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| Year : 2002
| Volume
: 5 | Issue : 17 | Page
: 15-22 |
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| A cross-sectional study of occupational noise exposure and blood pressure in steelworkers |
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E Powazka1, K Pawlas1, B Zahorska-Markiewicz2, Jan E Zejda3
1 Laboratory of Audiology and Noise, Institute of Occupational Medicine and Environmental Health, Koscielna, Poland
2 Department of Pathophysiology, Medical University of Silesia, Medyków, Poland
3 Department of Hygiene and Epidemiology, Medical University of Silesia, Medyków, Poland
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Objective: To determine the association of occupational noise exposure and blood pressure in a group of workers at the metallurgical plant.
Methods: Noise exposure at the workplace and blood pressure were measured in 178 male workers of steel mill company. Criteria for including in the study group were: age below 35 years, employment-exposure duration longer than 3 years, hearing threshold level in normal range and no cardiovascular history. Program of examination included: individual questionnaire, ORL - examination, tone audiometry, measure of weight, height and blood pressure. Cigarette smoking, diet habits and other risk factors of elevated blood pressure were controlled. Noise exposure was assessed for each work place, by means of direct and indirect measurements.
Results: Systolic blood pressure was statistically significantly higher in the group exposed to the higher noise levels and the results of multiple regression analyses revealed a significant relationship between the occupational exposure to noise and systolic blood pressure. No such relationship with diastolic blood pressure was found.
Conclusions: The results suggest the positive association between occupational exposure to noise and blood pressure. Keywords: blood pressure, occupational noise exposure, cross-sectional study
How to cite this article:
Powazka E, Pawlas K, Zahorska-Markiewicz B, Zejda JE. A cross-sectional study of occupational noise exposure and blood pressure in steelworkers. Noise Health 2002;5:15-22 |
How to cite this URL:
Powazka E, Pawlas K, Zahorska-Markiewicz B, Zejda JE. A cross-sectional study of occupational noise exposure and blood pressure in steelworkers. Noise Health [serial online] 2002 [cited 2023 Jun 4];5:15-22. Available from: https://www.noiseandhealth.org/text.asp?2002/5/17/15/31838 |
| Objectives | |  |
The relationship between occupational and daily life exposure to noise and blood pressure values is subject to debate in occupational medicine. Noise creates one of the most widespread and unresolved pollutants in all industrialized societies. High levels of noise results in hearing impairment and this effect is well established (ISO 1999, 1990). The experimental studies (Andren, 1983) as well as epidemiological (Abel, 1990 and Babisch, 1993 and Kjellberg, 1990 and Xu,1997) indicate that exposure to noise can contribute to other negative effects such as nervous, metabolic or cardiovascular diseases.
In 1983 the World Health Organization recognized noise as one of the risk factors of hypertension (World Health Organization, 1983). The question of whether noise plays a significant part in aetiopathogenesis of this disorder, however, has not been unequivocally resolved by the results of epidemiological studies (Morrell, 1997). Reliable assessment of the long term influence of noise on the level of blood pressure is very difficult due to a large number of factors that should be taken into account when this relationship is considered. This challenge requires the use of more valid research methods and renders the processing of the results more difficult.
The aim of the present study was to investigate the relationship between occupational noise exposure and blood pressure in a group of workers of the metallurgical plant. Criteria of including to the study group were selected to minimize the impact of the confounding factors on the relationship under exploration.
| Material and methods | | |
A cross-sectional study was carried out at the large metallurgical plant in Czestochowa, Poland. The examinations consisted of gathering information through questionnaires, measuring the arterial blood pressure, height and body weight, and audiometry tests in all subjects. All examinations were performed in company's Ambulatory Building in the morning prior to the work shift to reduce the influence of diurnal rhythm and effects of acute exposure to noise.
Subjects. The examinations included 302 blue collar workers aged below 35 years, randomized at the departments of metallurgical plant (every second person from the list of workers was selected for the primary study group). Individuals who had been working for less than three years at the present work place or who had history of hypertension or treatment with drugs for cardiovascular diseases were excluded from the study. 178 workers who met the criteria were selected as the final subjects for the study group .
Questionnaire. The detailed questionnaire involved questions about demographic status, the number of years in the workforce, specific job and workplace characteristics, the subjective measure of perceived work noise, the use of hearing protectors, exposure to noise outside the workplace, diet, tobacco use, alcohol consumption, family history of hypertension and cardiovascular diseases.
