PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Next steps in hospital noise research
Ilene J. BUSCH-VISHNIAC
Chief Innovation Officer, Sonavi Labs, Baltimore, MD USA1

ABSTRACT
Hospital noise is a topic of interest to medical staff, patients, and their families – i.e., to a large segment of the
population. A great deal of work has been done on hospital noise in the last 15 years, but there is still much tolearn. This paper summarizes the current state of knowledge of hospital noise and its impacts, more broadly
stated as our understanding of hospital soundscapes, and focuses on research avenues that would mosteffectively advance our understanding and ability to intervene to produce improvements. While there arecertainly opportunities to increase our knowledge of sound sources in hospitals and of the physiological andpsychological impacts of hospital noises using traditional methods, soundscape analytical approaches arepoised to provide much more clarity to the relationship between sound sources and human reactions, making
it possible to focus interactions onto the most pressing problems.
Keywords: Noise, soundscapes, hospital noise

1. INTRODUCTION
There are a number of reasons to be interested in the noise in hospitals. Almost everyone spends
time in a hospital at some point in their adult life, either as a patient, an employee, or a visitor and noise
has long been among the top complaints about hospitals. Because healthcare is among the fastest
growing labor sectors in the world, the number of people routinely exposed to hospital soundenvironments is rapidly growing. Additionally there are economic reasons to be concerned about
hospital soundscapes. The healthcare sector typically accounts for about 10% of the labor fo rce of acountry and about 10% of a country’s gross domestic product, with about half of that being for
hospitals. Thus the combination of engaging large numbers of people, and involving huge amounts offunding mean that there is an incentive to make hospital soundscapes pleasant – certainly not adescription that is typically applied to them now. Further, some countries have started monitoring
hospital performance on a variety of measures, including acoustic, and making the results of patient
surveys public as well as pinning government funding to results. In the US, the introduction in 2008of the HCAHPS (Hospital Consumer Assessment of Health Providers and Systems survey)
immediately sharpened the focus of healthcare systems on noise as the lowest score on that survey
nationwide was the question of whether patients found their environment sufficiently quiet at night (1).
Competitive pressure has thus added even greater incentive to improve hospital soundscapes.
Hospitals have several acoustic challenges. They tend to have walls, ceilings and floors that arehighly reflective because of a desire to use materials that can be easily and frequently cleaned.
Hospitals also have seen increasing rates of HVAC airflow in order to drive pathogens from circulation.
And hospitals are not like office buildings in which people sit at desks to work. Staff, patients,
visitors and equipment are constantly moving, creating non-stationary sources of noise. Hospitals
also have a plethora of noise sources, including alarms, helicopter landings and takeoffs, overhead
paging (although this is phasing out in many facilities), pneumatic tubes, motorized interior doors, andoften noisy medical equipment such as respirators.
The mission of a hospital is to promote the healing and wellbeing of its patients, but there issurprisingly little known today about how the health of patients relates to hospital soundscapes. We
don’t know definitively, for instance, whether hospital noises cause patient anxiety and increase
hospital stays or make patients more susceptible to hospital-acquired infections.
This paper will briefly present a summary of the current state of knowledge of hospital nois e and its
impacts on patients and staff, and then focus on potentially interesting avenues of research that follow
1ilenebv@sonavilabs.com

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on to the latest results. In particular, the use of statistical methods associated with soundscapeanalysis promises substantial progress in understanding what sound interventions are most likely tohave a positive impact on occupants of hospitals.

