue,
and non-contact noise cancellation also has advantages in
infection prevention.

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Table 2. Degree of Reduction in the Noise Level of Each Alarm Due to Non-contact Noise Cancellation
Using the Loudspeaker
50cm

60cm

70cm

80cm

90cm

100cm

LAeq for 10s when
only the positivephase sound wasplayed (dB)

60.0

60.4

59.9

59.1

57.6

54.6

LAeq for 10s when
positive- andnegative-phasesounds were played
simultaneously (dB)

40.1

40.1

43.7

43.7

41.7

38.4

Difference (dB)

-19.9

-20.3

-16.2

-15.4

-15.9

-16.2

LAeq for 10s when
only the positivephase sound wasplayed (dB)

60.0

57.1

56.9

55.9

55.4

54.3

LAeq for 10s when
positive- andnegative-phasesounds were played
simultaneously (dB)

42.5

41.5

37.3

45.6

43.7

43.1

Difference (dB)

-17.5

-15.6

-19.6

-10.3

-11.7

-11.2

Electrocardiogram
sounds from thebedside monitor

Alarm sounds fromthe syringe pumpsounds specifically for each alarm sound. Moreover, in
this study, the electrocardiogram sounds of the bedsidemonitor showed more noise reduction than the alarmsounds from the syringe pump. The inherent characteristicsof active noise cancellation, which performs better atlower frequencies. This may explain why the alarm sounds
from the syringe pump, characterized by high dB levels(approximately 4kHz), are less likely to be reduced.
Conventional loudspeakers diffuse sound in all directions.
However, in recent years, directional loudspeakers, whichtransmit sound in a straight line, have been utilized ineveryday situations. In the future, the use of directional
loudspeakers sending sound to a precise location may createa system that reduces the noise level perceived by the patient
without inhibiting alerts to medical professionals (Figure 6).

Figure 6. Conceptualization of a future system thatuses directional loudspeakers to reduce the noise level
perceived by patients without inhibiting alerts to medical
professionals.

The noise reduction recorded in this study surpassed
the noise reduction (6.8dB reduction) achieved withcommercially available noise-cancelling headphones
in a previous experimental study[16]. We attribute thisimprovement to the likely creation of negative-phase

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4.1 Limitations
This study had some limitations. It was a fundamental
experiment for developing non-contact noise cancellation
to reduce the noise level around patients’ ears caused by
medical device alarms. However, it is impossible to infer
noise reduction in an actual ICU. Additionally, the alarmsounds tested in this study were limited.
5 CONCLUSION
In conclusion, this experimental study provides
compelling evidence that non-contact noise cancellation
using the loudspeaker reduced the electrocardiogram sounds

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emitted from the bedside monitor by more than 15dB andthe alarm sounds from the syringe pump by more than
10dB. The results of this study demonstrate the promisingpotential of noise-cancelling loudspeakers for improving
patient comfort and well-being in ICUs. Further in vitro
experiments are needed for other medical device alarms
such as ventilators. Additionally, Further experiments inthe actual ICU are needed to develop non-contact noise
cancellation.
Acknowledgements
We were grateful to all investigators in this experimental
study. We thanked Yuionn Corporation and Japan Noise
Survey Company for their technical support. This work
was supported by the Fund from the Terumo Life Science
Foundation.
Conflicts of Interest
The authors declared no conflict of interest.

[5]

[6]

[7]

[8]

[9]

[10]

[11]

Ethical Statement
This study did not involve human participants and did not
require approval from the institutional review board.
Author Contribution
Sonoda N contributed to conceptualization, data collection,
analysis, funding acquisition, project administration,
and writing of the original draft. Fujii K contributed
to conceptualization, data collection, analysis, funding
acquisition, review, and editing. Morimoto A contributed
to conceptualization, data collection, funding acquisition,
project administration, review, and editing. All authors
thoroughly reviewed and endorsed the final version of themanuscript.
Abbreviation List
dB, Decibel
ICU, Intensive care unit
LAeq, Noise levels

[12]

[13]

[14]

[15]

[16]

[17]
[18]

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