J. Biomedical Science and Engineering, 2013, 6, 1137-1142 JBiSE
http://dx.doi.org/10.4236/jbise.2013.612142 Published Online December 2013 (http://www.scirp.org/journal/jbise/)
A cross-sectional study on the effects of occupational noise
exposure on hypertension or cardiovascular among
workers from automobile manufacturing company
of Chongqing, China
Shuai Wang, Qizhong Qin, Lu Liu, Lingli Han, Yu Chen*
Department of Labor and Environmental Health, School of Public Health and Management, Chongqing Medical University,
Chongqing, China
Received 14 October 2013; revised 16 November 2013; accepted 28 November 2013
Copyright © 2013 Shuai Wang et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. In accor-
dance of the Creative Commons Attribution License all Copyrights © 2013 are reserved for SCIRP and the owner of the intellectual
property Shuai Wang et al. All Copyright © 2013 are guarded by law and by SCIRP as a guardian.
ABSTRACT
For the past few years, noise pollution has been more
and more serious, and it may lead to several diseases.
While the humans expose to noise in quantity for a
long time, their blood pressure will change, and even
cause changes in cardiac function. In our study, we
attempt to find the relationship between occupational
noise and hypertension and impaired hearing, cardiac
function. It may be helpful to obtain some useful in-
formation on occupational noise exposure of humans.
The participants were divided into noisy group ≥90
dB (A) and non-noisy group ≤70 dB (A). We per-
formed this research in an automobile manufacturing
company of Chongqing, China during 2011-2012.
Our study showed that there may be positive associa-
tions between occupational noise and hypertension
and impaired hearing, but no conclusion can be
drawn between occupational noise and ECG.
Keywords: Occupational Noise; Hypertension; Impaired
Hearing; Automobile Manufacturing Company; Health
Examination
1. INTRODUCTION
Noise, defined as the boring or unnecessary sound, exists
in the environment and workplaces widely. Nowadays,
noise pollution has been an important problem which is
prevalent in the world [1-4]. Simultaneously, occupa-
tional noise is also the main section and a large number
of workers are suffering a high level of noise un-
acceptable. Chongqing City is an important large-scale
industrial city in China, including shipping, metallurgy,
automobile manufacturing, war industry and so on, and
automobile manufacturing industry is one of the pillar
estates (close to 250 thousand workers) [5,6]. Most of the
workers have to exposure high level of noise while work-
ing in workshops, so what effects of the occupational
noise would exert on workers is one of the most impor-
tant issues. However, there has been little research about
occupational noise and workers’ health in China.
Noise exposure can induce hearing impairment or
even hearing loss, but whether the workers working un-
der noisy environment are inclined to influence the blood
pressure or cardiovascular function is controversial. Some
research supports the relations between noise exposure
and hypertension or cardiovascular changes [7-11]. In
contrast, some investigators consider that there are no
associations between noise exposure and hypertension or
cardiovascular reactions [12-14]. Dutch researchers found
that different races showed different relationships be-
tween noise and blood pressure [15]. From this study we
know different races may show various reactions under
noise exposure, hence, studies in different people are
necessary.
To estimate whether or not workers working under
noisy environment will influence the blood pressure or
cardiovascular parameters in Chongqing, we perform a
health examination on automobile workers (n = 728).
2. MATERIALS AND METHODS
2.1. Participants
1050 workers of an automobile factory received occupa-
*Corresponding author.

S. Wang et al. / J. Biomedical Science and Engineering 6 (2013) 1137-1142 1138
tional health examinations held by the Center for Disease
Prevention and Control of Chongqing from November,
2011 to March, 2012. This study performed with the
Recommendations from the Declaration of Helsinki
(1983) and was approved by every subject and the ethics
committee of Chongqing Medical University, Chongqing,
before conducting it. Eliminating 35 workers who had
cardiovascular diseases before working in this company
and 287 workers who worked under the noise exposure
(75.0 - 88.2 dB, mean = 78.6 dB). Checking all the items,
the results of 728 workers were collected and analyzed in
the study. The workers who received health examination
were obtaining written informed consent (men 588,
women 140) and then taking medical examinations, in-
cluding general medical check, audition screening, blood
pressure, electrocardiogram, blood test, X-ray, ophthal-
mology and otorhinolaryngology, type-B ultrasonic, liver
function, lung function routine examinations etc. All the
examinations were carried out between 9:00 and 12:00,
requesting all workers to take test and not to eat anything
until completing the examinations day ahead.
Questionnaires with all inspection items were distrib-
uted to every worker the day before checking up and
objects were requested to paste the copy of identification
card on the top left corner of the cover and to fill in es-
sential information (including name, sex, age, weight,
body height and so on), history of diseases, smoking
years, drinking years, diet habits and so on. Whether the
family had hypertension or other cardiovascular diseases
was included in the history of diseases.