2. CURRENT STATE OF KNOWLEDGE OF HOSPITAL NOISE
A good bit of the work on hospital noise has focused on objective measures of the sound levels in
hospitals. As reported in Busch-Vishniac et al. (2), and later by Ryherd et al. (3), the sound levels
measured by the L eq in hospitals have been rising monotonically since the 1960s and well exceed theWorld Health Organization guidelines in virtually every hospital in the world. The sound levels,
which typically range from L eq values of 50-75 dB(A), are now sufficiently high that speechinterference levels (SII) suggest speech recognition at normal vocal levels is typically fair to poor, aconcerning result given the tradition of transfer of important medical information orally and thelikelihood that patients in hospital are also compromised medically (4-6).
Although somewhat less obvious from the literature, many studies of noise interventions at
hospitals have found that traditional acoustic measures such as the L eq are poor indicators ofperceptions of change in the acoustic environment. The Leq and similar measures average over timeand frequency and are ill-suited to the hospital environment, with its rare moments of quiet andfrequent peaks in the sound level. Attempts to find measures that better relate the sound level toperceptions have focused so far on the occurrence rate, defined as the fraction of time the level (usually
peak or maximum level) is above a specified value. The occurrence rate, which we write as OR(N),was built upon traditional levels such as the L 1 and L10, and is 100% at low levels (low values of N) and
0% at high levels. It was first introduced by Ryherd et al. (7) and later more fully discussed and usedby Williams et al. (8) and Okcu (9). The OR(N) seems to correlate better with perceptions of hospitalnoise, with noise interventions that lower the occurrence rate faster as level increases perceived as
acoustically improved. As an expansion of this metric for hospital environments, Bliefnickdeveloped secondary occurrence rate metrics and found correlations between the occurrence rate range
and patient satisfaction (10).
2.1 Soundscape Analytical Approaches
Starting in 2012 a number of researchers have studied hospital environments using the same
techniques as were used earlier to study the complicated interactions between sound and humanreactions in urban environments. These studies have significantly added to our kno wledge of thehospital soundscape.
Mourshed and Zhao studied design factors in hospitals with the aim of determining whicharchitectural features most related to satisfaction with the facility and delivery of safe care for patients(11). They analyzed the results of their questionnaire given to medical staff using principal
component analysis and found three significant dimensions: spatial, environmental and maintenance.
Overall they found cleanliness to be the top feature of concern for hospital staff, followed by air quality,
then noise, and then thermal comfort.
Mackrill et al. used soundscape analytical approaches to study the noise in a cardiothoracic ward
(12-14). These authors identified sound sources mentioned most often by hospital staff and pati ents
and then conducted a listening test using the most important of these sources, asking participants todescribe how the sounds made them feel. Remarks were used to generate bipolar scales and principal
component analysis used to determine significant dimensions. They found two significant
dimensions: relaxation and understanding, with understanding relating to the extent to which
participants comprehended the need for the sound, and with relaxation accounting for more than fourtimes the variance of the understanding dimension. Finally, based on the results, these researchers
studied the impact of a noise intervention designed to produce greater calm and relaxation, namely the
introduction of nature sounds for masking. They found that introduction of nature sounds was far
more effective in improving the hospital soundscape than was traditional acoustic masking noise.
2.2 Alarm NoiseOne of the key acoustic challenges in hospitals comes from the constantly sounding alarms.
Alarms are specifically made to grab one’s attention and are intended to indicate a situation that must
be dealt with urgently. As analyzed by Busch-Vishniac, the literature suggests that alarms sound over
130 times per day per person in hospital in the US, with it not unusual for patie nts in intensive care to
produce alarms at 2-5 times that rate (15).

