Prevalence of Hypertension among workers exposed to occupational noise in Baiji power plants with Hearing Impairment

Abstract

Background: Noise induced hearing loss, a permanent bilateral hearing impairment due to  long  term  exposure  to  high  levels  of  noise,  represents  one  of  the  most  common occupational hazards. This cross sectional study was undertaken to evaluate the auditory effects of noise and to further examine the hypothesis that a link between noise exposure and hypertension exists. 
Objectives:  The  objectives  of  the  present  study  were  to  study  the  (i)prevalence  of hypertension and hearing impairment in electric power plants workers, (ii) association between hypertension and hearing impairment, (iii) association between hypertension and hearing impairment, with duration of exposure, and (iv) correlation between levels of sound and noise induced health problems viz. hypertension and hearing impairment in a cross sectional study involving Workers working in Baiji electric power plants. Methods: This was a cross-sectional study. The study sample (population)   consisted of 240 healthy male employees from  Baiji electric power plants with a history of past and present  exposure  to  noise.  The  study  was  conducted  during  the  period  from  the  15 December of 2012`to the 15 February of 2013. There are four sections in the power plants. Turbine, Boiler, central control room and fuel . All workers who worked in the power stations for 5-7 years or more were included in the study.Data was gathered from the results of available portable audiometric test and the blood pressure was measured in supine position by using mercury sphygmomanometer. 
Hearing impairment was defined as average hearing threshold  for frequencies 0.5kHz, 1kHz ,2kHz and 3kHz equal or more than 25 dB(A) in  both ears. Workers are classified according to expoeure time in to two groups. The workers are working in turbine and boiler  formed  continuously  exposed  group(CEG).While  the  workers  are  working  in central control room and fuel formed intermittently exposed group(IEG). 
Results:The prevalence of hearing impairment in this study was 17.08% among all the exposed workers .The prevalence of hearing impairment was significantly more in(CEG 14.58%)as compared to (IEG 2.5%).The Prevalence of hypertension among continuous exposure group to noise was(12.5%) significantly higher than the  intermittent exposed group  to noise ( 2.08%) .There was a positive association between duration of exposure and prevalence of Hypertension .Both hearing impairment and hypertension showed in the  current  study  increasing  frequency  in  relation  to  the  duration  of  exposure( employment). The results of the present study indicate that  hypertension and hearing impairment are commoner in workers continuously exposed more than that in workers intermittent exposed group to high level of occupational noise. The prevalence of hearing impairment and hypertension distributed according to the age of workers, we found that the 12.95%  of bilateral neurosensory in age below 40 years, while 30.04% of cases in age above 40 years. While the prevalence of hypertension,  we found 10.47% of cases in age below 40 years and 30.6% in  age above 40 years .          
Conclusions: These findings provide corroborative evidence to further substantiate the notion that exposure to noise is associated with hearing impairment .They also support the proposition that long term occupational exposure to noise appears to be a risk factor for arterial hypertension.