For the present study, the workers (n = 728) were as-
signed into noisy group and non-noisy group, different
types of work in production had different levels of noise,
so 442 workers from workshops where the level of noise
was ≥90 dB (A) were divided into noisy group, and an-
other 286 workers from office rooms and one depository
where the level of noise was ≤70 dB (A) were divided
into non-noisy group, none of the workers used ear pro-
tectors.
2.2. Determination of Workplace Noise
The levels of noise exposure were measured by sound
level meters (TES-1357 sound level meter, Taiwan),
workshops, offices and two depositories were all meas-
ured from 9:00 to 17:00 consecutively. The meters were
placed 1.5 m above the workshops’ ground surface and
1.1 m above the offices’ and depositories’ ground surface.
To exclude the interference of results by wind, we sur-
veyed the wind velocity of all destinations which were
all below 1 m/s. The average A-weighted sound levels of
8 h were accounted before examinations, those who
worked in the environment which the average level and
the maximum level both ≤70 dB (A) were assigned into
non-noisy group. Similarly, the average level and the
minimum level both ≥90 dB (A) were assigned into
noisy group. The level of noise in one depository was
80.2 dB and workplaces which some cleansers worked
were between 75.0 - 88.2 dB (mean = 78.6), so these
workers were excluded from the research.
2.3. Determination of Blood Pressure
The measurements of blood pressure were performed in
a quiet room in the morning using mercurial sphygmo-
manometer, conducted by the policy of Bailey and Bauer
[16]. The workers must have a rest at least for 10 min-
utes before entering the room, and then were guided in
the sitting position after about 5 minutes rest testing the
blood pressure of brachial artery for three times, the data
was used in mean of them to express individuals’ blood
pressure in this study. Hypertension was defined by the
World Health Organization: a systolic BP ≥ 140 mmHg
or a diastolic BP ≥ 90 mmHg, or had been treated for
hypertension [17].
2.4. Determination of ECG and Hearing
In this study, doctors used electrocardiographs (ECG-
E31A, Guangdong, SHENZHEN ORIENTAL SCIENCE
& TECH. CO. LTD) to test every participant’s ECG, and
they determined weather normal or abnormal by the re-
sults of examinations. In these workers, the types of ab-
normal were sinus tachycardia, sinus bradycardia, left
axis deviation, right axis deviation, premature ventricular
contraction, sinus arrhythmia, incomplete right bundle
branch block and hart rate over 100 times/min; when a
worker had one of these symptoms was defined as ab-
normal ECG. After taking examinations, we collected all
the data together to analyze.
Simultaneously, doctors use audiometers (MM622,
Denmark, Madsen) to test every participant’s hearing,
and they determined weather normal or abnormal by the
results of audiogram. The abnormal hearing ability of
most workers of was V type audiogram, when the aver-
age value of 3000 Hz - 6000 Hz > 50 dB was defined as
hearing impairment.
2.5. Statistical Analyses
In this study, we used the logistic regression to analysis
the relations between noise and hypertension, ECG, im-
paired hearing, and used x2 test to compared the differ-
ences between noisy group and non-noisy group, includ-
ing the rate of hypertension, the abnormal rate of ECG,
the abnormal rate of hearing and the rate of them in dif-
ferent working years. All the values are presented as
means ± SD, and analyzed by SPSS17.0 (a = 0.05).
3. RESULTS
In present study, all questionnaires were collected by

S. Wang et al. / J. Biomedical Science and Engineering 6 (2013) 1137-1142 1139
staffs of the CDC after health examination, and then all
data was recorded as Excel format in computers. BMI
was calculated and showed a decrease in noisy group but
did not reach statistical significance (data not shown).
As shown in Table 1, more than one fifth workers
were diagnosed with hypertension (21.49%) in noisy
group and was significance compared with non-noisy
group (p < 0.01). Equally, workers who worked in noisy
worksites had a worse audition than those who worked in
control conditions (p < 0.01), while ECG presented an
increase abnormal rate but showed no significance.
In this factory, about one fifth workers are women and
four fifth workers are men, to eliminate the effects of
sexuality we compared sex structure between two groups
which shown no significant difference (data not shown).
Both in two groups, the rate of hypertension in women
was significantly higher compared with men; in noisy
group was higher than non-noisy group (p < 0.01). On
the contrary, the prevalence of ECG in women was lower
compared with men but still showed no significant dif-
ference (p > 0.05). The percentage of hearing damage
was similar in men and women, no significance was ob-
served in Table 2.