Audiometry. Tone audiometry was conducted by use of the Beckesy audiometer. The hearing thresholds of both ears were examined at frequencies of 0.5, 1, 2, 4, 6, 8, 10, 12, 14 and 15 kHz.
Body mass index. The body weight and height measurements of the subjects barefoot and their outer garments removed were made. The Qutelet's index was used (BMI = weight/height 2 [kg/m 2 ]) to adjust the influence of weight and height on blood pressure.
Blood pressure. Blood pressure was measured by mercury sphygmomanometer (Fazzini, Italy) according to the standardized WHO method (World Health Organization, 1983). During blood pressure measurement the subjects were in the sitting position, after resting for at last 10 minutes. In each subject two measurements were made (Korotkoff phases I and V). If two readings of any worker differed by more then 4 mm Hg in either systolic or diastolic pressure, measurements were repeated after further rest intervals until the difference met this criterion.
Exposure assessment. The exposure to noise was determined for each work places by the direct or indirect measurements of noise levels. The choice of the method depended on the variability of the noise. Exposure to steady-state noise was assessed on the basis of measurements equivalent sound levels (Leq) and exposure time. Exposure to non steady-state noise was measured directly by noise-dose meter. Duration of the measurement lasted for representative time and it included whole pattern of noise levels. Noise dosimeter Sonopan D20 was used for the direct method and the sound analyzer SVAN 910A was used for measurements of sound level.
Statistical methods. The SAS program was used for statistical analysis. The data analysis involved correlation analysis, comparison of mean values and multiple step linear regression with dependent variable representing systolic and diastolic blood pressure. The results of analyses according to linear regression technique were verified by general linear model. According to the method the values of variables were treated either as categorical or absolute variables. The results of analyses were similar so for the simplification of the presentation only the results obtained by linear regression technique are presented in the paper.
| Results | | |
Mean values of age, number of years in employment, exposure to noise, body mass index and blood pressure are shown in [Table - 1]. The distributions of the values of systolic and diastolic blood pressure in examined group were Gaussian.
The distributions of the qualitative variables describing the examined group of steelworkers are shown in [Table - 2].
The variable describing exposure to noise was created on the basis of the distribution of noise levels at the work places of examined subjects. The cut-off point between "high"(1) and "low"(0) exposure to noise was the median of the distribution amounting to 85 dBA (mode 84 dBA). The average values of noise levels attributed to the variable describing exposure to noise are presented in [Table - 3].
The results of audiometric measurements in the examined group were within the normal values and there was no statistically significant difference between the values of the hearing threshold found in workers exposed to different levels of noise, at any tested frequencies. The thresholds patterns for both ears were similar.
The relationship between blood pressure values (systolic, diastolic) and their potential correlates was examined on the basis of the results of variance analysis. Systolic blood pressure was statistically significantly higher in the group exposed to the higher noise levels.
The statistically significant relationship was also found between the values of diastolic blood pressure and BMI. The other examined variables had no statistically significant influence on the level of blood pressure.
Before implementing the multivariate regression analysis the likely relationships between the examined variables were explored in order to identify a potential for multicollinearites. The correlation coefficient between variables describing age and the number of years in exposure to noise was statistically significant (r=0.47; p=0.0001). The results of additional analyses showed similar statistical meaning of these variables, thus age was included to the regression equation.
The following explanatory variables were tested into the regression model: noise exposure at work, age, body mass index, physical exertion at work, shift-work, the level of subjective perception of noise at work, alcohol consumption, tobacco smoking, coffee consumption, subjective perception of environmental noise, marital status, educational level, and family history of hypertension. The results of regression analysis with backward elimination procedure revealed an association between occupational exposure to noise and the level of systolic pressure (p = 0.01). The other statistically significant factor (p = 0.05) was physical exertion at work.
Diastolic blood pressure was associated with the value of body mass index and the amount of coffee cups drunk per day.