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Alarms have been established as one of the more irritating and disruptive sound sources in hospitals,
affecting not only patients and their visitors, but staff as well. The strong bias i n favor of false
positive alarms rather than false negative alarms has created a situation in which it is estimated thatover 90% of clinical alarms result in no action being taken. Further, clinical alarms are difficult to
localize being largely pure tones, and very hard to distinguish from one another. Thus they provide
caregivers with little information about location (patient) or the nature of the problem. Yet in spite of
the constant sounding of alarms, their failure to sound or the failure of clinic ians to respond to them has
been shown to cause enough medical problems for patients (including death) that the Emergency Care
Research Institute listed clinical alarms as among the top few medical hazards in years 2011 -2014.
2.3 The Impact of Hospital Soundscapes on Staff and Patients
The most studied medical staff in hospitals are nurses, who are not only the majority of the medical
staff but interact most closely with patients. Nursing in hospitals is a very stressful occupation,marked by burnout, large employee turnover, and a higher than normal rate of addiction, depression
and suicide. Clearly the soundscape in hospitals contributes to the stress but our knowledge of the
precise interactions is quite limited.
Topf reported one of the first studies linking noise to stress in nursing staff in hospitals (16). She
showed that self-reported sensitivity to noise correlated with similar reports of stress -related
symptoms. Morrison et al. later conducted a more nuanced study that showed elevated levels ofcortisol, a known stress indicator, correlated with periods of increase d sound levels (17). Morerecently, Ryherd et al. surveyed nurses in a neurological intensive care unit and found that theoverwhelming majority (91%) reported that noise negatively affects them in their daily work (7). We
conclude from these studies that noise is certainly a stressor to nurses.
Beyond stress, concerns for clinical staff include noise-induced hearing loss and impacts on task
performance. Although noisy, hospitals generally don’t present a level of noise sufficient to cause
hearing loss. The exception to this rule is the operating room, where peak sound levels have beenshown to be over 120 dB(C) on occasion. As Kracht et al. showed this is particularly a problem forneurosurgery and orthopedic surgeries (18). The impact of noise on performance is not clear based on
research to date, with some results indicating performance is independent of noise and otherssuggesting that individual preferences for quiet play a role in determining whether noise impacts
performance.
The impact of hospital soundscapes on patients has generally focused on sleep and otherphysiological measures, and psychological measures. One of the first studies lin king sleep
physiological measures to sound on the hospital unit was conducted by Gabor et al. and showed that
only about 20% of patient arousals could be linked to noise events (19). More recently, the Sound
Sleep Study by Buxton et al. found that as sounds got louder they were more likely to result in patientarousals (20). Further, they found that heart rate increases correlated with arousals, particularly
during REM sleep. The sound sources most likely to arouse patients were alarms a nd ringing phones
although self-reports of sources that awakened patients were not well correlated to these actual
arousing sounds.
In addition to sleep, there are a few studies that have considered other physiological impacts of
hospital soundscapes. For instance, Hsu et al. studied patient physiological measures as a function ofsound levels and found increasing sound levels correlate with increases in patient heart rate respiration
rate, and systolic and diastolic blood pressure, and a decrease in blood oxygen level. P atients exposed
to sound levels over 50 dB(A) were found to have a 22% risk of having an increased heart rate (21).
There are fewer psychological studies of patients exposed to hospital soundscapes thanphysiological studies. Research in this area has tended to concentrate on the impact of music andpatient perceptions of wellbeing. For instance, a study by McClurkin and Smith showed that listening
to as little as 15 minutes of music by preoperative patients can significantly reduce patient anxiety (22).
This result might well correlate with the soundscape studies that found the most important dimension
for the hospital soundscape to be relaxation.
Patient wellbeing is measured using the Positive and Negative Affect Schedule (PANAS). Cunha
and Silva studied the link between wellbeing and sound levels and found statistically significant
correlations between them, with higher noise levels linking to a decreased sense of wellbeing (23).
More recently, Bliefnick showed that listening to hospital sounds for 30 minutes was sufficient to
reduce listening participant mood (10).

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3. RESEARCH QUESTIONS TO PURSUE
While the research literature on hospital soundscapes is growing significantly, almost all studies
rely on objective measures from a small number of units in, at most, a couple of hospitals. This makes
it very difficult to generalize results except at a very high level, and rarely produces information thatcan be used directly to suggest useful noise interventions. Thus, a first step in increasing ourknowledge of noise sources that help form hospital soundscapes would be to gather information that is
as independent as possible of specific location – i.e. to gather sound power measurements anddirectivity in frequency bands for common sound sources such as medical equipment (e.g. cardiac
monitors and ventilators), system equipment (e.g. floor cleaners and motorized doors), externalsources (e.g. helicopter landings and takeoffs). By adding these to sound sources that are somewhat
known (e.g. human speech and telephone ringing) we can build the important components of a hospitalsoundscape. Given advances in acoustical modeling of spaces, this would permit us to study the
relative impacts of various noise sources and hospital geometries through simulation. Results would
then apply more universally than current studies of a given geometry.
Additionally, it would be quite useful to pursue further studies of objective measures and how theycorrelate with subjective assessments. Again, through simulations using room acoustics programs,
we might be able to determine the sensitivity of various measures such as the occurrence rate inpredicting perceptions.
A clearly underappreciated problem in hospitals is speech intelligibility. This is an area welldeserving of much greater attention. Starting with straightforward research, it would be useful tohave a broader range of SII studies (more units in more hospitals) from which to draw conclusions.
Additionally it would be useful to determine the extent to which patients and their caregivers are awareof the speech recognition challenges in the hospital. Progressing from that, it would be useful toidentify the sound sources that most cause interference with speech intelligibility as this would
identify prime targets for remediation.
3.1 Soundscape Analytical Approaches
While recent work using sophisticated statistical and semantic approaches to characterizesoundscapes is transformative, the work is still in its infancy. We not only require more studies ofunits using such approaches, but also work to determine how well conclusions drawn from one study orunit apply to others. For instance, the work by Mackrill and colleagues considered a single
cardiovascular ward in a single hospital. Would the same approach of introducing nature sounds tomask noise work as well in other units? Further, are there other interventions that would increase thesense of relaxation/calm and thus produce improvements in soundscape perceptions? A particularlyinteresting aspect of this work would be to investigate the interactions between acoustics and othersensory triggers (lighting or wall art for instance) to determine whether calming interventions need tobe acoustic in order to produce improved acoustic perceptions.
Work to date on hospital soundscapes has effectively lumped staff and patients together, but anotherinteresting question is whether these two groups truly respond the same to the soundscape or
differently. If there are significant differences, why do these exist and what interventions make themost sense for each group? Similarly, are there interventions that are more appropriate for young
patients and interventions that are best for older patients based on soundscape analysis?
As a broader view, it would be very interesting to determine how hospital soundscape preference s
relate to those found in homes and other work environments. Is there a universal acoustic goal, forinstance, for what people prefer in the space where they live or work? To the extent that we see
distinctions in places used in various ways, how do we understand those differences?
3.2 Alarm NoiseThe hospital soundscape certainly could be improved by reducing the number of clinical alarms andchanging the sound they produce. There are many issues with use of alarms that suggest further
avenues for research. Currently alarms sound not because of a medical diagnosis (as in stroke orheart attack) but rather because a physiological measure, such as blood oxygen saturation level,violates an established threshold. Additionally, we have not made clinical alarms smart even though
we have the technology to do so. As a result we encourage multiple independent alarms to sound,sometimes producing conflicting information and sometimes producing an alarm cascade with many
alarms sounding simultaneously but all indicating a single medical problem. We have virtually no
information available at this point on whether the presence of alarms sounding at a patient bedside has