The rates of hypertension and audiometric injuries
were significantly increased (p < 0.01) with working
years growing in noisy group, but this trend was not seen
in ECG. Only in noisy group, ECG among workers
worked 10-year were significantly higher than those who
worked 0-year, workers who worked more than 15 years
increased but did not reach statistical significance. In
non-noisy group, ECG was no significant difference
among working years groups. As is shown in Table 3,
the rate of impaired hearing indicated an increase with
working years while 15- group was below significance (p
> 0.05).
After analyzed the data shown in previous tables, we
further used the logistic regression statistics and the re-
sults are presented in Table 4. The total odds ratios of
hypertension, ECG, impaired hearing were 2.63, 1.19,
2.21 and the 95%CI were 1.66 - 4.15, 0.76 - 1.86, 1.31 -
3.70. To certify the relation of noise and hypertension,
ECG, impaired hearing, we must evacuate the effects of
other factors such as age, BMI, lifestyle items (including
smoking, drinking, exercise, diet and so on). The results
after adjusted these factors were shown in Table 4.
4. DISCUSSION
Nowadays, noise pollution has been an important prob-
lem in the world. Many studies researched about occupa-
tional noise exposure and hearing, blood pressure, car-
diovascular changes in various countries [18-23], how-
ever, similar research was seldom carried out in China
and no report was found in large-scale industrial city of
Chongqing. To resolve this problem in the area, we did
this study. In the study, we found the percentage of hy-
pertension in the noise exposure group was significantly
higher than the control group. This result was in accor-
dance with previous studies [9,24-27]. These studies re-
ported that there was a positive relation between hyper-
tension and noise exposure, and some of them analyzed
the possible reasons. 1301 workers in Taiwan were used
independently and joint effect methods suggested that
those who have TT variant allele (one genotype of an-
giotensinogen gene) would get hypertension easily [25].
In addition, there were different effects when the meta-
bolic syndrome (MetS) was defined differently while
occupational exposure to workload or noise adjusted
coronary heart disease (CHD) risk. When MetS defined
by high triglycerides, BMI and low HDL-C, the occupa-
tional noise exposure has a protective effect and can de-
crease the risk of CHD. While if MetS defined by high
blood pressure, BMI and glucose, no protective effect is
shown [26], and when noise exposure above 80 dB (A)
correlated with hypertension and 4000 HZ has the most
enormous effect [9]. All these are the possible reasons
for why noise could impact blood pressure of people.
In our study, we found another special phenomenon
that the prevalence of hypertension in women was sig-
nificant higher than men, and the result was not consis-
tent with the previous study [28]. The possible reasons
were as follows: firstly, men both in noisy and non-noisy
group did more physical work than women; secondly, fat
accumulated with age and exorbitant fat of body was one
of induced factors leading to hypertension, and body fat
of women is higher than men with age increasing; thirdly,
the questionnaires showed most of male workers had a
drinking habit about 50 - 100 ml/day, and only a few of
them were used to drinking abuse.
ECG is the main parameter responding the functions
of cardiovascular, weather noise exposure is related with
it or not is controversial. The abnormal rate of it in our
study presents that there may be no associations with
occupational noise. The result is not in concordance with
some previous studies which showed no relations be-
tween noise exposure and hypertension or cardiovascular
diseases [29-31]. This may be as a result of the data only
collected from a company, and in order to achieve a
more credible conclusion, further research on general
population is needed in our team.
The rate of hypertension and impaired hearing in-
creased with noise exposure years, and we analyzed the
data by the logistic regression model. The results showed
positive relations between occupational noise exposure
and hypertension, impaired hearing. The possible con-
founding factors are age, BMI, smoking, drinking, exer-
cise, diet and so on. A study suggested that BMI, waist
circumference and weight were associated with chronic
diseases such as hypertension, hyperlipemia and diabetes

S. Wang et al. / J. Biomedical Science and Engineering 6 (2013) 1137-1142 1140
Table 1. Detection rate of hypertension, ECG and impaired hearing in two exposure groups.
All (n) Hypertension % (n) ECG % (n) Impaired Hearing % (n)
Noisy group 442 21.49 (95)** 13.80 (61) 14.25 (63)**
Non-noisy group 286 9.44 (27) 11.89 (34) 6.99 (20)
p-value - 0.000 0.454 0.003
All 728 16.76 (122) 13.05 (95) 11.40 (83)
Notes: The rates of hypertension, ECG and impaired hearing were used x2 test to compared the differences between noisy group and non-noisy group. ECG: It
was defined as the rate of workers who were diagnosed sinus tachycardia, sinus bradycardia, left axis deviation, right axis deviation, premature ventricular
contraction, sinus arrhythmia, incomplete right bundle branch block or hart rate over 100 times/min. **p < 0.01 noisy group vs non-noisy group.
Table 2. Detection rate of hypertension, ECG and impaired hearing in male and female groups.