Additional analyses carried out in order to estimate the influence of interactions between independent variables showed no effects of interaction between exposure to noise and the number of years in employment (or age) on the value of blood pressure. However, the interaction between variables describing exposure to noise and physical exertion at work appeared to statistically significantly explain the level of systolic blood pressure (R 2 = 0.06; p = 0.002). No results showed the effects of examined factors on diastolic blood pressure.
| Discussion | | |
Our results support the view that chronic occupational exposure to noise has the influence on systolic blood pressure. The mean level of systolic blood pressure was significantly higher in the group exposed to the higher levels of noise and the influence of the other examined variables did not affect the results. The results of multivariate analysis confirm that noise exposure was the explanatory factor for systolic blood pressure in the examined group. There was not such effect in relation to the diastolic blood pressure. This finding is consistent with the results of other studies suggesting that systolic blood pressure is first to respond to noise and diastolic pressure elevates after longer exposure (Deyanov, 1995 and Fogari, 1994 and Fouriard, 1984 and Green, 1991 and Lang, 1992 and Talbott, 1999).
The subjective perception of noise is considered by some authors as the primary factor that induces a cardiovascular reaction (Kjellberg, 1990 and Lercher, 1993 and Westman, 1981). Our results did not support this view. Physical exertion at work was the only other factor associated with systolic blood pressure although its statistical significance had the borderline value. However, the influence of physical exertion was also shown in the interaction term which could suggest that those two factors may act additionally. On the basis of other reports (Dorian, 1984 and Fouriard, 1984), the physical workload is also associated with high blood pressure levels.
The level of diastolic blood pressure was associated with BMI and the number of coffee cups drunk per day. The former finding is compatible with the other studies indicating BMI as an important risk factor for elevated diastolic blood pressure among the young people (Rywik, 1990). The negative correlation between the level of diastolic blood pressure and the number of coffee cups drunk per day could be explained by the observation that people with low blood pressure are more likely to drink coffee. However, cannot be resolved on the basis of our data.
In our study many factors with presumed influence on the level of blood pressure were taken into account. Most of them did enter in statistically significant association. The age of examined group is the most possible reason why the influence of the potential risk factors for elevated blood pressure was less apparent than in general population. However, the duration of exposure to noise according to the literature (Verbeek, 1987 and Yiming,1991) was long enough to observe the results of the examined factor.
The use of the personal hearing protectors in the examined group was not tested in the final regression equation because all of the workers were obliged to use hearing protectors as the participants of the hearing conservation program. As a result the noise exposure of workers was probably lower that indicated by environmental noise measurements (Babish, 1998).
Mean hearing thresholds in examined group were placed in the range of normal values and there was no significant differences among the workers exposed to the different levels of noise. No differences in the hearing thresholds were found also for the highest frequencies, the most vulnerable for the harmful effects of noise exposure. It is likely that duration of noise exposure was too short to evoke the hearing impairments. The sustained elevation in blood pressure prior to significant changes in auditory sensitivity were shown by Peterson et al (Peterson, 1981). The similar results showed also Yiming et al (Yiming, 1991). Their hypothesis was that the effects of noise exposure on blood pressure became apparent within five years of the beginning of exposure.
Our study is not free from a number of limitations. One of them is the definition of individual noise exposure. The reliable estimation of exposure is a difficult task and the lack of precision may affect causative inference. Nevertheless, even such a crude way of classification of noise exposure subjects resulted in statistically significant differences in the value of systolic blood pressure in the groups with different exposure to noise although the difference was very small. Another factor that could weaken the association was that blood pressure measurements were made on a single occasion. Readings carried out during consecutive days could be more reliable in estimating blood pressure of the individual, but screening procedures as presented here were used in other epidemiological studies examining association between blood pressure and cardiovascular morbidity (World Health Organization,1984).
In conclusion, the findings of our study show a positive association between noise exposure and blood pressure levels. The prospective observation would be essential in an attempt to verify the hypothesis that occupational exposure to noise is a risk factor for sustained elevation of systolic blood pressure in the first years of exposure. Our data provide a promising ground for future follow-up evaluation of this association.
Acknowledgements This study was supported by grant from the Polish Committee of Research. Thanks are due Dr A.Bronder, Dr E.DebowskaJarzebska who assisted with audiometric tests and Natalia Pawlas, Violetta Maksymowicz for their technical assistance.[23]
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Correspondence Address:
E Powazka
Laboratory of Audiology and Noise, Institute of Occupational Medicine and Environmental Health, 41-200 Sosnowiec, ul. Koscielna 13
Poland
 Source of Support: None, Conflict of Interest: None  | Check |
PMID: 12537831 
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5], [Table - 6], [Table - 7] |
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