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an impact on the medical outcomes for that patient – yet hospital staff would agree that there is no
medical reason for patients to hear the alarms going off.
There also are a host of questions relating to acoustic alarms themselves. A basic question is whenalarms should sound rather than providing an electronic notice or visual alarm, and what sound s might
be used to provide information beyond merely a location. Work on the latter question is being
pursued by Edworthy and her collaborators (Edworthy and Hellier 2006 for example (24)). Further, it
is worth considering whether there is a means to standardize alarms so that there is a single soundeither for a given situation (as in a cardiac lead has failed), or a given level of urgency, or a given sortof medical device (as in an infusion pump). To date, medical equipment manufacturers have resisted
standardizing alarms in any fashion and this has resulted in confusion and pandemonium.
3.3 Impacts on Staff and Patients
In spite of significant work, we have merely scratched the surface in terms of what we could know
about the impacts of hospital soundscapes on staff and patients. To date, most studies have focused ona single impact such as sleep in the hospital or, occasionally, the impact of noise on physiologic
measures of patients. What has been missing, largely because it is so difficult to determine , is a meansof determining whether hospital soundscapes directly impact the medical outcomes of patients asmeasured, perhaps, by length of hospital stay, rate of readmission, or rate of negative outcome. The
problem with such a study is in trying to conduct it opportunistically, i.e. trying to compare patient
outcomes in existing hospitals that have different soundscapes. Naturally, there are many
confounding factors in different hospitals that make it nearly impossible to single out the soundscapeas the only changing variable. One possible means around this problem would be to conduct a small
study using relatively quiet rooms for patients (such as sleep study rooms) and adding hospitalsoundscape noises with various levels through speakers. This wou ld, of course, limit the sorts ofpatients that could be studied since quiet rooms are not typically outfitted with the sorts of equipment
required for intensive care.
A similar problem exists for determining the impact of soundscapes on staff. Issues of the extent
to which the soundscape affects stress or task performance are terribly difficult to determine using
opportunistic studies. One might even argue that sound levels generally increase when there is more
activity on the unit, and increased activity generally also means increased likelihood of stress, leading
to the question of whether the soundscape is a consequence of the stress or the cause of increased stressin nurses. One could imagine a study using a hospital with very different units (perhaps one old and
one new) and using the same staff to work a week in each while being monitored for stress andperformance level, but even in new versus old hospitals the soundscapes don’t vary much so it isunclear that this would uncouple the soundscape sufficiently from other variables, such as patient loadand patient acuity at any specific time, to allow conclusions to be drawn.

4.0 CONCLUSIONS
While there is clearly great progress being made on understanding hospital soundscapes, there
remain many unanswered questions. By addressing these questions we make it possible to set
priorities for interventions to improve hospital soundscapes, with improvement being defin ed as
making the environment more appropriate for healing and more pleasant for those who work in it.

ACKNOWLEDGEMENTS
The author is eternally indebted to Erica Ryherd for her many conversations re hospitalsoundscapes and her research in the area.

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