Hypertension % (n) ECG % (n) Impaired Hearing % (n)
All (n) Noisy Group Non-noisy GroupNoisy GroupNon-noisy GroupNoisy Group Non-noisy Group
Men 588 10.54 (62)& 2.89 (17) 9.01 (53) 5.10 (30) 8.50 (50)& 2.55 (15)
Women 140 23.57 (33)**&& 7.14 (10)* 5.71 (8) 2.86 (4) 2.21 (13) 3.57 (5)
p-value - 0.000 0.017 0.205 0.258 0.767 0.707
All % (n) 728 21.49 (95) 9.44 (27) 13.80 (61)11.89 (34) 14.25 (63) 6.99 (20)
Notes: To see the differences between men and women, the data used x2 test to analyze. *,**p < 0.05, 0.01 men group vs women group; &,&&p < 0.05, 0.01 noisy
group vs non-noisy group.
Table 3. Detection rate of hypertension, ECG and impaired hearing in different exposure years.
Noisy Group Non-noisy Group
Working
years
(y) All
(n)
Hypertension
% (n) p-value ECG % (n) p-value
Impaired
Hearing
% (n)
p-value All
(n)
Hypertension
% (n) p-value ECG % (n) p-value
Impaired
Hearing
% (n)
p-value
0- 186 5.91 (11) - 11.29 (21) - 5.91 (11)- 89 8.99 (8) - 11.24 (10) - 3.37 (3)-
5- 83 6.02 (5) 1.000 8.43 (7) 0.479 6.02 (5) 1.00064 7.81 (5) 0.797 10.94 (7) 0.954 1.56 (1)0.640
10- 48 43.75 (21)** 0.000 22.92 (11)* 0.037 27.08 (13)** 0.00047 2.13 (1) 0.243 12.77 (6) 0.792 8.51 (4)0.083
15- 53 24.53(13)** 0.000 18.87 (10) 0.147 13.21 (7)0.13953 16.98 (9) 0.156 13.21 (7) 0.726 11.32 (6)0.127
20- 72 62.50 (45)** 0.000 16.67 (12) 0.246 37.50 (27)** 0.00033 12.12 (4) 0.862 12.12 (4) 1.000 18.18 (6)*0.002
All 442 21.49 (95) - 13.80 (61) - 14.25 (63)- 2869.44 (27) - 11.89 (34) - 6.99 (20)-
Notes: To assess the associations between the rate of hypertension, ECG or impaired hearing and noise exposure years, separately. *,**p < 0.05, 0.01. 5-, 10-,
15- and 20- groups vs 0- group, respectively.
Table 4. Odds ratios of hypertension, ECG, impaired hearing in noisy and non-noisy group workers (n = 728).
Odds Ratio 95%CI
Hypertension 2.63 1.66 - 4.15
adjusted by age 3.64 2.01 - 6.60
adjusted by BMI 3.89 2.08 - 7.28
adjusted by lifestyle factors 3.56 1.98 - 6.39
ECG 1.19 0.76 - 1.86
adjusted by age 1.21 0.73 - 1.99
adjusted by BMI 0.91 0.71 - 1.17
adjusted by lifestyle factors 0.84 0.53 - 1.33
Impaired Hearing 2.21 1.31 - 3.70
adjusted by age 2.57 1.39 - 4.75
adjusted by BMI 2.86 1.44 - 5.67
adjusted by lifestyle factors 2.34 1.35 - 4.07
Notes: OR values were calculated and adjusted Confounding factors such as age, BMI, lifestyle items (including smoking, drinking, exercise, diet and so on).
R > 1 means positive correlations between hypertension, ECG or impaired hearing and noise exposure. O

S. Wang et al. / J. Biomedical Science and Engineering 6 (2013) 1137-1142 1141
mellitus [32]. To receive more credible results, we ad-
justed these factors. The values of OR were changing
slightly, but the conclusions were invariable.
Finally, from this study we could draw several conclu-
sions: 1) There may be a positive relationship between
exposure occupational noise and hypertension and im-
paired hearing; 2) The risk of hypertension and impaired
hearing increased with working years; 3) Whether occu-
pational noise affected cardiovascular or not was unclear.
Further study with more samples from different areas
was needed; 4) Wearing personal protective equipments
(PPE) is very important for workers, but the workers in
the study hardly use them for various reasons. Therefore
forcible measures should be taken to guarantee PPE
wearing rate among workers in China.
5. ACKNOWLEDGEMENTS
We appreciate Professor Yu Chen, Dr. Mindi He, Yan Wang, Hongjuan
Wu and Lu Liu for their hospitable and professional technical assis-
tance. Grant support was from The Center for Disease Prevention and
Control of Chongqing.
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